Lluis Sola

Characterization of a (2R,3R)-2,3-butanediol dehydrogenase as the Saccharomyces cerevisiae YAL060W gene product. Disruption and induction of the gene

The completion of theSaccharomyces cerevisiae genome project in 1996 showed that almost 60% of the potential open reading frames of the genome had no experimentally determined function. Using a conserved sequence motif present in the zinc-containing medium-chain alcohol dehydrogenases, we found several potential alcohol dehydrogenase genes with no defined function. One of these,YAL060W, was overexpressed using a multicopy inducible vector, and its protein product was purified to homogeneity. The enzyme was found to be a homodimer that, in the presence of NAD+, but not of NADP, could catalyze the stereospecific oxidation of (2R,3R)-2,3-butanediol (K m = 14 mm, k cat = 78,000 min− 1) and meso-butanediol (K m = 65 mm,k cat = 46,000 min− 1) to (3R)-acetoin and (3S)-acetoin, respectively. It was unable, however, to further oxidize these acetoins to diacetyl. In the presence of NADH, it could catalyze the stereospecific reduction of racemic acetoin ((3R/3S)- acetoin; K m = 4.5 mm, k cat = 98,000 min− 1) to (2R,3R)-2,3-butanediol andmeso-butanediol, respectively. The substrate stereospecificity was determined by analysis of products by gas-liquid chromatography. The YAL060W gene product can therefore be classified as an NAD-dependent (2R,3R)-2,3-butanediol dehydrogenase (BDH).S. cerevisiae could grow on 2,3-butanediol as the sole carbon and energy source. Under these conditions, a 3.5-fold increase in (2R,3R)-2,3-butanediol dehydrogenase activity was observed in the total cell extracts. The isoelectric focusing pattern of the induced enzyme coincided with that of the pure BDH (pI 6.9). The disruption of the YAL060W gene was not lethal for the yeast under laboratory conditions. The disrupted strain could also grow on 2,3-butanediol, although attaining a lesser cell density than the wild-type strain. Taking into consideration the substrate specificity of the YAL060W gene product, we propose the name of BDH for this gene. The corresponding enzyme is the first eukaryotic (2R,3R)-2,3-butanediol dehydrogenase characterized of the medium-chain dehydrogenase/reductase family.

Structural optimization of enantiopure 2-cyclialkylamino-2-aryl-1,1-diphenylethanols as catalytic ligands for enantioselective additions to aldehydes.

The structural optimization of a family of modular, enantiopure beta-amino alcohol ligands with a common 2-amino-2-aryl-1,1-diphenylethanol skeleton, whose stereogenicity was introduced through the Jacobsen epoxidation of 1,1-diphenyl-2-arylethylenes, has led to the identification of a small set of optimal catalysts with enhanced activity and enantioselectivity in the addition of alkylzinc and arylzinc reagents to aldehydes. Criteria for the discrimination between apparently analogous, highly enantioselective ligands are proposed.

Low temperature X-ray diffraction analysis of 4,5,10,11-tetramethyl-heptacyclo[8.2.1.12,5.14,7.18,11.01,8.02,7]hexadecane: DSC, MM2 and 1H NMR study of its [2 + 2]retrocycloaddition to an isomeric diene

Abstract The synthesis of pure 3 has been achieved by deiodination of 1 with NaK alloy at r.t. and by [2+2] photocyclization of diene 4 . X-ray diffraction analysis at −30°C of the thermally unstable 3 shows the cyclobutane ring to be highly rectangular with large central and short lateral bonds. Also, the C4C5 and C10C11 bonds in 3 and diene 4 are very large. A clear neat DSC conversion of 3 to 4 allowed us to obtain the ΔH and the Ea values for this transformation. ΔH is in good agreement with MM2 calculations, while Ea compares well with kinetic measurements in CDCl 3 solution.

Divergent stereoselective synthesis of (E) and (Z) O-Alkyl enol ethers

Abstract While the reduction of alkynyl ethers with lithium aluminum hydride (or with sodium bis(2-methoxyethoxy) aluminum hydride) gives almost exclusively O-alkyl enol ethers with (E) configuration, the reaction with sodium bis(2-methoxyethoxy) aluminum hydride pretreated with one equivalent of a free alcohol leads stereoselectively to enol ethers with (Z) configuration.

New indane derived aminoalcohols as chiral ligands for the catalytic enantioselective addition of diethylzinc to aldehydes

Abstract Secondary amines react with (1R,2S)-indene oxide 1 in a completely regioselective manner leading to trans-2-dialkylamino-1-indanols 4a—d in high yield. A Mitsunobu inversion via the corresponding p-nitrobenzoates, followed by reduction with DIBALH leads to the cis-2-dialkylamino-1-indanols 5a—d also in high yield. These two new classes of aminoindanols have been tested as chiral ligands for the enantioselective addition of diethylzinc to both aliphatic and aromatic aldehydes, leading to 1-substituted 1-propanols with up to 80% e.e. A very simple procedure for the enantiomeric enrichment of 1 from 88% to ≥99% e.e. is also reported.

Cross-coupling of a functionalized highly pyramidalized alkene: DSC and NMR study of the [2+2] retrocycloaddition of cyclobutane cross products, hyperstability and pyramidalization of the formed dienes

Abstract The synthesis, chemical trapping and ab initio calculations of the highly pyramidalized 5α,6α:11α,12α-bis(isopropylidenedioxy)pentacyclo[6.4.0.0 2,10 .0 3,7 .0 4,9 ]dodec-8-ene, 25 , are reported. Its cross-coupling reaction with 3,7-dimethyltricyclo[3.3.0.0 3,7 ]oct-1(5)-ene, 1b , gave a cyclobutane derivative, 29 , which on further manipulations gave the cyclobutane derivatives 32 and 33 and the derived [2+2] retrocycloaddition dienes, 31 and 34 . Molecular Mechanics calculations show these dienes to be slightly pyramidalized but highly hyperstable. The neat conversion of 32 and 33 to 31 and 34 , respectively, has been studied by DSC, 1 H NMR and theoretical methods (MM2 and ab initio).