C-Glycosylflavonoids. III. The Synthesis of 5,7,4'-Tri-O-methylvitexin (8-C-β-D-Glucopyranosyl-5,7,4'-trimethoxyflavone)

Abstract

The reaction between 1,3,5-trimethoxybenzene and tetraacetyl-a-D-glucosyl bromide in the presence of zinc oxide gave ß-D-glucopyranosyl-2,4,6-trimethoxybenzene tetraacetate (12). The tetraacetate (12) was converted by acetic anhydride and anhydrous aluminium chloride into 3-ß-D- glucopyranosyl-2-hydroxy-4,6-dimethoxyacetophenone tetraacetate (15). Condensation of the acetophenone tetraacetate (15) with 4-methoxybenzaldehyde in the presence of sodium hydroxide gave 3'-ß-D-glucopyranosyl-2'-hydroxy-4,4',6'-trimethoxychacone (6). Reaction of the chalcone (6) with selenium dioxide gave 8-C-ß-D-glucopyranosyl-5,7,4'-trimethoxyflavone (5,7,4'-tri- O - methylvitexin)(10). The chemical shifts of the olefinic protons of chalcones are discussed.