Structure and conformation of 2 beta,3 beta-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 synthe tic products with antibiotic and antitumor properties. Its structure was pr oposed 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-epox yestr-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 t he 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 thr ough the ring A and epoxy ring plane form an angle of 89.6(2)degrees. Confo rmational analysis of the steroid rings are performed by calculating the ri ng puckering parameters and asymmetry factors. The conformation of the A ri ng 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 st ructure is stabilised by the weak C-H ... O hydrogen bonds and van der Waal s interaction. (C) 2000 Elsevier Science B.V. All rights reserved.