Andrzej Zimniak

SOLVENT-DEPENDENT CONFORMATIONAL TRANSITIONS IN DEACETYLCEPHALOTHIN INVESTIGATED BY 1H NMR AND IR

Abstract Solvent effects on molecular conformations in antibiotic cephalothin and its metabolites exhibiting lower biological activity (deacetylcephalothin and cephalothin lactone) have been compared. In deacetylcephalothin, the structural ability of protecting the carboxyl group at the dihydrothiazine ring by two intramolecular hydrogen bonds is discussed.

Structural studies of bis(μ2-acetophenoniminato)-bis(tricarbonyliron) by NMR and X-ray diffraction: deviations from symmetry in anti and syn isomers

Abstract Two distinct structural isomers obtained in the reaction of 1,4-dimethyl-1,4-diphenyl-2,3-diazabuta-1,3-diene {(CH 3 )(Ph)CN} 2 with triiron dodecacarbonyl were separated, characterized by NMR, and their molecular structures were determined by X-ray diffraction. Only idealized symmetry in both resolved anti and syn forms have been observed. Geometry analysis indicated in the syn form a substantial deviation from symmetry, especially in the peripheral region of the molecule. This deviation is preserved in solution, as demonstrated by 13 C NMR.

Molecular properties of a bis(ketoiminato)-bis(tricarbonyliron) complex obtained by symmetric cleavage from acetophenone azine. Idealized symmetry in anti and syn isomers studied by X-ray diffraction, NMR and density functional theory

Abstract Distinct anti and syn isomers of the bis(μ 2 -acetophenoniminato)-bis(tricarbonyliron) obtained from iron dodecacarbonyl and 1,4-dimethyl-1,4-diphenyl-2,3-diazabuta-1,3-diene by symmetric cleavage of the azine have been compared in terms of molecular deviations from symmetry. The study was carried out by the analysis of intra- and intermolecular close contacts in crystals, quantum chemical DFT calculations for the isolated molecules and by NMR in solution. In the crystalline state the intramolecular contacts and also the symmetry perturbations were more strongly expressed in the syn form as compared with anti , and the same relation was perceived in the DFT-optimized single molecules. However, in solution only symmetric conformations were observed for both isomers anti and syn by 1 H and 13 C NMR at room temperature and at −70°C.

Comparative13C relaxation study ofR andS isomers of the 1-acetoxyethyl ester of cefuroxime. Influence of C—H bond lengths on relaxation data consistency

13C NMR longitudinal relaxation times and nuclear Overhauser enhancements were measured for two diastereomers of the 1‐acetoxyethyl ester of cefuroxime at two magnetic fields. The relaxation parameters of 13C nuclei located in the rigid core of the cefuroxime ester showed inconsistency within the frame of the relaxation model assuming axially symmetric overall reorientation and C—H bond lengths derived from the PM3 method. The consistency of relaxation data was restored allowing for the increase in C—H bond lengths reflecting the influence of vibrational corrections. The diastereomers, exhibiting differences in biological activity, differ in the 13C relaxation parameters of the side ester moiety. This difference was analysed with the aid of the model‐free approach.

Molecular properties of a bis(1,1-diphenylallenylidene)-octacarbonyltriiron complex obtained by symmetric cleavage from 1,1,6,6-tetraphenylhexapentaene. Idealized symmetry studied in synperiplanar and synclinal conformers by X-ray diffraction, NMR and density functional theory

Molecular deviations from symmetry of bis(1,1-diphenylallenylidene)-octacarbonyltriiron are compared in two distinct synperiplanar and synclinal conformers expressed as two polymorphic forms by the analysis of close contacts in crystals, quantum chemical DFT calculations for the isolated molecules and by 13C-NMR in solution.

Investigation of the reaction product of 1,4,7,10-tetraphenyl-cyclododecahexa-1,2,3,7,8,9-ene with dodecacarbonyl-triiron by X-ray diffraction and MS: comparative structural study of the hexacarbonyl-μ2-(1η2-1,2-ene-2η3-3,4,5-allyl-1σ1-5)diiron(FeFe) system

Abstract Reaction of dodecacarbonyl-triiron with the 12-membered bis(butatriene) results in phenyl ring metallation and an intramolecular crosslinking of the macrocycle with the formation of a system of three condensed rings. The central core of the complex is formed by Fe2(CO)6 unit bridged by an organic ligand which is η3:η1-bonded by the π-allylic system and η2-bonded by the olefinic group. The molecular structure of the complex was determined by X-ray diffraction. Differences in fragmentation patterns in MS (EI and LSIMS) were examined. Comparative studies of the geometry of the complex obtained and a series of compounds with isostructural core have been carried out.

Structural studies of the C4H8N2Fe2(CO)6 complex obtained by cyclization of acetaldazine in the presence of dodecacarbonyl-triiron: investigations by X-ray diffraction and NMR of μ-1,2-(1,2-diaza-3-methylcyclopentane)diyl-bis(tricarbonyliron)

Abstract The molecular structure of a complex obtained from 3,4-diazahexa-2,4-diene in reaction with dodecacarbonyl-triiron proceeding via cyclization of the azine was determined by X-ray diffraction. On the basis of X-ray conformational data, the complete assignment of 1 H-NMR signals and a determination of geminal and vicinal coupling constants have been performed. The agreement of X-ray and NMR conformational parameters indicated that the differences in the structure of the title complex in the solid state and in solution are negligible.

Influence of acetylation on anomeric effect in methyl glycosides

abstract In the following research acetylation as an unexplored factor in the anomeric effect in carbohydrate chemistry has been examined. Crystallographic data for methyl glycosides and their acetates have been compared and discussed. Some of the methyl glycosides form hydrogen bonding with the participation of acetal oxygen atoms. This seems to have the most significant influence on the structural diagnostic parameters for anomeric effect. Abbreviations: Me-α-Glc: methyl α-D-glucopyranoside; Me-β-Glc: methyl β-D-glucopyranoside; Me-α-Gal: methyl α-D-galactopyranoside; Me-β-Gal: methyl β-D-galactopyranoside; Me-α-Man: methyl α-D-mannopyranoside; Me-β-Man: methyl β-D-mannopyranoside; Ac-Me-α-Glc: methyl 2,3,4,6-tetra-O-acetyl-α-D-glucopyranoside; Ac-Me-β-Glc: methyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside; Ac-Me-α-Gal: methyl 2,3,4,6-tetra-O-acetyl-α-D-galactopyranoside; Ac-Me-β-Gal: methyl 2,3,4,6-tetra-O-acetyl-β-D-galactopyranoside; Ac-Me-α-Man: methyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranoside; Ac-Me-β-Man: methyl 2,3,4,6-tetra-O-acetyl-β-D-mannopyranoside; GIPAW (Gauge Including Projector Augmented Waves) calculations: a DFT based method used for calculating nuclear magnetic resonance parameters; CP/MAS NMR: cross-polarisation (CP) magic angle spinning (MAS) NMR spectroscopy; δss: chemical shift in 13C CP/MAS NMR spectrum; δt: theoretical chemical shift: as derived from GIPAW DFT; dis: distorted multiplet in 1H NMR spectrum. GRAPHICAL ABSTRACT

The hydrogen-bonding network in deacetylcephalothin.

The structural analysis of deacetylcephalothin [systematic name: (6R,7R)-3-hydroxymethyl-8-oxo-7-(2-thiophen-2-ylacetylamino)-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid], C(14)H(14)N(2)O(5)S(2), shows that the geometry of the central bicyclic moiety is close to the geometry exhibited by other biologically active cephalosporin antibiotics. The molecules are arranged in a helical chain running parallel to the 2(1) axis via a strong O-H...O hydrogen bond. The main helices are zipped together via N-H...O interactions, forming infinite layers. The supramolecular architecture is stabilized by O-H...S and C-H...O hydrogen bonds.