Crystal Structure, Absolute Configuration, Conformational Analysis and Molecular Dynamics Study of the Novel Steroidal Tetrazole Derivative: (25R)-3,12a-diaza-A,C-bishomo-5α-spirostano[3,4-d] [12a,12d] bistetrazole [HS-989

Abstract

The X-ray crystal structure of the bistetrazole steroid derivative: (25R)-3,12a-diaza-A,C-bishomo-5α-spirostano[3,4-d] [12a,12d] bistetrazole (HS-989) has been determined at room temperature. The crystals are orthorhombic, space group P212121 with a = 16.855(1) A, b = 25.048(2) A, c = 6.402(1) A, V = 2702.7(5) A3 Z = 4, Density (calculated) = 1.250 Mg/m3. The tetrazole-modified 7-membered rings A and C have similar modified uniaxial chair conformations, with pseudo-symmetry m through the extra C–N tetrazole bond; the 6-membered rings B and F are symmetrical chairs; of the 5-membered rings, D is in a half-chair and ring E an envelope conformation; tetrazole rings T1 and T2 are both planar and oriented towards the α-face. The spirostan moiety is β-oriented. Overall the modified steroid skeleton is reasonably flat, with a pseudo-torsion angle C(19)–C(10)···C(13)–C(18) of −6.2°. Conformational sampling, using high temperature SYBYL molecular dynamics was used to investigate different arrangements of the steroid skeleton. Predicted low energy conformations were found to compare favourably in some respects with both X-ray crystallographic and NMR observations but with important differences. Determination of the crystal structure and absolute configuration of the novel steroidal tetrazole derivative (25R)-3,12a-diaza-A, C-bishomo-5α-spirostano[3,4-d] [12a 12d] bistetrazole [HS-989] are reported. The report includes a detailed conformational analysis and comparative molecular dynamics study.