LECTURE 14LECTURE 14Carbonhydrates. Monosacchrides. Carbonhydrates. Monosacchrides.

StructureStructure. I. Isomersomery.y.

Reactionary ability of the Reactionary ability of the monosaccharides.monosaccharides.

Ass. Medvid I.I.Ass. Medvid I.I.ass. Burmas N.I.ass. Burmas N.I.

Outline:Outline:

1.1. Carbohydrates.Carbohydrates.

2.2. Classification of carbohydrates.Classification of carbohydrates.

3.3. Chirality: handedness in molecules. Chirality: handedness in molecules. Stereoisomers. Fisher Projections.Stereoisomers. Fisher Projections.

4.4. Classification of monosaccharides. Classification of monosaccharides. 5.5. Reactions of monosaccharides.Reactions of monosaccharides.

6.6. Biologically important monosaccharides.Biologically important monosaccharides.

1. Carbohydrates.1. Carbohydrates.Carbohydrates are the most abundant class of Carbohydrates are the most abundant class of

bioorganic molecules on planet Earth. Although their bioorganic molecules on planet Earth. Although their abundance in the human body is relatively low, abundance in the human body is relatively low, ccarbohydrates constitute about 75%arbohydrates constitute about 75% by mass of dry by mass of dry plant materialsplant materials. Green (chlorophyll-containing) plants . Green (chlorophyll-containing) plants produce carbohydrates via photosynthesis. In this produce carbohydrates via photosynthesis. In this process, carbon dioxide from the air and water from the process, carbon dioxide from the air and water from the soil are the reactants, and sunlight absorbed by soil are the reactants, and sunlight absorbed by chlorophyll is the energy source. chlorophyll is the energy source. Plants have two main Plants have two main uses for the carbohydrates they produce. In the form of uses for the carbohydrates they produce. In the form of cellulose, carbohydrates serve as structural elements, cellulose, carbohydrates serve as structural elements, and in the form of starch, they provide energy reserves and in the form of starch, they provide energy reserves for the plantsfor the plants. Dietary intake of plant materials is the . Dietary intake of plant materials is the major carbohydrate source for humans and animals. The major carbohydrate source for humans and animals. The average human diet should ideally be about two-thirds average human diet should ideally be about two-thirds carbohydrate by mass.carbohydrate by mass.

Carbohydrates have the following functions in Carbohydrates have the following functions in human organism:human organism:

1. Carbohydrate oxidation provides energy.1. Carbohydrate oxidation provides energy.2. Carbohydrate storage, in the form of glycogen, 2. Carbohydrate storage, in the form of glycogen,

provides а short- term energy reserve.provides а short- term energy reserve.3. Carbohydrates supply carbon atoms for the 3. Carbohydrates supply carbon atoms for the

synthesis of other biochemical substances synthesis of other biochemical substances (proteins, lipids, and nucleic acids).(proteins, lipids, and nucleic acids).

4. Carbohydrates form part of the structural 4. Carbohydrates form part of the structural framework of DNA and RNA molecules.framework of DNA and RNA molecules.

5. Carbohydrate "markers" on cell surfaces play 5. Carbohydrate "markers" on cell surfaces play key roles in cell -cell recognition processes.key roles in cell -cell recognition processes.

Classification of carbohydrates.Classification of carbohydrates.

Most simple carbohydrates have empirical Most simple carbohydrates have empirical formulas that fit the general formula СnН2nОn. formulas that fit the general formula СnН2nОn. An early observation by scientists that this An early observation by scientists that this general formula can also be written as general formula can also be written as Сn(Н2О)n is the basis for the term carbohydrate Сn(Н2О)n is the basis for the term carbohydrate - that is, "hydrate of carbon." It is now known - that is, "hydrate of carbon." It is now known that this hydrate viewpoint is not correct, but the that this hydrate viewpoint is not correct, but the term carbohydrate still persists. Today the term term carbohydrate still persists. Today the term is used to refer to an entire family of is used to refer to an entire family of compounds, only some of which have the compounds, only some of which have the formula СnН2nОn.formula СnН2nОn.

Examples of carbohydratesExamples of carbohydrates

IUPAC nomenclature doesn't use for carbohydrates, trivial nomenclature uses for them.

Carbohydrates Carbohydrates are polyhydroxy aldehydes, are polyhydroxy aldehydes, polyhydroxy ketones, or compounds that yield such polyhydroxy ketones, or compounds that yield such substances upon hydrolysis. The carbohydrate glucose substances upon hydrolysis. The carbohydrate glucose is а polyhydroxy aldehyde, and the carbohydrate is а polyhydroxy aldehyde, and the carbohydrate fructose is а polyhydroxy ketone. А striking structural fructose is а polyhydroxy ketone. А striking structural feature of carbohydrates is the large number of feature of carbohydrates is the large number of functional groups present. In glucose and fructose there functional groups present. In glucose and fructose there is а functional group attached to each carbon atom. is а functional group attached to each carbon atom.

Carbohydrates are classified on the basis of molecular Carbohydrates are classified on the basis of molecular size as monosaccharides, oligosaccharides, and size as monosaccharides, oligosaccharides, and polysaccharides.polysaccharides.

MonosaccharidesMonosaccharides are carbohydrates that contain are carbohydrates that contain a single polyhydroxy aldehyde or polyhydroxy ketone a single polyhydroxy aldehyde or polyhydroxy ketone unit. Monosaccharides cannot be broken down into unit. Monosaccharides cannot be broken down into simpler units by hydrolysis reactions. Both glucose and simpler units by hydrolysis reactions. Both glucose and fructose are monosaccharides. Naturally occurring fructose are monosaccharides. Naturally occurring monosaccharides have4rom three to seven carbon monosaccharides have4rom three to seven carbon atoms; five- and six-carbon species are especially atoms; five- and six-carbon species are especially common. Pure monosaccharides are water-soluble, common. Pure monosaccharides are water-soluble,

white, crystalline solidswhite, crystalline solids..

OligosaccharidesOligosaccharides are carbohydrates that contain from two to ten are carbohydrates that contain from two to ten monosaccharide units. Disaccharides are the most common type of monosaccharide units. Disaccharides are the most common type of oligosaccharide. oligosaccharide. DisaccharidesDisaccharides are carbohydrates composed of two are carbohydrates composed of two monosaccharide units covalently bonded to each other. Like monosaccharide units covalently bonded to each other. Like monosaccharides, disaccharides are crystalline, water-soluble monosaccharides, disaccharides are crystalline, water-soluble substances. Sucrose (table sugar) and lactose (milk sugar) are substances. Sucrose (table sugar) and lactose (milk sugar) are disaccharides. Within the human body, oligosaccharides are often disaccharides. Within the human body, oligosaccharides are often found associated with proteins and lipids in complexes that have found associated with proteins and lipids in complexes that have both structural and regulatory functions. Free oligosaccharides, both structural and regulatory functions. Free oligosaccharides, other than disaccharides, are seldom encountered in biological other than disaccharides, are seldom encountered in biological systems. Complete hydrolysis of an oligosaccharide produces systems. Complete hydrolysis of an oligosaccharide produces monosaccharides. Upon hydrolysis, а disaccharide produces two monosaccharides. Upon hydrolysis, а disaccharide produces two monosaccharides, а trisaccharide three monosaccharides, а monosaccharides, а trisaccharide three monosaccharides, а hexasaccharide six monosaccharides, and so on.hexasaccharide six monosaccharides, and so on.

Polysaccharides Polysaccharides are carbohydrates made up of many monosaccharide are carbohydrates made up of many monosaccharide units. Polysaccharides, which are polymers, often consist of tens of units. Polysaccharides, which are polymers, often consist of tens of thousands of monosaccharide units. Both cellulose and starch are thousands of monosaccharide units. Both cellulose and starch are polysaccharides. We encounter these two substances everywhere. polysaccharides. We encounter these two substances everywhere. The paper on which this book is printed is mainly cellulose, as are The paper on which this book is printed is mainly cellulose, as are the cotton in our clothes and the wood in our houses. Starch is а the cotton in our clothes and the wood in our houses. Starch is а component of many types of foods including bread, pasta, potatoes, component of many types of foods including bread, pasta, potatoes, rice, corn, beans, and peas.rice, corn, beans, and peas.

3. Chirality: handedness in molecules. 3. Chirality: handedness in molecules. Stereoisomers. Fischer Projections.Stereoisomers. Fischer Projections.

Before considering structures for and reactions of Before considering structures for and reactions of specific carbohydrates, we will consider handedness, а specific carbohydrates, we will consider handedness, а biologically important structural property exhibited by biologically important structural property exhibited by most carbohydrates. Most carbohydrate molecules can most carbohydrates. Most carbohydrate molecules can exist in two forms - а left-handed form and а right-exist in two forms - а left-handed form and а right-handed form. Significantly, these different forms often handed form. Significantly, these different forms often elicit different responses within the human body. elicit different responses within the human body. Mirror Images.Mirror Images. The concept of mirror images is the The concept of mirror images is the key to understanding molecular handedness. All key to understanding molecular handedness. All objects, including all molecules, have mirror images. objects, including all molecules, have mirror images. The The mirror imagemirror image of an object is the object’ reflection of an object is the object’ reflection in а mirror. For example: human hands.in а mirror. For example: human hands.

A person’s left and right hands are not superinposable upon each other.

Chirality. Chirality. Objects that cannot be superimposed upon their Objects that cannot be superimposed upon their mirror image are said to be chiral objects. А mirror image are said to be chiral objects. А chiral objectchiral object is an object that is not identical to its mirror image. Your is an object that is not identical to its mirror image. Your hands and feet are chiral objects, as are gloves and shoes. hands and feet are chiral objects, as are gloves and shoes. Objects that can be superimposed upon their mirror Objects that can be superimposed upon their mirror images are achiral. An images are achiral. An achiral object achiral object is identical to its is identical to its mirror image. Achiral objects include tube socks, solid-mirror image. Achiral objects include tube socks, solid-colored ties and Т-shirts.colored ties and Т-shirts. Molecules, like larger objects, can be chiral or achiral. А Molecules, like larger objects, can be chiral or achiral. А simple example of а chiral molecule is the trisubstituted simple example of а chiral molecule is the trisubstituted methane bromochloroiodomethane. methane bromochloroiodomethane.

The simplest example of а chiral The simplest example of а chiral carbohydrate is the three-carbon carbohydrate is the three-carbon molecule glyceraldehyde.molecule glyceraldehyde.

Trying to superimpose the mirror image of а Trying to superimpose the mirror image of а molecule on that molecule visually, is one way to molecule on that molecule visually, is one way to determine molecular chirality. Another method, determine molecular chirality. Another method, which is much easier to apply, makes use of the which is much easier to apply, makes use of the observation that generally, whenever а carbon atom observation that generally, whenever а carbon atom in а molecule is bonded to four different groups, the in а molecule is bonded to four different groups, the molecule as а whole is chiral. Any organic molecule molecule as а whole is chiral. Any organic molecule containing а single carbon atom with four different containing а single carbon atom with four different groups attached to it exhibits chirality. Such а carbon groups attached to it exhibits chirality. Such а carbon atom is called а chiral center. А atom is called а chiral center. А chiral centerchiral center is an is an atom in а molecule that has four different groups atom in а molecule that has four different groups tetrahedrally bonded to it. Chiral centers within tetrahedrally bonded to it. Chiral centers within molecules are often denoted by а small asterisk. Note molecules are often denoted by а small asterisk. Note the chiral centers in the following moleculesthe chiral centers in the following molecules..

Organic molecules, especially Organic molecules, especially carbohydrates, may contain more than one carbohydrates, may contain more than one chiral center. For example, the following chiral center. For example, the following carbohydrate has two chiral centers.carbohydrate has two chiral centers.

2-butanol 1-chloto-1-iodoethane 3-methylhexane

Stereoisomers Stereoisomers are isomers whose atoms are connected in the are isomers whose atoms are connected in the same way but differ in their arrangement in space. The two same way but differ in their arrangement in space. The two nonsuperimposable mirror-image forms of а chiral molecule are nonsuperimposable mirror-image forms of а chiral molecule are stereoisomers.stereoisomers.

There are two major causes of stereoisomerism: (1) the presence There are two major causes of stereoisomerism: (1) the presence of а chiral center in а molecule, and (2) the presence of of а chiral center in а molecule, and (2) the presence of "structural rigidity" in а molecule. Structural rigidity is caused "structural rigidity" in а molecule. Structural rigidity is caused by restricted rotation about chemical bonds. It is the basis for cis by restricted rotation about chemical bonds. It is the basis for cis - trans stereoisomerism, а phenomenon found in some - trans stereoisomerism, а phenomenon found in some substituted cycloalkanes and some alkenes.substituted cycloalkanes and some alkenes.

For example, aldopentose has 3 asymmetric carbon atoms and For example, aldopentose has 3 asymmetric carbon atoms and can forms 8 stereoisomers (2 in 3 power = 8). Aldohesose has 4 can forms 8 stereoisomers (2 in 3 power = 8). Aldohesose has 4 asymmetric carbon atoms and can forms 16 stereoisomers (2 in 4 asymmetric carbon atoms and can forms 16 stereoisomers (2 in 4 power = 16). power = 16).

For representation of stereoisomers use formulas of Fisher. All For representation of stereoisomers use formulas of Fisher. All isomers of monosaccharides deviated into D- and L-isomers of monosaccharides deviated into D- and L-stereoisomers.stereoisomers.

Handedness (D and L configuration) is determined by Handedness (D and L configuration) is determined by the configuration at the highest-numbered chiral the configuration at the highest-numbered chiral center (for pentoses – Ccenter (for pentoses – C44, for hexoses – C, for hexoses – C55).).

Majority of monosaccharides refer to D-row.Majority of monosaccharides refer to D-row.

Stereoisomers can be subdivided into two types: enantiomers and Stereoisomers can be subdivided into two types: enantiomers and diastereomers. diastereomers.

Enantiomers Enantiomers are stereoisomers whose molecules are are stereoisomers whose molecules are nonsuperimposable mirror images of each other. Left- and right-nonsuperimposable mirror images of each other. Left- and right-handed forms of а molecule with а single chiral center are handed forms of а molecule with а single chiral center are enantiomers.enantiomers.

Diastereomers Diastereomers are stereoisomers whose molecules are not are stereoisomers whose molecules are not mirror images of each other. Cis - trans isomers (of both the mirror images of each other. Cis - trans isomers (of both the alkene and the cycloalkane types) are diastereomers. We will see alkene and the cycloalkane types) are diastereomers. We will see additional examples of carbohydrate diastereomers in the next additional examples of carbohydrate diastereomers in the next section. Stereoisomers that are not enantiomers are diastereomers; section. Stereoisomers that are not enantiomers are diastereomers; they must be one or the other.they must be one or the other.

Enantiomers Diastereomers

Fisher Projections. Fisher Projections. Drawing three-dimensional Drawing three-dimensional representations of chiral molecules, can be both time-representations of chiral molecules, can be both time-consuming and awkward. Fischer projections represent consuming and awkward. Fischer projections represent а method for giving molecular chirality specifications in а method for giving molecular chirality specifications in two dimensions. А two dimensions. А Fisher projectionFisher projection is а two- is а two-dimensional notation showing the spatial arrangement dimensional notation showing the spatial arrangement of groups about chiral centers in molecules. In а Fischer of groups about chiral centers in molecules. In а Fischer projection, а chiral center is represented as the projection, а chiral center is represented as the intersection of vertical and horizontal lines. The atom at intersection of vertical and horizontal lines. The atom at the chiral center, which is almost always carbon, is not the chiral center, which is almost always carbon, is not explicitly shown.explicitly shown.

The tetrahedral arrangement of the four groups attached The tetrahedral arrangement of the four groups attached to the atom at the chiral center is governed by the to the atom at the chiral center is governed by the following conventions: (1) Vertical lines from the chiral following conventions: (1) Vertical lines from the chiral center represent bonds to groups directed into the center represent bonds to groups directed into the printed page. (2) Horizontal lines from the chiral center printed page. (2) Horizontal lines from the chiral center represent bonds to groups directed out of the printed represent bonds to groups directed out of the printed page. page. Fischer projectionFischer projection

Our immediate concern is Fisher projections for Our immediate concern is Fisher projections for monosaccharides. Such projections have the monosaccharide monosaccharides. Such projections have the monosaccharide carbon chain positioned vertically with the carbonyl group carbon chain positioned vertically with the carbonyl group (aldehyde or ketone) at or near the top.(aldehyde or ketone) at or near the top.

The smallest monosaccharide that has а chiral center is The smallest monosaccharide that has а chiral center is the compound glyceraldehydes (2,3-dihydroxypropanal). The the compound glyceraldehydes (2,3-dihydroxypropanal). The structural formula and Fischer projections for the two structural formula and Fischer projections for the two enantiomers of glyceraldehyde are:enantiomers of glyceraldehyde are:

D-glyceraldehyde L-glyceraldehydeD-glyceraldehyde L-glyceraldehyde

The handedness (right and left) of these two enantiomers The handedness (right and left) of these two enantiomers is specified by using the designations D and L. The enantiomer is specified by using the designations D and L. The enantiomer with the chiral center - ОН group on the right in the Fischer with the chiral center - ОН group on the right in the Fischer projection is by definition the right-handed isomer (D-projection is by definition the right-handed isomer (D-glyceraldehyde), and the enantiomer with the chiral center - ОН glyceraldehyde), and the enantiomer with the chiral center - ОН group on the left in the Fisher projection is by definition the left-group on the left in the Fisher projection is by definition the left-handed isomer (L-glyceraldehyde).handed isomer (L-glyceraldehyde).

We now consider Fisher projections for the compound We now consider Fisher projections for the compound 2,3,4-trihydroxybutanal, а monosaccharide with four carbons and 2,3,4-trihydroxybutanal, а monosaccharide with four carbons and two chiral centers.There are four stereoisomers for this two chiral centers.There are four stereoisomers for this

compound - two pairs of enantiomers:compound - two pairs of enantiomers:

In the first enantiomeric pair, both chiral center - ОН In the first enantiomeric pair, both chiral center - ОН groups are on the same side of the Fischer projection, and in the groups are on the same side of the Fischer projection, and in the second enantiomeric pair, the chiral center - ОН groups are on second enantiomeric pair, the chiral center - ОН groups are on opposite sides of the Fisher projection. These are the only - ОН opposite sides of the Fisher projection. These are the only - ОН group arrangements possible.group arrangements possible.

A B First enantiomeric pair Second enantiomeric pair

C D

The D, L system used to designate the handedness of The D, L system used to designate the handedness of glyceraldehyde enantiomers is extended to monosaccharides with glyceraldehyde enantiomers is extended to monosaccharides with more than one chiral center in the following manner. The carbon more than one chiral center in the following manner. The carbon chain is numbered, starting at the carbonyl group end of the chain is numbered, starting at the carbonyl group end of the molecule, and the highest-numbered chiral center is used to molecule, and the highest-numbered chiral center is used to determine D or L configuration.determine D or L configuration.

The D, L nomenclature gives the configuration The D, L nomenclature gives the configuration (handedness) only at the highest-numbered chiral center. The (handedness) only at the highest-numbered chiral center. The configuration at other chiral centers in а molecule is accounted for configuration at other chiral centers in а molecule is accounted for by assigning а different common name to each pair of D, L by assigning а different common name to each pair of D, L enantiomers. In our present example, compounds А and В (the first enantiomers. In our present example, compounds А and В (the first enantiomeric pair) are D-erythrose and L-erythrose; compounds С enantiomeric pair) are D-erythrose and L-erythrose; compounds С and D (the second enantiomeric pair) are D-threose and L-threoseand D (the second enantiomeric pair) are D-threose and L-threose. .

A B C D

D- isomer L-isomer D-isomer L- isomer

А and С are diastereomers, stereoisomers that are not А and С are diastereomers, stereoisomers that are not mirror images of each other. Other diastereomeric pairs in our mirror images of each other. Other diastereomeric pairs in our example are А and D, В and С, and В and D. These four pairs are example are А and D, В and С, and В and D. These four pairs are epimers. epimers. Epimers Epimers are diastereomers that differ only in the are diastereomers that differ only in the configuration at one chiral center. In general, а compound that configuration at one chiral center. In general, а compound that has n chiral centers may exist in а maximum of 2n has n chiral centers may exist in а maximum of 2n stereoisomeric forms. For example, when three chiral centers are stereoisomeric forms. For example, when three chiral centers are present, at most eight stereoisomers (23 = 8) are possible (four present, at most eight stereoisomers (23 = 8) are possible (four pairs of enantiomers).pairs of enantiomers).

Stereoisomers.Stereoisomers.

1. Isomers in which the atoms have the same connectivity but differ 1. Isomers in which the atoms have the same connectivity but differ in spatial arrangement.in spatial arrangement.

2. Stereoisomerism results either from the presence of а chrial 2. Stereoisomerism results either from the presence of а chrial center or from structural rigidity caused by restricted rotation center or from structural rigidity caused by restricted rotation

about chemical bonds.about chemical bonds.

Enantiomers.Enantiomers.

1. Stereoisomers that are nonsuperimposable mirror 1. Stereoisomers that are nonsuperimposable mirror images of each other.images of each other.

2.Handedness (D and L configuration) is determined by 2.Handedness (D and L configuration) is determined by the configuration at the highest-numbered chiral center.the configuration at the highest-numbered chiral center.

3. Enantiomers rotate plane-polarized light in different 3. Enantiomers rotate plane-polarized light in different directions. (+) Enantiomers are dextrorotatory directions. (+) Enantiomers are dextrorotatory (clockwise), and (-) enantiomers are levorotatory (clockwise), and (-) enantiomers are levorotatory (counterclockwise). (counterclockwise).

Diastereomers.Diastereomers.

1. Stereoisomers that are not mirror images of each other.1. Stereoisomers that are not mirror images of each other.

2. Epimers are diastereomers whose configurations differ 2. Epimers are diastereomers whose configurations differ only at one chiral center. only at one chiral center.

Properties of Enantiomers.Properties of Enantiomers. Structural isomers differ in most chemical Structural isomers differ in most chemical

and physical properties. For example, structural and physical properties. For example, structural isomers have different boiling points and isomers have different boiling points and melting points. Diastereomers also differ in most melting points. Diastereomers also differ in most chemical and physical properties. They also chemical and physical properties. They also have different boiling points and freezing points. have different boiling points and freezing points. In contrast, nearly all the properties of а pair of In contrast, nearly all the properties of а pair of enantiomers are the same; for example, they enantiomers are the same; for example, they have identical boiling points and freezing points. have identical boiling points and freezing points. Enantiomers exhibit property differences in only Enantiomers exhibit property differences in only two areas: their interaction with plane-polarized two areas: their interaction with plane-polarized light and their interaction with other chiral light and their interaction with other chiral substances.substances.

Interactions between chiral compounds. Interactions between chiral compounds. А left-handed baseball player (chiral) and а right-handed baseball А left-handed baseball player (chiral) and а right-handed baseball

player (chiral) can use the same baseball bat (achiral) or wear the same player (chiral) can use the same baseball bat (achiral) or wear the same baseball hat (achiral). However, left- and right-handed baseball players baseball hat (achiral). However, left- and right-handed baseball players (chiral) cannot use the same baseball glove (chiral). This nonchemical (chiral) cannot use the same baseball glove (chiral). This nonchemical example illustrates that the chirality of an object becomes important when the example illustrates that the chirality of an object becomes important when the object interacts with another chiral object. Applying this generalization to object interacts with another chiral object. Applying this generalization to molecules, we find that the two members of an enantiomeric pair, because of molecules, we find that the two members of an enantiomeric pair, because of their differing chirality, interact differently with other chiral molecules. We their differing chirality, interact differently with other chiral molecules. We find that:find that:

1. А pair of enantiomers have the same solubility in an achiral solvent, such as 1. А pair of enantiomers have the same solubility in an achiral solvent, such as ethanol, but differing solubilities in а chiral solvent, such as в-2-butanol.ethanol, but differing solubilities in а chiral solvent, such as в-2-butanol.

2. The rate and extent of reaction of enantiomers with another reactant are the 2. The rate and extent of reaction of enantiomers with another reactant are the same if the reactant is achiral but differ if the reactant is chiral. The different same if the reactant is achiral but differ if the reactant is chiral. The different reactions that different enantiomers undergo are further considered in the reactions that different enantiomers undergo are further considered in the paragraph that follows.paragraph that follows.

3. Enantiomers have identical boiling points, freezing points, and densities, 3. Enantiomers have identical boiling points, freezing points, and densities, because such properties depend on the strength of intermolecular forces, and because such properties depend on the strength of intermolecular forces, and intermolecular force strength does not depend on chirality. Intermolecular intermolecular force strength does not depend on chirality. Intermolecular force strength is the same for both forms of а chiral molecule, because both force strength is the same for both forms of а chiral molecule, because both forms have identical sets of functional groupsforms have identical sets of functional groups

The two enantiomeric forms of а chiral molecule often The two enantiomeric forms of а chiral molecule often generate different responses from the human body. Sometimes generate different responses from the human body. Sometimes both enantiomers are biologically active, each form giving a both enantiomers are biologically active, each form giving a different response; sometimes both give the same response, but different response; sometimes both give the same response, but one isomer’s response is many times greater than that of the other; one isomer’s response is many times greater than that of the other; and sometimes only one of the two forms is biologically active, and sometimes only one of the two forms is biologically active, the other form giving no response. For example, the body’s the other form giving no response. For example, the body’s response to the D isomer of the hormone epinephrine is 20 times response to the D isomer of the hormone epinephrine is 20 times greater than its response to the L isomer. Epinephrine exerts its greater than its response to the L isomer. Epinephrine exerts its effect by binding to specialized receptors. It binds to the receptor effect by binding to specialized receptors. It binds to the receptor site by means of а three-point contact, D-epinephrine makes а site by means of а three-point contact, D-epinephrine makes а perfect three-point contact with the receptor surface, but the perfect three-point contact with the receptor surface, but the biologically weaker L-epinephrine can make only а two-point biologically weaker L-epinephrine can make only а two-point contact. Because of the poorer fit, the binding of the isomer is contact. Because of the poorer fit, the binding of the isomer is weaker, and less physiological response is observed.weaker, and less physiological response is observed.

4. Classification of monosaccharides.4. Classification of monosaccharides. Now that we have considered molecular chirality and its Now that we have considered molecular chirality and its

consequences, we return to the subject of carbohydrates by consequences, we return to the subject of carbohydrates by considering further details about monosaccharides, the simplest considering further details about monosaccharides, the simplest carbohydrates. Although there is no limit to the number of carbohydrates. Although there is no limit to the number of carbon atoms that can be present in а monosaccharide, only carbon atoms that can be present in а monosaccharide, only monosaccharides with three to seven carbon atoms are monosaccharides with three to seven carbon atoms are commonly found in nature. А three-carbon monosaccharide is commonly found in nature. А three-carbon monosaccharide is called а triose, and those that contain four, five, and six carbon called а triose, and those that contain four, five, and six carbon atoms are called tetroses, pentoses, and hexoses, respectively. atoms are called tetroses, pentoses, and hexoses, respectively.

Monosaccharides are classified as aldoses or ketoses on Monosaccharides are classified as aldoses or ketoses on the basis of type of carbonyl group present. Aldoses are the basis of type of carbonyl group present. Aldoses are monosaccharides that contain an aldehyde group. Ketoses are monosaccharides that contain an aldehyde group. Ketoses are monosaccharides that contain а ketone group. monosaccharides that contain а ketone group. Monosaccharides are often classified by both their number of Monosaccharides are often classified by both their number of carbon atoms and their functional group. А six-carbon carbon atoms and their functional group. А six-carbon monosaccharide with an aldehyde functional group is an monosaccharide with an aldehyde functional group is an aldohexose; а five-carbon monosaccharide with а ketone aldohexose; а five-carbon monosaccharide with а ketone functional group is а ketopentose.functional group is а ketopentose.

Monosaccharides are also often called sugars. Hexoses Monosaccharides are also often called sugars. Hexoses are six-carbon sugars, pentoses five-carbon sugars, and so on. are six-carbon sugars, pentoses five-carbon sugars, and so on. The word sugar is associated with "sweetness," and most (but not The word sugar is associated with "sweetness," and most (but not all) monosaccharides have а sweet taste. The designation sugar is all) monosaccharides have а sweet taste. The designation sugar is also applied to disaccharides, many of which also have а sweet also applied to disaccharides, many of which also have а sweet taste. Thus sugar is а general designation for either а taste. Thus sugar is а general designation for either а monosaccharide or а disaccharide.monosaccharide or а disaccharide. The simplest aldose and The simplest aldose and ketose are the trioses glyceraldehyde and dihydroxyacetone.ketose are the trioses glyceraldehyde and dihydroxyacetone.

The D and L designations specify the configuration at the The D and L designations specify the configuration at the highest-numbered chiral center in а monosaccharide. The highest-numbered chiral center in а monosaccharide. The configurations about other chiral centers are accounted for by configurations about other chiral centers are accounted for by assigning а different common name to each pair of D and L assigning а different common name to each pair of D and L enantiomers. This naming system, for simple aldoses, is given enantiomers. This naming system, for simple aldoses, is given

glyceraldehydes dihydroxycaetone

The L forms are mirror images of the molecules shown.The L forms are mirror images of the molecules shown.А major difference between glyceraldehyde and dihydroxyacetone is that А major difference between glyceraldehyde and dihydroxyacetone is that the latter does not possess а chiral carbon atom. Thus, D and L forms are the latter does not possess а chiral carbon atom. Thus, D and L forms are not possible for dihydroxy acetone. This reduces by half (compared with not possible for dihydroxy acetone. This reduces by half (compared with aldoses) the number of stereoisomers possible for ketotetroses, ketopentoses, aldoses) the number of stereoisomers possible for ketotetroses, ketopentoses, and ketohexoses. An aldohexose has four chiral carbon atoms, but а and ketohexoses. An aldohexose has four chiral carbon atoms, but а ketohexose has only three. atoins.ketohexose has only three. atoins.

Structure of monosaccharidesStructure of monosaccharides Aldehyde react with alcohols with formation Aldehyde react with alcohols with formation

of of hemiacetals:hemiacetals:

Monosaccharides as polyhydroxyaldehydes or polyhydroxyketons also form cyclic hemiacetals by intermolecular interaction between carbonyl and spatially approximate alcohol group. These interaction cases formation of five- and sixmember cycles. Sixmember cycle called pyranose and fivemember cycle – furanose.

Pyranose cycle forms after interaction of oxo-group with hydroxy-group at C5 carbon atom of aldohexoses or C6 carbon atom of ketohexoses.

Furanose cycle forms after interaction of oxo-group with hydroxy-group at C4 carbon atom of aldohexoses or C5 carbon atom of ketohexoses.

Shown higher formulas of monosaccharides name formulas of Colly-Tollens.

Cyclic forms of monosaccharidesCyclic forms of monosaccharides.. So far in this chapter, the structures of monosaccharides So far in this chapter, the structures of monosaccharides

have been depicted as open-chain polyhydroxy aldehydes or have been depicted as open-chain polyhydroxy aldehydes or ketones. However, experimental evidence indicates that for ketones. However, experimental evidence indicates that for monosaccharides containing five or more carbon atoms, such monosaccharides containing five or more carbon atoms, such open-chain structures are actually in equilibrium with two cyclic open-chain structures are actually in equilibrium with two cyclic structures, and the cyclic structures are the dominant forms at structures, and the cyclic structures are the dominant forms at equilibrium. The cyclic forms of monosaccharides result from equilibrium. The cyclic forms of monosaccharides result from the ability of their carbonyl group to react intramolecularly with the ability of their carbonyl group to react intramolecularly with а hydroxyl group. The result is а cyclic hemiacetal or cyclic а hydroxyl group. The result is а cyclic hemiacetal or cyclic hemiketal. Such an intramolecular cyclization reaction for D-hemiketal. Such an intramolecular cyclization reaction for D-glucose is shown:glucose is shown:

Structure 2 is а rearrangement of the projection formula for D-Structure 2 is а rearrangement of the projection formula for D-glucose in which the carbon atoms have locations similar to glucose in which the carbon atoms have locations similar to those found for carbon atoms in а six-membered ring. All those found for carbon atoms in а six-membered ring. All hydroxyl groups drawn to the right in the original projection hydroxyl groups drawn to the right in the original projection formula appear below the ring. Those to the left in the projection formula appear below the ring. Those to the left in the projection formula appear above the ring. Structure 3 is obtained by rotating formula appear above the ring. Structure 3 is obtained by rotating the groups attached to carbon-5 in а counterclockwise direction the groups attached to carbon-5 in а counterclockwise direction so that they are in the positions where it is easiest to visualize so that they are in the positions where it is easiest to visualize intramolecular hemiacetal formation. The intramolecular reaction intramolecular hemiacetal formation. The intramolecular reaction occurs between the hydroxyl group on carbon-5 and the carbonyl occurs between the hydroxyl group on carbon-5 and the carbonyl group (carbon-1). The - ОН group adds across the carbon - group (carbon-1). The - ОН group adds across the carbon - oxygen double bond, producing а heterocyclic ring that contains oxygen double bond, producing а heterocyclic ring that contains five carbon atoms and one oxygen atom. Addition across the five carbon atoms and one oxygen atom. Addition across the carbon - oxygen double bond with its accompanying ring carbon - oxygen double bond with its accompanying ring formation produces а chiral center at carbon-l, so two formation produces а chiral center at carbon-l, so two stereoisomers are possible. These two forms differ in the stereoisomers are possible. These two forms differ in the orientation of the - ОН group on the hemiacetal carbon atom orientation of the - ОН group on the hemiacetal carbon atom (carbon-1). In (carbon-1). In -D-glucose, the - ОН group is on the opposite -D-glucose, the - ОН group is on the opposite side of the ring from the CH2OH group attached to carbon-5. In side of the ring from the CH2OH group attached to carbon-5. In -D-glucose, the СН2ОН group on carbon-5 and the - ОН group -D-glucose, the СН2ОН group on carbon-5 and the - ОН group on carbon-1 are on the same side of the ringon carbon-1 are on the same side of the ring

In an aqueous solution of In an aqueous solution of ββ-glucose, а dynamic equilibrium exists -glucose, а dynamic equilibrium exists among the among the , , , and open-chain forms, and there is continual , and open-chain forms, and there is continual interconversion among them. For example, a freshly mixed solution of pure interconversion among them. For example, a freshly mixed solution of pure -D-glucose slowly converts to а mixture of both -D-glucose slowly converts to а mixture of both - and - and -D-glucose by -D-glucose by an opening and а closing of the cyclic structure. When equilibrium is an opening and а closing of the cyclic structure. When equilibrium is established, 63 % of the molecules are established, 63 % of the molecules are -D-glucose, 37 % are -D-glucose, 37 % are -D-glucose, -D-glucose, and less than 0.01 % are in the open-chain form. Intramolecular cyclic and less than 0.01 % are in the open-chain form. Intramolecular cyclic hemiacetal formation and the equilibrium between forms associated with it hemiacetal formation and the equilibrium between forms associated with it is not restricted to glucose. All aldoses with five or more carbon atoms is not restricted to glucose. All aldoses with five or more carbon atoms establish similar equilibria, but with different percentages of the alpha, establish similar equilibria, but with different percentages of the alpha, beta, and open-chain forms. Fructose and other ketoses with а sufficient beta, and open-chain forms. Fructose and other ketoses with а sufficient number of carbon atoms also cyclize; here, cyclic hemiketal formation number of carbon atoms also cyclize; here, cyclic hemiketal formation occurs. Galactose, like glucose, forms а six-membered ring, but both D-occurs. Galactose, like glucose, forms а six-membered ring, but both D-fructose and D-ribose form а five-membered ring.fructose and D-ribose form а five-membered ring.

D-Fructose cyclization involves carbon-2 (the keto group) and D-Fructose cyclization involves carbon-2 (the keto group) and carbon-5, which results in two CHcarbon-5, which results in two CH22OH groups being outside the ring OH groups being outside the ring (carbons 1 and 6). D-Ribose cyclization involves carbon-1 (the aldehyde (carbons 1 and 6). D-Ribose cyclization involves carbon-1 (the aldehyde group) and carbon-4.group) and carbon-4.

D-fructose D-ribose

Haworth projection formulas. Haworth projection formulas.

The structural representations of the cyclic forms of The structural representations of the cyclic forms of monosaccharides found in the previous section are examples of monosaccharides found in the previous section are examples of Haworth projection formulas. А Haworth projection formulas. А Haworth projectionHaworth projection is а of а is а of а carbohydrate. In а Haworth projection, the hemiacetal ring carbohydrate. In а Haworth projection, the hemiacetal ring system is viewed "edge on" with the oxygen ring atom at the system is viewed "edge on" with the oxygen ring atom at the upper right (six-membered ring) or at the top (five-membered upper right (six-membered ring) or at the top (five-membered ring).ring).

The D or L form of а monosaccharide is determined by the position The D or L form of а monosaccharide is determined by the position of the terminal СН2ОН group on the highest-numbered ring carbon atom. In of the terminal СН2ОН group on the highest-numbered ring carbon atom. In the в form, this group is positioned above the ring. In the ь form, which is not the в form, this group is positioned above the ring. In the ь form, which is not usually encountered in biological systems, the terminal CH2OH group is usually encountered in biological systems, the terminal CH2OH group is positioned below the ring.positioned below the ring.

or or configuration is determined by the position of the - configuration is determined by the position of the -ОН group on carbon-1 relative to the CH2OH group that ОН group on carbon-1 relative to the CH2OH group that determines D or L series. determines D or L series.

-D-Monosaccharide -D-Monosaccharide -D-Monosaccharide -D-Monosaccharide -L-Monosaccharide-L-Monosaccharide

Where Where or or configuration does not matter, the -ОН configuration does not matter, the -ОН group on carbon-1 is placed in a horizontal position, and а wavy group on carbon-1 is placed in a horizontal position, and а wavy line is used as the bond that connects it to the ringline is used as the bond that connects it to the ring..

The specific identity of а monosaccharide is The specific identity of а monosaccharide is determined by the positioning of the other: - ОН groups determined by the positioning of the other: - ОН groups in the Haworth projection. Any - ОН group at а chiral in the Haworth projection. Any - ОН group at а chiral center that is to the right in а Fisher projection formula center that is to the right in а Fisher projection formula points down in the Haworth projection. Any group to points down in the Haworth projection. Any group to the left in а Fisher projection points up in the Haworth the left in а Fisher projection points up in the Haworth projection. The following is a matchup between projection. The following is a matchup between Haworth projection and Fisher projection.Haworth projection and Fisher projection.

-form -form

Transition from Colly-Tollens formulas to Haworth Transition from Colly-Tollens formulas to Haworth formulasformulas

TautomeryTautomeryIn crystal state monosaccharides have cyclic structure. In water solution In crystal state monosaccharides have cyclic structure. In water solution

monosaccharides have five tautomeric forms – open form, monosaccharides have five tautomeric forms – open form, αα- and - and ββ--pyranose, pyranose, αα- and - and ββ-furanose.-furanose.

These kind of tautomery called cyclo-oxo-tautomery

Conformation of monosaccharidesConformation of monosaccharides Furanose forms of monosaccharides have plain structure, Furanose forms of monosaccharides have plain structure,

for pyranoses more profitable is form of armchair.for pyranoses more profitable is form of armchair. There are two kinds of armchair conformation of pyranose There are two kinds of armchair conformation of pyranose

forms. More stable is conformation with maximal number of forms. More stable is conformation with maximal number of substitutions (OH- and CH2OH-groups) in equatorial substitutions (OH- and CH2OH-groups) in equatorial locations.locations.

For aldohexose more profitable is form of armchairprofitable is form of armchair

Transition from Haworth formulas to armchair configuration:Transition from Haworth formulas to armchair configuration:

Methods of getting of monosaccharidesMethods of getting of monosaccharides 1. In green plants by photosynthesis: 1. In green plants by photosynthesis:

2. Disaccharides, oligosaccharides, and polysaccharides can be Disaccharides, oligosaccharides, and polysaccharides can be broken down to monosaccharide subunits by hydrolysis.broken down to monosaccharide subunits by hydrolysis.

3. Disintegration by Ruff. By these method we can get shorter carbon chain based on oxidation of monosaccharides.

4. Cyanhydrinic synthesis. 4. Cyanhydrinic synthesis. By these method we can get bigger carbon chain::

5. Reactions of monosaccharides5. Reactions of monosaccharides..

1.The reduction1.The reduction of D-fructose forms D-mannitol and D- of D-fructose forms D-mannitol and D-glucitol, the C-2 epimer of D-mannitol. D- lucitol—also called glucitol, the C-2 epimer of D-mannitol. D- lucitol—also called sorbitol—is about 60% as sweet as sucrose. It is found in plums, sorbitol—is about 60% as sweet as sucrose. It is found in plums, pears, cherries, and berries and is used as a sugar substitute in the pears, cherries, and berries and is used as a sugar substitute in the manufacture of candy.manufacture of candy.

1.Reduction. 1.Reduction. The carbonyl group present in а The carbonyl group present in а monosaccharide (either an aldose or а ketose) can be reduced to а monosaccharide (either an aldose or а ketose) can be reduced to а hydroxyl group, using hydrogen as the reducing agent. For aldoses hydroxyl group, using hydrogen as the reducing agent. For aldoses and ketoses, the product of the reduction is the corresponding and ketoses, the product of the reduction is the corresponding polyhydroxy alcohol, which is sometimes called а sugar alcohol. For polyhydroxy alcohol, which is sometimes called а sugar alcohol. For example, the reduction D-glucose gives D-glucitol.example, the reduction D-glucose gives D-glucitol.

D-Glucitol is also known by the common name D-D-Glucitol is also known by the common name D-sorbitol. Hexahydroxy alcohols such as D-sorbitol have sorbitol. Hexahydroxy alcohols such as D-sorbitol have properties similar to those of the trihydroxy alcohol glycerol. properties similar to those of the trihydroxy alcohol glycerol. These alcohols are used as moisturizing agents in foods and These alcohols are used as moisturizing agents in foods and cosmetics because of their affinity for water. D-Sorbitol is also cosmetics because of their affinity for water. D-Sorbitol is also used as а sweetening agent in chewing gum; bacteria that cause used as а sweetening agent in chewing gum; bacteria that cause tooth decay cannot use polyalcohols as food sources, as they can tooth decay cannot use polyalcohols as food sources, as they can glucose and many other monosaccharides.glucose and many other monosaccharides.

2. Oxidation. 2. Oxidation. Monosaccharide oxidation can yield three different types of Monosaccharide oxidation can yield three different types of oxidation products. The oxidizing agent used determines the product. oxidation products. The oxidizing agent used determines the product. Weak Weak oxidizing agents, such as Tollens, Fehling's, and Benedict's solutions, oxidize oxidizing agents, such as Tollens, Fehling's, and Benedict's solutions, oxidize the carbonyl group end of а monosaccharide to give an -the carbonyl group end of а monosaccharide to give an -onic acidonic acid. Oxidation . Oxidation of the aldehyde end of glucose produces gluconic acid, and oxidation of the of the aldehyde end of glucose produces gluconic acid, and oxidation of the aldehyde end of galactose produces galactonic acid. The structures involved aldehyde end of galactose produces galactonic acid. The structures involved in the glucose reaction arein the glucose reaction are::

Because monosaccharides act as reducing agents in such reactions, they are Because monosaccharides act as reducing agents in such reactions, they are called reducing sugars. With Tollens solution, glucose reduces Ag+ ion to Ag, called reducing sugars. With Tollens solution, glucose reduces Ag+ ion to Ag, and with Benedict's and Feling's solutions, glucose reduces Cu2+ ion to Cu+ and with Benedict's and Feling's solutions, glucose reduces Cu2+ ion to Cu+ ion. А ion. А reducing sugar reducing sugar is a carbohydrate that gives a positive test with is a carbohydrate that gives a positive test with Tollens, Benedict's and Feling's solutions. All monosaccharides are reducing Tollens, Benedict's and Feling's solutions. All monosaccharides are reducing sugars.sugars.

Tollens, Feling's, and Benedict's solutions can be used to test for Tollens, Feling's, and Benedict's solutions can be used to test for glucose in urine, а symptom of diabetes. For example, using Benedict's glucose in urine, а symptom of diabetes. For example, using Benedict's solution, we observe that if no glucose is present in the urine (а normal solution, we observe that if no glucose is present in the urine (а normal condition), the Benedict's solution remains blue. The presence of glucose is condition), the Benedict's solution remains blue. The presence of glucose is indicated by the formation of а red precipitate. Testing for the presence of indicated by the formation of а red precipitate. Testing for the presence of glucose in urine is such а common laboratory procedure that much effort has glucose in urine is such а common laboratory procedure that much effort has been put into the development of easy-to-use test methods. Strong oxidizing been put into the development of easy-to-use test methods. Strong oxidizing agents can oxidize both ends of а monosaccharide at the same time (the agents can oxidize both ends of а monosaccharide at the same time (the carbonyl group and the terminal primary alcohol group) to produce а carbonyl group and the terminal primary alcohol group) to produce а dicarboxylic acid. Such polyhydroxy dicarboxylic acids are known as dicarboxylic acid. Such polyhydroxy dicarboxylic acids are known as -aric -aric acidsacids. For glucose, such an oxidation produces glucaric acid.. For glucose, such an oxidation produces glucaric acid.

At selective oxidation primary alcohol group in aldoses molecules form uronic acids:

Although it is difficult to do in the laboratory, in Although it is difficult to do in the laboratory, in biological systems enzymes can oxidize the primary alcohol end biological systems enzymes can oxidize the primary alcohol end of an aldose such as glucose, without oxidation of the aldehyde of an aldose such as glucose, without oxidation of the aldehyde group, to produce а -group, to produce а -uronic aciduronic acid. For glucose, such an oxidation . For glucose, such an oxidation produces D-glucuronic acid.produces D-glucuronic acid.

D-Glucitol is also known by the common name D-D-Glucitol is also known by the common name D-sorbitol. Hexahydroxy alcohols such as D-sorbitol have sorbitol. Hexahydroxy alcohols such as D-sorbitol have properties similar to those of the trihydroxy alcohol glycerol. properties similar to those of the trihydroxy alcohol glycerol. These alcohols are used as moisturizing agents in foods and These alcohols are used as moisturizing agents in foods and cosmetics because of their affinity for water. D-Sorbitol is also cosmetics because of their affinity for water. D-Sorbitol is also used as а sweetening agent in chewing gum; bacteria that cause used as а sweetening agent in chewing gum; bacteria that cause tooth decay cannot use polyalcohols as food sources, as they can tooth decay cannot use polyalcohols as food sources, as they can glucose and many other monosaccharides.glucose and many other monosaccharides.

D-Glucose D-Glucitol

3. Transformation of monosaccharides by action of 3. Transformation of monosaccharides by action of alkali (epimerization)alkali (epimerization)

4. Ozazone formation.4. Ozazone formation.The tendency of monosaccharides to form syrups that do The tendency of monosaccharides to form syrups that do

not crystallize made the purification and isolation of not crystallize made the purification and isolation of monosaccharides difficult. Emil Fisher found that when monosaccharides difficult. Emil Fisher found that when phenylhydrazine is added to an aldose or a ketose, a yellow phenylhydrazine is added to an aldose or a ketose, a yellow crystalline solid that is insoluble in water is formed. He called crystalline solid that is insoluble in water is formed. He called this derivative an ozazone (“ose” for sugar; “azone” for this derivative an ozazone (“ose” for sugar; “azone” for hydrazone). Ozazones are easily isolated and purified and were hydrazone). Ozazones are easily isolated and purified and were once used once used extensively to identify monosaccharides extensively to identify monosaccharides

Mechanism of reaction of ozazone formationMechanism of reaction of ozazone formation

By the action of conc. HCl or heating wjth By the action of conc. HCl or heating wjth benzaldehyde forms ozones (ketoaldehydes).benzaldehyde forms ozones (ketoaldehydes).

At the reduction of ozones forms ketoses.At the reduction of ozones forms ketoses.

5. Mutarotation. 5. Mutarotation. - and - and -forms of -forms of monosaccharides are readily interconverted when dissolved in monosaccharides are readily interconverted when dissolved in water. This spontaneous process, called water. This spontaneous process, called mutarotation,mutarotation, results in results in an equilibrium mixture of an equilibrium mixture of - and - and -furanose forms and -furanose forms and - and - and --pyranose forms. The open chain that is formed during pyranose forms. The open chain that is formed during muterotation can participate in oxidation-reduction reactionsmuterotation can participate in oxidation-reduction reactions

6. Interaction with hydroxylamine6. Interaction with hydroxylamine

Aldoses with hydroxylamine forms oxymes.Aldoses with hydroxylamine forms oxymes.

This method use for obtaining lower aldoses from higher aldoses

7. Intermolecular dehydratation7. Intermolecular dehydratation

These reaction allow to distinguish hexoses from pentoses. Furfurol gives red color with aniline at the presence of HCl, 5-hydroxymethylfurfurol forms red color with resorcine (Selivanov reaction)

8.Glycoside Formation8.Glycoside Formation.. As you known, that hemiacetals and As you known, that hemiacetals and hemiketals can react with alcohols in acid solution to produce acetals and hemiketals can react with alcohols in acid solution to produce acetals and ketals. Because the cyclic forms of monosaccharides are hemiacetals and ketals. Because the cyclic forms of monosaccharides are hemiacetals and hemiketals, they react with alcohols to form acetals and ketals, as is illustrated hemiketals, they react with alcohols to form acetals and ketals, as is illustrated for the reaction of for the reaction of -D-glucose with methyl alcohol.-D-glucose with methyl alcohol.

The general name for monosaccharide acetals and ketals is glycoside. А The general name for monosaccharide acetals and ketals is glycoside. А glycosideglycoside is an acetal or а ketal fragment in а cyclic monosaccharide. More is an acetal or а ketal fragment in а cyclic monosaccharide. More specifically, а glycoside produced from glucose is а glucoside, from galactose specifically, а glycoside produced from glucose is а glucoside, from galactose а galactoside, and so on. Glycosides, like the hemiacetals and hemiketals from а galactoside, and so on. Glycosides, like the hemiacetals and hemiketals from which they are formed, can exist in both which they are formed, can exist in both and and forms. Glycosides are named forms. Glycosides are named by listing the alkyl or aryl group attached to the oxygen, followed by the name by listing the alkyl or aryl group attached to the oxygen, followed by the name of the monosaccharide involved, with the suffix –ide appended to it.of the monosaccharide involved, with the suffix –ide appended to it.

-D-glucose Methyl -D-glucopyranoside

Methyl--D-glucopyranoside

Methyl--D-glucopyranoside

The acetal (or ketal) of a sugar is called a The acetal (or ketal) of a sugar is called a glycosideglycoside, and the bond , and the bond between the anomeric carbon and the alkoxy oxygen is called a between the anomeric carbon and the alkoxy oxygen is called a glycosidic glycosidic

bondbond..

Similar to the reaction of a monosaccharide with an Similar to the reaction of a monosaccharide with an alcohol is the reaction of a monosaccharide with an amine in the alcohol is the reaction of a monosaccharide with an amine in the presence of a trace amount of acid. The product of the reaction is presence of a trace amount of acid. The product of the reaction is an an NN-glycoside. An -glycoside. An NN-glycoside -glycoside has a nitrogen in place of the has a nitrogen in place of the

oxygen at the glycosidic linkage.oxygen at the glycosidic linkage. An An SS-glycoside -glycoside has a sulfur in has a sulfur in

place of the oxygen at the glycosidic linkage.place of the oxygen at the glycosidic linkage.

Ancarbohydrate part of the glycoside Ancarbohydrate part of the glycoside molecule called aglicone.molecule called aglicone.

Glycosides very easy hydrolyses in acid medium:

O-, N- and S-glycosidesO-, N- and S-glycosides

99.Phosphate ester formation.Phosphate ester formation. . The hydroxyl groups of а The hydroxyl groups of а monosaccharide can react with inorganic oxyacids to form monosaccharide can react with inorganic oxyacids to form inorganic esters. Phosphate esters, formed from phosphoric acid inorganic esters. Phosphate esters, formed from phosphoric acid and various monosaccharides, are commonly encountered in and various monosaccharides, are commonly encountered in biological systems. For example, specific enzymes in the human biological systems. For example, specific enzymes in the human body catalyze the esterification of the carbonyl group (carbon-1) body catalyze the esterification of the carbonyl group (carbon-1) and the primary alcohol group (carbon-6) in glucose to produce and the primary alcohol group (carbon-6) in glucose to produce the compounds glucose 1-phosphate and glucose б-phosphate, the compounds glucose 1-phosphate and glucose б-phosphate, respectivelyrespectively

These phosphate esters of glucose are stable in aqueous solution These phosphate esters of glucose are stable in aqueous solution and play important roles in the metabolism of carbohydratesand play important roles in the metabolism of carbohydrates

-D-Glucose-1-phosphate -D-Glucose-6-phosphate

10. Amino Sugar Formation.10. Amino Sugar Formation. Amino sugars of Amino sugars of glucose, mannose, and galactose are common in nature. Such glucose, mannose, and galactose are common in nature. Such sugars are produced by replacing the hydroxyl group on carbon-2 sugars are produced by replacing the hydroxyl group on carbon-2 on the monosaccharide with an amino group. Amino sugars and on the monosaccharide with an amino group. Amino sugars and their N-acetyl derivatives are important building blocks of their N-acetyl derivatives are important building blocks of

polysaccharides found in cartilagepolysaccharides found in cartilage..

The N-acetyl derivatives of D-glucosamine and The N-acetyl derivatives of D-glucosamine and D-galactosamine are present in the biochemical markers D-galactosamine are present in the biochemical markers on red blood cells, which distinguish the various blood on red blood cells, which distinguish the various blood types. types.

-D-Glucosamine -D-Glalactosamine N-acety1-D-glucosanune

11. Acylation and alkylation of monosaccharides.11. Acylation and alkylation of monosaccharides.The OH-groups of monosaccharides show the chemistry The OH-groups of monosaccharides show the chemistry

typical of alcohols. For example, they react with acetyl chloride typical of alcohols. For example, they react with acetyl chloride or acetic anhydride to form esters.or acetic anhydride to form esters.

The OH-groups also react with dimethylsulfate/BaO or methyl iodide/silver oxide to form ethers. The OH group is a relatively poor nucleophile, so silver oxide or BaO is used to increase the leaving tendency of the iodide ion in the SN2 reaction.

9. Isomerization. 9. Isomerization. Monosaccharides undergo several types Monosaccharides undergo several types of isomerization, for example, after several hours an alkaline of isomerization, for example, after several hours an alkaline solution of D-glucose will also contain D- mannose and D- solution of D-glucose will also contain D- mannose and D- fructose. Both isomerizations involve an intramolecular shift of fructose. Both isomerizations involve an intramolecular shift of a hydrogen atom and a charge in the location of a double bonda hydrogen atom and a charge in the location of a double bond

The intermediate that is formed during this process is called an The intermediate that is formed during this process is called an endiol.endiol. The reversible transformation of glucose to fructose is an example of The reversible transformation of glucose to fructose is an example of an aldose-ketose interconversation. Because there is a change in the an aldose-ketose interconversation. Because there is a change in the conversion of glucose to mannose is referred to as an epimerization. Several conversion of glucose to mannose is referred to as an epimerization. Several enzyme-catalyzed reactions involving endiols occur in carbohydrate enzyme-catalyzed reactions involving endiols occur in carbohydrate metabolism.metabolism.

Representatives of monosaccaridesRepresentatives of monosaccarides

Representatives of dezoxy- and Representatives of dezoxy- and aminosaccharidesaminosaccharides

Derivatives of monosacchridesDerivatives of monosacchrides

Ascorbinic acid – strong reduction agent.Ascorbinic acid – strong reduction agent.

Synthesis of ascorbinic acidSynthesis of ascorbinic acid

Biologically important monosaccharides.Biologically important monosaccharides. Of the many monosaccharides, the most important in the human body are the Of the many monosaccharides, the most important in the human body are the

D-forms of glucose, galactose, fructose, and ribose. Glucose and galactose are D-forms of glucose, galactose, fructose, and ribose. Glucose and galactose are aldohexoses, fructose is а ketohexose, and ribose is an aldopentose. All four aldohexoses, fructose is а ketohexose, and ribose is an aldopentose. All four

of these monosaccharides are water-soluble, white, crystalline solidsof these monosaccharides are water-soluble, white, crystalline solids..

D-Glucose.D-Glucose. Of all monosaccharides, Of all monosaccharides,

о-glucose is the most abundant in о-glucose is the most abundant in nature and the most nature and the most

important from а important from а nutritional standpoint. Its nutritional standpoint. Its Fischer Fischer projection. projection.

D-Glucose

Ripe fruits, particularly ripe grapes (20% - 30% glucose by mass), are а good source of glucose, which is often referred to as grape sugar. Two other names for о-glucose are dextrose and blood sugar. The name dextrose draws attention to the fact that the optically active D-glucose, in aqueous solution, rotates plane-polarized light to the right. The term blood sugar draws attention to the fact that blood contains dissolved glucose. The concentration of glucose in human blood is fairly constant; it is in the range of 70 - 100 mg per 100 mL of blood. Cells use this glucose as а primary energy source.А 5% (m/v) glucose solution is often used in hospitals as an intravenous source of nourishment for patients who cannot take food by mouth. The body can use it as an energy source without digesting it.

D-Galactose.D-Galactose. А comparison of the Fischer projections for D- А comparison of the Fischer projections for D-galactose and D-glucose shows that these two compounds differ galactose and D-glucose shows that these two compounds differ only in the configuration of the - ОН group and - Н group on only in the configuration of the - ОН group and - Н group on carbon-4.carbon-4.

D-Galactose and D-glucose are epimers. D-Galactose is seldom D-Galactose and D-glucose are epimers. D-Galactose is seldom encountered as а free monosaccharide. It is, however, а component of encountered as а free monosaccharide. It is, however, а component of numerous important biochemical substances. In the human body, galactose is numerous important biochemical substances. In the human body, galactose is synthesized from glucose in the mammary glands for use in lactose (milk synthesized from glucose in the mammary glands for use in lactose (milk sugar), а disaccharide consisting of а glucose unit and а galactose unit. D-sugar), а disaccharide consisting of а glucose unit and а galactose unit. D-Galactose is sometimes called brain sugar because it is а component of Galactose is sometimes called brain sugar because it is а component of glycoproteins (protein-carbohydrate compounds) found in brain and nerve glycoproteins (protein-carbohydrate compounds) found in brain and nerve tissue. D-Galactose is also present in the chemical markers that distinguish tissue. D-Galactose is also present in the chemical markers that distinguish various types of blood - А, В, АВ, and O.various types of blood - А, В, АВ, and O.

D-Galactose D-Glucose

D-FructoseD-Fructose is the most important ketohexose. It is also is the most important ketohexose. It is also known as levulose and fruit sugar. Aqueous solutions of known as levulose and fruit sugar. Aqueous solutions of naturally occurring D-fructose rotate plane-polarized light to the naturally occurring D-fructose rotate plane-polarized light to the left hence the name levulose. The sweetest-tasting of all sugars, left hence the name levulose. The sweetest-tasting of all sugars, D-fructose is found in many fruits and is present in honey in D-fructose is found in many fruits and is present in honey in equal amounts with glucose. It is sometimes used as a dietary equal amounts with glucose. It is sometimes used as a dietary sugar, not because it has fewer calories per gram than other sugar, not because it has fewer calories per gram than other sugars but because less is needed for the same amount of sugars but because less is needed for the same amount of sweetness. From the third to the sixth carbon, the structure of D-sweetness. From the third to the sixth carbon, the structure of D-fructose is identical to that of D-glucose. Differences at carbons fructose is identical to that of D-glucose. Differences at carbons 1 and 2 are related to the presence of а ketone group in fructose 1 and 2 are related to the presence of а ketone group in fructose and an aldehyde group in glucose.and an aldehyde group in glucose.

D-Fructose D-Glucose

D-Ribose.D-Ribose. The three monosaccharides previously discussed in The three monosaccharides previously discussed in this section have all been hexoses. D-Ribose is а pentose. If carbon-3 and its this section have all been hexoses. D-Ribose is а pentose. If carbon-3 and its accompanying - Н and - ОН groups were eliminated from the structure of D-accompanying - Н and - ОН groups were eliminated from the structure of D-glucose, the remaining structure would be that of D-riboseglucose, the remaining structure would be that of D-ribose

D-Ribose is а component of а variety of complex molecules, D-Ribose is а component of а variety of complex molecules, including ribonucleic acids (RNAs) and energy-rich compounds such as including ribonucleic acids (RNAs) and energy-rich compounds such as adenosine triphosphate (ATP). The compound adenosine triphosphate (ATP). The compound 2-deoxy-D-ribose2-deoxy-D-ribose is also is also important in nucleic acid chemistry. This monosaccharide is а component of important in nucleic acid chemistry. This monosaccharide is а component of DNA molecules. The prefix deoxy- means "minus an oxygen"; the structures DNA molecules. The prefix deoxy- means "minus an oxygen"; the structures of ribose and 2-deoxyribose differ in that the latter compound lacks an oxygen of ribose and 2-deoxyribose differ in that the latter compound lacks an oxygen atom at carbon-2.atom at carbon-2.

D-Glucose D-Ribose

D-Ribose 2-Deoxy-D-ribose

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