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Optically active (−)589ethyl (S)-2-phenylbutyl thioether, (−)(S)C-Et(PhBu)S (I), and its new diastereoisomeric mercury (II) chloride adduct, 1:2, (−)[(S)S(S)C-Et(PhBu)S.(HgCl2)2]2, (II) were stereoselectively synthesized; the absorbance (UV) and circular dichroism (CD) spectra were measured and the crystal and molecular structure of complex (II) was determined by single-crystal X-ray diffraction. Two different Hg centres are present whose coordination environments are built by two short bonds to chloride ligands in one case, and to one chloride and one sulphur in the other one. These originate digonal units. Electroneutrality is achieved by a further chlorine, which can be considered prevalently ionic and bonded to the two Hg centres, forming square bridging systems nearly perpendicular to the digonal molecules. The coordination polyhedra can be interpreted as 2 + 4 tetragonally-compressed octahedra with the four longer contacts lying in the equatorial plane. IR spectroscopic data are consistent with the presence of one bent and one linear Cl–Hg–Cl moiety. The absolute configurations at both stereogenic centres of the formed diastereoisomeric complex (II) are (S). The (S)S absolute configuration at the stereogenic sulphur atom bonded to the mercury(II) atom in complex (II) has been related with the negative Cotton effect assigned in its circular dichroism (CD) spectrum to a charge-transfer transition at ca. 230 nm. The stereoselective oxidation of (I) and (II) with hydrogen peroxide, induced by the stereogenic carbon atom (S)C of the enantiopure sulphide, gave (−)598ethyl (S)C-2-phenylbutyl(S)S-sulphoxide, (−)598[(S)S(S)C-Et(PhBu)SO], (III), having 18.1% de. Oxidations carried out in the presence of a 200 molar excess of mercury(II) chloride gave (−)598ethyl (S)C-2-phenylbutyl(R)S-sulphoxide, (−) 598[(R)S(S)C-Et(PhBu)SO], (IV) with 31% de, showing the cooperative influence of mercury(II) chloride on the selectivity of the oxidation reaction.

In this work, we report on a non-solvate and on a new solvate forms of rifamycin S, demonstrating that another stable conformation of the active molecule exists and it may be isolated by planning the crystallization conditions. In fact, in these structures rifamycin S has a previously uncharacterised, bent conformation: implications of these findings on the models used to explain rifamycin activity are discussed. Polymorphism has also been reported for the rifamycin-based antibiotic rifaximin, but without single-crystal X-ray diffraction characterization. Here the structure of a tetrahydrate form of rifaximin is discussed; confirming the flexibility of the drug, the two independent molecules in the unit cell are an example of conformational isomorphism. [ABSTRACT FROM AUTHOR]

Azide complexes [M(RN3)(CO)3P2]BPh41–3[M = Mn, Re; R = C6H5CH2, 4-CH3C6H4CH2, C6H5, 4-CH3C6H4, C5H9; P = PPh(OEt)2, PPh2(OEt)] were prepared by allowing tricarbonyl MH(CO)3P2 hydride complexes to react first with Brønsted acid (HBF4, CF3SO3H) and then with organic azide in the dark. In sunlight the reaction yielded tetraazabutadiene [M(η2-1,4-R2N4)(CO)2P2]BPh44–6 complexes or, with benzyl azide, imine [M{η1-NH=C(H)Ar}(CO)3P2]BPh47(Ar = C6H5, 4-CH3C6H4) derivatives. Tetraazabutadiene [M(η2-1,4-R2N4)(CO)2P2]BPh4 complexes were also prepared by reacting dicarbonyl MH(CO)2P3 species first with Brønsted acid and then with an excess of organic azide. Complexes were characterised spectroscopically (IR, 1H, 31P, 13C, 15N NMR data) and by the X-ray crystal structure determination of complex [Re{η2-1,4-(C6H5CH2)2N4}(CO)2{PPh(OEt)2}2]BPh4(5a). Strong evidence for coordination of the organic azide was obtained from the 15N NMR spectra of labelled [M(C6H5CH215NN15N)(CO)3P2]BPh4 derivatives. [ABSTRACT FROM AUTHOR]

The octahedral copper(II) complex with two 2'-[1-(2-pyridinyl)ethylidene]oxalohydrazide molecules was synthesized from bis(acetylacetonato)copper(II) and 2'-[1-(2-pyridinyl)ethylidene]oxamohydrazide (Hapsox). The complex is unstable when not in solution. X-ray analysis confirmed the tridentate coordination of the ligands in the monoanionic form. In addition, the stable tetrahedral copper(II) complex with one ligand molecule coordinated as a tridentate in the dianionic form was prepared by direct synthesis from Cu(NO3)2·3H2O and Hapsox, and characterized by elemental analysis, magnetic measurements and by i.r. and u.v./vis. spectrophotometry. [ABSTRACT FROM AUTHOR]