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.

The title host compound, C62H84N4O4, designed to self-assemble to form a new type of extended core Piedfort unit reminiscent of an eight-legged spider host, forms a number of crystalline inclusion compounds favouring oxygen-containing guest molecules. We have established the presence of this unit in the unsolvated molecular crystal at 100 K, which is monoclinic, space group P21/n, with Z = 8. The new Piedfort unit is chiral and its core structure closely approximates to D2 symmetry, with both enantiomers present in the crystal. Rather than being superposed with a staggered arrangement of nitrogen atoms, the rings are rotated by an angle of approximately 45° with respect to each other, and the shortest contact between them is 3.181 (2) Å. The compound's significant inclusion properties may be taken to suggest the participation of an extended Piedfort unit in the microcrystalline adducts formed. The presence of such a dimeric host unit in the clathrates has, however, not yet been established because of the current lack of suitable single crystals for X-ray analysis.

The title sulfoxide, C 18 H 20 O 2 S, was prepared by controlled oxidation of thia -Dianin's compound using hydrogen peroxide in glacial acetic acid. On recrystallization from glacial acetic acid, it was found to form unsolvated, spontaneously resolved crystals, the initial crystal structure analysis revealing the presence of both sulfoxide epimers in the crystal. On multiple recrystallization a single epimer was observed, with crystallization occurring in the unchanged orthorhombic space group P 2 1 2 1 2 1 , with Z′ = 1. The molecule possesses a distal conformation, referring to the juxtaposition of the p -hydoxyphenyl substituent with respect to its syn- related methyl group, with the sulfoxide oxygen atom anti to the aromatic substituent. The molecular packing features O—H...O hydrogen bond chains running parallel to the b axis of the unit cell.

The title compound, C22H22OS [systematic name: 4-(1,3,3-trimethyl-2,3-di-hydro-1H-4-thia-phenanthren-1-yl)phenol], crystallizes unsolvated from nitro-methane as colourless prisms (m.p. 425-427 K) in the polar monoclinic space group Ia with Z' = 2 (mol-ecules A and B). Both independent mol-ecules possess a very similar proximal conformation, this referring to the juxtaposition of the 4-hy-droxy-phenyl substituent with respect to the syn-related methyl group. In the crystal, mol-ecule A is linked to mol-ecule B by an O-H⋯O hydrogen bond. In turn, mol-ecule B exhibits a weak O-H⋯π inter-action with the phenolic group of mol-ecule A related by a-glide symmetry. Together, these lead to [100] chains.

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 R3 being retained. This ultimate unit cell with a quadrupled a-axis has a = 111.7910.5) angstrom and c = 10.8568(1) angstrom and the crystal packing now features not only the prototypal [OH](6) hexamer host unit but also novel hydrogenbonded octameric host-guest units with respective symmetries C (i) and C-1. In addition it has been established that the corresponding achiral selena-Dianin's clathrate and the polar chiral quasiracemic isopropanol clathrate, space group R3, formed from R-Dianin's and S-thia-Dianin's components also exhibit novel related temperature-dependant behaviour.

The structure of the estrone-related steroid, Equilenin, C18H18O2 (systematic name 3-hydroxy-13-methyl-11,12,13,14,15,16-hexahydrocyclopenta[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 C atoms of the A and B rings are almost coplanar, with an r.m.s. deviation from planarity of 0.0104 Å. 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 O atom and the methyl group are translated 0.78 and 0.79 Å, respectively, from the equivalent positions on 17β-estrone. In the crystal, molecules are linked by O—H...O hydrogen bonds, forming chains parallel to the c-axis direction.

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 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.

In the trigonal CCl4quasiracemic clathrate, space group R3, formed from host components S-(−)-Dianin's compound, 4, and its (+)-2R,4R 2-nor methyl analogue, 2, the unprecedented complete ordering of a C–Cl bond of the guest with respect to the c-axial direction and the participation of an unexpected host conformation is reported for the first time.

The R-(+)-enantiomeric form of Dianin's compound and the S-(+)-enantiomeric form of its direct thiachroman analogue both obtained chromatographically employing a cellulose tris(3,5-dimethylphenylcarbamate) column, are shown to undergo supramolecular assembly to form a polar clathrate lattice which is stable even in the absence of a consolidating guest component.

The title tetrasulfone 1, in common with higher members of the multi-armed aromatic hosts, forms host-guest complexes with polar guest molecules. In the sulfolane and cycloheptanone complexes the host molecule possesses an abab conformation with exact C(2,) and approximate D(2) symmetry with deviations owing to crystal packing forces. The conformation of the well-ordered cycloheptanone molecule, which normally undergoes facile pseudorotation, is unambiguously defined in the voids of the crystalline inclusion compound.

The title compounds, C 18 H 21 NO and C 18 H 21 NS, in their enantiomerically pure forms are isostructural with the enantiomerically pure 4-(4-hydroxyphenyl)-2,2,4-trimethylchroman and 4-(2,4-dihydroxyphenyl)-2,2,4-trimethylchroman analogues and form extended linear chains via N—H...O or N—H...S hydrogen bonding along the [100] direction. The absolute configuration for both compounds was determined by anomalous dispersion methods with reference to both the Flack parameter and, for the light-atom compound, Bayesian statistics on Bijvoet differences.

The title compounds, C(18)H(21)NO and C(18)H(21)NS, in their enantiomerically pure forms are isostructural with the enantiomerically pure 4-(4-hydroxyphenyl)-2,2,4-trimethylchroman and 4-(2,4-dihydroxyphenyl)-2,2,4-trimethylchroman analogues and form extended linear chains via N-H···O or N-H···S hydrogen bonding along the [100] direction. The absolute configuration for both compounds was determined by anomalous dispersion methods with reference to both the Flack parameter and, for the light-atom compound, Bayesian statistics on Bijvoet differences.

Octakis(m-tolyloxymethyl)naphthalene, the first Type I spider host produced, crystallises from tetraglyme forming a novel channel structure with the host molecule attaining exact D(2) symmetry. The (flexible) channel structure is retained for guest CS(2), the host now only having exact C(2) symmetry. The octa-sulfone octakis(m-tolylsulfonylmethyl)naphthalene is also of Type I in its triclinic DMSO clathrate. DNMR establishes a substantial difference in molecular flexibilities in solution.

The title host molecule exhibits remarkable conformational flexibility in its crystalline inclusion compounds. The alteration in molecular conformation, between the red dioxane and yellow benzene clathrates, corresponds to a dramatic change in the boat conformation of the seven-membered thiepin ring and reorientation of the side chains.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The structures of the highly substituted title heterocycles, C(20)H(22)N(2)S and C(20)H(22)N(2)O(2)S, have been determined at 123 (1) K. Both molecules possess exact C(2) symmetry and the seven-membered rings have very similar twist-boat conformations. The magnitudes of the C-S-C bond angles, 107.13 (6) and 108.27 (7) degrees, respectively, are influenced significantly by the four substituent methyl groups on the seven-membered rings.

The structures of the highly substituted title heterocycles, C 20 H 22 N 2 S and C 20 H 22 N 2 O 2 S, have been determined at 123 (1) K. Both mol­ecules possess exact C 2 symmetry and the seven-membered rings have very similar twist-boat conformations. The magnitudes of the C—S—C bond angles, 107.13 (6) and 108.27 (7)°, respectively, are influenced significantly by the four substituent methyl groups on the seven-membered rings.

The title compound, (I), crystallizes unsolvated in the triclinic space group P\overline 1, with one mol­ecule per unit cell and a centrosymmetric ababab conformation (a and b denote side-chain units projecting, respectively, above and below the plane of the aromatic core), which possesses non-crystallographic \overline 3 (S6) symmetry. The CH2 C atoms, in cyclic order, deviate from the mean plane of the central benzene ring by 0.042, −0.029, 0.050, −0.042, 0.029 and -0.050 Å (r.m.s. deviation 0.041 Å).

The structure of the title ozonide, C20H22O3S, produced without the use of ozone, has been defined at 123 (1) K. In the triclinic crystal, the molecule has symmetry close to Cs, and its ozonide and 1,4-oxathiane rings have envelope and chair conformations, respectively. The ozonide unit has an O-O bond length of 1.4721 (12) Angstrom and a C-O-O-C torsion angle of -1.45 (12)degrees.