Determination of the absolute configuration at C-20 and C-24 of ergosterol in Ascomycetes and Basidiomycetes by proton magnetic resonance spectroscopy.

Samples of ergosterol isolated from Saccharomyces cerevisiae, Neurospora crassa, and Agaricus sp., and commercial ergosterol all displayed identical proton magnetic resonance (PMR) spectra at 220 MHz. From the effects produced on the doublet for C-21 by epimerization at C-20 and C-24 in sterols of known configuration, the absolute configurations at these positions in ergosterol were determined. The data demonstrate that ergosterol from both Ascomycetes and Basidiomycetes is the same and that at C-20 and C-24, the two H-atoms are on the alpha-side of the asymmetric carbon atoms and that C-22 is trans-oriented with respect to C-13 about the 17(20)-bond.