Synthesis and structural confirmation of calibagenin and saxosterol

Calibagenin and saxosterol are cholesterol-based plant steroids isolated from Calibanus hookerii and Narthecium ossifragum, respectively. To date, the configurations of their 16- and 22-hydroxy groups have not yet been determined. In this study, all the four 16,22-stereoisomers were chemically synthesized. The H-1 and C-13 NMR spectra were fully assigned using 2D NMR techniques, and the structures were determined unambiguously using X-ray crystallography. The H-18 and H-22 signals in the NMR spectra of the products are diagnostic for determining the configurations of the 16- and 22-hydroxy groups. A comparison of the NMR, [alpha](D), and mp data of the four isomers with those of natural calibagenin and saxosterol confirmed that the configurations of the 16- and 22-hydroxy groups of the former and the later are identical to 16 beta,22S and 16 beta,22R, respectively. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

In this study, all four 16,22-stereoisomers of Calibagenin and saxosterol were chemically synthesized and their structures were determined by X-ray crystallography. The configurations of the 16- and 22-hydroxy groups were confirmed to be 16 beta,22S and 16 beta,22R, respectively, through comparison with natural calibagenin and saxosterol.