The enzymes benzaldehyde lyase (BAL) from Pseudomonas fluorescens, benzoylformate decarboxylase (BFD) from Pseudomonas putida and pyruvate decarboxylase (PDC) from Saccharomyces cerevisiae provide different C À C bond forming possibilities of a,b-unsaturated aldehydes with aliphatic and aromatic aldehydes. Structure elucidation and determination of the absolute configuration of the products, which were obtained with high regio-and stereoselectivity were carried out. Selective 1,2-reactivity with yields of 75% and > 98% ee, for one single isomer (A) were obtained, by choosing the suitable enzyme in combination with the appropriate substrates. By varying enzymes or substrates the regioisomeric hydroxy ketones C, with up to > 99% ee, can be obtained. The application of these new chiral building blocks in the synthesis of natural products or biological active substances is considerably facilitated by applying the different ThDP-dependent enzymes as catalysts.Abbreviations: BAL, benzaldehyde lyase; BFD, benzoylformate decarboxylase; PDC, pyruvate decarboxylase; His, hexahistidine; 2-HPP, 2-hydroxy-1-phenylpropan-1-one; PAC, phenylacetylcarbinol; NTA, nitrilotriacetic acid; ThDP, thiamin diphosphate; wt, wild-type.Keywords: benzaldehyde lyase; benzoylformate decarboxylase; biocatalysts; pyruvate decarboxylase; stereochemistry IntroductionThiamin diphosphate (ThDP)-dependent enzymes are well-known to catalyse a broad range of asymmetric reactions.[1] Enzymes of this class like benzaldehyde lyase (BAL) from Pseudomonas fluorescens, [2] benzoylformate decarboxylase (BFD) from Pseudomonas putida [3] and pyruvate decarboxylase (PDC) from Saccharomyces cerevisiae [4] enable various modes of C À C bond forming reactions. Besides the physiological reactivity, several of these enzymes can catalyse, for example, the C À C bond formation between two aldehydes, giving chiral 2-hydroxy ketones with high enantioselectivity. The reactions of aromatic aldehydes as donor and aliphatic aldehydes as acceptor give rise to 2-hydroxy-1-phenyl-1-propanone derivatives with S absolute configuration in the case of BFD catalysis [5] and R for BAL.[6] If aromatic aldehydes are employed as donor and acceptor, (R)-benzoins are optained with both enzymes. [7,8] (R)-Phenylacetylcarbinol is formed in the PDC-catalysed reaction of decarboxylated pyruvate with benzaldehyde as acceptor aldehyde. [4,9] Here we describe the use of a,b-unsaturated aldehydes as substrates for C À C bond ligation in BAL-, BFD-and PDC-catalysed reactions. These substrates might act as donor and as acceptor for the 1,2-(A, C) and the 1,4-addition (B, D) (Scheme 1). Adv. Synth. Catal. 2008, 350, 759 -771 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 759 FULL PAPERSIn reactions according to Equation (1) the a,b-unsaturated aldehyde is bound to ThDP and reacts as donor resulting in the formation of hydroxy ketone A or hydroxy enone B. In reactions according to Equation (2) the a,b-unsaturated aldehyde is attacked by an "active aldehyde" and reacts as acceptor resulti...

[reaction: see text] Two intramolecular C[bond]H...X (X = O, S) interactions in (S)-N-acyl-4-isopropyl-1,3-thiazolidine-2-thiones are documented through crystallographic and spectroscopic evidence and high-level theoretical calculations. The key role played by the sulfur atoms has been made clear by comparison with structurally related (S)-N-acyl-4-isopropyl-1,3-oxazolidin-2-ones.

Addition of the chiral titanium enolate arising from 1 to dibenzyl acetals gives access to anti-b-benzyloxy-a-methyl carboxylic adducts in good yields and with diastereomeric ratios up to 99:1. These adducts can be easily converted into a plethora of enantiopure protected derivatives.

AlcoholsAlcohols P 0110 Synthesis of O-Benzyl Protected anti Aldols Through the Cross-Coupling Reaction of Dibenzyl Acetals with a Chiral Titanium Enolate. -The titanium enolate derived from amide (I) reacts with acetals (II) in the presence of SnCl4 with good diastereoselectivity. This result is further improved with acetal (V) providing the Felkin type diastereomer (VI) exclusively. Removal of the chiral auxiliary under different reaction conditions gives access to a variety of building blocks (VII), (VIII) and (X). -(COSP, A.; LARROSA, I.; VILASIS, I.; ROMEA*, P.; URPI*, F.; VILARRASA, J.; Synlett 2003, 8, 1109-1112; Dep. Quim. Org., Univ. Barcelona, E-08028 Barcelona, Spain; Eng.) -Mais 41-075