Biotransformation of 4,5-O-dicaffeoylquinic acid methyl ester by human intestinal flora and evaluation on their inhibition of NO production and antioxidant activity of the products

4,5-O-Dicaffeoylquinic acid methyl ester (1) was anaerobically incubated with human intestinal flora and four biotransformation products (2–5) were obtained. Their structures were elucidated as 3,4-O-dicaffeoylquinic acid methyl ester (2), 3-hydroxyphenylpropionic acid (3), trans-caffeic acid (4) and 3,4-dihydroxyphenylpropionic acid (5) on the basis of their spectroscopic data. Using high-performance liquid chromatography equipped with a diode array detector, chromatographic separation of 1–5 was performed on an analytical C18 column. The time course of the biotransformation was studied to probe into the biotransformation mechanism of 1 by human intestinal flora. In addition, the inhibitory activity of the parent compound 1 and its four main biotransformation products 2–5 on the inhibition of nitric oxide production induced by lipopolysaccharide in macrophage cell line RAW 264.7 and their DPPH free radical-scavenging activity in cell-free bioassay system were estimated.