Structure and conformation of 2β,3β-epoxyestr-5(10)-en-1,4, 17-trione, spectroscopic and X-ray crystallographic studies

Colourless single crystals were isolated as by-product during the synthesis of steroidal A-ring substituted 1,4-quinones (and epoxyquinols), as synthetic products with antibiotic and antitumor properties. Its structure was proposed by comparing IR, UV, H-1 and C-13 NMR spectra to the ones of quinone 2 and independently determined by an X-ray analysis, as 2 beta,3 beta-epoxyestr-5(10)-en-1,4,17-trione. Crystals belong to the monoclinic system with space group P2(1): a = 6.767(3) Angstrom, b = 7.097(5) Angstrom, 15.748(5) Angstrom, beta = 97.070(5)degrees, V = 750.6(8) Angstrom(3), Z = 2, D-x = 1.329 Mg m(-3), mu(Mo K-alpha) = 0.093 mm(-1). The structure was solved by direct methods and refined to a final R = 0.064 for 1729 reflections with I > 2 sigma(I). The steroidal skeleton with chiral centre at C13 possesses the S configuration defining beta-orientation of O2 atom bridging C2 and C3 atoms and beta-oriented methyl group bonded to C13 atom. The best plane through the ring A and epoxy ring plane form an angle of 89.6(2)degrees. Conformational analysis of the steroid rings are performed by calculating the ring puckering parameters and asymmetry factors. The conformation of the A ring is screw-boat S-1(6), ring B half-chair H-4(3), ring C chair C-1(4), and the five-membered D ring is half-chair H-2(1) conformation. The crystal structure is stabilised by the weak C-H ... O hydrogen bonds and van der Waals interaction. (C) 2000 Elsevier Science B.V. All rights reserved.