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Tetrahedron etters No. 6 pp.22-25, 959. Pergamon Preee Ltd. Printed inGreat Britain.

TBE CONSTITUTION F RRYTHROLACCINK. G, Dave, B. S. Joshi, A. V. Patwardhan nd K. Venkataraman

National Chemical Laboratory, oona(Reoeived 2 May 1959)

TSCHIRCH and Liidy' solated from stick-lac yellow pigment, C15Hlo06,which had the 'I ntire behaviour f a tetrahydroxymethylanthraquinonefthe tentative tructure (I) . It was stated that the positions f themethyl and hydroxyl groups were still to be determined nd that thesuggested rientation as in view of the relationship o kermeeic acidand carminic cid. The only derivative repared was a tetra-acetate, ndno melting point was cited for erythrolaccin r the tetra-acetate.

0I 11

' A. Techirch and F. Liidy, elv. Chim. Acta 8, 994 (1923).

22

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The constitution f erythrolaccin 23

By a slight modification f Tschirch and Liidy's rooedure e haveisolated rythrolaccin s orange needlee, m.p. 314' (dec,). Theelementary nalysis and molecular eight (Rest) corresponded o C15'10'6*Kuhn-Roth oxidation ndicated ne C-methyl roup. Zinc dust distillationyielded 2-metbylanthraoene. tetra-acetate, .p. 17S , and a tetramethylether, m.p. 150, were obtained, he latter by means of dimethyl eulphateand potassium arbonate n acetone. rythrolaccin s thereforetetrehydroxy-2-mnthylanthraquinone.vo hydroxyl groups are in a- andtro in &positions, because methylation ith ethereal diazomethane ave adimethyl ether, m.p. 224', which yielded a diacetate, .p. 199O.Erythrplaccin s an alizarin erivative s shorn by the shades obtainedon mordanted ool; and it is not a quinizarin er.ivativeince a solutionin glacial aoetic bid ie non-fluorescent. he infra-red pectra oferythrolaccin nd its dimethyl ether have strong absorption ands at1617 and 1614 cm 1 respectively chelated arbonyl), nd none around1672 om (unchelated arbonyl); he tvo a-hydroxyls n erythrolaccinare therefore n the 1,5 and not in the l,B-positions. hree hydroxylgroups in erythrolacoin re thus in the 1,2,5-positions. nlike anthragallolerythrolaccin id not give the Bargellini est, excluding he presence ofthree hydroxyls in 1,2,3-positions. e have shozn earlier,thatxanthopurpurin ndergoes ydroxymethylation eadily in the P-position ytreatment ith aqueous sodium hydroxide nd formaldehyde, nd have usedthe method for the synthesis f lucidin and 1,3,8-tribydroxy-2&ydroxy-

2 A. R. a and K. Venkataraman, . Soi. Ind. Res, B);i,359 (1956).

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24 The constitution f erythrolacoin

methylanthraquinone. We have now found that the reactiondiagnostic est for the presence of two hydroxyl groups in

is a usefull,T-positions

and the absence of a substituent n the 2-position. hythrolaocin ondensedreadily with alkaline formaldehyde o form a hydroxymethyl erivative(dec.>J60 ), proving simultaneously hat the fourth hydroryl group inerythrolaccin s in the 7-position nd the methyl group is in the3-position. nly one possibility, ,2,5,7-tetrahydroxycy-j-methylanthra-quinone (II), therefore emains for the structure f erythrolaccin.

hriggs et al 4-- isolated rom the bark of Rhamnus alaternus pigment,for which the trivial ame alaternin ay be suggested, nd to which theyassigned the structure ,2,6,8-tetrshydroxy-+methylanthraquinoneIII);the chemical nd spectral vidence equally supported n alternative IV)with the methyl group in the T-position, ut (III) was preferred n

3 N. R. Ayyangsx, . S. Joshi and K. Venkataraman, etrahedron 6,In press 1959).

4 L. H. Briggs, F. E. Jacombs and G. A. Nicholls, . Chem. SOD,3069 1953).

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The constitution f erythrolacoin 25

*lphytochemicalrounder@ s a derivative f emodin, the major colouringmatter of the plant. Further support for (III) is provided y the factthat alaternin, small sample of which was sent to ue by ProfessorL. H. Briggs to whom we are greatly indebted, ondensed eadily withalkaline formaldehyde, lthough the quantity at our disposal was too smallfor charaoterization f the product. he synthesis f (II) and (III) isin progress.

Our thanks are due to the Indian Lac Cese Committee or a SeniorResearch Fellowship warded to one of us (K, G. D.) and to the Ministryof Education or a Junior Reeearoh Fellowehip warded to one of us(A, V. P.).