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.