Chlorogenic Acid Biosynthesis. Chemical Synthesis and Properties of the Mono-O-cinnamoylquinic Acids

Abstract

Rational syntheses of the 1- and 3-0-cinnamoylquinic acids are reported. Negligible wandering of the cinnamoyl group occurred under the mildly acidic conditions used to remove the protecting groups from the substituted quinic acid molecule. The 4- and 5-O-cinnamoylquinic acids were isolated from the mixture formed when barium hydroxide acted on 1-0-cinnamoylquinide. Once the lactone ring was opened, the cinnamoyl group migrated from hydroxyl to hydroxyl group. The results of experiments with [U-14C]quinic acid establish that the base-catalyzed migration of cinnamoyl groups about the quinic acid molecule is an intramolecular process. Three lines of evidence establish that migrations occur in the sequence 1⇌5⇌4⇌3:(a) studies of migration when the carboxyl is methylated; (b) studies of migration when the 4,5-hydroxyl groups are blocked by an isopropylidene group; and (c) studies of the rates of migration in buffered solutions (pH 6-10). It is improbable that a 1 → 3 migration, by way of a cinnamic-quinic mixed anhydride, is of importance. © 1965, American Chemical Society. All rights reserved.