Assignment of stereochemistry in open-chain steroidal saponins

Abstract

The major phytochemical constituents of the widely used medicinal herb Chamaelirium luteum (“false unicorn”) are open-chain cholesterol-derived steroidal saponins. These are unusual in lacking the extra ring(s) derived from the steroidal side chain that are characteristic of the more commonly isolated furostanol and spirostanol saponins. The structures of the major steroidal saponins of C. luteum were determined using a combination of multistage mass spectrometry (MSn), 1D and 2D NMR experiments, and chemical degradation. The flexible nature of the steroidal side chain in these saponins necessitated determination of their absolute stereochemistry via total synthesis and X-ray crystallography.