Plant Steroidal Saponins: A Focus on Open-Chain Glycosides

Abstract

Saponins are a large and structurally diverse class of phytochemicals that consist of a nonpolar steroidal or triterpenoid skeleton that is glycosylated by varying numbers of sugar residues at different positions. Steroidal saponins exhibit a large range of biological activities, including cytotoxic, anti-inflammatory, hemolytic, antifungal, and antibacterial properties. Saponins possessing a steroidal skeleton are usually divided into two main structural categories, namely, spirostanol and furostanol saponins. However, the open-chain steroidal glycosides represent a further structural class with numerous representatives, some of which possess potent cytotoxic activity. Different patterns of steroid oxygenation and glycosylation in furostanol, spirostanol, and open-chain steroidal saponins generate considerable structural diversity, which may account for their wide range of observed biological activities. The structures and stereochemistry of steroidal saponins are typically elucidated via a combination of multistage mass spectrometry, 1D and 2D NMR spectroscopy, and chemical degradation and synthesis.