Randomization of the Flavonoid A Ring during Biosynthesis of Kaempferol from |l,2 -,3C2j Acetate in Cell Suspension Cultures of Parsley

13C-NMR, Apigenin, Kaempferol, Flavonoid, Biosynthesis Cell suspension cultures of parsley (Petroselinum hortense) were incubated with [l,2-13C2]acetate during a period of active flavonoid production. The flavonoid glycosides were extracted with ethanol, hydrolyzed in dilute acid, and the aglycones purified by chromatography. Apigenin, a flavone, and kaempferol, a flavonol, were analyzed at 67.9 MHz by 13C FT NMR. The 13C enrich­ ment confirmed that acetate contributes primarily to the flavonoid A ring. The coupling patterns between adjacent 13C atoms of the A ring indicate that the cyclization direction of the A ring is random in both compounds. While randomization of apigenin could have occurred chemically through opening of the pyrone ring under the acid conditions used for glycoside hydrolysis, ran­ domization of the more stable flavonol must have occurred biosynthetically. The latter result supports the conclusion that a chalcone is an intermediate in flavonoid biosynthesis.