Azastilbene Analogs as Tyrosinase Inhibitors: New Molecules with ...

Hindawi Publishing CorporationThe Scientific World JournalVolume 2013 Article ID 274643 7 pageshttpdxdoiorg1011552013274643

Research ArticleAzastilbene Analogs as Tyrosinase InhibitorsNew Molecules with Depigmenting Potential

Larissa Lavorato Lima1 Rebeca Moacutel Lima2

Annelisa Farah da Silva2 Antocircnio Maacutercio Resende do Carmo3

Adilson David da Silva1 and Naacutedia Rezende Barbosa Raposo2

1 Departamento de Quımica Instituto de Ciencias Exatas Universidade Federal de Juiz de Fora Campus Universitario36036-900 Juiz de Fora MG Brazil

2 Nucleo de Pesquisa e Inovacao em Ciencias da Saude (NUPICS) Universidade Federal de Juiz de Fora Campus Universitario36036-900 Juiz de Fora MG Brazil

3 Faculdade de Odontologia Universidade Federal de Juiz de Fora Campus Universitario 36036-900 Juiz de Fora MG Brazil

Correspondence should be addressed to Adilson David da Silva davidsilvaufjfedubr andNadia Rezende Barbosa Raposo nadiafoxgmailcom

Received 7 November 2012 Accepted 14 January 2013

Academic Editors H Pellissier G B Shulrsquopin and Y-W Yang

Copyright copy 2013 Larissa Lavorato Lima et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

This research has been an effort to develop synthetic resveratrol analogs in order to improve the depigmenting potential ofnatural resveratrol Six resveratrol analogs were synthesized and tested for tyrosinase inhibitory activity in vitro by qualitative andquantitative steps The results showed the analog C as being the most powerful tyrosinase inhibitor (IA

50= 6567 plusmn 060 120583gmL)

followed by the analogs B E FA andD respectively The analog C presented a tyrosinase inhibition potential better than naturalresveratrol (119875 lt 0001)The best depigmenting activity was provided by the presence of hydroxyl in the orthoposition on the secondphenolic ring

1 Introduction

Animal and human skin color is mainly determined by thecontent of melanin pigment Although melanin has a mainlyphotoprotective function in human skin the accumulationof an abnormal amount of melanin in different parts of theskin resulting in more pigmented patches might become anaesthetic problem [1] Such conditions may appear due tonumerous factors including sun exposure [2] genetic factors[3] pregnancy [4] diseases [5] use of certain medicines andothers [6]

Tyrosinase (phenol oxidase) is known to be a key enzymeimplicated in the anabolism of melanin biosynthesis inmelanocytes [7 8] This enzyme catalyzes two different reac-tions the hydroxylation of monophenolic compounds to o-diphenols and the oxidation of the o-diphenols to o-quinonesThe enzyme converts tyrosine to 34-dihydroxyphenylalanine(L-DOPA) and oxidizes L-DOPA to form dopaquinone

which plays a prominent part in melanin biosynthesis [6 7](Figure 1) The inhibition of the enzyme tyrosinase has beenthe subject of many studies [6ndash10]

The compounds utilized in the treatment of hyper-pigmentation usually act as either competitive or non-competitive inhibitors of tyrosinase thereby blocking reac-tion steps of the pathway shown above and consequentlyblocking melanin synthesis [6 7 11] Among the skin-lightening and depigmenting agentsmagnesium-L-ascorbyl-2-phosphate hydroxyanisole N-acetyl-4-S-cysteaminylphe-nol arbutin (hydroquinone-beta-D-glucopyranoside) sali-cylhydroxamic acid dioic acid kojic acid and hydroquinoneare the most widely used in the cosmetic industry being pre-scribed worldwide [8 12ndash14] However there are reports onpotential mutagenicity and epidemics of ochronosis as wellas on adverse reactions that may aggravate the appearance ofthe spots and damage the health of patients who make use ofsuch agents [6 12]

2 The Scientific World Journal

HO

HO

HO

HO

HO

HO

HO

HO HO

HO

HO

HO

COOH

COOH

COOH

COOH

COOH

COOH

COOHCOOH

COOH

COOH

Tyrosine

TYR

TYR

O

O

S

NHN

O

O NH

O

NH

N

S

HBTA

NH

DHI

O NH

O

IQ

TYR

TRP-1

TRP-2

NH2

NH2

NH2

NH2NH2Dopaquinone

Dopa

ICAQDHICA

minusCO2

minusOH+

LeukodopachromeDopachrome

Glutathione orcysteine

Eumelanogenesis Pheomelanogenesis

Pheomelanin

Cysteinyldopa

H2N

Mixed melaninEumelanin

Figure 1Melanin biosynthetic pathway [27] TYR tyrosinase TRP tyrosinase related protein DOPA 34-dihydroxyphenylalanine DHICA56-dihydroxyindole-2-carboxylic acid DHI 56-dihydroxyindole ICAQ indole-2-carboxylic acid-56-quinone IQ indole-56-quinoneHBTA 5-hydroxy-14-benzothiazinylalanine

The use of hydroquinone for instance has been asso-ciated with a number of adverse effects including skinirritation contact dermatitis and exogenous ochronosis indark-skinned people [15 16] Other commonly availabletopical agents such as corticosteroids are either less effectiveor more likely to cause local or systemic side effects afterlong-term use [17]Moreover the use of cosmetics containinghydroquinone is prohibited in the European Union and isstrictly controlled in the United States by the Food andDrug Administration (FDA) [18] Instead dioic acid has beenused to treat hyperpigmentation with good efficacy but withsimilar side effects as hydroquinone [19] For that reasonthere has been an increasing impetus to find alternativeherbal and synthetic pharmaceutical depigmenting agents[6 12 17]

Resveratrol (3541015840-trihydroxystilbene) a natural mole-cule found in many plants including mulberries peanutsand principally grapes [7] has been considered in previousstudies due to its pharmacological properties such as antiox-idant anti-inflammatory antiaging cardioprotective neuro-protective and anticancer effects [20ndash23] Resveratrol and itshydroxyl derivatives have also been presented as inhibitors ofmushroom tyrosinase [6 7 24] However some studies have

N

Stilbene skeleton Azastilbene skeleton

Figure 2 Comparison of the basic structures of stilbene and azastil-bene skeletons

demonstrated that resveratrol does not inhibit the synthesisof melanin to such a degree that enables it to be utilized aloneas skin whitening agent in pharmaceutical formulations andso its use as an adjuvant in hyperpigmentation treatments issuggested [6 7 25]

In a recent effort our research group has been developingthe synthesis and biological evaluation of synthetic resvera-trol analogs particularly the azastilbenes and bioisosteres ofnatural stilbenes (Figure 2) seeking to improve the potentialof the resveratrol analogues Such compounds have showngood antioxidant activity [23 26] which encouraged us to testthe potential of this class of compounds in other areas suchas depigmenting action Thus this paper presents a study of

The Scientific World Journal 3

the in vitro inhibitory activity of six other resveratrol analogsin tyrosinase activity

2 Materials and Methods

21 Samples Azastilbene analogs (AndashF) were synthesizedby means of condensation between 2-hydroxyaniline with avariety of aromatic aldehydes in ethanol (Scheme 1) All com-pounds were characterized by 1H and 13C nuclear magneticresonance (NMR) infrared (IR) and melting point (MP)(Table 1) and were in accordance with data in the literature[28ndash32]

22 Preparation of Samples The six azastilbene analogswere dissolved in 25 dimethyl sulfoxide (DMSO) aqueoussolution to obtain solutions with concentrations between 35ndash350mgsdotmLminus1 used in the tyrosinase inhibition activity assayThe resveratrol (RV03081F6 Attivos Magisttrais Sao PauloBrazil) was tested in parallel with the test substances forcomparison purposes

23 Test for Tyrosinase Inhibitory Activity The ability toinhibit the activity of the tyrosinase enzyme was evaluatedusing the enzymatic method described by Macrini et al [10]with modifications This method relies on the inhibition oftyrosinase in the presence of its substrate tyrosine interrupt-ing the melanin synthesis

231 Tyrosinase Inhibition Qualitative Enzymatic ReactionScreening Aliquots of 10 120583L of a solution composed of125UsdotmLminus1 of mushroom tyrosinase (Sigma-Aldrich USA)were added to 96-well microplates and then 70 120583L of pH68 phosphate buffer solution and 60 120583L of the substances(350 120583gsdotmLminus1 in 25 DMSO) were also added For positivecontrol 60120583L of kojic acid (175 120583gsdotmLminus1 in 25DMSO) wasused instead of the test substances and for negative control60120583L of 25 DMSO were added To the resultant mixture70 120583L of L-tyrosine (Sigma-Aldrich USA) at a concentrationof 03mg mLminus1 in distilled water were added (final volume inthe wells = 210 120583L)

The absorbances of the microplate wells were readin a microplate spectrophotometer reader (SpectraCountPackard USA) at 510 nm (119879

0) Then the microplates were

incubated at 30 plusmn 1∘C for 60 minutes and the absorbanceswere registered again (119879

1) An additional incubation for 60

minutes at 30 plusmn 1∘C was done and after this period a newspectrophotometric reading was conducted (119879

2)

The inhibitory percentage at the two times (1198791and1198792)was

obtained according to the following formula for inhibitoryactivity percentage

IA =119862 minus 119878

119862

times 100 (1)

where IA= inhibitory activity 119862 =negative control absorb-ance and 119878 = sample or positive control absorbance (absorb-ance at time 119879

1or 1198792minus the absorbance at time 119879

0)

232 Tyrosinase Inhibition Quantitative Enzymatic ReactionAssay For samples which reached an IA greater than 50

Table 1 Spectral data of resveratrol analogs

Compounds 120575CH=N 120575C=N 120584C=N Melting point(∘C)

Yield()

A 890 15718 16258 1600ndash1610 780B 862 15846 16220 901ndash920 660C 896 16077 16316 1490ndash1503 900D 850 15884 16143 1180ndash1190 500E 869 15973 16258 908ndash915 830F 863 15887 16239 1187ndash1196 720lowast

The NMR experiments were performed at 300MHz for 1H and 75MHzfor 13C in dimethyl sulfoxide (DMSO-1198896) (ppm) and IR experiments wereperformed at KBr support (cmminus1)

a quantitative assay was conducted With this purpose theabove experimental protocol was followed with modifica-tions (a 500UsdotmLminus1 tyrosinase solution was used instead ofthe 125UsdotmLminus1 and the absorbances were measured every 10minutes for 1 hour)

The quantitative determination was obtained through ananalytical curve and its respective linear equation For thatthe analogs were diluted in microplate wells to 5 concentra-tions between 35 and 350 120583gsdotmLminus1 with 25 DMSO and thekojic acid was diluted to concentrations of 10 5 25 125and 0625 120583gsdotmLminus1 Samples were assayed in triplicate Theanalytical curvewas plotted between the tyrosinase inhibitionactivity percentage at each time and the concentrations of theanalogspositive controlThe inhibitory activity at 50 (IA

50

in 120583gsdotmLminus1) was calculated by using linear equation

24 Statistical Analysis A descriptive statistical analysis andANOVA followed by the Tukey post hoc test were per-formedwith the Statistical Package for Social Sciences (SPSS)v140 for Windows software to compare the average valuesobtained between the resveratrol analogs and the resveratrolanalogs versus positive control (kojic acid) standardThe levelof significance was 119875 lt 0001

3 Results and Discussion

The results obtained by the tyrosinase inhibitory ability assaydemonstrated that all the analogs presented IA greater than50 in screening (qualitative assay) In the first hour of theassay the analogs A B C E and F presented the samecapacity to inhibit tyrosinase compared with kojic acid (119875 =0116 119875 = 0895 119875 = 0002 119875 = 0045 and 119875 = 0936resp) while in the second hour of the assay all the analogsanalyzed and the resveratrol showed better capacity to inhibittyrosinase than kojic acid (119875 lt 0001)

Regarding the quantitative assay all the analogs and theresveratrol showed 4 tyrosinase inhibitory capacity statisti-cally lower than the kojic acid standard (119875 lt 0001) Incomparison with resveratrol the analog Cwas the one whichpresented the best AI

50 while analog D was the one which

presented the worst AI50(119875 lt 0001 for both)The analogsA

B E and F presented AI50

statistically similar to resveratrol(119875 = 0177 119875 = 0001 119875 = 0217 and 119875 = 0999 resp) Allresults are shown in Table 2


N

OHO

1

2

3

4

5

OH

R

R

Aromaticaldehydes

NH2

EtOH

R3 = OMe

R1 = OH

R3 = NMe2R12356 = H

R234 = OMe

12

3

4

5

R3 = NO2A

B

C

D

E

F

19984002998400

3998400

4998400

59984006998400

Scheme 1 Synthetic pathway for resveratrol analogs

All the analogs showed a more stable IA (capacity tokeep their depigmenting ability in the first hour until thesecond hour) in qualitative assay compared to kojic acidPhenolic compounds such as the analogs tested form rel-atively stable intermediates because of the resonance of thearomatic ring present in their structure [33] Similar resultswere found by Franco et al [6] who studied the depigmentingactivity of phenolic compounds (azastilbene analogs) threeanalogs (119899 = 6) showed inhibitory ability statistically equalto kojic acid in the second hour of the qualitative assay(119875 gt 005) However the compounds studied by Franco et al[6] have a structural difference when compared with thoseevaluated in this study due to the existence of an additionalhydroxyl group at 21015840-position of A ring which characterizesthe originality of our work

The best tyrosinase inhibition potency was found inanalog C (IA

50= 6567 plusmn 060 120583gmL) which has an insertion

of a hydroxyl in ortho position C61015840 on the second phenolicring It presented depigmenting ability better than resveratrol(119875 lt 0001) However it was statistically different from kojicacid (119875 lt 0001) The presence of a hydroxyl group in suchposition of the aromatic ring thus appears to be critical forgood tyrosinase inhibitor activity This is an expected resultsince resveratrol has hydroxyl groups in its structure whichare directly linked to its antioxidant activity as described inthe literature [23 34]

In sequence the analogs A (IA50

= 9557 plusmn 074120583gmL)B (IA50= 7060 plusmn 122120583gmL) E (IA

50= 7903 plusmn 178120583gmL)

and F (IA50= 8880 plusmn 044 120583gmL) presented AI

50statistically

similar to resveratrol (119875 = 0177 119875 = 0001 119875 = 0217 and119875 = 0999 resp) All of them were statistically different fromkojic acid (119875 lt 0001)

Analog B has a methoxy in paraposition (C41015840) whileanalog F has three methoxy groups in meta- (C31015840 and C51015840)and para- (C41015840) positions which demonstrates that theinclusion of methoxy groups was not interesting to improvetyrosinase inhibition potency as was also noted by Franco etal [6]The analog E without substituent in the aromatic ringcontinued presenting depigmenting potential statisticallysimilar to analogs B and F (119875 = 0180 and 119875 = 0085 resp)

and to resveratrol (119875 = 0217) Finally analog A presentedan insertion of a nitrogroup in paraposition C41015840 which maybe able to chelate metals and block the action of tyrosinasedue to unshared pair of electrons in their molecular structurethat is able to complex with copper [6 35] This happensbecause tyrosinase is a copper-protein enzymatic complexthat requires copper ions to promote the redox reactionsessential in production of melanin [35 36] However it wasnot enough to improve the tyrosinase inhibition potency ofsaid analog

The analog D showed worse AI50

than resveratrol andkojic acid (119875 lt 0001 for both)

It demonstrated that the insertion of an amine in parapo-sition C41015840 was the least interestingmodificationmade in thisstudy for depigmenting action [33] Franco et al [6] observedthat the analog with insertion of disubstituted amine on thebase molecule was not an interesting modification for thequantitative tyrosinase inhibitory activity assay

Among the six compounds evaluated in this work threeof them (A B and D)mdashwhich do not owe hydroxyl groupat the ortho-position of the ring and present more lipophilicgroupsmdashhave been previously synthesized [6] and exhibitedsimilar depigmenting activity However the compoundsCEand F present a significantly different structure and duringthe assay a good tyrosinase inhibition potency was observedbeing that C and E were even better than resveratrol (119875 lt0001 for both)

Although only six analogs have been analyzed in thisstudy it is possible to observe that molecules with polargroups such as hydroxyl confer a higher tyrosinase inhibi-tory activity than the analogs with fewer polar groups such asmethoxyl nitro and amine highlighting the importance of apolar substituent to the molecule

The above results showed that skin depigmenting andlightening agents must continue to be the subjects of exten-sive research due to their easy availability and vast clinicalresults Different types of compounds from both natural andsynthetic sources with depigmenting activity deserve furtherinvestigation Moreover such agents for skin whitening havea great potential in the cosmetics industry as they are con-sidered to be safe and largely free from adverse side effects


Table 2 Tyrosinase inhibitory activity of new molecules and kojic acid

Analogs (119899 = 6) Chemical structure IA 60min () IA 120min () IA50 (120583gsdotmLminus1)

A N

OH

NO28783 plusmn 150a 8560 plusmn 061h 9557 plusmn 074p

B N

OH

OMe8237 plusmn 118b 8150 plusmn 050i 7060 plusmn 122pq

CN

OH

HO

7743 plusmn 059ac 7457 plusmn 065hj 6567 plusmn 060pr

D

OH

NN 7513 plusmn 084abd 7400 plusmn 044hl 14013 plusmn 075pqrs

E

OH

N 7950 plusmn 070ae 6883 plusmn 006him 7903 plusmn 178st

F N

OHOMe

OMe

OMe

8547 plusmn 076cdf 8440 plusmn 085jlmn 8880 plusmn 044qrsu

Resveratrol

OH

OH

HO6947 plusmn 344abcefg 7552 plusmn 499hno 8710 plusmn 1036rsv

Kojic acid

OH

HO

O

O

8400 plusmn 141dg 5560 plusmn 056hijlmno 530 plusmn 017pqrstuv

lowast

Means followed by the same letters differ by ANOVA followed by Tukey post hoc test (andashv119875 lt 0001)


However more concrete studies with a human clinical pointof view are required [12]

4 Conclusions

The number and position of substituents seem to play animportant role in the inhibitory effects of azastilbene com-pounds on tyrosinase activity According to the data the pres-ence of hydroxyl in the ortho position was the molecu-lar modification which gave the best evaluated tyrosinaseinhibitory activity

Despite the fact that the tyrosinase inhibitory activitywas lower than that of the reference standard tested (kojicacid) the azastilbene compound (analog C) with orthohy-droxylation presented better depigmenting activity (lowerIC50) as well as when compared with the natural compound

(resveratrol) which indicates that said molecule may havepharmacological utility in a near future Studies on in vivoefficacy and tissue biocompatibility of such analogs must beperformed to make them feasible for therapeutic use in skinwhitening treatments

Acknowledgments

The authors were provided with grants by CAPES CNPQand MEC

References

[1] H Y Ding T S Chang H C Shen and S S Tai ldquoMurinetyrosinase Inhibitors from Cynanchum bungei and evaluationof in vitro and in vivo depigmenting activityrdquo ExperimentalDermatology vol 20 no 9 pp 720ndash724 2011

[2] S Plensdorf and J Martinez ldquoCommon pigmentation disor-dersrdquo American Family Physician vol 79 no 2 pp 109ndash1162009

[3] S K Fistarol and PH Itin ldquoDisorders of pigmentationrdquo Journalder Deutschen Dermatologischen Gesellschaft vol 8 no 3 pp187ndash202 2010

[4] M B M Urasaki ldquoSkin physiological alterations perceivedby pregnant women attended at public health servicesrdquo ActaPaulista de Enfermagem vol 23 no 4 pp 519ndash525 2010

[5] A Costa T Cordero J Marmirori T A Moiseis and CR T Alves ldquoAssociacao de emblica licorice e belides comoalternativa a hidroquinona no tratamento clınico do melasmardquoAnais Brasileiros de Dermatologia vol 85 no 5 pp 613ndash6202010

[6] D C Z Franco G S G de Carvalho P R Rocha R STeixeira A D da Silva and N R B Raposo ldquoInhibitoryeffects of resveratrol analogs on mushroom tyrosinase activityrdquoMolecules vol 17 no 10 pp 11816ndash11825 2012

[7] P Bernard and J Y Berthon ldquoResveratrol an original mecha-nismon tyrosinase inhibitionrdquo International Journal of CosmeticScience vol 22 no 3 pp 219ndash226 2000

[8] N Baurin E Arnoult T Scior Q T Do and P Bernard ldquoPre-liminary screening of some tropical plants for anti-tyrosinaseactivityrdquo Journal of Ethnopharmacology vol 82 no 2-3 pp 155ndash158 2002

[9] A Adhikari H P Devkota A Takano et al ldquoScreening ofNepalese crude drugs traditionally used to treat hyperpigmen-tation in vitro tyrosinase inhibitionrdquo International Journal ofCosmetic Science vol 30 no 5 pp 353ndash360 2008

[10] D J Macrini I B Suffredini A D Varella R N Younes andM T Ohara ldquoExtracts from Amazonian plants have inhibitoryactivity against tyrosinase an in vitro evaluationrdquo BrazilianJournal of Pharmaceutical Sciences vol 45 no 4 pp 715ndash7212009

[11] E Chodurek A Orchel J Orchel et al ldquoEvaluation of melano-genesis in A-375 cells in the presence of DMSO and analysisof pyrolytic profile of isolatedmelaninrdquoTheScientificWorldJour-nal vol 2012 Article ID 854096 7 pages 2012

[12] S Parvez M Kang H S Chung et al ldquoSurvey and mechanismof skin depigmenting and lightening agentsrdquo PhytotherapyResearch vol 20 no 11 pp 921ndash934 2006

[13] Y S Lin M T Chuang C H Chen M Y Chien andW C Hou ldquoNicotinic acid hydroxamate downregulated themelanin synthesis and tyrosinase activity through activatingtheMEKERK andAKTGSK3120573 signaling pathwaysrdquo Journal ofAgricultural and Food Chemistry vol 60 no 19 pp 4859ndash48642012

[14] Y-S Lin S H ChenW J Huang et al ldquoEffects of nicotinic acidderivatives on tyrosinase inhibitory and antioxidant activitiesrdquoFood Chemistry vol 132 no 4 pp 2074ndash2080 2012

[15] M Rendon M Berneburg I Arellano and M PicardoldquoTreatment of melasmardquo Journal of the American Academy ofDermatology vol 54 no 5 pp S272ndashS281 2006

[16] P Nigam ldquoAdverse reactions to cosmetics and methods of test-ingrdquo Indian Journal of Dermatology Venereology and Leprologyvol 75 no 1 pp 10ndash19 2009

[17] W Zhu and J Gao ldquoThe use of botanical extracts as topical skin-lightening agents for the improvement of skin pigmentationdisordersrdquo Journal of Investigative Dermatology SymposiumProceedings vol 13 no 1 pp 20ndash24 2008

[18] V M Sheth and A Pandya ldquoMelasma a comprehensive up-datemdashpart IIrdquo Journal of theAmericanAcademy ofDermatologyvol 65 no 4 pp 699ndash714 2011

[19] F M Cerqueira M H G Medeiros and O Augusto ldquoAntioxi-dantes dieteticos controversias e perspectivasrdquo Quımica Novavol 30 no 2 pp 441ndash449 2007

[20] J C Cheng J G Fang W F Chen B Zhou L Yang and Z LLiu ldquoStructure-activity relationship studies of resveratrol andits analogues by the reaction kinetics of low density lipoproteinperoxidationrdquo Bioorganic Chemistry vol 34 no 3 pp 142ndash1572006

[21] M Savio T Coppa L Bianchi et al ldquoThe resveratrol analogue441015840-dihydroxy-trans-stilbene inhibits cell proliferation withhigher efficiency but different mechanism from resveratrolrdquoInternational Journal of Biochemistry and Cell Biology vol 41no 12 pp 2493ndash2502 2009

[22] Y Shukla and R Singh ldquoResveratrol and cellularmechanisms ofcancer preventionrdquoAnnals of the New York Academy of Sciencesvol 1215 no 1 pp 1ndash8 2011

[23] NOCalil G SG deCarvalhoA F da Silva AD da Silva andN R B Raposo ldquoAntioxidant activity of synthetic resveratrolanalogs a structure-activity insightrdquo Letters in Drug Design ampDiscovery vol 9 no 7 pp 676ndash679 2012

[24] Y M Kim J Yun C K Lee H Lee K R Min and Y KimldquoOxyresveratrol and hydroxystilbene compounds Inhibitoryeffect on tyrosinase and mechanism of actionrdquo Journal ofBiological Chemistry vol 277 no 18 pp 16340ndash16344 2002

[25] H Satooka and I Kubo ldquoResveratrol as a kcat type inhibitor fortyrosinase potentiated melanogenesis inhibitorrdquo Bioorganic ampMedicinal Chemistry vol 20 no 2 pp 1090ndash1099 2012


[26] N O Calil G S G de Carvalho D C Z Franco A D daSilva and N R B Raposo ldquoAntioxidant activity of resveratrolanalogsrdquo Letters in Drug Design amp Discovery vol 9 no 1 pp8ndash11 2012

[27] T S Chang ldquoAn updated review of tyrosinase inhibitorsrdquo Inter-national Journal of Molecular Sciences vol 10 no 6 pp 2440ndash2475 2009

[28] F G Singleton and C B Pollard ldquoReactions of aldehydeswith amines I With o-aminophenolrdquo Journal of the AmericanChemical Society vol 62 no 9 pp 2288ndash2289 1940

[29] M RManrao C Kanta R C Sharma P S Kalsi andVK KaulldquoSynthesis and biological studies of 345-trimethoxybenzalani-linesrdquo Asian Journal of Chemistry vol 7 pp 27ndash32 1995

[30] AMobinikhaledi P J Steel andM Polson ldquoRapid and efficientsynthesis of schiff bases catalyzed by copper nitraterdquo Synthesisand Reactivity in Inorganic Metal-Organic and Nano-MetalChemistry vol 39 no 4 pp 189ndash192 2009

[31] J Lu C Li Y F Chai D Y Yang andC R Sun ldquoThe antioxidanteffect of imine resveratrol analoguesrdquo Bioorganic amp MedicinalChemistry Letters vol 22 no 17 pp 5744ndash5747 2012

[32] Y Zhang B Zou K Wang et al ldquoAntioxidant activities andtransition metal ion chelating studies of some hydroxyl Schiffbase derivativesrdquo Medicinal Chemistry Research vol 21 no 7pp 1341ndash1346 2012

[33] J H Holthoff K A Woodling D R Doerge S T Burns JA Hinson and P R Mayeux ldquoResveratrol a dietary polyphe-nolic phytoalexin is a functional scavenger of peroxynitriterdquoBiochemical Pharmacology vol 80 no 8 pp 1260ndash1265 2010

[34] S Rayne C D Goss K Forest and K J Friesen ldquoQuantitativestructure-activity relationships for estimating the aryl hydro-carbon receptor binding affinities of resveratrol derivativesand the antioxidant activities of hydroxystilbenesrdquo MedicinalChemistry Research vol 19 no 8 pp 864ndash901 2010

[35] V C Ramalho andN Jorge ldquoAntioxidantes utilizados em oleosgorduras e alimentos gordurososrdquoQuımica Nova vol 29 no 4pp 755ndash760 2006

[36] M Picardo andM Carrera ldquoNew and experimental treatmentsof cloasma and other hypermelanosesrdquo Dermatologic Clinicsvol 25 no 3 pp 353ndash362 2007

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

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Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


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Applied ChemistryJournal of



Theoretical ChemistryJournal of


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Spectroscopy

Analytical ChemistryInternational Journal of


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Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


HO

HO

HO

HO

HO

HO

HO

HO HO

HO

HO

HO

COOH

COOH

COOH

COOH

COOH

COOH

COOHCOOH

COOH

COOH

Tyrosine

TYR

TYR

O

O

S

NHN

O

O NH

O

NH

N

S

HBTA

NH

DHI

O NH

O

IQ

TYR

TRP-1

TRP-2

NH2

NH2

NH2

NH2NH2Dopaquinone

Dopa

ICAQDHICA

minusCO2

minusOH+

LeukodopachromeDopachrome

Glutathione orcysteine

Eumelanogenesis Pheomelanogenesis

Pheomelanin

Cysteinyldopa

H2N

Mixed melaninEumelanin

Figure 1Melanin biosynthetic pathway [27] TYR tyrosinase TRP tyrosinase related protein DOPA 34-dihydroxyphenylalanine DHICA56-dihydroxyindole-2-carboxylic acid DHI 56-dihydroxyindole ICAQ indole-2-carboxylic acid-56-quinone IQ indole-56-quinoneHBTA 5-hydroxy-14-benzothiazinylalanine

The use of hydroquinone for instance has been asso-ciated with a number of adverse effects including skinirritation contact dermatitis and exogenous ochronosis indark-skinned people [15 16] Other commonly availabletopical agents such as corticosteroids are either less effectiveor more likely to cause local or systemic side effects afterlong-term use [17]Moreover the use of cosmetics containinghydroquinone is prohibited in the European Union and isstrictly controlled in the United States by the Food andDrug Administration (FDA) [18] Instead dioic acid has beenused to treat hyperpigmentation with good efficacy but withsimilar side effects as hydroquinone [19] For that reasonthere has been an increasing impetus to find alternativeherbal and synthetic pharmaceutical depigmenting agents[6 12 17]

Resveratrol (3541015840-trihydroxystilbene) a natural mole-cule found in many plants including mulberries peanutsand principally grapes [7] has been considered in previousstudies due to its pharmacological properties such as antiox-idant anti-inflammatory antiaging cardioprotective neuro-protective and anticancer effects [20ndash23] Resveratrol and itshydroxyl derivatives have also been presented as inhibitors ofmushroom tyrosinase [6 7 24] However some studies have

N

Stilbene skeleton Azastilbene skeleton

Figure 2 Comparison of the basic structures of stilbene and azastil-bene skeletons

demonstrated that resveratrol does not inhibit the synthesisof melanin to such a degree that enables it to be utilized aloneas skin whitening agent in pharmaceutical formulations andso its use as an adjuvant in hyperpigmentation treatments issuggested [6 7 25]

In a recent effort our research group has been developingthe synthesis and biological evaluation of synthetic resvera-trol analogs particularly the azastilbenes and bioisosteres ofnatural stilbenes (Figure 2) seeking to improve the potentialof the resveratrol analogues Such compounds have showngood antioxidant activity [23 26] which encouraged us to testthe potential of this class of compounds in other areas suchas depigmenting action Thus this paper presents a study of













2)



IA =119862 minus 119878

119862

times 100 (1)



0)




Yield()





50











N

OHO

1

2

3

4

5

OH

R

R

Aromaticaldehydes

NH2

EtOH

R3 = OMe

R1 = OH

R3 = NMe2R12356 = H

R234 = OMe

12

3

4

5

R3 = NO2A

B

C

D

E

F

19984002998400

3998400

4998400

59984006998400








50= 7903 plusmn 178120583gmL)


50statistically













A N

OH


B N

OH


CN

OH

HO


D

OH


E

OH


F N

OHOMe

OMe

OMe


Resveratrol

OH

OH


Kojic acid

OH

HO

O

O


lowast




4 Conclusions




Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of













2)



IA =119862 minus 119878

119862

times 100 (1)



0)




Yield()





50











N

OHO

1

2

3

4

5

OH

R

R

Aromaticaldehydes

NH2

EtOH

R3 = OMe

R1 = OH

R3 = NMe2R12356 = H

R234 = OMe

12

3

4

5

R3 = NO2A

B

C

D

E

F

19984002998400

3998400

4998400

59984006998400








50= 7903 plusmn 178120583gmL)


50statistically













A N

OH


B N

OH


CN

OH

HO


D

OH


E

OH


F N

OHOMe

OMe

OMe


Resveratrol

OH

OH


Kojic acid

OH

HO

O

O


lowast




4 Conclusions




Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


N

OHO

1

2

3

4

5

OH

R

R

Aromaticaldehydes

NH2

EtOH

R3 = OMe

R1 = OH

R3 = NMe2R12356 = H

R234 = OMe

12

3

4

5

R3 = NO2A

B

C

D

E

F

19984002998400

3998400

4998400

59984006998400








50= 7903 plusmn 178120583gmL)


50statistically













A N

OH


B N

OH


CN

OH

HO


D

OH


E

OH


F N

OHOMe

OMe

OMe


Resveratrol

OH

OH


Kojic acid

OH

HO

O

O


lowast




4 Conclusions




Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




A N

OH


B N

OH


CN

OH

HO


D

OH


E

OH


F N

OHOMe

OMe

OMe


Resveratrol

OH

OH


Kojic acid

OH

HO

O

O


lowast




4 Conclusions




Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



4 Conclusions




Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Azastilbene Analogs as Tyrosinase Inhibitors: New Molecules with ...

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