Synthetic Study of Carthamin: Biomimetic Synthesis of Carthamin Model via Peroxidase-Catalyzed Oxidative Decarboxylation of Its Precursor Model

A chiral carthamin model (3S,3′S)-1-[5-acetyl-2,6-diketo-3-C-β-d-glucopyranosylcyclohex-4-enylidene]-1′-[5′-acetyl-3′-C-β-d-glucopyranosyl-2′,3′,4′-trihydroxy-6′-oxocyclohexa-1′,4′-dienyl]methane, in which two cinnamoyl groups were replaced by an acetyl group, was synthesized by the dimerization of (S)-2-acetyl-4-C-(per-O-acetyl-β-d-glucopyranosyl)cyclohexadienone with glyoxylic acid, followed by peroxidase-catalyzed oxidative decarboxylation and de-O-acetylation, or de-O-acetylation and peroxidase-catalyzed oxidative decarboxylation. The corresponding total yields were 12.5% or 17.1% from 3-C-(per-O-acetyl-β-d-glucopyranosyl)phloroacetophenone, and the reaction pathway was identical to the biosynthetic pathway.