Research progress on naturally-occurring and semi-synthetic ocotil- lol-type ginsenosides in the genus Panax L. (Araliaceae)

Ocotillol (OT)-type ginsenosides, one subtype of ginsenosides, consist of a dammarane skeleton and a tetrahydrofuran ring. Most naturally-occurring OT-type ginsenosides exist in Panax species, particularly in Panax quinquefolius, which may be attributed to the warm and humid climate of its native areas. Till now, merely 28 types of naturally-occurring OT-type ginsenosides have been isolated. In contrast, semi-synthesized OT-type ginsenosides are attracted considerable attentions. These ginsenosides can be obtained through oxidation and cyclization of side chains of dammarane-type ginsenosides, and other methods, which may change their physical and chemical properties and further improve their bioavailabilities. It is also notable that the pharmacological activities of ginsenosides are closely related to the stereoisomers caused by the configuration at C-20. Semi-synthesis of OT-type ginsenosides can facilitate our understanding of the biosynthesis, transformation and metabolism of OT-type ginsenosides in the body. This review will systematically summarize the research progress on naturally-occurring and semi-synthetic OT-type ginsenosides, which provides a theoretical basis for their bioactivity-guided research.