3,5-Di-O-caffeoyl-epi-quinic Acid from the Leaves and Stems of Erigeron annuus Inhibits Protein Glycation, Aldose Reductase, and Cataractogenesis

In our ongoing project directed toward the discovery of novel treatments for diabetic complications from herbal medicines, sixteen compounds including three caffeoylquinic acids and four flavonoids were isolated from an EtOAc-soluble extract of the stems and leaves of Erigeron annuus. All the isolates were evaluated in vitro for inhibitory activity on the formation of advanced glycation end products (AGEs) and rat lens aldose reductase (RLAR). Of these, 3,5-di-O-caffeoyl-epi-quinic acid (3) exhibited the most potent inhibitory activity in both the AGEs and aldose reductase (AR) assays. Compound 3 markedly reduced AGEs-bovin serum albumin (BSA) cross-linking in a dose-dependent manner. Furthermore, opacity of lenses was significantly prevented when they were treated with 3 in an ex vivo experiment.