Identification and complete spectral assignment for two 4 alpha-methylsterols in an inseparable mixture using 2D NMR

Two acetylated 4 alpha -methylsterols were isolated as an inseparable mixtu re from the octocoral Psuedoplexaura flagellosa. By the use of concerted 2D NMR (COSY, HSQC, HMBC and T-ROESY) techniques, it was possible to both ide ntify the compounds as the acetates of 4 alpha, 24R-dimethyl-5 alpha -chole st-22-en-3 beta -ol and 4 alpha, 23, 24R-trimethyl-5 alpha -cholest-22-en-3 -beta -ol and to assign fully their H-1 and C-13 spectra. The general usefu lness of 2D NMR for identifying individual components of complex mixtures o f natural products is discussed. Copyright (C) 2001 John Wiley & Sons, Ltd.