• P Ramachandra Rao

      Articles written in Proceedings – Section A

    • Synthesis of Hibiscetin

      P Ramachandra Rao P Suryaprakasa Rao T R Seshadri

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      A convenient method of preparing 2∶4-dihydroxy-ω∶3∶6-trimethoxyacetophenone (I) directly from 2∶6-dibenzyloxy-1∶4-dimethoxybenzene is described. By the condensation of (I) with the sodium salt and anhydride of trimethylgallic acid, 7-hydroxy-3∶5∶8∶3′∶4′∶5′-hexamethoxyflavone (II) is obtained. Methylation of (II) yields a heptamethyl ether (III) identical with heptamethyl hibiscetin. Demethylation of (II) gives rise to a heptahydroxy flavone (IV) which is found to be identical with hibiscetin in all its properties and reactions. The constitution of hibiscetin is therefore confirmed by synthesis as 3∶5∶7∶8∶3′∶4′∶5′-heptahydroxy flavone.

    • 8-Hydroxy-galangin

      P Ramachandra Rao T R Seshadri

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      8-Hydroxy-galangin, the lowest member of the gossypetin series of flavonols, has been prepared and its properties and reactions compared with the other members. Its important derivatives are described. The tetramethyl ether has been obtained by two methods, one of which is the direct condensation of gossypetol-tetramethyl ether, obtained by the fission of herbacetin pentamethyl ether, with benzoic anhydride and sodium benzoate.

    • Constitution of Populnin

      P Ramachandra Rao T R Seshadri

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      Populnin is a monoglucoside of populnetin which is shown to be identical with kæmpferol. By the methylation and the subsequent hydrolysis of the glucoside a trimethyl ether of kæmpferol is obtained. Its colour reactions and properties indicate definitely that the free hydroxyl group is not in the 3− or 5-position. It has been compared with the isomeric 4′-hydroxy compound and found to be different. Thus the degradation product should have the hydroxyl in the 7-position. This is confirmed by ethylation and comparison of the ethyl ether and of its alkali degradation product (ketone) with synthetic samples.

    • Constitution of hibiscitrin. Part I

      P Ramachandra Rao T R Seshadri

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      Analysis and study of acid hydrolysis show that hibiscitrin is a monoglucoside of hibiscetin. It undergoes complete methylation with dimethyl sulphate and anhydrous potassium carbonate in anhydrous acetone medium; on hydrolysing the methyl ether a O-hexamethyl hibiscetin is obtained which yields trimethyl gallic acid on fission with alkali. From this reaction and from other characteristic properties of the above partial methyl ether it is concluded that the free hydroxyl is in the 3-position and that hibiscitrin is a 3-glucoside.

    • Constitution of hibiscitrin. Part II

      P Ramachandra Rao T R Seshadri

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      The constitution of hibiscitrin proposed in Part I as the 3-glucoside of hibiscetin is confirmed here by synthetic experiments. The O-hexamethyl hibiscetin (A) has been ethylated to (B). Using the method of nuclear oxidation a hexamethyl hibiscetin with a free hydroxyl in position 5 is now prepared and shown to be different from (A). Ethyl ethers of the isomeric 8- and 3-hydroxy compounds are also prepared. The former is different from (B) whereas the latter is identical with it.

      Though alkali fission of (A) does not yield the ketonic part, the ethyl ether (B) can be satisfactorily employed for this fission. The ketonic product is found to be identical with ω-ethoxy-2-hydroxy-3: 4: 6-trimethoxy-acetophenone obtained synthetically, thus confirming again the above constitution of (B) and of hibiscitrin.

    • Synthesis of some important partial methyl ethers of flavonols

      S Rajagopalan P Ramachandra Rao K Visweswara Rao T R Seshadri

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      The 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.

    • Analysis of sugars and uronic acids using paper chromatography (Horizontal Migration)

      P S Rao R M Beri P Ramachandra Rao

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      Using the horizontal migration method of filter paper chromatography, the separation and identification of glucuronic and galacturonic acids and their barium salts have been effected.

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