Crystal structures of two polymorphs of tixocortol pivalate.

Two polymorphs, (I) and (II), of (S)-{2-[(8S,9S,10R,11S,13S,14S,17R)-11,17-dihy-droxy-10,13-dimethyl-3-oxo-2,6,7,8,9,11,12,14,15,16-deca-hydro-1H-cyclo-penta-[a]phenanthren-17-yl]-2-oxoeth-yl} 2,2-di-methyl-propane-thio-ate, C26H38O5S, have been identified. They are ortho-rhom-bic, non-centrosymmetric (P212121). The structures display layers of mol-ecules conected via O-H⋯O hydrogen bonds along the b-axis direction in polymorph (I) and along the c-axis direction in polymorph (II). The structure of (II) exhibits disorder of the main mol-ecule.

Crystal structure of (R)-6-fluoro-2-[(S)-oxiran-2-yl]chroman.

The title compound, C11H11FO2, is a building block in the synthesis of the active pharmaceutical ingredient dl-nebivolol. The synthesis starting from the enanti-omerically pure (R)-6-fluoro-4-oxo-3,4-di-hydro-2H-chromene-2-carb-oxy-lic acid resulted in a mixture of two stereoisomers, namely (R)-6-fluoro-2-[(S)-oxiran-2-yl]chroman and (R)-6-fluoro-2-[(R)-oxiran-2-yl]chroman. The mixture was separated by column chromatography but only one stereoisomer crystallized. The X-ray structure analysis revealed that the solid consisted of the R,S isomer. A similar procedure was repeated for (S)-6-fluoro-4-oxo-3,4-di-hydro-2H-chromene-2-carb-oxy-lic acid and, in this case, the S,R isomer was produced as a crystalline solid. Thus, all four stereoisomers of the title epoxide were obtained and their absolute configuration was assigned. The crystal studied was refined as an inversion twin.

(R)-(-)-Quinuclidin-3-ol.

The structure of the title compound [alternatively called (R)-(-)-1-aza-bicyclo-[2.2.2]octan-3-ol], C7H13NO, at 100 K has hexa-gonal (P61) symmetry. The structure shows a twist along the C-N pseudo-threefold axis. In the crystal, mol-ecules are linked via O-H⋯N hydrogen bonds, forming infinite chains along the c-axis direction. The crystal studied was twinned by merohedry (twin law: 010, 100, 00-1; population: 0.925:0.075).

A triclinic polymorph of (-)-(S)-N-benzyl-2-[(R)-6-fluoro-chroman-2-yl]-2-hy-droxy-ethanaminium bromide.

The title salt, C18H21FNO2 (+)·Br(-), determined at 115 K, crystallizes in the triclinic space group P1. The previously reported polymorph occurs in the monoclinic space group P21 and has two independent mol-ecules in the asymmetric unit [Peeters et al. (1993 ▶). Acta Cryst. C49, 2157-2160]. In the title molecule, the pyran rings adopt half-chair conformations. The absolute configuration is S for the hy-droxy-bearing C atom and R for the asymmetric C atom in the di-hydro-pyran unit. In the crystal, the components are linked by N-H⋯Br and O-H⋯Br hydrogen bonds, forming chains along the c-axis direction. The crystal studied was refined as an inversion twin.

(S,S,S,S)-Nebivolol hydro-chloride hemihydrate.

The asymmetric unit of the title hydrated salt, C22H26F2NO4(+)·Cl(-)·0.5H2O, consists of an (S,S,S,S)-nebivolol {nebivol = bis-[2-(6-fluoro-3,4-dihydro-2H-1-benzopyran-2-yl)-2-hy-droxy-eth-yl]ammonium} cation, a chloride anion and a half-occupancy water mol-ecule. The dihedral angle between the mean planes of the benzene rings is 50.34 (12)°. The pyran rings adopt half-chair conformations. The crystal packing features O-H⋯O hydrogen bonds and weak N-H⋯Cl, O-H⋯Cl, and O-H⋯Cl inter-actions, producing layers along (010).