Correlation of the absolute conformation of sec alcohols derived from macrocyclic lactones of resorcylic acid and their stereoselective transacetylation in organic solvents by Pseudomonas fluorescens lipase
✍ Scribed by Mirjana Gelo-Pujić; Snježana Antolić; Biserka Kojić-Prodić; Vitomir Šunjić
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- French
- Weight
- 854 KB
- Volume
- 50
- Category
- Article
- ISSN
- 0040-4020
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✦ Synopsis
Abrbner: Transacetylation of diastereomeric pairs of sec. alcohols, derived from macrocyclic lactones of resorcylic acid; 7o.&franr-zearalenols (1.2, full names; (3S,7R and 3S,7S) fans-3,4,5,6,9.10-octahydro-7,14.16-trihydroxy-3-methyl-1H-2-benzoxacyclotetradecine-1-ones), 7o,g-cLrxeamlenols (SC). and 7o$-xearands (9.10, full names; (3S,7R and 3$7S) 3,4,5,6,9,10,11,12decahydro-714,16-trihydroxy-3-methyl-lH-2-benzoxacyclotetradecine-l-ones) by vinylacetate, catalyzed by Pse&monas sp. and Pseudonwnasfluorescenr lipase in n-heptane and acetonitrile has been studied. It is highly stereoselective; diastereomeric excess of 7g-O-acetates was usually near 100%. KM, Vmax and specificity constant Vmax/Khil do not significantly differ for 7g-stereoisomers 2, 6 and 10. However, they notably change on going from n-heptane to acetonitrile, and the specificity constant drops by factor or 10-100. The enzyme-bound water is assumed to be partly released in the latter solvent, thus diminishing the interaction with the hydrophilic region of the substrates, and affecting the activity, but not the stereoselectivity of lipases. To correlate the structuml and conformational properties of these substrates with unexpectedly high diastereoselectivity of enzymatic transacetylation, the solid state structures of 'I~isomers 2, 4.6.10 and 12 have been determined by X-ray analysis. The X-my structure analysis has revealed that the 7a and 78 isomers possess notably different and in some cases almost mirror-image related absolute conformations around the reactive center. The importance of conformational chirality in the hydrophobic region of these substrates for stereoselection in transacyhttion by microbial lipases is discussed.