Synthesis, structure and properties of N-acetylated derivatives of methyl 5-amino-1H-[1,2,4]triazole-3-carboxylate

Methyl 5-amino-1H-[1,2,4]triazole-3-carboxylate hydrochloride (1). and free ester (2). were obtained and 2 was reacted with Ac(2)O to give the acetylated products 3-6. Compounds 1-6 were studied using HPLC, GC-MS, FTIR and multinuclear NMR spectroscopy, including the cross-polarisation magic angle spinning (CPMAS) technique. The results of the acetylation of 2 were compared to those of the acetylation of 5-amino-1H-[1,2,4]triazole, and for 2 a significant decrease in the susceptibility to acetylation was found. The reaction of 2 with Ac(2)O at 20 degrees C, regardless of the amount and the concentration of the latter, including neat Ac(2)O, proceeds fully regioselectively and leads to one product: methyl 1-acetyl-5-amino-1H-[1,2,4]triazole-3-carboxylate (3). In sharp contrast to 5-amino-1H-[1,2,4]triazole, neither an additional monoacetylated isomer, whether annular or exocyclic, nor any diacetylated derivative could be detected. The diacetylation of 2 requires the process to be carried out in neat boiling Ac(2)O and, as in the case of 5-amino-1H-[1,2,4]triazole, gives two diacetylated isomers. These are methyl 1-acetyl-3-(acetylamino)-1H-[1,2,4]triazole-5-carboxylate (4) and 1-acetyl-5-(acetylamino)-1H-[1,2,4]triazole-3-carboxylate (5). Hypothetical pathways of their formation have been suggested. A mixture of 4 and 5 upon hydrolysis of the ring acetyl group gives the monoacetylated derivative methyl 5-(acetylamino)-1H-[1,2,4]triazole-3-carboxylate (6). The spectroscopic, structural and conformational characteristics of compounds 1-6 have been given and methods for their preparation have been provided.     

Oxathiaphospholane approach to the synthesis of oligodeoxyribonucleotides containing stereodefined internucleotide phosphoroselenoate function

5'-O-DMT-deoxyribonucleoside-3'-O-(2-selena-4,4-pentamethylene-1,3,2-oxathiaphospholane) monomers, derivatives of dA, dC, dG, and T, can be resolved into pure P-diastereomers by silica gel column chromatography. They have been used for DBU-promoted, either solution- or solid-phase synthesis of P-stereodefined phosphoroselenoate analogues of oligodeoxyribonucleotides. Fast- and slow-eluting monomers are precursors of phosphoroselenoate internucleotide linkage of R(P) and S(P) absolute configuration, respectively. [reaction: see text]     

Dispersity of Al2O3?SnO2 supported platinum from hydrogen pulse chemisorption

This study is concerned with the effect of various amounts of Sn species in modifying the dispersity of Al₂O₃–SnO₂ supported platinum catalysts by application of hydrogen chemisorption in a pulse chromatographic system, as well as determination of activity in water-gas shift reaction (WGS).     

Binding energies of ionized donor–exciton complexes in polar crystals

Binding energies of ionized donor–exciton complexes in crystals of CdSe, CdTe, and ZnSe are calculated using the most realistic effective potentials available for the electron–hole interaction.     

NMR relaxation study of the protonated form of 1,8-Bis(dimethylamino)naphthalene in isotropic solution: anisotropic motion outside of extreme narrowing and ultrafast proton transfer

The protonated form of 1,8-bis(dimethylamino)naphthalene (DMANH(+)) consists of a rigid, aromatic framework, substituted by two amino groups that are connected by a strong, symmetric (on the NMR time-scale) hydrogen bond bridge. The reorientational motion of the molecule in dimethylformamide-d7 solution was characterized by T(1) and NOE measurements for aromatic (13)C nuclei. Treating the reorientation of DMANH(+) as anisotropic rotational diffusion of a rigid body, the diffusion tensor was determined with good accuracy. Measurements and interpretation of (15)N T(1) and NOE indicate that the proton transfer between potential minima in the hydrogen bond bridge is faster than the molecular reorientation.     

On the theoretical determination of the electron affinity of ozone

Summary Multiconfigurational electron correlation methods have been analyzed in order to theoretically compute the electron affinity (EA) of ozone. The near-degeneracy correlation effects, which are so important in O₃ and O ₃ ^– , have been described using complete active space (CAS) SCF wave functions. Remaining dynamic correlation effects are computed using second-order perturbation theory (the CASPT2 method). The best calculated adiabatic value (including zero-point energy corrections), 2.19 eV, is about 0.09 eV larger than the experimental value. Comparative studies using size-consistent coupled pair functional approaches (CPF and ACPF) have also been performed. The harmonic frequencies in O ₃ ^– have been determined to be: ₁=992, ₂=572, and ₃=879 cm^–1, which gives a zero-point energy of 0.151 eV.     

Inapplicability of the Antiperiplanar Lone Pair Hypothesis to C-P Bond Breaking and Formation in Some S-C-P(+) Systems

Both C(2)-P bond breaking and formation in the S-C-P(+) system do not occur according to the antiperiplanar lone pair hypothesis. Experiments using 2-phosphonio derivatives of 5-tert-butyl-1,3-dithiane and cis-4,6-dimethyl-1,3-dithiane are against the participation of higher-energy boat conformers as reactive intermediates. The results obtained support a possibility of conformational adjustment in the course of the reaction. Stereoelectronic control of the C(2)-P bond breaking and formation results from interplay of several factors. The role of the n(S)-sigma(C(2))(-)(P) and sigma(C(4,6))(-)(S)-sigma(C(2))(-)(P) hyperconjugation, as well as of the repulsive interactions between lone electron pairs pi(S) of endocyclic sulfur atoms and pi-electrons of the phenyl ring(s) connected with phosphorus, is discussed.     

Do proficiency tests always verify laboratories’ performance? The case of FAPAS PT 0270

In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted. Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in PT 0270 are questionable.