Ferenc Aradi

Isomerization of Substituted Tricyclic 4,5-Dihydropyrazoles

SummaryThe acid and base catalyzed isomerization of some tricyclic 2-pyrazolines with N-Carbamoyl-,N-thiocarbamoyl-and N-phenyl substituents was investigated. Starting fromcis ortrans 3-H, 3a-H diastereomers, equilibrium mixtures ofcis andtrans diastereomers were prepared which were separated and subsequently studied by1H NMR and13C NMR spectroscopy. A mechanism for the isomerization of the pyrazolines is suggested, supported by a deuterium exchange at C-3a.ZusammenfassungDie Isomerisierung einiger tricyclischer 2-Pyrazoline mit N-Carbamoyl-, N-Thiocarbamoyl-und N-Phenyl-substituenten unter saurer und basischer Katalyse wurde untersucht. Ausgehend von dencis odertrans 3-H,3a-H-Diastereomeren wurdencis- undtrans Gleichgewichtsgemische gewonnen, die getrennt und durch1H- und13C-NMR-Spektroskopie untersucht wurden. Ein Mechanismus für die Isomerisierung von Pyrazolinen wird vorgeschlagen, der durch den Deuteriumaustausch in Position 3a-C unterstützt wird.

Comparative 1H NMR chemical shift study on the stacking interaction of pyrimidine with purine and 6-methylpurine

Abstract The pyrimidine-purine and pyrimidine-6-methylpurine cross-interactions were compared by measuring the mutually induced concentration-dependent changes in proton chemical shifts in deuterium oxide at 35°C. The chemical shift vs. concentration profiles were analysed using a competitive dimer model. The equilibrium constants (0.41 ± 0.06 and 0.74 ± 0.05 l mol −1 for the pyrimidine-purine and pyrimidine-6-methylpurine hetero-associations, respectively) and the dimer shifts imply that the methylation of purine significantly influences the stacking interaction between the parent molecules of nucleic acid bases and thus their plane-to-plane association structure.

Effect of methylation on the pyrimidine-pyrimidine stacking interaction studied by 1H NMR chemical shift

Mutually induced proton chemical shift changes were measured for the mixed solutions of pyrimidine and its methylated forms in deuterium oxide at 35 degrees C. The chemical shift vs. concentration profiles were analyzed using a three-state decomposition model based on competitive self- and hetero-association dimer equilibria. The equilibrium constants show an increasing association tendency within the series pyrimidine-5-methyl-pyrimidine (0.23 +/- 0.02 M(-1)) < pyrimidine-4,6-dimethyl-pyrimidine (0.32 +/- 0.04 M(-1)) < 5-methyl-pyrimidine-4,6-dimethyl-pyrimidine (0.51 +/- 0.04 M(-1)). The upfield dimer shifts suggest an offset stacked geometry for the structure of associations between the parent molecule of the pyrimidine nucleobases and its methylated derivatives in aqueous solution.

Fused heterocycles. Part 4. Synthesis and stereochemistry of hexahydrobenzo[6,7]cyclohepta[1,2-c]pyrazoles

Hexahydrobenzo[6,7]cyclohepta[1,2-c]pyrazoles have been synthesized by treating 2-benzylidene-1-benzosuberone with hydrazine derivatives. The cis and trans isomers have been distinguished and conformational equilibria studied by NMR techniques.

On the tautomerism of 2,4-disubstituted 3,4,5,6-tetrahydrobenzo[h]quinazolines

SummaryThe tautomerism of the title compounds was investigated by1H-,13C-NMR and UV spectroscopy. Compound5 was compared with respect to its spectra with those of appropriate model compounds1,3,4, and6. This gave evidence that5 predominates in the tautomeric from5A.ZusammenfassungDie Tautomerie von 2,4-disubstituierten 3,4,5,6-Tetrahydrobenzo[h]chinazolinen wurde durch1H-,13C-NMR- und UV-Spektroskopie untersucht. Der Vergleich der Spektren von5 und der Modellverbindungen1,3,4 und6 legt nahe, daß für5 das Tautomere5A dominiert.