Curtin-Hammett versus non-Curtin-Hammett frameworks is optimizing the enantioselective binolam/titanium(IV)-catalyzed cyanobenzoylation of aldehydes: Part 2

Extensive experimental and computational studies have been carried out on the enantioselective titanium(IV)-catalyzed cyanobenzoylation of aldehydes using 1:n Binolam:Ti(OiPr)4 mixtures as precatalysts, with the purpose of identifying the key mechanistic aspects governing enantioselectivity. HCN and isopropyl benzoate were detected in the reacting mixtures. This, as well as the reaction’s response to the presence of an exogenous base, and the failure to react in the presence of Binol:Ti(OiPr)4 mixtures, led us to propose not a direct cyanobenzoylation but an indirect process involving enantioselective hydrocyanation followed by O-benzoylation. Computational work provided positive evidence for the intervention of both indirect and direct cyanobenzoylation routes, the former being faster. However, the standard Curtin–Hammett-based optimization search ended with unsatisfactory results. Experimental and computational DFT studies (B3LYP/6-31G*) led us to conclude that: (1) the overall cyanobenzoylation of aldehydes catalyzed by 1:n Binolam:Ti(OiPr)4 mixtures involves an enantioselective hydrocyanation followed by an stereochemically inert O-benzoylation; (2) the initial complexes prevailing in a 1:1 Binolam:Ti(OiPr)4 mixture are the solvated mononuclear monomer 5·2(iPrOH) and solvated dinuclear dimer 9·2(iPrOH), whereas 9·2(iPrOH) is the major component in a 1:2 or higher 1:n mixture; (3) since the slowest step is that of benzoylation of ligated iPrOH which yields the actual catalysts 5–9, the catalytic system fits into a non-Curtin–Hammett framework, the final products deriving from a kinetic quench of the competing routes; and (4) accordingly, catalysis by 1:1 Binolam:Ti(OiPr)4 mixtures should involve cyanobenzoylations promoted by mononuclear 5, contaminated with those promoted by some dinuclear open dimer 9, whereas cyanobenzoylations catalyzed by a 1:2 and higher 1:n mixtures should be the result of catalysis promoted by the large amounts of dinuclear open dimer 9.

Efficient Diastereo- and Enantioselective Synthesis of exo-Nitroprolinates by 1,3-Dipolar Cycloadditions Catalyzed by Chiral Phosphoramidite⋅Silver(I) Complexes

Chiral complexes formed by privileged phosphoramidites and silver triflate or silver benzoate are excellent catalysts for the general 1,3-dipolar cycloaddition between azomethine ylides generated from α-amino acid-derived imino esters and nitroalkenes affording with high dr the exo-cycloadducts 4,5-trans-2,5-cis-4-nitroprolinates in high ee at room temperature. In general, better results are obtained using silver rather than copper(II) complexes. In many cases the exo-cycloadducts can be obtained in enantiomerically pure form just after simple recrystallization. The mechanism and the justification of the experimentally observed stereodiscrimination of the process are supported by DFT calculations. These enantiomerically enriched exo-nitroprolinates can be used as reagents for the synthesis of nitropiperidines, by ester reduction and ring expansion, which are inhibitors of farnesyltransferase.

Enantioselective Synthesis of exo-4-Nitroprolinates from Nitro­alkenes and Azomethine Ylides Catalyzed by Chiral Phosphor­amidite·Silver(I) or Copper(II) Complexes

Chiral complexes formed by privileged phosphoramidites derived from chiral binol and optically pure Davies’ amines, and copper(II) triflate, silver(I) triflate or silver(I) benzoate are excellent catalysts for the general 1,3-dipolar cycloaddition between nitroalkenes and azomethine ylides generated from α-amino acid derived imino esters. These three methods can be conducted at room temperature to afford the exo-cycloadducts (4,5-trans-2,5-cis-4-nitroprolinates) with high diastereoselectivity and high enantioselectivity. In general, the three procedures are complementary but silver catalysts are more versatile and less sensitive to sterically congested starting materials.

Effects of follicular versus luteal phase-based strength training in young women

Hormonal variations during the menstrual cycle (MC) may influence trainability of strength. We investigated the effects of a follicular phase-based strength training (FT) on muscle strength, muscle volume and microscopic parameters, comparing it to a luteal phase-based training (LT). Eumenorrheic women without oral contraception (OC) (N = 20, age: 25.9 ± 4.5 yr, height: 164.2 ± 5.5 cm, weight: 60.6 ± 7.8 kg) completed strength training on a leg press for three MC, and 9 of them participated in muscle biopsies. One leg had eight training sessions in the follicular phases (FP) and only two sessions in the luteal phases (LP) for follicular phase-based training (FT), while the other leg had eight training sessions in LP and only two sessions in FP for luteal phase-based training (LT). Estradiol (E2), progesterone (P4), total testosterone (T), free testosterone (free T) and DHEA-s were analysed once during FP (around day 11) and once during LP (around day 25). Maximum isometric force (Fmax), muscle diameter (Mdm), muscle fibre composition (No), fibre diameter (Fdm) and cell nuclei-to-fibre ratio (N/F) were analysed before and after the training intervention. T and free T were higher in FP compared to LP prior to the training intervention (P < 0.05). The increase in Fmax after FT was higher compared to LT (P <0.05). FT also showed a higher increase in Mdm than LT (P < 0.05). Moreover, we found significant increases in Fdm of fibre type ΙΙ and in N/F only after FT; however, there was no significant difference from LT. With regard to change in fibre composition, no differences were observed between FT and LT. FT showed a higher gain in muscle strength and muscle diameter than LT. As a result, we recommend that eumenorrheic females without OC should base the periodization of their strength training on their individual MC.

Effects of Bisphenol A on ion channels: Experimental evidence and molecular mechanisms

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) produced in huge quantities in the manufacture of polycarbonate plastics and epoxy resins. It is present in most humans in developed countries, acting as a xenoestrogen and it is considered an environmental risk factor associated to several diseases. Among the whole array of identified mechanisms by which BPA can interfere with physiological processes in living organisms, changes on ion channel activity is one of the most poorly understood. There is still little evidence about BPA regulation of ion channel expression and function. However, this information is key to understand how BPA disrupts excitable and non-excitable cells, including neurons, endocrine cells and muscle cells. This report is the result of a comprehensive literature review on the effects of BPA on ion channels. We conclude that there is evidence to say that these important molecules may be key end-points for EDCs acting as xenoestrogens. However, more research on channel-mediated BPA effects is needed. Particularly, mechanistic studies to unravel the pathophysiological actions of BPA on ion channels at environmentally relevant doses.