Structures of Two Novel Trimeric Stilbenes Obtained by Horseradish Peroxidase Catalyzed Biotransformation of trans-Resveratrol and (−)-ε-Viniferin

Two stilbenes, trans-resveratrol and (-)-epsilon-viniferin, as well as a mixture of both, were biotransformed using horseradish peroxidase and hydrogen peroxide. Under the applied conditions trans-resveratrol afforded one major product, which was identified as trans-delta-viniferin, a resveratrol-trans-dehydrodimer. Large-scale biotransformation of a mixture of trans-resveratrol and (-)-epsilon-viniferin yielded two novel resveratrol trimers, resviniferin A and resviniferin B, which were obtained in a pure form after fractionation by high-speed countercurrent chromatography and final purification by preparative HPLC. Their structures were established by means of mass spectrometry and 2D NMR spectroscopic analyses, including HSQC, HMBC, COSY, and ROESY.