Synthesis, Analytical Features, and Biological Relevance of 5-(3′,4′-Dihydroxyphenyl)-γ-valerolactone, a Microbial Metabolite Derived from the Catabolism of Dietary Flavan-3-ols

The physiological significance of 5-(3',4'-dihydroxyphenyl)-gamma-valerolactone, an important metabolite derived from the catabolism of flavan-3-ols by gut microbiota, has been often overlooked due to the lack of the commercial standard. In the present work, this metabolite has been chemically synthesized, and its analytical parameters and antioxidant capacity have been determined in comparison to other chemical analogues [isomer 3-(3',4'-dihydroxyphenyl)-delta-valerolactone and gamma-valerolactone] and other structurally related compounds [(+)-catechin, (-)-epicatechin, and 3-(3,4-dihydroxyphenyl)-propionic acid]. The synthesized compound was also used to perform a targeted analysis in samples collected during the in vitro fermentation of a grape seed flavan-3-ol extract with human fecal microbiota from three healthy volunteers. The time course formation of 5-(3',4'-dihydroxyphenyl)-gamma-valerolactone revealed large interindividual differences among volunteers, with concentrations ranging from 3.31 to 77.54 mu M at 10 h of fermentation. These results are further discussed in view of the scarce reports quantifying 5-(3',4'-dihydroxyphenyl)-gamma-valerolactone in in vitro fermentation studies, and pharmacokinetic and intervention studies.