Biotransformation of pinoresinol diglucoside to mammalian lignans by human intestinal microflora, and isolation of Enterococcus faecalis strain PDG-1 responsible for the transformation of (+)-pinoresinol to (+)-lariciresinol

Abstract

By anaerobic incubation of pinoresinol diglucoside (1) from the bark of Eucommia ulmoides with a fecal suspension of humans, eleven metabolites were formed, and their structures were identified as (+)-pinoresinol (2), (+)-lariciresinol (3), 3′-demethyl-(+)-lariciresinol (4), (-)-secoisolariciresinol (5), (-)-3-(3″,4″-dihydroxybenzyl)-2- (4′-hydroxy-3′-methoxybenzyl)butane-1,4-diol (6), 2-(3′,4′-dihydroxybenzyl)-3-(3″,4″-dihydroxybenzyl) butane-1,4-diol (7), 3-(3″-hydroxybenzyl)-2-(4′-hydroxy-3′- methoxybenzyl)butane-1,4-diol (8), 2-(3′,4′-dihydroxybenzyl)-3- (3″-hydroxybenzyl)butane-1,4-diol (9), (-)-enterodiol (10), (-)-(2R,3R)-3-(3″,4″-dihydroxybenzyl)-2-(4′-hydroxy-3′- methoxybenzyl)butyrolactone (11), (-)-(2R,3R)-2-(3′,4′- dihydroxybenzyl)-3-(3″,4″-dihydroxybenzyl)butyrolactone (12), (-)-(2R,3R)-3-(3″-hydroxybenzyl)-2-(4′-hydroxy-3′- methoxybenzyl)butyrolactone (13), 2-(3′,4′-dihydroxybenzyl)-3- (3″-hydroxybenzyl)butyrolactone (14), 2-(3′-hydroxybenzyl)-3- (3″,4″-dihydroxybenzyl)butyrolactone (15) and (-)-(2R,3R)- enterolactone (16) by various spectroscopic means, including two dimensional (2D)-NMR, mass spectrometry and circular dichroism. A possible metabolic pathway was proposed on the basis of their structures and time course experiments monitored by thin-layer chromatography. Furthermore, a bacterial strain responsible for the transformation of (+)-pinoresinol to (+)-lariciresinol was isolated from a human fecal suspension and identified as Enterococcus faecalis strain PDG-1. © 2003 Pharmaceutical Society of Japan.