Analysis of adenosine by RP-HPLC method and its application to the study of adenosine kinase kinetics

An RP-HPLC method for the analysis of adenosine (ADO) has been developed and validated. In the present study, we report an RP-HPLC-based method with modifications of mobile phase and shorter retention time that substantially improved the efficiency of ADO analysis. The HPLC separation of the ADO was achieved on a C18 column, using a mobile phase consisting of water, containing 7% v/v ACN, at a flow rate of 0.8 mL/min. The column effluent was monitored by UV detection at 260 nm. A linear response was achieved over the concentration range of 0.25-100.00 micromol/L. The analytical method inter- and intra-run accuracy and precision were better than +/- 15%. The LOQ was 0.25 micromol/L, with ADO detection in the range of 6.25 pmol per sample. The method has been applied to the study of adenosine kinase (AK) kinetics.     

Detailed 1H and 13C NMR structural assignment and relative stereochemistry determination for three closely related sesquiterpene lactones

A complete analysis of (1)H and (13)C NMR spectra of the trypanocidal sesquiterpene lactone eremantholide C and two of its analogues is described. These structurally similar sesquiterpene lactones were submitted to (1)H NMR, (13)C {(1)H} NMR, gCOSY, gHSQC, gHMBC, J-resolved and DPFGSE-NOE NMR techniques. The detailed analysis of those results, correlated to some computational calculations (molecular mechanics), led to the total and unequivocal assignment of all (1)H and (13)C NMR data. The determination of all (1)H/(1)H coupling constants and all signal multiplicities, together with the elimination of previous ambiguities were also achieved.     

Ueber die Methode der calorimetrischen Bestimmung mittelst Verbrennung in Sauerstoff bei hohem Druck

Ohne Zusammenfassung     

Core structure of eremophilanes and bakkanes through niobium catalyzed Diels-Alder reaction: synthesis of (+/-)-bakkenolide A

A suitable intermediate for the synthesis of eremophilanes and bakkanes was prepared by a highly regioselective and stereoselective one-step synthesis through a niobium catalyzed Diels-Alder reaction. As a demonstration of the versatility of this intermediate, a total synthesis of (+/-)-bakkenolide A is described.     

Analysis of a cycloheptenone derivative: an experimental and theoretical approach

A detailed analysis with total assignment of (1)H and (13)C NMR spectral data for a cycloheptenone derivative, a key intermediate for the synthesis of perhydroazulene terpenoids, is related. These assignments are based on 1D (1)H and (13)C NMR and on 2D NMR techniques including gCOSY, gHSQC, gHMBC, J-resolved and NOEDIF experiments. The unequivocal assignments were supported by theoretical chemical shifts and scalar coupling constant calculations at GIAO B3LYP/cc-pVDZ level from optimized structures at the same level of theory.     

Aromaticity and Homoaromaticity in Methano[10]annulenes

Aromaticity and neutral homoaromaticity have been evaluated in methano[10]annulenes systems, 1,4-methano[10]annulene (1), 1,5-methano[10]annulene (2), and 1,6-methano[10]annulene (3). C-C bond lengths indicate that 1 presents higher bond alternation than 2 and 3. The relative energies were determined at the B3LYP/6-311+G(d,p) level, and they pointed out that 3 is the most stable isomer. Strain energies, evaluated employing homodesmotic reactions, show the same order as the relative energies. Through a decomposition of strain energies, it could be concluded that the rings absorb more tension than the bridges. The changes in aromaticity were evaluated by magnetic susceptibilities, chiM, HOMA, NICS, and resonance energies, RE. HOMA, RE, and chiM indicate that 2 and 3 are strongly, and 1 is fairly, aromatic. NICS does not provide reliable results, due to interference of ring and bridge atoms. NBO analysis presents some interactions that suggest the existence of neutral homoaromaticity. GPA indices (evaluated at the B3LYP/6-31G* level) point out that homoaromaticity plays a relevant role only in 3. Moreover, this work is the first in the current literature that studies 1,4-methano[10]annulene (1).     

Synthesis of non-aggregating chlorins and isobacteriochlorins from meso-tetrakis(pentafluorophenyl)porphyrin: a study using 1,3-dipolar cycloadditions under mild conditions

The 1,3-dipolar cycloaddition of meso-tetrakis(pentafluorophenyl)porphyrin and its nickel complex, with the bulky azomethine ylide dipole was studied under mild conditions, and yielded chlorin and isobacteriochlorin derivatives self-prevented from aggregation. The reactions were performed at room temperature or 0 °C, and we were able to establish a set of reaction conditions to obtain only the chlorin or the isobacteriochlorin. These compounds were evaluated in solution, and no aggregation was observed at less than 25 mM (∼30 mg mL⁻¹) using ¹H NMR experiments.