The constitution suggested by Bose for gardenin (5-hydroxy-3∶6∶8∶3′∶4′∶5′-hexamethoxy-flavone) has been confirmed in the following manner.
Preparation of nor-gardenin and gardenin methyl ether and comparison with hibiscetin and 6-hydroxy-myricetin and their methyl ethers. There was no agreement.
Oxidative demethylation of gardenin and its methyl ether. This proved that groups exist in the 5 and 8 positions.
Alkali fission of methyl gardenin and study of the ketonic product. It condensed with the anhydride and sodium salt of trimethyl gallic acid to reform gardenin. Its oxidation with nitric acid and subsequent transformations showed that it has a methoxyl in the 5-position corresponding to the 6-position in gardenin.
The tetramethoxy flavone obtained from the fission ketone and benzoic anhydride and sodium benzoate was not identical with 5∶6∶7∶8-tetramethoxy-flavone, but was identical with 3∶5∶6∶8-tetramethoxy-flavone synthetically obtained by the method of nuclear oxidation.
Gardenin could be directly obtained by the partial methylation of nor-gardenin or gardeninol and by the Allan-Robinson condensation using the fission ketone and trimethyl gallic acid.