Fig. 1: Withanolides are steroidal lactones from Solanaceae plants derived from the general phytosterol pathway intermediate 24-methylenecholesterol (1).

a 24-Methylenecholesterol (1) is converted by the only known withanolide biosynthetic enzyme sterol Δ24-isomerase (24ISO)14 into 24-methyldesmosterol (2). The enzymes for all subsequent biosynthetic steps are not known. b Representative genera and species of withanolide-producing plants and characteristic compounds from them. Photographs by Jakob Maximilian Horz, TU Braunschweig, Germany.