K Visweswara Rao
Articles written in Proceedings – Section A
Volume 22 Issue 5 November 1945 pp 297-303
Starting 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.
Volume 22 Issue 6 December 1945 pp 383-388
Izalpinin (7-methyl ether of galangin) has been obtained by the demethylation of galangin di- and trimethyl ethers using both aluminium chloride and aluminium bromide. The synthetic sample has all the properties recorded for the naturally occurring substance. The condensation of ω:4:6-trimethoxy-phloroacetophenone with benzoic anhydride and sodium benzoate yields mainly 3:7-dimethyl ether of galangin.
Volume 23 Issue 2 February 1946 pp 60-66
Kanugin C19H16O7 yields myristicic acid and
Volume 23 Issue 3 March 1946 pp 147-151
The synthesis of 3-methoxy-7-hydroxy-3′∶4′-methylenedioxyflavone, kanugin and
Volume 23 Issue 4 April 1946 pp 213-214
Volume 24 Issue 4 October 1946 pp 352-356
The colouring matter of the flower petals of
Volume 24 Issue 4 October 1946 pp 375-381
The 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.
Volume 25 Issue 5 May 1947 pp 397-403
The constitution of gossypin as the 8-monoglucoside of gossypetin is confirmed by a detailed study of the pentamethoxy monohydroxy-flavone obtained by the complete methylation and subsequent hydrolysis of the glucoside. It is different from gossypetin-pentamethyl ether containing a free hydroxyl group in the 5-position but both give on oxidation the same quinone which is transformed into a quinol. Further its ethyl ether is shown to have the ethoxyl in the 8-position by unambiguous synthesis.
Volume 25 Issue 5 May 1947 pp 417-426
Nuclear oxidation leading to the preparation of 8-hydroxy-galangin and gossypetin has been carried out. 3∶7-dimethyl-ether of galangin and 3∶7∶ 3′∶4′-tetramethyl-ether of quercetin have been oxidised by means of potassium persulphate to the corresponding 5∶8-dihydroxy-compounds (quinols). Even the 5∶7-dihydroxy-compounds, 3-O-methyl-galangin and 3∶3′∶4′-O-trimethyl-quercetin could be oxidised to the corresponding 5∶7∶8-trihydroxy-derivatives in good yields. Subsequent methylation yields the fully methylated ethers of 8-hydroxy-galangin and gossypetin and demethylation the free hydroxy-flavonols. These experiments not only illustrate facile nuclear oxidation in the flavone series in support of the theory of biogenesis, but also constitute simple and elegant methods for the synthesis of 5∶7∶8-hydroxy-flavonols.
Volume 25 Issue 5 May 1947 pp 427-431
The nuclear oxidation of chrysin and tectochrysin has been successfully effected using potassium persulphate. The first yields norwogonin and the second the 7-methyl-ether now named isowogonin. The method of oxidative demethylation of the 5- and 8-positions has also been employed for the preparation of isowogonin from 5∶7∶8-trimethoxy-flavone.
Volume 25 Issue 5 May 1947 pp 432-437
The difficulty of the demethylation of synthetic primetin dimethyl ether into primetin has been solved by the use of anhydrous aluminium chloride in benzene medium. The possibility of the formation of primetin in the Primula through the intermediate stage of 5-hydroxy-flavone is suggested. This is supported by a new synthesis of primetin in which the nuclear oxidation of 5-hydroxy-flavone is effected by means of persulphate. 5-Hydroxy-flavone required for these experiments has been prepared by independent methods.
Volume 25 Issue 5 May 1947 pp 444-448
The synthesis of herbacetin and hibiscetin from kæmpferol and myricetin is described. As before, the partial methyl ethers of the latter have been subjected to nuclear oxidation with alkaline persulphate. The oxidation proceeds smoothly and gives rise to good yields of the products.
Volume 26 Issue 1 July 1947 pp 13-17
Using the new discovery of facile nuclear oxidation in hydroxy-flavones, (1) wogonin and (2) its 5-methyl ether have been synthesised. Starting with 7-O-benzyl-chrysin, oxidation followed by partial methylation and debenzylation yields (1) and by complete methylation and debenzylation hields (2).
Volume 26 Issue 1 July 1947 pp 18-21
It is shown that 5:6:7:8-hydroxy-flavonols (Calycopterein series) can be made from 5:6:7-hydroxy-flavonols (quercetagetin series) by the nuclear oxidation of the 8-position. Quercetagetin and nor-tangeretin have thus been converted into 6:8-dihydroxy-quercetin and calycopteretin in good yields.
Volume 26 Issue 3 September 1947 pp 182-188
Nuclear oxidation of baicalein and scutellarein takes place readily in the 8-position, the partial methyl ethers being employed. Further methylation yields fully methylated ethers of the nobiletin series and demethylation the corresponding nor-compounds. For purposes of comparison these substances have also been prepared from 2∶5-dihydroxy-3∶4∶6-trimethoxy acetophenone by the Allan-Robinson method. The characteristic properties and reactions of these compounds are described.
Volume 26 Issue 5 November 1947 pp 288-291
The 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.
Volume 26 Issue 5 November 1947 pp 292-295
Gossypin 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 of
Volume 27 Issue 4 April 1948 pp 245-257
Using 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: (
Under favourable conditions hydroxy quinones can be methylated by means of dimethyl sulphate and potassium carbonate to the corresponding methyl ethers,
Volume 27 Issue 5 May 1948 pp 1- Erratum
Volume 27 Issue 5 May 1948 pp 375-390
Pedicin is considered to be a
Volume 28 Issue 1 July 1948 pp 1- Erratum
Volume 28 Issue 3 September 1948 pp 96-97
Resokæmpferol, its tri-acetate and tri-methyl ether are prepared and described.
Volume 28 Issue 3 September 1948 pp 103-110
An essential point which has not been established in a simple manner by the previous study of pedicinin and its synthesis relates to the position of the methoxyl group. This has now been settled in an unambiguous manner by the reduction of pedicinin with stannous chloride to dihydropedicinin and its ethylation. The product is found to be identical with 4-methoxy-2∶3∶5∶6-tetraethoxy chalkone obtained synthetically starting from 2∶6 dimethoxy quinol. This chalkone undergoes oxidative de-ethylation with nitric acid yielding ethyl pedicinin and eventually pedicinin.
The toxic properties of dimethyl pedicinin (2∶4∶5-trimethoxy-quino chalkone) have been studied using fish.
Volume 28 Issue 4 October 1948 pp 198-209
Though despedicellin and dihydropedicinin are prepared from chalkones and were earlier given the chalkone constitution, their properties indicate that they are flavanones. This constitution is also in accordance with the recent discovery of the new effect of hydrogen bonds on the stability of flavanones. It is confirmed by the following experiments. (1) The two compounds undergo partial methylation with diazomethane yielding 5-hydroxy-6: 7∶8-trimethoxy-flavanone which forms with nitric acid 6∶7-dimethoxy-quinoflavanone identical with the sample obtained from 5∶6∶7∶8-tetramethoxy flavanone. (2) Dihydropedicinin undergoes oxidation with
Volume 28 Issue 4 October 1948 pp 210-215
The most important example of ortho-oxidation from the point of view of the biogenesis of the anthoxanthins is the conversion of quercetin into myricetin.
Volume 29 Issue 1 January 1949 pp 9-15
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.
Volume 29 Issue 2 February 1949 pp 72-79
Apigenin does not undergo persulphate oxidation satisfactorily. But acacetin, its monomethyl ether and analogous higher members do so. By the methylation of the products (quinols) the fully methylated ethers of isoscutellarein, 8-hydroxyluteolin and 8-hydroxytricetin could be readily obtained. Demethylation of the quinols or their methyl ethers with aluminium chloride is not successful. Boiling with hydriodic acid produces isomeric change yielding conveniently scutellarein and the higher members. 6-Hydroxy-tricetin and its derivatives are newly described.
Volume 29 Issue 4 April 1949 pp 218-220
Volume 30 Issue 1 July 1949 pp 30-34
A 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.
Volume 30 Issue 3 September 1949 pp 114-119
Employing the two stage process of ortho-oxidation eugenol is converted into 5-hydroxy eugenol. Methylation of this yield elemicin and methylenation myristicin. This constitutes the most convenient synthesis of these naturally occurring compounds and is highly significant from the point of view of biogenesis.
Volume 37 Issue 6 June 1953 pp 798-804
In 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 simple