Solid-state nuclear magnetic resonance investigation of neurosteroid compounds and magnesium interactions

Abstract

The neurosteroid trans-dehydroandrosterone (DHEA) and its analogs with slightly different modifications in the side chain attached to C17, that is, (3S)-acetoxypregn-5-en-20-one (1) and (3S,20R)-acetoxypregn-5-en-20-ol (2), have been synthesized to investigate DHEA-cation interactions. In this study, we applied solid-state H-1/C-13 cross-polarization/magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy to a series of DHEA analog/Mg2+ mixtures at different Mg2+ concentrations. The high-resolution C-13 NMR spectra of 1/Mg2+ mixtures exhibit two distinct C-13 spectral patterns, one attributable to 1 free from Mg2+, and the other attributable to 1 with bound Mg2+. For 2, the C-13 NMR spectra exhibit three distinct spectral patterns; besides that of the free form, the other two can be assigned to Mg2+-bound forms. Based on the analysis of the chemical shift deviations (CSDs), we conclude that both 1 and 2 might be subject to a cation-pi interaction via the C5-C6 double bond, in contrast to that observed previously for DHEA. As demonstrated, DHEA possesses two Mg2+ binding sites, that is, C17-O and C5-C6 double bond, in which the binding affinity of the former is at least three times stronger than that of the latter. The solid-state C-13 NMR investigation allows better understanding of the underlying cation binding effects of neurosteroid molecules in vitro.