COMPLETE H-1 AND C-13 NMR-SPECTRA OF PREGNENOLONE

Assignments for signals from H-1 and C-13 in the NMR spectra of pregnenolone (1), 16-dehydropregnenolone (2), and the 3-acetate of 1 (3) were validated by two-dimensional correlated spectroscopy (2D COSY) and heteronuclear single quantum coherence (HSQC). The narrow band of overlapping signals from H-7, H-2, and H-4 was resolved by exploiting three-bond coupling in the 20 COSY spectra and heteronuclear correlation. Assignments were based on high intensity cross peaks from long-range coupling by H-18 with H-17 and H-12 (axial). Similar cross peaks were observed for H-17 with H-21. Low intensity cross peaks were seen for H-4 coupled with H-6 and H-7, and also H-16 (quasi-arial) with H-14 of 1 and 3. Assignments bared on 20 COSY spectra were confirmed by correlation peaks from HSQC. This now corrects the earlier conflicts among assignments reported for C-13 signals of 1 and 3. Accurate assignments were similarly derived for signals from C-2, C-7, C-8, and C-21 of 1 and 3, and C-15 and C-16 of 1, 2, and 3. The complete sets of H-1 and C-13 NMR data for pregnenolone, pregnenolone 3-acetate, and 16-dehydropregnenolone serve as reference standards.