NMR Conformational Study Reveals that S-C-N Anomeric Effect in Thionucleosides Is Weaker than O-C-N Anomeric Effect in Natural Nucleosides

The comparative analysis by NMR and ab initio calculations of the energetics of North &#8644; South pseudorotational equilibrium in 4\u27-thio-nucleosides and in their natural 4\u27-oxo counterparts has shown that S-C-N anomeric effect in the former is weaker than O-C-N anomeric effect in the latter. The &Delta;&Delta;H° values between 2\u27-deoxy-4\u27-thio analogues and their 4\u27-oxo counterparts after accounting for the drive by 3\u27-OH group have been attributed to the weakening of the nucleobase-dependent S4\u27-C1\u27-N9/1 anomeric effect by 3.3, 6.5, 8.5 and 9.2 kJ mol-1 in adenine, guanine, cytosine and thymine, respectively. In addition, S-C-N anomeric effect is stronger in purine than in pyrimidine 4\u27-thionucleosides and increases in the following order: thymine < cytosine < guanine < adenine, which is in contrast to natural nucleosides

Identification of mixed di-cation forms of G-quadruplex in solution

Multinuclear NMR study has demonstrated that G-quadruplex adopted by d(G(3)T(4)G(4)) exhibits two cation binding sites between three of its G-quartets. Titration of tighter binding K(+) ions into the solution of d(G(3)T(4)G(4))(2) folded in the presence of [Formula: see text] ions uncovered a mixed mono-K(+)-mono- [Formula: see text] form that represents intermediate in the conversion of [Formula: see text] into di-K(+) form. Analogously, [Formula: see text] ions were found to replace Na(+) ions inside d(G(3)T(4)G(4))(2) quadruplex. The preference of [Formula: see text] over Na(+) ions for the two binding sites is considerably smaller than the preference of K(+) over [Formula: see text] ions. The two cation binding sites within the G-quadruplex core differ to such a degree that [Formula: see text] ions bound to the site, which is closer to the edge-type loop, are always replaced first during titration by K(+) ions. The second binding site is not taken up by K(+) ion until K(+) ion already resides at the first binding site. Quantitative analysis of concentrations of the three di-cation forms, which are in slow exchange on the NMR time scale, at 12 K(+) ion concentrations afforded equilibrium binding constants. K(+) ion binding to sites U and L within d(G(3)T(4)G(4))(2) is more favorable with respect to [Formula: see text] ions by Gibbs free energies of approximately −24 and −18 kJ mol(−1) which includes differences in cation dehydration energies, respectively

On the stability and degradation pathways of venetoclax under stress conditions

Venetoclax is an orally bioavailable, B-cell lymphoma-2 (BCL-2) selective inhibitor, used for the treatment of various types of blood cancers, such as chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL). In this study we investigated the degradation of venetoclax under various stress conditions including acidic, basic, oxidative, photolytic and thermolytic conditions. We isolated and identified six of its main degradation products produced in forced degradation studies. The structures of the isolated degradation products were determined by using nuclear magnetic resonance (NMR) spectroscopy, high resolution mass spectrometry (HRMS) and infrared (IR) spectroscopy. Additionally, one oxidation degradation product was identified with comparison to a commercially obtained venetoclax impurity. We proposed the key degradation pathways of venetoclax in solution. To the best of our knowledge, no structures of degradation products of venetoclax have been previously published. The study provides novel and primary knowledge of the stability characteristics of venetoclax under stress conditions. Venetoclax is currently the only BCL-2 protein inhibitor on the market. In addition to single agent treatment, it is effective in combinational therapy, so future drug development involving venetoclax can be expected. A better insight into the stability properties of the therapeutic can facilitate future studies involving venetoclax and aid in the search of new similar therapeutics