K. Visweswara Rao

Constitution of gossypin

SummaryGossypin has been ethylated and hydrolysed. The resulting pentaethyl ether of gossypetin is further methylated and the product converted into tetra-ethyl tambuletin by alkali fission and condensation of the ketonic product with the anhydride and sodium salt ofp-ethoxy benzoic acid. This confirms the relationship between gossypin and tambuletin.

A note on the formation of quinones by oxidative demethylation and the effect of methylating agents on them

SummaryUsing typical examples, some of which are new, oxidative demethylation of methoxy benzenes, ketones, chalkones and flavones with nitric acid is discussed. The flavones without exception undergo simple conversion into para quinones. The others fall into two categories: (a) 1∶2∶4∶5-Tetramethoxy benzene and its derivatives suffer only oxidative demethylation like the flavones to yield the corresponding para quinones: (b) 1∶2∶3∶5-Tetramethoxy benzene and its derivatives, either ketones or chalkones, on the other hand undergo further change involving demethylation of another methoxyl group yielding hydroxy quinones. In the case of ketones and chalkones this second stage demethylation involves the methoxyl which is situated ortho to the ketonic carbonyl and which is subjected to the combined influence of this carbonyl and the one in the quinone group. These results are of importance in the study of pedicellin-pedicinin conversion.Under favourable conditions hydroxy quinones can be methylated by means of dimethyl sulphate and potassium carbonate to the corresponding methyl ethers,e.g. lawsone. In some cases fully methylated ethers of the corresponding quinols could be obtainede.g. gossypetone. This is obviously due to the preliminary dismutation of the quinone into the corresponding quinol and complex products. The action of alkali on benzoquinone and tetramethyl gossypetone has been studied using different conditions.

Constitution of gossypin—Part II

SummaryThe analytical data indicate that gossypin is a monoglucoside. As a result of complete methylation and hydrolysis it yields an O-pentamethyl gossypetin. From a study of its decomposition with alcoholic potash whereby veratric acid is obtained and from a comparison of its properties with those of isomeric compounds, it is concluded that it has a free hydroxyl in the 8-position. Consequently gossypin should be 8-monoglucoside of gossypetin. The synthesis of O-pentamethyl gossypetin with a hydroxyl in the 3-position has been described.

A compound of 2:6-dimethoxy quinone and acetone

SummaryIn the presence of potassium carbonate or potash, acetone forms an addition product with 2∶6-dimethoxy quinone. Its properties and reactions are described. They give evidence for the presence of an aliphatic hydroxyl group and a ketone carbonyl. The combination is considered to involve addition of the acetone molecule at the C=O group in the 4-position of the quinone. Methyl ethyl ketone also forms a similar addition compound. Other simplep-benzoquinones do not give this type of compounds.

Synthesis of some important partial methyl ethers of flavonols

SummaryThe following three partial methyl ethers of flavonols which are derivatives of naturally occurring monoglucosides having only one free hydroxyl group have been conveniently synthesised by using the method of partial benzylation: (1) 3 ∶ 5 ∶ 4′-O-trimethyl-kæmpferol derived from populnin and related glycosides, (2) 3 ∶ 5 ∶ 3′ ∶ 4′-O-tetramethyl quercetin derived from quercimeritrin and (3) 3 ∶ 5 ∶ 7 ∶ 3′ ∶ 4′-O-pentamethyl gossypetin derived from gossypin.

A colour reaction of certain phenolic ethers and their derivatives with nitric acid

SummaryA characteristic blue or green colour reaction with concentrated nitric acid is given by the fully alkylated ethers of resorcinol and phloroglucinol and by a number of carbonyl derivatives of them. n the case of these carbonyl compounds one orthohydroxyl could be free. Certain flavanone derivatives of phloroglucinol also give this test whereas chalkones, flavones, diketons and coumaranones do not. It is useful for the differentiation and characterisation of closely related and isomeric compounds belonging to the above categories.

A note on Resokæmpferol

SummaryResokæmpferol, its tri-acetate and tri-methyl ether are prepared and described.

Nuclear oxidation of euxanthone

SummaryThe 6-methyl ether of euxanthone has been oxidised to 6-methoxy-1∶4-dihydroxy-xanthone by means of alkaline persulphate. By demethylation with hydriodic acid 1∶4∶6-trihydroxy-xanthone has been obtained. This compound and its derivatives differ from those obtained by Nierenstein by the oxidation of euxanthone itself with chromic acid and subsequent reduction.

Synthesis of kanugin and related compounds

SummaryThe synthesis of 3-methoxy-7-hydroxy-3′∶4′-methylenedioxyflavone, kanugin andiso-kanugin has been effected. Myristicic acid required for the synthesis of kanugin is prepared from oil of nutmeg by a simplified procedure and an improved method for its synthetic preparation worked out. There is marked difference in properties between kanugin andiso-kanugin (3∶5∶7-trimethoxy-3′∶4′-methylene-dioxyflavone).

6 : 7-Dihydroxy-flavonols - Part II

SummaryStarting from ε-methoxy-resacetophenone and adopting the procedure described in Part 1, 6:7-dihydroxy flavonols with 0,1 and 3 hydroxyls in the side-phenyl nucleus have been prepared. The characteristic properties of the group with reference to the hydroxy-compounds and their partial and complete methyl ethers are described. An alternative method starting with hydroxy-quinol has also been investigated and the simplest member of the group prepared by this method also.