Metabolism of paeoniflorin and related compounds by human intestinal bacteria. II. Structures of 7S- and 7R-paeonimetabolines I and II formed by Bacteroides fragilis and Lactobacillus brevis.

Paeoniflorin from peony roots was incubated with a cell suspension of Bacteroides fragilis or Lactobacillus brevis isolated from human intestinal flora. Paeoniflorin was converted into the 7S and 7R isomers of paeonimetaboline I as major metabolites, along with the 7R and 7S isomers of paeonimetaboline II as minor metabolites in the case of the former strain. The structures were elucidated by various spectroscopic methods, and the structure of 7R-paeonimetaboline I was confirmed by X-ray analysis.