Gábor Czira

Distinction of amino acid enantiomers based on the basicity of their dimers

Mixtures of several amino acid pairs, in all four chiral combinations, were studied. The protonated trimers (A(2)BH(+)) fragment, forming ABH(+) and A(2)H(+) dimers. Abundance ratios of these fragments were measured in the mass-analyzed ion kinetic energy spectra of the trimers. These were found to depend on the stereochemistry (homo- or heterochiral form) of the ABH(+) dimer. The results were evaluated using the kinetic method, and the chiral discrimination was related to a difference in gas-phase basicity (GB) between the homo- and the heterochiral dimers. Four amino acid pairs (proline-tryptophan, phenylalanine-alanine, phenylalanine-proline, and phenylalanine-valine) were studied. Chiral discriminations were observed in all cases, relating to 0.4-4 kJ/mol differences in GB. The technique described here can generally be used to study enantiomers by mass spectrometry and is capable of reliably distinguishing energy differences as small as 0.2 kJ/mol in cluster ions.

Carbonylation (hydroformylation and hydrocarbalkoxylation) reactions in the presence of transition metal: p-tert-butyl-calix[4]arene-based phosphine and phosphinite systems

Abstract In this study, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-diphenylphosphinoxy-ethoxy)calix[4]arene (5) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-diphenylphosphinoethoxy)-calix[4]arene (6), as well as their platinum and palladium complexes (PtCl2)2(5), (PdCl2)2(5) were synthesised and characterised. In addition to these transition metal-containing complexes the catalytic systems formed in situ, from catalytic precursors PtCl2(PhCN)2, [Rh(nbd)Cl]2 and PdCl2(PhCN)2 and the corresponding calixarene ligand, were tested as catalysts in hydroformylation and hydrocarbalkoxylation, respectively. High chemoselectivity was obtained in hydroformylation in the presence of rhodium-containing catalysts both with the above calixarene-based phosphine and phosphinite ligands. The regioselectivity towards branched aldehyde shows a strong temperature dependence in case of phosphinite derivative. Although the platinum-containing systems show much lower catalytic activity, the regioselectivities are undoubtedly higher than those obtained with PtCl2(diphosphine)–SnCl2 systems.

Useful base promoted elaborations of oxiranyl ethers

Abstract Functionalized oxiranyl ethers can be regio- and stereoselectively converted into hydroxy oxetanes or cis -diols by treatment with organometallic bases. These two rearrangements can be conveniently carried out either using different reaction conditions starting from the oxirane or in two consecutive steps from the oxirane via the oxetane.

Facile synthesis of 12-carboxamido-11-spirostenes via palladium-catalyzed carbonylation reactions

12-Carboxamido- and 12-carboxyl-11-spirostenes were synthesized from the corresponding 12-iodo-11-ene derivative in palladium-catalyzed carbonylation reactions under mild reaction conditions. The synthesis of the iodo-alkene substrate is based on the transformation of the 12-keto derivative (hecogenin) to hydrazone, which was treated with iodine in the presence of a base (1,1,3,3-tetramethyl guanidine). While various 12-carboxamides were synthesized in moderate to high yields by using simple alkyl/arylamines or amino acid methylesters as N-nucleophiles, low yields can be achieved with alcohols as O-nucleophiles. The homogeneous carbonylation reactions tolerate the 3-hydroxy substituent and the spiroacetal moiety.

Metabolism of mesocarb in the rat

1. Rats treated orally with [14C]mesocarb (I; 3-(1-methyl-2-phenyl[2-(14C]ethyl)-N-(phenylaminocarbonyl)sydnone imine) (50 mg/kg) excrete 35% of the radioactivity in 24 h urine and 51% in 48 h urine. 2. Only traces of unchanged drug were found in urine. Hydroxy-mesocarb (II), dihydroxy-mesocarb (III), amphetamine (VII) and the conjugates of II and III account for 86% of the urinary radioactivity. 3. Cannulated male rats excrete about 40% of the radioactivity in 30 h in bile, mainly as conjugates of II and III.

Temperature dependences of ion currents of alcohol clusters under low-temperature secondary ion mass spectrometric conditions

The dependences of ion currents on temperature (ion thermograms) obtained by monitoring the abundance of different types of ions during the thawing of frozen samples of methanol and ethanol in low-temperature secondary ion mass spectrometry revealed special features in the temperature behaviour of the samples. Correlations between the changes in ion production and phase transitions (melting, boiling, evaporation) in the sample with temperature increase were revealed.

Comparison of Positive and Negative Ion Clusters of Methanol and Ethanol Observed by Low Temperature Secondary Ion Mass Spectrometry

Positively and negatively charged cluster ions were produced from methanol and ethanol samples under low temperature secondary ion mass spectrometric conditions. Neat alcohol clusters [Mn. H+], [Mn − H]− and mixed alcohol–water cluster sets [Mn. (H2O)m.H+] and [Mn.(H2O)m − H]− sets were recorded as the most prominent peaks in the spectra. Clusters composed of up to 30 molecules have been observed. Distributions of these cluster series, and also some satellite ion clusters observed with lower abundances, are discussed.

CHARACTERIZATION AND DIFFERENTIATION OF HETEROCYCLIC ISOMERS. TANDEM MASS SPECTROMETRY AND MOLECULAR ORBITAL CALCULATIONS ON 3-METHYLISOXAZOLO- AND 2- METHYLOXAZOLOPYRIDINES

Metastable mass-analyzed ion kinetic energy (MIKE) and collision-induced dissociation MIKE spectrometries have been applied to the study of all members of two classes of heteroaromatic isomers: 3-methylisoxazolo-and 2-methyloxazolopyridines. The study revealed that tandem mass spectrometry can characterize and differentiate the isomeric ion structures produced by these heterocycles. In particular, the MIKE spectra of both the molecular ions and abundant fragments formed by CO and CH3CN losses show characteristic differences that allow distinction among the isomers dependent on the position of the nitrogen atom in the pyridine ring, and distinction of isoxazole derivatives from oxazoles. The results indicate that the isomerization of the isoxazole moiety to oxazole-proposed for other analogous compounds—does not occur in these heterocyclic systems. The experimental work is supported by molecular orbital calculations both on neutral molecules and on molecular and fragment ions.

The reaction of N-cyanoamines with 1-(t-butyl)-3,3-diphenylaziridinone: A general method for the synthesis of 1-alkyl-, 1-aralkyl- and 1-aryl-5,5-diphenylhydantoins and -glycocyamidines

Abstract N-Cyanomanines react with aziridinone 1 to yield the amides 2 . Base catalysed ring closure of the latter furnished the glycocyamidines 3 . Acid catalysed de-t-butylation, and deimination combined with de-t-butylation of the compounds 3 leads to 1-substituted 5,5-diphenylglycocyamidines ( 4 ) and -hydantoins ( 5 ), respectively. Part of the hydantoins 5 were also directly obtained by hydrochloric acid treatment of amides 2 . Selective de-t-butylation in position 3 of the glycocyamidine 3 (R = t-Bu) was brought about by heating with methanolic NH 3 in the presence of NH 4 I. Reaction of 1 with the un substituted N-cyanoamine furnished carbodiimide 7 which was cyclized to the glycocyamidine 8 . The mass spectra of some glycocyamidines 4 and hydantoins 5 , as well as of compounds 7 and 8 are discussed.

Electron impact studies on some organochlorogermanes: Mass spectra and bond dissociation energies

The mass spectra of the methylchlorogermanes and the (chloromethyl)-trichlorogermanes are described and analysed. It is shown by consideration of the ionisation and appearance potentials that the surprisingly high abundance of (MCl)+ ions in the spectrum of Cl3GeCH3 is due to a large decrease of the GeCl bond strength in the molecular ions of methylchlorogermanes with increase in the number of Cl atoms on Ge. Calculated bond energies indicate that this phenomenon reflects GeCl bond energy differences in the neutral molecules.