GB875164A - New hydroxyflavones, their production and use as anti-oxidants - Google Patents

Abstract

The invention comprises (a) 7-alkyl ether derivatives of 3:7:21:51-tetrahydroxyflavone, which may be substituted at one or more of the 5-, 6-, 8-, 31-, 41- and 61- positions by alkyl groups and which have alkoxy or aralkoxy groups in place of the hydroxy groups in the 21- and 51- positions; (b) 3:7:21:51-tetra hydroxyflavone derivatives substituted at the 5-, 6-, 8-, 31-, 41-, and 61- positions by one o more alkyl groups; and (c) 3:7:8:21:51-pentahydroxyflavone and 7- and/or 8- and/or 21-and/or 51-alkyl ether derivatives thereof which may be substituted at the 5-, 6-, 31-, 41-, and 61- positions by one or more alkyl groups, together with their preparation by oxidising a chalkone of the general formula:- <FORM:0875164/IV (b)/1> <FORM:0875164/IV (b)/2> wherein X and/or X1 are protecting groups (e.g. benzyl, isopropyl or methyl) which can subsequently be removed or are hydrogen atoms, R is alkoxy and R1 is hydrogen, alkyl, or alkoxy, and any unoccupied position in either ring may be substituted by alkyl, and thereafter if necessary removing the protecting groups and/or converting R and R1 into hydroxy groups. The oxidation is preferably carried out with alcoholic potassium hydroxide and hydrogen peroxide, and the protecting groups may be removed by treatment with HCl or HBr and acetic acid or HI and phenol. In Examples:- (1) gentisaldehyde is benzylated and the dibenzyl ether condensed with 2-hydroxy-4-methoxyacetophenone in aqueous ethanolic alkali giving 2,5-bis(benzyloxy)-21-hydroxy-41-methoxy chalkone, which is oxidised with H2O2 in alcoholi KOH to 21,51-bis (benzyloxy)-3 - hydroxy - 7 - methoxy flavone, characterized as its acetate, and debenzylated with HCl-acetic acid to 3,21,51-trihydroxy-7-methoxyflavone; (2) 2,5-bis(benzyloxy)-41-n-butoxy-2-hydroxychalkone prepared as in (1) is oxidised and debenzylated to 7-n-butoxy-3,21,51-trihydroxyflavone, characterized as its 7,8-dimethoxyflavone is refluxed with aqueous HBr giving 3,7,8,21,51-pentahydroxyflavone; (4) paenol is condensed with 2-hydroxy-5-methoxybenzaldehyde and the resulting chalkone oxidised to 3,21-dihydroxy-7,51-dimethoxyflavone; (5) resacetophenone is monoetherified with cetyl bromide and condensed with 2,5-dibenzyloxybenzaldehyde, the chalkone oxidised with H2O2 and debenzylated to 7-cetyloxy-3,2151-trihydroxyflavone, characterized as its triacetate; (6) 5 - ethyl - 2,4 - dihydroxyacetophenone is monomethylated and then treated as in (4) giving 3,21-dihydroxy-7,51-dimethoxy-6-ethylflavone and its diacetate; (7) demethylation yields 6-ethyl-3,7,21,51-tetrahydroxyflavone; (8) and (9), 3,4-dimethoxy-5-ethyl-2-hydroxyacetophenone and 5 - n - hexyl - 2 - hydroxy-4-methoxyacetophenone similarly give 6-ethyl-3,7,8,21,51-pentahydroxyflavone and 6-n-hexyl-3,7,21,51-tetrahydroxyflavone respectively; (10) O-benzylhydroquinone is treated with chloroform and alkali giving 5-benzyloxy-2-hydroxybenzaldehyde, which is methylated and condensed with 2-hydroxy-3,4-dimethoxy-5-stearylacetophenone (prepared from pyrogallol by treatment with stearic acid and BF3, reduction of the resulting 2,3,4-trihydroxystearophenone, C-acetylation with BF3 of the 4-stearylpyrogallol and methylation of the 2,3,4-trihydroxystearylacetophenone) giving a chalkone which on oxidation yields 3,51-dihydroxy-7,8,21-trimethoxy-6-stearylflavone and is then demethylated with HI in phenol; (11) 3,7,21,51-tetrahydroxy-6-stearyl flavone is similarly obtained; (12) 2-hydroxy-3,4-dimethoxyacetophenone and dibenzylgentisaldehyde as in (1) yield 3,21,51-trihydroxy-7,8-dimethoxyflavone.ALSO:Fatty oils, fats and other liquids subject to oxidative rancidity are protected against oxidation by the incorporation therein of a small proportion of one or more hydroxy flavones selected from the following:-(a) 7-alkyl ethers of 3:7:21:51-tetrahydroxyflavone, which may be substituted at one or more of the 5-, 6-, 8, 31, 41, and 61- positions by alky groups and which may have alkoxy or aralkoxy groups in place of the hydroxy groups in the 21- and 51- positions; (b) 3:7:21:51-tetrahydroxyflavone derivatives substituted at the 5-, 6-, 8-, 31, 41, and 61- positions by one or more alkyl groups; (c) 3:7:8:21:51-pentahydroxyflavone and 7- and/or 8- and/or 21-and/or 51- alkyl ether derivatives thereof which may be substituted at the 5-, 6-, 31-, 41-, and 61- positions by one or more alkyl groups. A table gives the anti-oxidant efficiencies of twenty-two flavones (including known compounds) in linoleic acid, methyl linoleate, their aqueous emulsions and benzene solutions using cobaltous stearate and ferrous phthalocyanine as catalysts.ALSO:Lipid-containing foods and feeds are protected against oxidative rancidity by the incorporation of a small proportion of one or more of the hydroxyflavones: (a) 7-alkyl ethers of 3 : 7 : 21 : 51 - tetrahydroxyflavone, which may be alkyl substituted at positions 5, 6, 8, 31, 41 or 61, and which may have alkoxy or aralkoxy groups in place of hydroxy groups at 21 and 51 positions; (b) 3 : 7 : 21 : 51 - tetrahydroxyflavones substituted at the 5, 6, 8, 31, 41 or 61 positions by one or more alkyl groups; (c) 3 : 7 : 8 : 21 : 51 - pentahydroxyflavone and its 7 and/or 8 and/or 21 and/or 51 alkyl ether derivatives, which may be substituted at 5, 6, 31, 41 or 61 positions by one or more alkyl groups. The flavones may be incorporated during cooking in food manufacture.