The structure of 20 oximo-5α-pregnano-16-eno[3,4-C]-1′,2′,5′-oxadiazole (HS976)

The crystal and the molecular structure of the steroidal oxadiazole 20-oximo-5-pregnano-16-eno[3,4-C]-1,2,5-oxadiazole (C₂₁H₂₈N₂O₃) has been determined by direct methods, and refined to a finalR of 0.086 for 3100 observed reflections. The compound crystallizes in space groupP2₁, with cell dimensionsa=18.284(6),b=13.992(4),c=7.370(3)Å,=96.97(3)°;V=1885 ų,Z=4,D _x =1.27 g cm^–3, =1.5418 Å, (CuK =5.95 cm^–1. The two independent molecules are related by a pseudo twofold axis. Both molecules exhibit similar overall topography, rings A, B, C, and D adopting distorted sofa, chair, chair, and distorted envelope conformations, respectively.     

Structure, absolute configuration, and conformation of the antimalarial drug artesunate

The crystal and molecular structure of the antimalarial compound artesunate has been determined by direct methods. Crystals are orthorhombic, P2₁2₁2₁, a = 9.8371(12), b = 10.517(2), c = 18.7594(5) Å, Z = 4, D _c = 1.316 mg/mL. The molecule is comprised of a fused ring system containing a six-membered ring C which includes an oxygen bridge and a peroxy bridge. The 9-atom oxygen–carbon chain from O(5)—C(12)... to ... O(2)—C(6) displays a striking sequence of short, long, short, long ... bonds while these distances are all within the ranges of a normal single bond or partial double bond. It is proposed that this pattern is caused by the delocalization of the lone pair electrons on the oxygen atoms. The ring C has a distorted boat conformation and the C—O—O—C torsion angle is 46.3(2)°. Rings A and D have ideal chair conformations. Ring junctions A/B and A/D are cis junctions, B/D and C/D are trans. Packing of the molecules is stabilized by one strong hydrogen bond involving the hydroxyl group on the ester linkage and the oxygen atom of the lactone ring.     

Crystal structure of 17β-hydroxy-17α-methyl-5α-androstano [2,3-C] Furazan (Furazabol)

The crystal and molecular structure of 17-hydroxy-17-5-androstano [2,3-C] Furazan, Furazabol (C₂₀H₂₄N₂O₂), has been determined by direct methods and refined by full matrix least squares to a final R of 0.0528 for 1927 observed reflections and 216 parameters, CuK, = 1.54178 Å. The compound crystallizes with two molecules in the asymmetric unit, Z = 4, Dc = 1.131 Mg m^–3 space group P2₁, with unit cell parameters a = 18.747(3), b = 6.346(5), c = 15.647(4) Å, = 99.96(2)°, V = 1833.9 ų, (CuK) = 0.584 mm^–1. Whilst the two independent molecules have similar overall geometry there are small differences in bond lengths, bond angles and torsion angles in rings A and D and significant conformational differences in ring A. The A ring adopts a half-chair conformation in molecule A and an intermediate between a half-chair and a sofa in molecule B. The D ring in molecule A has a 13/14 half-chair conformation and in molecule B a conformation between an envelope and half-chair.     

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) ?, b = 25.048(2) ?, c = 6.402(1) ?, V = 2702.7(5) ?³ 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.