NMR Spectroscopic Identification of Urolithin G, a Novel Trihydroxy Urolithin Produced by Human Intestinal Enterocloster Species

Urolithins are gutmicrobiota metabolites of ellagic acid. Here,we have identified and chemically characterized a novel urolithinproduced from urolithin D (3,4,8,9-tetrahydroxy urolithin) by in vitroincubation with different human gut Enterocloster species under anaerobic conditions. Urolithin G (3,4,8-trihydroxyurolithin) was identified by H-1 NMR, C-13 NMR,UV, HRMS, and 2D NMR. For the identification, NMR spectra of otherknown urolithins were also recorded and compared. Urolithin G waspresent in the feces of 12% of volunteers in an overweight-obese groupafter consuming an ellagitannin-rich pomegranate extract. The productionof urolithin G required a bacterial 9-dehydroxylase activity and wasnot specific to the known human urolithin metabotypes A and B. Theability to produce urolithin G could be considered an additional metabolicfeature for volunteer stratification and bioactivity studies. Thisis the first urolithin with a catechol group in ring A while havingonly one hydroxyl in ring B, a unique feature not found in human andanimal samples so far.