Metabolism of aromatic amino acids by lactic acid bacteria is an important source of off-flavor compounds in Cheddar cheese. Previous work has shown that alpha-keto acids produced from Trp, Tyr, and Phe by aminotransferase enzymes are chemically labile and may degrade spontaneously into a variety of off-flavor compounds. However, dairy lactobacilli can convert unstable alpha-keto acids to more-...

The phenomenon of beta-phenyl quenching has been examined by laser-flash photolysis in a series of alpha- and/or beta-substituted ketones 4-8 with similar excited-state characteristics. It is found that alpha-substitution markedly increases the triplet lifetimes in contrast to beta-substitution. The force field calculations for the various staggered conformers of ketones 4-6 and 8-syn show that...

Terminal vicinal diols are important chiral building blocks and intermediates in organic synthesis. Reduction of α-hydroxy ketones provides a straightforward approach to access these important compounds. In this study, it has been found that asymmetric reduction of a series of α-hydroxy aromatic ketones and 1-hydroxy-2-pentanone, catalyzed by Candida magnolia carbonyl reductase (CMCR) with gluc...

Enantiopure α-hydroxy acids (AHAs) are versatile building blocks in organic synthesis. They are used for obtaining pharmaceutically and biologically active substances, such as vitamins. α-Hydroxy acids are easily synthesized from cyanohydrins. Thus, molecules with cyanohydrin substructures are interesting intermediates for the synthesis of AHAs. Usually, cyanohydrins are prepared by the additio...

[reaction: see text] Very practical synthesis of ephedrine analogues in high yields and enantiopurity was realized by a highly diastereoselective Meerwein-Ponndorf-Verley (MPV) reduction of protected alpha-amino aromatic ketones using catalytic aluminum isopropoxide. The high anti selectivity resulted from the chelation of the nitrogen anion to the aluminum. In contrast, high syn selectivity wa...

Cortisol, 11-deoxycorticosterone, progesterone, 17 alpha-hydroxy-progesterone, 17 alpha-hydroxy-20 beta-dihydroprogesterone, or a combination of the last 2 steroids, were injected into different groups of immature female Epinephelus. None of the steroids tested had significant effects on serum electrolyte level, and hepatosomatic and gonadosomatic indices. Serum glucose concentration was elevat...

The oxidative ring-opening reaction of a variety of activated aziridines by pyridine N-oxide provided alpha-amino ketones or alpha-amino aldehydes in good yields.

Cells of the wild-type yeast strain Zygosaccharomyces bisporus CBS 702 form alpha-hydroxy ketones from aromatic amino acid precursors during fermentation. Pyruvate decarboxylase (PDC, E.C. 4.1.1.1), the key enzyme of this biotransformation catalysing the non-oxidative decarboxylation of pyruvate and other 2-oxo-acids, was purified and characterised. The active enzyme is homotetrameric (alpha4) ...