Many lipases are potent catalysts of stereoselective reactions and are therefore of interest for use in chemical synthesis. The crystal structures of lipases show a large variation in the shapes of their active site environments that may explain the large variation in substrate specificity of these enzymes. We have determined the three-dimensional structure of Candida antarctica lipase B (CALB) cocrystallized with the detergent Tween 80. In another crystal form, the structure of the enzyme in complex with a covalently bound phosphonate inhibitor has been determined. In both structures, the active site is exposed to the external solvent. The potential lid-forming helix alpha 5 in CALB is well-ordered in the Tween 80 structure and disordered in the inhibitor complex. The tetrahedral intermediates of two chiral substrates have been modeled on the basis of available structural and biochemical information. The results of this study provide a structural explanation for the high stereoselectivity of CALB toward many secondary alcohols.

Five derivatives of 2-imino-3-(4-arylthiazol-2-yl)-thiazolidin-4-ones and a series of their 5-arylidene derivatives have been synthesized and tested for antifungal activity against seven agricultural fungi. 2-Imino-3-(2,4-dichloro-5-fluorophenylthiazol-2-yl)-4-thiazolidi-none and 2-imino-3-(2,4-dichlorophenylthiazol-2-yl)-4-thiazolidione, both of them new compounds, exhibited higher fungicidal effects than the other compounds prepared.

[1] Isoprene, a compound emitted by vegetation, could be a major contributor to secondary organic aerosols (SOA) in the atmosphere. The main evidence for this contribution were the 2-methylbutane-1,2,3,4-tetraols, or 2-methyltetrols (2-methylerythritol and 2-methylthreitol) present in ambient aerosols. In this work, the four stereoisomers of these tetraols were analyzed in aerosols from Aspvreten, Sweden. 2-Cmethyl-D-erythritol was found in excess over its enantiomer in the Spring/Summer, by up to 29% in July. This clearly indicated some biological origins for this enantiomer, consistent with its well-documented production by plants and other living organisms. In addition, a minimum of 20 to 60% of the mass of racemic tetraols appeared from biological origin. Thus, the SOA mass produced by isoprene in the atmosphere is less than what indicated by the 2-methyltetrols in aerosols. Our results also demonstrate that stereochemical speciation can distinguish primary and secondary organic material in atmospheric aerosols. Citation: Nozière, B., N. J.

No abstract

No abstract