Lipase-Catalyzed Michael Addition

Significance

Conjugate additions of nucleophiles such as thiols and amines to α,β-unsaturated carbonyl compounds, catalyzed by different enzymes, have previously been reported. The authors of this paper now present a C-C bond forming Michael addition, mediated by mutated Candida antarctica lipase B. In this enzyme, serine₁₀₅ has been replaced by alanine, reasoning that this substitution both opens up extra space in the catalytic center of the enzyme and avoids the unproductive formation of a hemiacetal.

The test reactions were run under solvent-free conditions and were found to be faster with the mutated enzyme than with the wild-type enzyme in all cases. The reaction of acetylacetone with acrolein, for example, is found to lead to full conversion with the mutated enzyme in 10 min, at a specific rate of 4000 s^-1 (which is 36 times higher than for the wild-type enzyme). Moreover, for the reaction of acetylacetone with methyl vinyl ketone, the catalytic proficiency (k^app _cat/ K^app _M)/k_non) is found to be over 10⁸.