Stereoselective formation of Bis(alpha-hydroxy-ketones) via enzymatic carboligation

The enzymatic approach to a novel class of chiral bis(alpha-hydroxy ketones) of type 5 and 8, which enable the synthesis of new multidentate ligands for asymmetric transition metal catalysis, is described. The key step is the second benzoylformate decarboxylase catalyzed C-C-bond formation between an aromatic dialdehyde and acetaldehyde, which proceeds with complete stereocontrol. Transformation of enantiomerically enriched monoadduct (S)-4 (ee 88%) and (S)-7 (ee 79%) resulted in optical pure (S,S)-5 and (S,S)-8 besides minor amounts of the corresponding diastereomeric meso-forms

Enantioselective synthesis of (S)-2-hydroxypropanone derivatives by benzoylformate decarboxylase catalyzed C-C-bond formation

Chiral 2-hydroxypropanone derivatives 5a-v, 8a-d, and 10a, b were formed by benzoylformate decarboxylase (BFD) catalyzed C-C bond formation. A donor aldehyde and acetaldehyde as an acceptor were carboligated in aqueous buffer solution with remarkable ease in high chemical yield and good to high optical purity. The substrate range of this thiamin diphosphate dependent enzyme was examined to employ this benzoin condensation type reaction in stereoselective synthesis. The observed dependence of the enantiomeric excess on the substitution pattern could be exploited to design substrates resulting in high selectivity Best substrates with regard to optical purity were meta-substituted benzaldehyde derivatives. To enable a general and convenient applicability of the BFD-catalyzed C-C bond formation, analytical batch experiments were scaled up to give (S)-2-hydroxy ketones in good to high yields on a preparative scale. Further, the solubility of some of the organic substrates in aqueous solution was increased by the use of cyclodextrin or buffer/DMSO mixtures

Metabolic Adaptations May Counteract Ventilatory Adaptations of Intermittent Hypoxic Exposure during Submaximal Exercise at Altitudes up to 4000 m

Intermittent hypoxic exposure (IHE) has been shown to induce aspects of altitude acclimatization which affect ventilatory, cardiovascular and metabolic responses during exercise in normoxia and hypoxia. However, knowledge on altitude-dependent effects and possible interactions remains scarce. Therefore, we determined the effects of IHE on cardiorespiratory and metabolic responses at different simulated altitudes in the same healthy subjects. Eight healthy male volunteers participated in the study and were tested before and 1 to 2 days after IHE (7 × 1 hour at 4500 m). The participants cycled at 2 submaximal workloads (corresponding to 40% and 60% of peak oxygen uptake at low altitude) at simulated altitudes of 2000 m, 3000 m, and 4000 m in a randomized order. Gas analysis was performed and arterial oxygen saturation, blood lactate concentrations, and blood gases were determined during exercise. Additionally baroreflex sensitivity, hypoxic and hypercapnic ventilatory response were determined before and after IHE. Hypoxic ventilatory response was increased after IHE (p<0.05). There were no altitude-dependent changes by IHE in any of the determined parameters. However, blood lactate concentrations and carbon dioxide output were reduced; minute ventilation and arterial oxygen saturation were unchanged, and ventilatory equivalent for carbon dioxide was increased after IHE irrespective of altitude. Changes in hypoxic ventilatory response were associated with changes in blood lactate (r = -0.72, p<0.05). Changes in blood lactate correlated with changes in carbon dioxide output (r = 0.61, p<0.01) and minute ventilation (r = 0.54, p<0.01). Based on the present results it seems that the reductions in blood lactate and carbon dioxide output have counteracted the increased hypoxic ventilatory response. As a result minute ventilation and arterial oxygen saturation did not increase during submaximal exercise at simulated altitudes between 2000 m and 4000 m

Asymmetric benzoin reaction catalyzed by benzoylformate decarboxylase

Aromatic aldehydes are converted into benzoins by benzoylformate decarboxylase catalyzed C-C bond formation. The reaction affords (R)-benzoins with high enantiomeric excess and in good chemical yields. A broad range of aromatic aldehydes can be used as substrates in aqueous buffer or buffer/DMSO-solutions