Alessandro Vaciago

N-oxides and related compounds. Part XL. Chemical and X-ray crystallographic investigation of the oxidation products of α-diketone bisacylhydrazones

Oxidation of the title compounds yields O-acyl imidic acids derived from 1-amino-1,2,3-triazoles. This structure best explains the chemical and spectroscopic data and is confirmed by an X-ray crystallographic study of 1-(α-benzoyloxybenzylideneamino)-4,5-dimethyl-1,2,3-triazole (10). Crystals are monoclinic, space group P21/c with Z= 4 in a unit cell of dimensions: a= 5·94 ± 0·03, b= 10·76 ± 0·05, c= 27·31 ± 0·14 A, β= 100·8°± 0·3°. The structure was solved by direct methods and refined to R 0·094.

A study on the structures of 3-methoxycarbonylrifamycins by X-ray crystallography and 1H nuclear magnetic resonance spectroscopy

The structures of 3-methoxycarbonylrifamycins were studied by X-ray crystallography and 1H n.m.r. spectroscopy. The results obtained by the two different methods are consistent. The comparison with the conformations of some ansamycins in the solid state shows that in this and in other active compounds the central part of the ansa-chain, directly involved in the inhibitory interaction with the bacterial enzyme DNA-dependent RNA polymerase, remains in general the same, while large conformational changes may occur at the junctions of the ansa-chain with the chromophore-rings, thus generating four kinds of conformers. Therefore the 3-methoxycarbonyl substituent does not seem to exert any influence on the conformation of the ansa-chain which can be related to the decrease of the antibacterial activity of 3-methoxycarbonylrifamycin S.

X-Ray crystal structures of 1,2,4,5-tetra-azacyclohexanes: molecular dimensions for examples of three out of the four conformations existing in solution

The 1,4-dimethyl-2,5-dibenzyl monocycle (2), the unsaturated tricycle (3), and the saturated tricycle (4) exist in the crystal in the aeae, ae3, and e4 conformations, respectively. The conformation behaviour is compared with that in solution and the molecular dimensions with those of similar compounds. The conformations deduced by n.m.r. spectroscopy for solutions are generally those found for the crystals.

1,3-Dipolar character of six-membered aromatic rings. Part XXXII. Derivatives of 1-aryl-3-imidopyridiniums: preparation and X-ray crystal structure

Various 3-imidopyridiniums have been prepared. The X-ray structure of 1-methyl-3-methylsulphonylimidopyridinium confirms the betaine structure.

1,3-DIPOLAR CHARACTER OF SIX-MEMBERED AROMATIC RINGS. PART XXXII. DERIVATIVES S OF 1-ARYL-3-IMIDOPYRIDINIUMS- PREPARATION AND X-RAY CRYSTAL STRUCTURE

Various 3-imidopyridiniums have been prepared. The X-ray structure of 1-methyl-3-methylsulphonylimidopyridinium confirms the betaine structure.

Crystal and molecular structure of the major products from the benzylation of 1-ethyl-4-phenylpiperidine and 1-isopropyl-4-phenylpiperidine

The structures of the major isomers of 1-benzyl-1-ethyl-(1) and of 1-benzyl-1-isopropyl-4-phenylpiperidinium chloride (2), as determined by X-ray analysis, indicate that N-benzylation of piperidines normally occurs by preferential equatorial attack. Crystals of (1) are orthorhombic, space group Pbca, with Z= 8 in a unit-cell of dimensions: a= 9·41(3), b= 17·94(6), c= 20·47(6)A. Crystals of (2) are monoclinic, space group C2/c, with Z= 8 in a unit-cell of dimensions a= 27·778(19), b= 9·483(7), c= 19·911(12)A, β= 133·05(2)°. The structures were solved by the symbolic addition procedure and refined by block-diagonal least-squares methods to R 0·13 [(1), 2036 photographic data] and 0·048 [(2), 2089 diffractometer data].