Baker's Yeast Reduction of β-Hydroxy Ketones

New Strategy for the Synthesis of Some Valuable Chiral 1,3-Diols with High Enantiomeric Purity: New Organocatalyst, Asymmetric Aldol Reaction, and Reduction

Chiral 1,3-diols are highly valuable molecules used in industries such as pharmaceuticals, cosmetics, and agriculture. Therefore, in this study, a new strategy was developed to synthesize enantiomerically pure (>99% ee) 1,3-diols. New chiral 1,3-diols (5a-5q) with high enantiomeric purity were synthesized from aldol products chiral 1,3-keto alcohols (4a-4q), which are aldol products with different structures. Chiral 1,3-keto alcohols (4a-4q) were synthesized by a new asymmetric aldol method in the first step. This method was developed using a new proline-derived organocatalyst (3g) and Cu(OTf)2 as an additive in DMSO-H2O for the first time. Almost >99% ee was obtained using our developed aldol procedure. In the second step, original chiral diols (5a-5q) of high enantiomeric purity were obtained by asymmetric reduction of chiral keto alcohols with chiral oxazaborolidine reagents. In this way, a two-step asymmetric reaction was developed for chiral 1,3-diol enantiomers with high enantiomeric purity. The structures of all the original chiral compounds obtained were elucidated by infrared and nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis methods. Their enantiomeric excesses were determined by the chiral high-performance liquid chromatography method. Both keto alcohols and their corresponding chiral diols synthesized can be used as chiral starting materials and chiral source materials or intermediates in the synthesis of many biologically active molecules, or they can be used as chiral ligands in asymmetric synthesis, serving as organocatalysts.

Organic Solvent-Tolerant Marine Microorganisms as Catalysts for Kinetic Resolution of Cyclic β-Hydroxy Ketones

Chiral cyclic β-hydroxy ketones represent key motifs in the production of natural products of biological interest. Although the molecules are structurally simple, they require cumbersome synthetic steps to get access to them and their synthesis remains a challenge in organic chemistry. In this report, we describe a straightforward approach to enantiomerically enriched (R)- and (S)-3-hydroxycyclopentanone 2a, (R)- and (S)-3-hydroxycyclohexanone 2b, and (R)- and (S)-3-hydroxycycloheptanone 2c involving a transesterification resolution of the racemates using whole cells of marine microorganisms as catalysts and vinyl acetate the acyl donor and solvent. Twenty-six strains from a wide collection of isolates from marine sediments were screened, and seven strains were found to markedly catalyze the resolution in an asymmetric fashion. Using the strain Serratia sp., (R)-2a was isolated in 27% yield with 92% ee and (S)-2a in 65% yield with 43% ee, corresponding to an E-value of 37; (R)-2b was isolated in 25% yield with 91% ee and (S)-2b in 67% yield with 39% ee, corresponding to an E-value of 40; and (R)-2c was isolated in 30% yield with 96% ee and (S)-2c in 63% yield with 63% ee, corresponding to an E-value of 75.

Design and synthesis of chiral Zn2+ complexes mimicking natural aldolases for catalytic C-C bond forming reactions in aqueous solution

Extending carbon frameworks via a series of C-C bond forming reactions is essential for the synthesis of natural products, pharmaceutically active compounds, active agrochemical ingredients, and a variety of functional materials. The application of stereoselective C-C bond forming reactions to the one-pot synthesis of biorelevant compounds is now emerging as a challenging and powerful strategy for improving the efficiency of a chemical reaction, in which some of the reactants are subjected to successive chemical reactions in just one reactor. However, organic reactions are generally conducted in organic solvents, as many organic molecules, reagents, and intermediates are not stable or soluble in water. In contrast, enzymatic reactions in living systems proceed in aqueous solvents, as most of enzymes generally function only within a narrow range of temperature and pH and are not so stable in less polar organic environments, which makes it difficult to conduct chemoenzymatic reactions in organic solvents. In this review, we describe the design and synthesis of chiral metal complexes with Zn2+ ions as a catalytic factor that mimic aldolases in stereoselective C-C bond forming reactions, especially for enantioselective aldol reactions. Their application to chemoenzymatic reactions in aqueous solution is also presented.

Stereoselective synthesis of 1,3-anti diols by an Ipc-mediated domino aldol-coupling/reduction sequence

A novel domino process for 1,3-anti diol synthesis by the union of a methyl ketone with an aldehyde is described. The operationally simple procedure is based on an Ipc-boron-aldol coupling and subsequent Ipc-mediated reduction of the intermediate β-hydroxy-ketone. The sequence proceeds with excellent anti-selectivities and enables the rapid construction of complex polyketide fragments.

One-pot chemoenzymatic synthesis of chiral 1,3-diols using an enantioselective aldol reaction with chiral Zn2+ complex catalysts and enzymatic reduction using oxidoreductases with cofactor regeneration

We previously reported on enantioselective aldol reactions of acetone and some aldehydes catalyzed by chiral Zn(2+) complexes of L-prolyl-pendant [12]aneN(4) (L-ZnL(1)) and L-valyl-pendant [12]aneN(4) (L-ZnL(2)) in aqueous solution. Here, we report on the one-pot chemoenzymatic synthesis of chiral 1,3-diols in an aqueous solvent system at room temperature by a combination of enantioselective aldol reactions catalyzed by Zn(2+) complexes of L- and D-phenylalanyl-pendant [12]aneN(4) (L-ZnL(3) and D-ZnL(3) ) and the successive enantioselective reduction of the aldol products using oxidoreductases with the regeneration of the NADH (reduced form of nicotinamine adenine dinucleotide) cofactor. The findings indicate that all four stereoisomers of 1,3-diols can be produced by appropriate selection of a chiral Zn(2+)-complex and an oxidoreductase commercially available from the "Chiralscreen OH" kit.