Enzymatic asymmetrization of some prochiral and meso diols through monoacetylation with pig pancreatic lipase (PPL)
摘要:
Monoacetates 1-8 and 10-11, derived from asymmetric monoesterification of prochiral or meso diols, have been obtained in good to excellent enantiomeric excess by using inexpensive crude PPL supported on celite, and vinyl acetate as both solvent and acylating agent. Under these conditions reactions are fast and reproducible, and the enzyme can be recycled.
Chemoenzymic preparation of asymmetrized tris(hydroxymethyl)methane (THYM*) and of asymmetrized bis(hydroxymethyl)acetaldehyde (BHYMA*) as new highly versatile chiral building blocks
摘要:
A series of asymmetrized tris(hydroxymethyl)methanes 2 and bis(hydroxymethyl)acetaldehydes 3 have been prepared in both enantiomeric forms through a chemoenzymatic methodology. The key step is the highly enantioselective PPL-catalyzed monohydrolysis of 2(E)-alkenyl-1,3-diacetoxypropanes 25-27. A careful study on the effect of unsaturations adjacent to the prochiral center in a series of 2-substituted 1,3-diacetoxypropanes has confirmed the suggested beneficial effect of a pi-system in that position but has also unveiled an unprecedented dramatic effect of double-bond configuration on enantioselectivity. A new empirical model for the interpretation of these and other results, based both on polarity and steric arguments, is proposed. This study provides a general protocol for the efficient synthesis of asymmetrized 1,3-propanediols bearing in position 2 saturated or unsaturated carbon chains.