Structure of Equilenin at 100 K: an estrone related steroid

The structure of the estrone related steroid, Equilenin, C18H18O2 (systematic name 3-hydroxy-13-methyl-11,12,13,14,15,16-hexahydro-cyclopenta[a]phenanthren-17-one), has been determined at 100 K. The crystals are orthorhombic, P212121, and the absolute structure of the molecule in the crystal has been determined by resonant scattering [Flack parameter = 0.05 (4)]. The carbon atoms of the A and B rings, are coplanar with an r.m.s. deviation from planarity of 0.0104 A. The C ring has a sofa conformation while the D ring has an envelope conformation with the methine C atom as the flap. The keto oxygen and the methyl group are translated 0.78 A and 0.79 A, respectively, from the equivalent positions on 17β-estrone 3. In the crystal, molecules are linked by O—H・・・O hydrogen bonds forming 14 chains parallel to the c-axis direction

Novel Ansa-Chain Conformation of a Semi-Synthetic Rifamycin Prepared Employing the Alder-Ene Reaction: Crystal Structure and Absolute Stereochemistry

Copyright: © 2021 by the authors. Rifamycins are an extremely important class of antibacterial agents whose action results from the inhibition of DNA-dependent RNA synthesis. A special arrangement of unsubstituted hydroxy groups at C21 and C23, with oxygen atoms at C1 and C8 is essential for activity. Moreover, it is known that the antibacterial action of rifamycin is lost if either of the two former hydroxy groups undergo substitution and are no longer free to act in enzyme inhibition. In the present work, we describe the successful use of an Alder-Ene reaction between Rifamycin O, 1 and diethyl azodicarboxylate, yielding 2, which was a targeted introduction of a relatively bulky group close to C21 to protect its hydroxy group. Many related azo diesters were found to react analogously, giving one predominant product in each case. To determine unambiguously the stereochemistry of the Alder-Ene addition process, a crystalline zwitterionic derivative 3 of the diethyl azodicarboxylate adduct 2 was prepared by reductive amination at its spirocyclic centre C4. The adduct, as a mono chloroform solvate, crystallized in the non-centrosymmetric Sohnke orthorhombic space group, P212121. The unique conformation and absolute stereochemistry of 3 revealed through X-ray crystal structure analysis is described.Malaysia HIR MOHE (Grant No.F000009-21001)

Total CCl₄ guest alignment in a quasiracemic clathrate closely related to Dianin’s compound

Single crystal X-ray analysis at 100 K reveals that in the trigonal CCl4 quasiracemic clathrate, space group R3, formed from host components S-(-)-Dianin’s compound and its (+)-2R,4R 2-nor methyl analogue there is an unprecedented complete ordering of a C-Cl bond of the guest with respect to the c-axial direction. In this clathrate and that formed from the (+-)2R,4R and (+)-2R,4S epimers the participation of an unexpected host conformation is reported for the first time

Crystal structure of 4-p-hydroxyphenyl-2,2,4-trimethyl-7,8- benzothiachroman: a fused-ring counterpart of thia-Dianin's compound.

Abstract The title compound, C22H22OS [systematic name 4-(1,3,3-tri­methyl-2,3-di­hydro-1H-4-thia- phenanthren-1-yl)-phenol] crystallizes unsolvated from nitro­methane as colourless prisms m.p. 152–154 °C, in the polar monoclinic space group Ia with Z' = 2, (molecules A and B). Both independent molecules possess a very similar proximal conformation, this referring to the juxtaposition of the p-hy­droxy­phenyl substituent with respect to the syn related methyl group. In the crystal, molecule A is linked to molecule B by an O—H···O hydrogen bond. In turn, molecule B exhibits a weak O—H··· inter­action with the phenolic group of molecule A related by a-glide symmetry. Together, these lead to [100] chains

An unprecedented Dianin clathrate structure with Z ' (host) = 16

The structure of the iso-propanol clathrate of 4-p-hydroxyphenyl 2,2,4-trimethylthiachroman, the direct thia- analogue of Dianin's compound, has been studied by single-crystal X-ray diffraction as a function of temperature from 371 K down to 90 K. The standard Dianin unit cell, observed at high temperature, undergoes two sequential commensurate thermal phase transformations which results at low temperature in a unit cell with 16 times the original volume and with Z'(host) = 16 and Z = 288, the space group R-3 being retained. This ultimate unit cell with a quadrupled a-axis has a = 111.7910(5)Å and c = 10.8568(1)Å and the crystal packing now features not only the prototypal [OH]6 hexamer host unit but also novel hydrogen-bonded octameric host-guest units with respective symmetries Ci and C1. In addition it has been established that the corresponding achiral selena-Dianin‘s clathrate and the polar chiral quasiracemic iso-propanol clathrate, space group R3, formed from R-Dianin's and S-Thia-Dianin's components also exhibit novel related temperature-dependant behaviour.Financial support from the Malaysia HIR MOHE, Grant No:F000009-21001 is gratefully acknowledged. We also wish to thank Dr Alex. R. Eberlin, Johnson-Matthey (Pharmorphix), Cambridge (UK), for assistance with the DSC experiments

Charge densities from high-resolution synchrotron X-ray diffraction experiments

The combination of intense X-ray sources, especially synchrotron radiation, with area-detector technology has accomplished an enormous advance in the experimental conditions available for charge-density analysis by single-crystal high- resolution X-ray diffraction. Such experiments can now be carried out in a time measured in hours rather than weeks. Some features of these experiments are examined and preliminary results are reported for charge-density studies of 2-hydroxy-5- nitrobenzaldehyde N-cyclohexylimine (1), octakis(m- tolylthio)naphthalene (2), and 7-fluoro-4-styrylcoumarin (3). Weak interactions in crystals of (1) and (3) are found to have similar charge-density characteristics. Cages in the crystal lattice of (2) have a complex charge distribution