Indian Journal of Chemistry Vol. 398, July 2000, pp. 483 - 496

Review Article

Polyhydroxy alkaloids from plants: NMR shielding behaviourt Neerja Pant, Dharam C Jain·, Rajendra S Bhakuni & RamP Sharma

Central Institute of Medicinal and Aromatic Plants, Lucknow 226015, India

Polyhydroxy alkaloids comprise a relatively small group of less than 49 members, consisting of five and six membered monocyclic and fused bicyclic ring systems. The majority of them show a general property as glycosidase inhibitors . The NMR shielding data for the polyhydroxy compounds are tabulated and critical spectral features are discussed briefly.

Polyhydroxy alkaloids are those compounds in which a nitrogen containing ring carries a number of hydroxyl groups and they are very soluble in water. Hydroxyl substituents on a ring are found in a definite configuration that suggest a structural resemblance to monosaccharides. These compounds are recognised as one class of compounds because of their common structural features and possessing general properties as glycosidase inhibitors 1

,2. The glycosidase inhibitors are the enzymes which remove the sugar units one at a time from the end of ol igosaccharides.

Alkaloidal glycosidase inhibitors have ability to modulate the metabolism of mammals, insects and viruses. It has been clearly demonstrated that they have a widespread defensive strategy in nature3

-5

. The use of these compounds as tools in glycoprotein studies has opened up new frontiers in cancer, AIDS and other immunological research . Remarkable diversity of biological activities has generated considerable interest in the polyhydroxy alkaloids and has led to the expansion of the class as a whole.

The diverse spectrum of biological activities of polyhydroxy alkaloids has also stimulated the synthesis of numerous analogues as well as discovery of novel alkaloids from natural sources. The use of novel isolation and purification techniques and specific detection methods has increased the number of these alkaloids6

-8

.

Polyhydroxy alkaloids known to-date have been isolated from the families of higher plants, such as Legum inoceae, Polygonaceae, Euphorbiaceae, Moraceae, Aphidiaceae, Solanaceae and from many

. . 9 m1cro-orgamsms .

The compounds isolated till now from the plants

te l MAP C01;1munication No. 98-341

are presented with their physical constants (ao, M+) and enzyme activity in Table I.

Structure determination. Chemical methods for determining the structure of polyhydroxy alkaloids are generally limited since these compounds are present in small quantities in the plants. Derivatization, particularly peracetylation is a useful method for establishing the number of hydroxy l groups present in the alkaloid. The colour developed with certain spray reagents on TLC provides some preliminary information about the presence of ring system8

·10

. UV and IR are not very useful for identification. The structure elucidation of the alkaloids primarily depends upon mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. X-ray crystallography is a powerful technique which has provided information about stereochemistry and absolute configuration in many compounds. Circular dichorism (CD) technique has also been used to determine the absolute configuration by the use of the benzoate chirality method .

Mass spectrometry (MS) provides useful information with regard to molecular formula of an unknown alkaloid, number and distribution of particular substituents 11

•

From the literature survey, it is evident that NMR (

1 H and 13C) spectroscopy plays a distinctive role in structure elucidation of these compounds. Both 1 H and 13C NMR provide gross structural information and particularly 1 H NMR produces considerable stereochemical information. Protons geminal to hydroxyl group genera lly appear at low field , 8 3.5-4.5 ppm in the spectrum of the molecule. The remaining protons appear in the region 8 1-3 ppm, as a complex of overlapping signals at low field strengths; coupling constant between adjacent protons usually indicate their stereochemical relationship to

484 INDIAN J CHEM, SEC B, JULY 2000

Miss Neerja Pant PAis currently working as a research scholar in Department of Phytochemical Technology Division, CIMAP, Lucknow. She obtained her MSc degree in chemistry in 1996 from Lucknow University and has a throughout first class carreer. Her field of research is mainly based on the bioactive natural product compounds.

Dr D C Jain, Scientist-E, Central Institute of Medicinal and Aromatic Plants (CIMAP) Lucknow, India received his master ' s degree in organic chemistry from the University of Rajasthan, Jaipur, India and Ph.D. from the Un iversity of Indore in 1982. In 1982 he joined CIMAP. Dr Jain has wide research interest in natural products chemistry and developed a new antimalanal drug arteether from the plant Artemisia annua. He is author of 60 publications and I 0 patents including two international patents.

Dr R S Bhakuni, Scientist, Central Institute of Medicinal & Aromatic Plants, Lucknow, India received his M.Sc degree in 1978 and Ph.D. in 1987 in organic chemistry from Kumaun University, Nainital. He has worked on anti­cancer drug Taxol as PDF with Prof K V Rao at the University of Gaimvi.Jie, Florida USA for two years. Working in natural products chemistry since 1981, he has published 31 research papers, 7 patents including one international patent.

Dr. Ram Prakash Sharma is retired from Central Institute of Medicinal & Aromatic Plants (CS IR) as Director Grade Scientist and is presently working as an Emeritus Scientist (CSIR), Chemistry Department, . Lucknow University, Lucknow. He worked as a Research Associate from 1972- 1975 with Prof. Werner Herz at the Florida State University, USA. In 1976-77, he was appointed as a pool officer at NCL, Pune with a project " Synthesis of carbofuran-a pesticide¥-. From 1977-92, he served in Regional Research Laboratory, Jorhat in Natural Products Chemistry Division . In 1992-99 Dr. Sharma served as Head of the Phytochemical Technology Division at CIMAP, Lucknow and worked on Artemisinin--an antimalarial drug and Taxol --an ant icancer drug. He posseses 150 research publications, 6 review artic les and 18 patents.

PANT eta/.: POL YHYDROXY ALKALOIDS FROM PLANTS: NMR SHIELDING BEHAVIOUR 485

Table 1---Polyhydroxy alkaloids isolated from natural sources

Sl. Chemical /Common Physical Plant/Organism name Plant Enzyme activity Ref No name Constants[a]0 ; M+ part

Pyrrolidine group

I. 2R-Hydroxymethyl-3S- + 46.5° (c I,H20) Castanospermum Seeds Some activity against 3,9 hydroxy pyrrolidine Australe Mammalian gut SUI

(CYB-3) otherwise inactive

2. 2R-Hydroxymethyl-3R, + 6.3° (c I, H20); Angylocalyx Seeds and Inhibitor of amylog- 3,9,17, 4S-dihydroxypyrrolidine 133 boutiqueanus Fruits lucosidase 18, 19, (DAB-I) angy/ocalyx 20,21

pynaertii arachniodes standishii a/exa leiopetala

3. 2R,5R-Dihydroxymethyl-3R, + 56.9° (c 0.54, Lonchocarpus sericeus Seeds, leaves Inhibit a - and 13 3,9,22 4R,-dihydroxypyrrolidine H20) 163 Derris elliptica glucosidase, trehalase (DMDP) Ompha/ea sp. and human 13-mannosid

Urania fulgens Ag/aonema treubii

4. 2-Hydroxymethyl-3 , 4- + 26.2° (c 1.10, Angylocalyx Seeds and Inhibit 13- mannosidase 17 dihydroxy-6-methyl MeOH); 147 pynaertii Pods pyrrolidine ( 6-deoxy DMDP)

5. N-(Hydroxy-ethyl)-2- 161 Castanospermum Seeds 23 (hydroxymethyl)-3-hydroxy austra/e pyrrolidine

6. 2,5-Dideoxy-2,5-imino-D2 + 33 .38 (c 0.95, Hyacinthoides Leaves 24,25 glycero-D-mannoheptitol H20); 193 Non-scripta (Homo DMDP) Hyacinthus orienta/is Bulb

6a. 2,5-lmino-2,5,6-trideoxy- + 98.48 (c 1.13,H20); Hyacinthus Bulb It suppressed act ivity 25 D-manno-heptitol 177 orienta/is toward B. glucosidase (6-deoxy Homo DMDP) B-galactosidase &

trehalase

6b. 2,5-Imino-2,5,6-tideoxy- + 41 .38 (c 0.56,H20); Hyacinthus Bulb Very specific inhibiton 25 D-gulo-haptitol 177 orienta/is of a-L-fucosidase

Piperidine group

7. I ,2,5-Trideoxy-1 ,5-imino- + 19.5° (c l .O,H20); F OROpyrum escu/entum Seeds, leaves Good inhibitor of 3,9,17, D-arabinohexitol 147 Xanthocercis zambesiO< isomaltase and 22,26 (Fagomine) Castanospermum Roots certain a and 13- 27,28

!lustrale Morus sp. galactosidase !lngylocalyx pynaertii

8. 3-epi-Fagomine + 69° (c 0.5,H20); Xanthocercis Leaves More potent inhibitor 25 147 ::ambesiaca of isomaltase and 13-

galactosidase

Contd.

486 INDIAN 1 CHEM, SEC B, JULY 2000

Table 1--Polyhydroxy alkaloids iso lated from natural sourcesL:Contd.

SL Chemical /Common Physical Plant/Organism name Plant Enzyme activity Ref No name Constants[a]0 ; M+ part

9. 3,4 -Diepifagomine -8 .7° (c 0.3,H20); Xanthocercis Leaves No inhibition 25 147 zambesiaca

10. 1.5-Dideoxy- 1 ,5-imino- + 42 .1 o (c I ,H20); Morus sp. Root bark Potent inhibitor of 3,9,22, D-glucitol 163 Bacillus subtilis Culture a - and !3- glucosidase 29 ( 1- Deoxynojirimyc in) Streptomyces Fi ltrates

Lavendulae

II. 3-0-f.l-D-Glucopyranosyl -18 .2° (c 0.48,H20); Xanthocercis Leaves No inhibition 25 Fagomine 309 zambesiaca

12. 4-0-f.l-D-Glycopyranosyl -3 .0° (c 0.82,Hz0); Xanthocercis Leaves No inhibit ion 25 Fagomine 309 zambesiaca

13 . 5-Amino-5-deoxy-D- + 100° (c I ,H20); Streptomyces Culture 3,9 Glucopyranose roseochromogenes fi ltrates (Noji rimycin)

14. I ,5-Dideoxy-1 ,5-imino- -41.4° (c 0.74,H20); Lonchocarpus Seeds Effective inhibitor 3,9, 17, D-mannitol 163 sericeus of a-mannosidase 22,30 (Deoxymannojirimycin) Angylocalyx sp. a-fucosidase,

Uraniafulgens a-glucosidase (yeast) Omphalea sp. f.l-glucosidase {emulsin (host plant of U. fulgen: and insect trehalase

15. 5-Amino-5 -deoxy- + 4.6° (c 0.5,H20) Streptomyces Culture 3,9 D-mannopyranose Lavendulae filtrates (Noj irimycin-B)

16. 5-Amino-5-deoxy-D- + 85.6° (c l.O,HzO) Streptomyces Culture 3,9 Ga lactopyranose Lydicus filtrates (Galactostatin)

17. 2,6-Dideoxy-2,6-imino + 77.2° (c 0.57,H20); Omphalea diandra Leaves Potent inhibitor of 3,31 ,32 D-glycero-L-gl lo-heptitol 193 Urania fulgens digestive a-glucosidas< ( a -Homonoj irimycin)

18. f.l- Homonoji rimycin - 1.7° (c 0.35,Hz0) ; Aglaonema treubii Whole plant Weak inhibi tor of 32 193 f.l -g lucosidase

19. a-Homomannojirimycin + 4.3° (c 0.62,H20); Aglaonema treubii Whole plant Very weak inhibitor 32 193 of human liver-a.-

mannosidase

20. 13-Homomannojirimycin + 12.0° (c 0.27,H20); Aglaonema treubii Whole plant Weak inhibitor of 32 193 !3-glucosidase

21. 7 -0-f.l- D-G lucopyranosyl + 24 .6° (c 0.70,H20 ); Aglaonema treubii Whole plant 32

-a- homonojirimycin 355

22. 2 -0-a-D-Galactopyranosy I + 168.8° (c 0.54, Aglaonema treubii Whole 32

a-homonoj irimycin H20)3 55 plant

23. a-3,4-Di-epihomono- + 39.1 o (c 0.51 ,H20); Aglaonema lreubii Whole plant 32 Jirimyci n 193

Contd.

PANT eta/. : POL YHYDROXY ALKALOIDS FROM PLANTS: NMR SHIELDING BEHAVIOUR 487

Table 1--Polyhydroxy alkaloids isolated from natural sources:.......Contd.

Sl. Chemical /Common Physical Plant/Organism name Plant Enzyme activity Ref No name Constants[a]0 ; M+ part

Pyrrolizidine group

24. (I R,2R,3R,7S,7aR)-3- + 19.3° (c 2.09,MeOH) Castanospermum Seeds Inhibitory activity 28 hydroxy methyl-1 ,2,7- 189 Australe towards trihydroxy-pyrrolizidine amyloglucosidase and

(Australine) a- glucosidase (7-epi-Aiexine)

25 . (IS, 2R, 3R, 7S, 7aR)-3- Castanospermum Leaves Inhibit 10,33 amyloglucosidase

hydroxy methyl-1 ,2,7- Australe and a-glucosidase trihydroxy-pyrrolizidine ( 1-epi-Australine)

26. (I R, 2R, 3S, 7S, 8R)-3- -3 .5° (c 1.35,H20); Castanospermum Seeds Poor inhibitor of 3,33,34

Hydroxymethyl- I ,2, 7- 189 Australe glucosidase Trihydroxypyrrolizidine (3 , 7a-diepi-Alexine)

27 . (IR,2R,3R,6S,7S,7aR)- + 16.9 (c 0.8,H20); Casuarina Bark 35

(3-hydroxymethyl)- 1 ,2,6, 7- Equisetifolia Tetrahydroxypyrrolizidine (Casuarine)

27a. Casuarine-6-a-gl ucoside Casuarina Bark 36 Equistifolia Eugeniajambolana Leaves

28 . (I R, 2R, 3R, 7S, 8S)-3- + 40.0° (c 0.25,H20); Alexa leiopetala Dried pod Poor inhibitor of 3,19,33

Hydroymethyl-1 ,2, 7- 189 mammalian digestive

Trihydroxypyrrolizidine B-glucosidase and

(A lexine) B-galactosidase

29. (IS, 2S, 3S, 7S, 7aS)-3- + 11.6° (c 0.37,H20); Castanospermum Seeds 33

Hydroxymethyl-1 ,2, 7- 189 australe Trihydroxypyrrolizidine ( 1,2,3-triepi-Alexine)

30. ( 1 S, 2R, 3R, 7R, 7aS)-3- + 8.5° (c 0.41 ,H20); Castanospermum Seeds Active against 33

Hydroxymethyl-1 ,2, 7- 189 australe a-glucosidase Trihydroxypyrrolizidine (I , 7a-diepi-Alexine)

31. (IS, 2R, 3R, 7R, 7aS)-3- + 42.2° (c 0.27,MeOH) Castanospermum Seeds 33

hydroxymethyl-1 ,2, 7- 229 australe trihydroxypyrro1izidine (I , 7-isopropylidine)

Indolizidine group

32. (IS, 2S, 8aS)-1 ,2- -3 .3° (c 0.33,MeOH); Astragalus Leaves Good inhibitor of 37 Diydroxyindolizidine 157 Lentiginosus Amyloglucosidase (Lentiginosine) And fungual

a-glucosidase

Contd.

488 INDIAN J CHEM, SEC 8 , JULY 2000

Table 1--Polyhydroxy alkaloids isolated from natural sources-Con/d.

Sl. Chemical /Common No name

33. ( IS, 2S, 8aS)-I ,2-Diydroxyindolizidine (2-ep i-Lenti gi nosine)

34. (IS, 2R, 8R, 8aR)-I ,2,8-

Trihydroxyoctahydro-indoli zidine (Swai nson ine)

35 . Swainsonine-N-oxide

36. 7-Deoxy-6-epi-Castanosperminc

37. ( IS. 6S, 7R, 8R, 8AR)-I ,6,7 ,8-Tetrahydroxy-octahydroindol izidine (Castanospermine)

38. ( IS, 6R, 7R, 8R, 8AR)-I ,6, 7,8-Tetrahydroxy-Octahydroindolizid ine (6-epi -Castanospermine)

39. 6,7-Diepicastanospermine

40. 8-Azab icyclo (3 .2.1 .) Oct an- I ,2.3-triol (Calystegine A3)

Physical Plant/Organism name Plant Constants[a) 0 ; M+ part

-32.5° (c 0.1 3,MeOH); Astragalus Leaves 157 Lentiginosus

-78.9° (c I. 14,MeOH); Rhizontonia Mycelium mats

173 leguminicola Plant, Swainsona canescens woody part Astragalus lentiginosus Astragalus emoryanus Oxytropis sp. Metarhizium an~opliaE Broth filtrat Ipomoea sp.

Astragalus Abovegrour lentiginosus Parts Oxytropis sericea

+ !8.3° (c 0.712,MeOH Castanospermum Seeds 173 Australe

+ 79.T (c 0.93,H20); Castanospermum Seeds, 189 Australe Dri ed pod

Alexa sp.

+ 8.0 (c 1.09,MeOH); Castanospermum Seeds 189 Australe

+ 42.7° (c 0.675,MeOH Castanospermum Seeds 189 australe

Nortropane group

159 Convolvulus arvensis Roots Calystegia sepium Atropa bel/adona Solanum tuberosum Hyoscyamus species Scopolia carniolica Mandragora officinaru Daturasp.

Enzyme act ivity

Inactive against Amyloglucosidase And other glucosidase

Inhibitor of lysosoma l

a-mannosidase

Inhibit amyloglucosidasc And yeast a-glucosidase

Potent inhibitor of a , 13-glueosidase, Amyloglucosidase and f3-glucocerebrosidase

Inhibit a -glucosidase Potent. inhibitor of Amyloglycosidas~

Moderate inhibitor of f3-galactosidase Poor inhibitor of f3-glucosidase

Inhibitor of amylo-Glucosidase a-g lucosidase Moderate Inhib itor of P-glucosidase

Good inhibitor of f3-glucosidase and a weak inhibitor of a-galactosidase

Ref

37

3,9. 11

38.39. 40,4 1

2, 41

42

9.43. 44.45

3.9. 46

3.23

6, 15. 16,47 48

Con! d.

PANT eta/.: POL YHYDROXY ALKALOIDS FROM PLANTS: NMR SHIELDING BEHAVIOUR 489

Table 1---Polyhydroxy alkaloids isolated from natural sources-Contd.

Sl. Chemical /Common Physical Plant/Organism name Plant Enzyme activity Ref No name Constants[ a ]o; M+ part

41. 8-Azabicyclo (3.2. 1) 175 Calystegia sepium Cultured root 6, 15.16 Octan-1 ,2,3 ,6-tetraol Atropa bel/adona and leaves 48,49 (Calystegine B1) Hyoscyamus niger

Scopolia carniolica Solanum tuberosum Mandragora officinaru Duboisia leichhardtii

42. 8-Azabicyclo (3 .2.1 )- 175 Calystegia sepium Root Potent inhibitor 6.15 . 16 Octan- I ,2,3,4-tetraol Ipomoea sp. tuber and Of 13-glucosidase 40,47 (Calystegine B2) Solanum tuberosum leaves a -galactosidase and 48,49

Datura wrightii fruits and Trehalase Archerontia atropus seeds Atropa bel/adona Hyoscyamus niger Scopolia carniolica Mandragora officinaru Duboisia leichharadtii

43 . (Ia, 2a, 3a, 4B, 6a)- 40.6°(C 0.32,H20); Duboisia leichhardtii Leaves Active agai nst 49 Pentahydroxy-nortropane 191 a-mannosidase (Calystegine - C2) No inhibitory

Activity against 13-galactos idase And 13-glucosidase

44. Calystegine C 1 Morz1s alba Leaves Potent inhibitor of 49 Scopolia japonica roots 13-glucosidase Physalis alkekengi 13-galactosidase Duboisia leichhardtii but not agai nst

a-galactosidase

45 . Calystegine B3 Scopolia japonica Roots 49 Physalis alkekengi

46. Calystegine B. Physalis alkekengi Leaves 49 Duboisia leichhardtii Scopolia japonica Roots

one another 11•

13C NMR spectroscopy provides useful confirmatory evidence for the carbon atoms bearing an oxygen or nitrogen substituent as they are identifiable by their shift to low-field.

the literature and there is no systematic compilation of it for the biologically significant polyhydroxy alkaloids till now, despite availability of several reviews and chapters in various books. A review of the available NMR literature of the important class of polyhydroxy alkaloids is therefore, timely given . The 1H and 13C NMR chemical shifts for the alkaloids isolated from the plants are given in Tables II(a-e) and III(a-e), respective ly. The solvent used in the NMR experiments for most a lkaloids is deuterated water (020). Other so lvents used to obtai n the data are listed in the tables . The interna l standard used was trimethylsilane (TMS) or in some cases a chemica l shift related to it was used . The critical features which cou ld readily be employed for the identifi cation,

The 20 NMR techniques are now available, and the selection of these best suited to the problem under investigation is an important factor in establishing the structure with a minimum expenditure of time and money. The complexity of the structure resides mainly in the stereochemistry of the hydroxyl groups which control the glycosidase inhibitory properties of each alkaloid . So it is important to establish

h . . II 12 stereoc em tstry unequtvoca y .

However, NMR shielding data are sti ll scattered in

490 INDIAN J CHEM, SEC B, JULY 2000

Table Ila--- 11-1 NMR data of pyrrolidine group of alkaloids 2-6b

Proton No. (2l0 (4)17 (5)23 (6)24 (6a)2s (6b )25

H-2 3.62 3.19 2.62 3. 13 3.05 3.07 1-1-3 4.10 3.83 4.18 . 4. 12 3.84 3.92 H-4a 4.34 3.62 1.97 3.91 3.74 4.03 H-4b 1.80 1-1-Sa 3.37 2.97 3.14 3. 16 3.0 1 3.34 H-5b 3.58 2.64 H-6a 3.84 1.20 3.03 3.74 3.65 3.71 H-6b 3.96 2.72 3.69 3.71 3.78 H-7a 3.68 3.73 3.84 1.71 1.79 H-7b 3.63 3.73 1.93 1.90 H-8a 3.67 3.74 3.64 3.72 H-8b 3.55 3.64 3.77 3.72

Table llb-- 11-1 NMR data of piperidine group of alkaloids 9-23

Proton No. 926 11 26 1732 1832 193 ~ 2032 21 32 2232 2332.'

1-1-la 2.91 2.65 3.29 2.66 3.15 2.87 3.44 3.50 3.65 H-ib 2.92 3. 11 H-2a 1.62 1.51 3.75 3.25 4.02 4.0 1 3.75 3.81 4.48 H-2b 2.04 2.19 H-3 3.93 3.79 3.50 3.39 3.68 3.56 3.53 3.64 4.39 H-4 3.75 3.38 3.2 1 3.25 3.65 3.59 3.24 3.27 4.26 H-5 3. 16 2.63 2.87 2.66 2.75 2.59 2.90 2.87 3.87 H-6a 3.68 3.7 1 3.57 3.64 3.75 3.74 3.60 3.59 4.2 1 H-6b 3.71 3.87 3.90 3.89 3.80 3.84 3.88 3.90 4.30 H-7a 3.79 3.64 3.69 3.62 3.933 3.83 4.42 H-7b 3.86 3.89 3.748 3.7 1 4.13 3.9 1 4.6 1 32

II :Giu (1-1 1 '-H6b') : 1.58, 3.30, 3.5 1, 3.41 , 3.47, 3.73 , 3.92 . 21: Gi u (H1'-H6b') : 4.50, 3.32, 3.51 , 3.40, 3.50, 3.74, 3.927. 22: Galac (H1'-H6b'): 5.13 , 3.87, 3.93, 4.00, 4. 17. 3.75 , 3.75 ' solvent used Pyridine-£4 -DzO (3 : I)

Table llc- 1 H NMR data of pyrro li zicline group of polyhydroxy alkaloids 24-28

Proton No. 2428 2634 2735 27a36-' 2819

H-1 4.4 1 4. 12 4. 16 4.14 4.05 H-2 3.92 3.96 ·3.79 3.79 3.64 H-3 3.03 3. 16 303 3. 11 2.79 H-5a 2.93 2.96 2.9 1 3. 11 2.79 H-5b 3.1 8 2.74 3.27 3. 26 2.79 H-6a 2.02 1.82 4.2 1 4.22 2.04 H-6b 2.02 1.82 1.60 H-7 4.58 4.24 4 .1 9 4.36 4.29 H-7a 3.46 :us 3.07 3. 11 3. 19 H-8a 3.64 3.80 3.77 3.62 3.69 H-8b 38 1 3.70 3.6 1 3.75

27a :Giu (1-1 1'- H6b') : 5.0 1, 3 59, 3.7 1, 3.43, 3.75. 3.89, 3.78 *So lvent used - Acetone

Table lld- 111 NMR da ta of ln clo lizidinc group of polyhyclroxy alka lo ids 32-39

Proton No. 3237 33Ji.' 3642 3743 3923

H-1 3.66 3.70 4.3 1 4.40 4.44

H-2a 4.08 4.24 1.71 2.33 1. 73 H-2b _ 2. 12 1.70 2.28

tl-3a 2.63 2.22 2.12 3.06 2 . 3~

H-3b 2.85 3.54 3. 11 2.20 3.25 1-1-Sa 2.06 2. 10 2. 12 3. 16 2.65

Contd

PANT et al.: POL ¥HYDROXY ALKALOIDS FROM PLANTS: NMR SHIELDING BEHAVIOUR 491

Table llci-1H NMR data oflndolizidine group ofpolyhydroxy alkaloids 32-39 -contd

Proton No. 3lJ1 ,)ln.• w2 3~J

H-5b 2.95 3.04 H-6a 1.85 1.94 H-6b 1.20 1.20 H-7a 1.85 1.94 H-7b 1.20 1.20 H-8a 1.85 1.94 H-8b 1.20 1.20 H-9 1.95 1.98

'solvent used : 33, CDCh; 36,CD30D

3.03 3.99

1.38 2.12 4.12

1.65

2.04 3.60

3.30

3.58

2.01

3.08 3.98

3.98

4.08

2.48

Table ue---·H NMK <lata or Nortropane group otpolyhydroxy alkaloids 40-43

Proton No. 40'6 41 16 41 16 4349

H-2 3.3 3.2 3.17 3.783 H-3 3.6 3.3 3.25 3.476 H-4a 1.4 1.3 3.4 3.618 H-4b 1.9 1.88 H-5 3.4 3.12 3.12 3.171 H-6a 1.4 3.95 1.8 4.276 H-6b 1.9 1.8 H-7a 1.4 1.3 1.5 1.648 H-7b 1.9 2.3 1.37 2.371

Table llla-13C NMR data ofpyrrolidine group ofpolyhydroxy alkaloids (1-6b)

Carbon No. 1zo 311 4 '7 523 624 6a15 6b1S

C-2 67.4 64.4 64.3 76.8 61.3 64.4 68.9 C-3 76.4 80.7 80.8 76.1 76.7 80.5 82.0 C-4 75 .1 80.7 86.0 34.9 77.0 84.3 80.7 C-5 50.8 64.4 58.5 54.8 61.7 60.3 61.0 C-6 59.7 64.9 19.9 59.6 60.6 38.3 64.5 C-7 64.9 65 .1 62.1 71.7 64.9 32.9 C-8 64.2 62.9 62.0 62.2

Table lllb-13C NMR data for piperidine group ofpolyhydroxy alkaloids 7-13

Carbon No 726.28 826 926 1022 1126

C-1 45 .4 41.2 41.4 51.5 45 .1 C-2 35.6 33 .8 29.9 73 .6 32.5 C-3 76.1 70.7 70.0 81.3 83 .6' C-4 76.1 72.4 71.0 74.4 73 .7 C-5 63 .7 58.6 58.2 63 .3 63.6 C-6 64.5 64 .9 63 .3 64.2 64.0 C-7

ll*:Glu (C 1'-C6') : 103 .0, 75.7, 78.6, 72.5, 78.8, 63 .6. u" :Glu (C 1'-C6') : 105.6, 76.1, 78.4, 72.3, 78.8, 63.4. 21':Glu (C 1'-C6'): 105.8, 76.0, 78.5, 72.5, 78 .8, 63 .6. 22" :Galac (C 1'-C6') : 98 .2, 71.0, 72.0, 72.0, 73 .6, 63.4.

1126

44.8 34.0 74.0

85.3'' 62.5 62.9

structure elucidation and stereochemical at-location of these and related compounds are described.

Structural Class Polyhydroxy alkaloids are classified in five

fundamental ring systems which are as follows:

(i) Pyrrolidines, monocyclic five membered rmg (Figure-1)

1422 1732 1832 1932 1032 1132 2232 2332

51.5 59.7 62.6 61.4 60.8 58.2 56.1 58.1 72.1 74.4 74.3 71.6 71.8 74.1 78.2'' 72.2 77.5 77.1 81.0 74.7 77.8 77.2 75.8 72.1 71.3 74.9 74.3 71.4 71.3 74.7 74.7 72.0 63.4 56.9 62.6 58.6 63 .0 57.2 57.0 57.2 63 .7 64.8 64.3 63 .9 63 .8 64.6 64.8 63 .5

59.1 64.3 62.2 64.2 68.4•' 59.7 62.7

(ii) Piperidines, monocyclic six membered ring (Figure-2)

(iii) Pyrrolizidines, fused bicyclic five/five-membered ring (Figure-3)

(iv) Indolizidines, fused bicyclic six/five membered ring system (Figure-4) and

492 I;NDIAN J CHEM, SEC B, JULY ~000

Table III~l3C NMR data of pyrrolizidine group of polyhydroxy .alkaloids 24-30

Carbon No. 2421 2634 2735 27a34•• 2819 3033

C-1 74.9 74.0 77.77 77.22 75.9 73.7

C-2 77.3 78.5 76.63 76.36 76.1 75.1

C-3 72.9 63.5 69.97 69.02 64.2 72.8

C-5 54.9 44.9 57.96 55 .54 45.5 52.9

C-6 38.1 34.8 77.40 83 .36 •• 34.0 35 .9

C-7 75 .8 69.6 78.79 77.67 69.9 70.8

C-7a 68.9 74.8 72.09 72.53 70.1 67.0

C-8 65.6 56.9 62.24 62.20 58.9 63 .2

27a** :Giu (C1'- C6'): 97.15, 70.68, 72.27, 69.28, 71.92, 60.23 *Solvent used-Acetone

Table llld - 13C NMR data for indolizidine group of polyhydroxy alkaloids 32-39.

Carbon No 3237 3337.• 3642.•

C-1 78.2 67.9 71.6 C-2 85.5 75.0 33.4 C-3 62.8 61.9 53 .5 C-5 55.3 52.8 58.9 C-6 30.2 28.7 . 67.6 C-7 25.7 23.8 '40.7 C-8 26.6 25.0 63.8 C-9 71.2 67.3 75.4

·solvent used: 33, CDC!; 36, CD30D

Table llle - 13C NMR data of nortropane group of polyhydroxy alkaloids 410-43. Carbon No.. 4016 41 16 42 16 4349

C- l 93 .0 93 .0 93.0 93.2 C-2 82.5 70.0 80.0 76.3 C-3 72.5 73.0 80.0 72.8 C-4 29.0 25.0 80.0 73.4 C-5 54.0 60.0 58.0 66.9 C-6 3 1.5 82.0 24.0 70.2 C-7 42.5 32 .0 31.0 45 .7

(v) Nor-tropane-fused bicyclic system (Figure-S)

The last group is a very recent addition to the class, containing a bicyclic system. There are a numb~" - of different conventions for numbering the atoms in the

polyhydroxy alkaloid skeletons. In tr ~ present review all categories of alkaloids have been numbered as shown on structures associated with each group.

(i) Pyrrolidine alkaloids. The pyrrolidine group comprises the smallest c lass consisting of only eight members, each of which represents a different degree of hydroxylation and resembles to furanose sugars.

3743 3846 3923 69.4 72.5 72.4 33 .1 35.4 34.2 51.6 54.6 54.92 55.4 58.6 54.94 68.8 74.5 71.9 78.7 78.6 72.9 69.9 69.8 67.8 71.2 71.5 69.2

2R, 5R-Dihydroxymethyi-3R, 4R-dihydroxypyrro­lidine (DMDP) 3 is a fructose analogue initially isolated from the African legume Derris elliptica but also found to occur in Lonchocarpus sericeus and Omphalea species. 2R-Hydroxymethyl -3R,4S-dihy­droxypyrrolidine (DAB-I) 2 which resembles to DMDP but lacks one-CH20H group when occurring in Angylocal}X species. 6-Deoxy DMDP 4 contains a methyl group in place of hydroxy group, N-(Hydroxy ethyl)-2-(hydroxy-methyl)-3-hydroxypyrrolidine 5, initially isolated from Castanospermum australe seeds, and homo-DMDP 6 have been isolated from leaves of Hyacinthoides non-scripta. The char­acteristic features of these compounds are a methine bonded nitrogen (CH-N), methylene bonded nitrogen (CH 2_N) resulting in the 13C NMR absorptions at 8 64 .3-67.4 ppm and 50.8-54.8 ppm respectively, and methine carbon bonded to oxygen (CH-0) (8 75.1-80.7 ppm).

(ii) Piperidine alkaloids. The piperidines may be considered as simple analogues of 1-deoxy-pyranose sugar with ring oxygen replaced by nitrogen. The

PANT eta/. : POL YHYDROXY AlKALOIDS FROM PLANTS: NMR SHIELDING BEHAVIOUR 493

~'"'IIOH HN''l

CHf>H 6

(1)

.f$:~ 6 CH.zOH

( 2)

7 6 c:{""OH HOH2C-CH2N

CH20H 8

( 5)

HOH1~'''4 " 1110H

HN

7 cH20H

( 3)

i R3 .: i 7 8

Rt, CH 20H

Rl R2 R3 CH 20H OH OH

( 6) -< {3 -< ·( 6a) -< (3 o(

( 6b) (3 -< /3

Ri,

OH

H

H

Hl~~ c$H '·~ ··•11101-{

HN

7 CH2oH

( 4)

Figure 1-Pyrrolidine group of polyhydroxy alkaloids -(l)CYB-3 droxy-ethyl)-2-(hydroxymethyl)-3-hydroxypyrrolidlne (6)Homo 2,5-Imino-2,5,6-trideoxy-D-gulo-heptitol

(2)DAB-I (3)DMDP DMDP; (6a)6-deoxy

(4)6-Deoxy-DMDP ;(S)N-(Hy­Homo DMDP (6b)

piperidines consist of 17 compounds and among them 13C NMR shielding data have been reported for 14 compounds only. The characteristic features of this group are the appearance of methine (CH-N) and methylene resonances between 8 56.9-64.8 and 8 41.4-45.4 ppm, respectively which are generally associated with nitrogen substituted carbon signals. The spectral region at 8 62.9-64.5 ppm contains signals for all the unsubstituted hydroxy methylene resonances at C-6 or C-7. The unglycosylated and glycosylated methine resonances appear in the region 8 71.4-85.0 ppm. Glycosylation tends to shift the a-carbon to lowerfield ( 8 7-9 ppm) and (3-carbon to a somewhat higherfield (8 2-3 ppm).

(iii) Pyrrolizidine alkaloids. This class contains nine members of a bicyclic ring system and are fused hybrids of monocyclic pyrrolidine alkaloids. Recent discovery of pyrrolizidine alkaloids in both Alexa and Castanospermum also suggests that the two genera are related . So far these compounds have only been found to be weak glycosidase inhibitors. But all the compounds of this group are strong inhibitors of amyloglucosidase13

. All pyrrolizidine alkaloids

isolated till n.ow possess C-substituent at C-3 position . The signal for the -CH20H group occurs at 8 65.6 ppm and bridged C-7a at 8 68 .9 ppm; generally the signal for the other methine bounded to oxygen or nitrogen atom appeaf~ in the range of 8 72 .9 to 77.3 ppm.

(iv) Indolizidine alkaloids. Indolizidines represent the most interesting class of alkaloids comprising eight members; swainsonine 34 and castanospermine 37 are the most important alkaloi.ds . Lentiginosine 32 is of particular interest since it represents the only dihydroxy alkaloid of the whole group that possesses glycosidase inhibitory properties.

Among all the above classes, members of four-fold degree of hydroxylation have been the maximum, found to-date with the exception of pentahydroxypiperidine (a-homonojirimycin 17).

Substitution of the relatively simple ring systems by hydroxyl groups leads to a wide diversity of potential structures due to the large number of possible stereoisomers which may arise. A wide diversity of biological activity can therefore be expected from molecules having the same overall substitution pattern .

494 INDIAN J CHEM, SEC B, JULY 2000

~ : '

HQ'CrCHzOH 1 ~

. 2 1 H

(7)

( 9)

( 11)

( 1'3)

•.

( 8)

( 10)

~-f3·D-glu

HO"CXCH20H

(12)

QH

HO~CH70H

HO~~H

(1q

QH

HO__,~~H,OH HO_.;yH

OH ( 15)

QH

: ' HOJ~CHzOH HO'''' ~NH

'CKzOH (17)

oH

Ho..,:yCH2oH ~fiH

HO :

CH20H

(19)

RH HO)~CH20H

OH

HO~CH,OH HO''··Y

OH (16)

~ HOyYCH20H

Ho·····yNH CHpl

( 18)

~ HO~CH20H HO~NH

CHzOH

(20)

<fH HO :

CllzCI~

Ho'···YH cH2o-.s-o-9tu

(21)

I 9al-0-e(-0 !

OH

HOt,,,~CHp4

HO'"'··Y~H CHzOH

( 23)

CHzOH (22)

Figure :t.-Piperidine group of polyhydroxy alkaloids -(7) I Fagomine;(8)3-epi-Fagomine;(9)3 ,4-Diepi-Fagomine; (10) 1-Deoxynojirimycin;(ll) 3-0-13-o-Giucopyranosylfagomine; (12) 4-0-13-o-Giucopyranosylfagomine; (13) Nojirimycin; (14) Demcymannojirimycin; (15) Nojlrimycin-B; (16) Galactostatin; (17) a-Homonojirimycin; (18) 13-Homonoj ~rimycin ;(19) a-

Homomannojirimycin; (20) 13-Homomanno-jirimycin; (21) 7-0-13-o-Giucopyranosyl-a-homomannoj irimycin; (22) 2-0-a-o-Galactopyranosyl-a-homomannojirimycin; (23) a-3 ,4-diepi-Homomannojirimycin

(v) Nor-tropane alkaloids. Calystegines are a new group of polyhydroxy alkaloids that have recently been idellltified from Calystegia sepium. Calystegines constitutte a unique subgroup having nor-tropane skeleton with several hydroxy groups substituted in various positions, and characterized by the absence of N-methyl susbstituent. Recently, there appeared a report on the occurrence of calystegines in Solanum species. The calystengines are thus the third structural class of bicylic polyhydroxy alkaloids with such

properties to be discovered. In comparison with the indolizidine and pyrrolizidine types of bicyclic alkaloids, the pyrrolidine and piperidine ring moieties in calystegines, rather than possessing the nitrogen atom at the point of fusion, have conjunction points at positions a- to the nitrogen atom to give the bridged tropane structure. The heterocycl ic nitrofen is secondary instead of tertiary in nature' . The characteristic. feature of this group of compounds is quaternary carbon bonded to nitrogen, methine

PANT eta/. : POL YHYDROXY ALKALOIDS FROM PLANTS: NMR SHIELDING BEHAVIOUR 495

OH W -

.. u()H

CHf>H

(26)

<!f OH ~ H :-

d("~ CHzOH

(25)

c;w ~ fH . OH

N

~cH20H ( 29)

(26)

OH OH ~ H ::

<ii"'""' c~OH

(30)

OH H OH

··-ttl""" CH20H

(27) R,=-< -OH (27a) RJ = -<-0 glucosi c

(31)

Figure 3-Pyrrolizidme group of polyhydroxy alkaloids -(24) Australine; (25) 1-epi-Australine; (26) 3, 7a-diepi-Aiexine; (27) Casuarine;

(27a) Casuarine 6a-glucoside; (28) Alexine; (29) I ,2,3-triepi-Aiexine; (30) I ,7a-diepi-Aiexine; (3 1) I ,7-Isopropylidine-diepi-Aiexine.

d£- d): I OH

1 II()H

(32) ( 33)

Cb ru ,,I()H ... ,oH

(34) ~ 0

( 35)

HO &

QH

··x)j~ HO''''' N

(36) ( 37)

OH OH ~ ~ OH ": H OH ::w ··xn '· ':

HO

(38) ( 39)

Figure 4-lndolizidine group of polyhydroxy alkaloids- (32) Lentigi nosi ne; (33) 2-epi-Lentinginosine; (34) Swainsonine; (35) Swainsonine N-oxide; (36) 7-Deoxy-6-epi- Castanospermine; (37) Castanospermine; (38) 6-epi-Castanospermine; (39) 6, 7 -Diepi-Castanospermine.

OH

OH 1

.

• H • OH : H : L---J ' 7

( 40)

oH·

HO,, cX,,,OH ,,,

: H : OH : H : \___J

(42)

oH

A .. ·"'OH HO,,,,,,l .. J.oH

I N I I H I

Ho)-_l (44)

OH aH

OH ' H ' ' H '

HO)--J

HQ/,.,,,

( ,, 1)

OH

OH

OH I N • I H '

HO,;--; ( 43)

R1 R1

( 45) ~-OH .(- OH

(46) .Z- OH f:l - OH

Figure 5--Nort ropane group of alkalo ids -(40) Calystegine A3;

(41) Calystegine 8 1; (42) Calystegine 8 2; (43) Calystegine C2;

(44) Calysteg in c C 1; (45) Calystegine 8 3; (46) Calystegine R. \

496 INDIAN J CHEM, SEC B, JULY 2000

bonded ao nitrogen (CH-N) resulting in absorption at 8 93.0 ppm and 54-66.9 ppm, respectively16

.

Acknowledgement Authors are thankful to the Director, CIMAP for

providing necessary laboratory facilities, constant encouragement and for the award of Project Assistant Fellowship toMs Neerja Pant.

References I Elbein A D & Molyneux R J, Alkaloids:chemical and

biological perspective, Vol 5, edited by S W Pelletier (Wiley lnterscience, New York), 1987, p 1.

2 Molyneux R J, Methods in plant Biochemistry, Vol. 8 (Academic PressLtd) 1993, p 511.

3 Fellows L E & Nash R J, Sci Progress Oxford, 74, 1990, 245.

4 Fellows L E. Pestic Sc{, 17, 1986, 602. 5 Fellows L E, Kite G C, Nash R J, Simmonds M S J &

Scofield A M, Plant Nitrogen Metabolism. edited by J E Poulton, J T Romeo and E E Conn, (Plenum Publishing Corporation) 1989, p 395.

6 Drager B, Phytochemical Analysis, 6, 1995, 31. 7 Molyneux R J, Phytochemical Analysis. 4, 1993, 193 . 8 Molyneux R J, James L F, Panter K E & Ralphs M H,

Phytochemical Analysis, 2, 1991 , 125 . 9 Fellows L E & Fleet G W J, In : Natural products isolation,

Separa tion methods for antimicrobials, antivirals and enzyme inhibitors, edited by (G H Wagman and R Cooper), (Elsevier Amsterdam), 1989, p 539.

I 0 Harris C M, Harris T M, Molyneux R J, Tropea J E & Elbein AD, Tetrahedron Lett, 30, 1989, 5685.

II Colegate S M, Dorling P R & Huxtable C R, Aust J Chern, 32, 1979, 2257.

12 Kardono L B S, Kinghorn A D & Molyneux R J, Phytochemical Analysis, 2, 1991 , 120.

13 Nash R J, Fellows L E. Scofield A M & Fleet G W J, Poisonous plants Prac, . 3rd International. Symposium. Ed ited by , J.Vieele, Cheeke.B (Jowa State Univ. Press, 1992, 169.

14 Pastw;zak I, Molyneux R J, James L F & Elbein A D, Biochemistry, 29, 1990, 1886.

15 Molyneux R J, Pan Y T, Goldmann A, Tepfer D A & Elbein A D, Arch Biochem Biophys, 304, 1993, 81.

16 Goldmann A, Milat M L, Ducrot PH, Lallemand .I Y, Maille M, Lapingle .A, Charpin I & Tepfer D, Phytochemistry, 29, 1990, 2125 .

17 Molyneux R J, Pan Y T, Tropea J E. Elbein A D. Lawyer C H, Hughes D J & Fleet G W J, J Nat Prod, 56. 1993, 1356.

18 Nash R J, Bell E A & Williams J M, Phytochemistry, 24. 1985. 1620.

19 Nash R J, Fellows L E, Dring J V, Fleet G W .1 . Derome A E. Hamor T A, Scofield A M & Watkin D J, Tetrahedron Lell. 29, 1988, 2487.

20 Furukawa J, Okuda S, Saito K, Hatanaka S I. Phytochemistry. 24, 1985, 593 .

2 1 Jones D W C, Nash R .1 . Rell E A & Williams M. Tetrahedron Lett, 26, 1985, 3 125.

22 Asano N, Oseki K, Kizu H & Matsui K. J Med Chem. 37, 1994, 3701.

23 Molyneux R J, Pan Y T, Tropea J E, Benson M,.Kaushal G P & Elbein AD, Biochemistry, 30, 1991,9981. ;

24 Watson A A, Nasll R J, Wormald M R, Harvey D J, Dealler S, Lees E, Asano N, Kizti H, Kato A, Griffiths R C, Caiins A J & Fleet G W J, Phytochemistry, 46, 1997, 22~

25 Asano N, Kato A, Miyauchi M, Kizu H, Kameda Y, Watson A A, Nash R J & Fleet G W J, J Nat Prod, 61, 1998, 625.

26 Kato A, Asano N, Kizu H, Matsui K, Watson A A&. Nash R J, J Nat Prod, 60, 1997, 312.

27 Evans S V, Hayman A R, Fellows L E, Shing T K M, Derome A E & Fleet G W J, Tetrahedron Lett 26 1985 1465. . ' , '

28 Molynuex R J, Benson M, Wong R Y, Tropea J E & Elbein AD, J Nat Prod. 51 , 1988, 1198. ,

29 Ezure Y, Maruo S, Miyazaki K & Kawamaia M, Aust J Cflem, 49, 1985, 1119.

30 Evans S V, Fellows L E & Bell E A, Phytochemistry, 22, 1983, 768.

31 Kite G C, Fellows L E, Fleet G W J, ' Liu P S, Scofield A M & Smith N G, Tetrahedron Lett, 29, 1988, 6483.

32 Asano N, Nishida M, Kizu H, Matsui K, Watson A A & Nash R J, J Nat Prod, 60, 1997, 98.

33 Nash R J, Fellows L E, Dring J V, Fleet G W J, Girdhar A, Ramsden N d, Peach J M, Hegarty M P & Scofield A M, Phytochemistry, 29, 1990, Ill.

34 Nash R J, Fellows L E, Plant A C, Fleet G W J, Derome A E, Baird P D, Hegarty M P & Scofield A M, Tetrahedron, 44, 1988, 5959.

35 Nash R J, Thomas P I, Waigh R D, Fleet G W J, Wormald M R, Lilley P M & Watkin D J, Tetrahedron Lett, 35, 1994, 7849.

36 Wormald M R, Nash R J, Watson A A. Bhadoria B K, Langford R, Sims M & Fleet G W J, Carbohydrates Lett, 2, 1996, 169.

37 Pastuszak I, Molyneux R J, James L F & Elbcin A D. Biochemistry, 29, 1990, 1886.

38 Davis D, Schwarz P, Hernandez T, Mitche ll M, Warnock B & Elbein A. D, Plant Physiology, 76, 1984, 972 .

39 Schneider M J, Ungemach F S, Broquist H P, Harri s T M, Tetrahedron, 39, 1983, 29.

40 Molyneux R J, McKenzie R A. O'Sul li van B M. Elbein A D. J Nat Prod, 58, 1995, 878.

41 Molyneux R .I & James L F. Science. 216. 1982, 190. 42 Molyneux R .1 , Tropea .I E & Elbein A D, J Nat Prod. 53.

1990, 609. 43 llohenschutz L D. Bell E A . .Jewess P .I . Lcworthy D' P.

Pryce R .1 , Arnold E & Clardy .1 . Phytochemistry. 20, 1981. 811.

44 Saul R, Chambers .I P, Molyneux R J. Elbc in A D. Arch Biochem Biophys. 22 1. 1983, 593 .

45 Nash R J, Fellow L E. Dring J V, Stirton C: II. Carter D, Hegarty M P & BellE A. Phytochemis11y . 27, 1988, 1403.

46 Molyneux R J, Roitman J N. Dunnheim G. Szumilo T & Elbcin A D, Arch Biochem Biophys. 25 ~. 1986, 450.

47 Nash R .1 , Rothschild M, Porter E A, Watson A A. Wai gh R D & Waterman P G, Phytochemistry, 34, 1993. 1281 .

48 Drager 13, Funk C. Hohler A, Mrachatz G, Nahrsted t A. Portsteffen A, Schaal A & Schmidt R, l'l"?nt Cell Tissue and Organ Culture, 38, 1994,23 5.

49 Kato A, Asano N, Ki zu H, Matsui K, Suzuki S & Arisawa M, Phytochemistry. 45, 1997, 425.