Hydroxylation of a hederagenin derived saponin by a Xylareaceous fungus found in fruits of Sapindus saponaria

During our screening of tropical plants for endophyte microorganisms, a Xylareaceous fungus was found living on the internal part of Sapindus saponaria fruits. The fruits of S. saponaria accumulate great amounts of triterpenoidal and sesquiterpenoidal saponins. The saponin 3-O-(beta-D-xylopyranosyl)-(1 -> 3)-alpha-L-rhamnopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl-hederagenin was isolated using chromatographic methods, after alkaline hydrolysis of the crude extract obtained from S. saponaria fruits and added to the culture medium used to grows the fungus. A new saponin was isolated from this experiment by preparative scale HPLC and characterized as a 22 alpha-hydroxy derivative. The structure of this hydroxylated saponin was elucidated based on interpretation of MS/MS data and NMR spectra.