NOVEL OBSERVATIONS ON THE MAIN-PART ISOSTRUCTURALISM EXHIBITED BY VARIOUS STEROID MOLECULES - STRUCTURES OF 5-ANDROSTENE-3-BETA,17-BETA-DIOL MONOHYDRATE AND A 1/2 ADDUCT OF DIGITOXIGENIN AND DIGIREZIGENIN

An X-ray study of the 'main-part' isostructuralism observed among cardiotonic steroids has been continued on binary systems of co-crystallized isostructural pairs and extended to a few pairs of the structurally simpler androstane derivatives. The 1:1 adducts of arenobufagin-gamabufotalin and cinobufagin-cinobufotalin are solid solutions which remained isostructural with their components. Consequently, in these binary systems the component molecules are distributed at random. In contrast, the adduct of digitoxigenin-digirezigenin is partially ordered at the expense of the symmetry which is decreased from P2(1)2(1)2(1) to P112(1). The size of the unit cell remains, however, quite close to that of the components. This phenomenon seems to be governed by a mutual recognition of the component molecules. The 'main-par-t' isostructuralism of the androstane derivatives offers new possibilities for investigating the role of the solvent (water) and epimerization (also observed among the cardenolides: digitoxigenin, 3-epidigitoxigenin and uzarigenin) at the C(3) and C(5) atoms. Altogether they help to shed further light on the conditions and limits of isostructuralism in general. Digitoxigenin-digirezigenin (1/2), 0.36C23H34O4.0.64C23H32O4, M(r) = 746.47, monoclinic, P2(1) (P112(1)), a = 7.290 (3), b = 14.817 (7), c = 18.520 (4) angstrom, gamma = 90.35 (5)-degrees, V = 2000.5 (21) angstrom3, Z = 2, F(000) = 812, D(x) = 1.240 Mg M-3 , lambda(Cu Kalpha) = 1.54184 angstrom, mu = 0.626 mm-1, R = 0.062 for 1709 unique observed reflections, T = 296 (1) K. 5-Andro-stene-3beta,17beta-diol monohydrate, C19H30O2.H2O, M(r) = 308.46, orthorhombic, P2(1)2(1)2(1), a = 6.250 (1), b = 12.143 (3), c = 23.440 (2) angstrom, V = 1779.0 (9) angstrom, z = 4, F(000) = 680, D(x) = 1.152 Mg m-3, lambda(Cu Kalpha) = 1.54184 angstrom, mu = 0.562 mm-1, R = 0.055 for 1491 unique observed reflections, T = 296 (1) K. Beyond these two fully reported structure determinations, three others have also been performed. However, the structures of the 1:1 disordered adducts of arenobufagin-gamabufotalin and cinobufagin-cino-bufotalin are not worthy of publication as that of 5alpha-androstane-3beta,17beta-diol.H2O has already been reported with similar accuracy. Instead, pi and I(D) descriptors of isostructuralism were applied in order to check the internal consistency of the old and novel structure determinations of 5alpha-androstane-3beta,17beta-diol.H2O.