Stereochemical assignment at C-24 and C-25 of marine 24-ethyl-26-hydroxy steroids through comparison with synthetic (24S,25S)-, (24S,25R)-, (24R,25R)-, and (24R,25S)-models

Abstract

Stereoisomeric Δ^22E-24-ethyl-26-hydroxy steroids (7a), (7b), (8a), and (8b) and the corresponding 22,23-dihydro derivatives (9a), (9b), (10a), and (10b) were synthesized. Analysis of ¹H and ¹³C NMR spectra of the synthetic model compounds and of their MTPA derivatives provided data suitable for the assignment of configuration at C-24 and C-25 in 24-ethyl-26-hydroxy steroids. From those models and the related spectral data, the stereochemistry (24S,25S) has been assigned to 24-ethyl-5β-cholestane-3α,4α,21,26-tetraol 3,21-disulphate, recently isolated from the marine ophiuroid Ophiolepis superba.