It was first observed that PPL, lipase from porcine pancreas, and several other lipases have a promiscuous ability to catalyse asymmetric aldol reactions between acetones and aldehydes in the presence of water.Biocatalytic promiscuity, a new frontier extending the use of enzymes in organic synthesis, has attracted much attention and expanded rapidly in recent years. 1 It focuses on the enzyme catalytic activities with unnatural substrates and alternative chemical transformations, such as the side ability harbored by decarboxylase to catalyse acyloin condensation. 2 Exploiting enzyme catalytic promiscuity might lead to improvements in existing catalysts and provide novel synthesis pathways that are currently not available. Some elegant works have been done in the last decades. 3 Among the promiscuous enzymes, hydrolases (such as lipase, protease and esterase) undoubtedly play an important role due to their high stability, wide sources and broad range of substrates. 4 Recently, several promiscuous hydrolase-catalysed reactions have been reported. 5 For instance, Wu et al. demonstrated that penicillin G acylase, a hydrolase which is widely used as a biocatalyst in the enzymatic synthesis of b-lactam antibiotics, can catalyse Markovnikov addition of allopurinol to vinyl ester. 6 A further example is reported by the group of Gotor. 7 They found an unprecedented lipase catalysed Michael addition of secondary amines to acrylonitrile. These cases and other relevant reports encouraged us to believe that the catalytic activities for addition reaction rather than the well-known hydrolytic function may also have a natural role in hydrolase evolution.Aldol addition is one of the most useful methods for carboncarbon bond formation in organic synthesis. 8 Berglund and co-workers once used mutant CAL-B (lipase from Candida antarctica) to catalyse aldol addition in 2003. 9 Although the Ser105Ala mutant CAL-B exhibited an increased reaction rate as compared with the wide type in their experiments, both of them showed quite low activities (reaction time more than 50 days). Besides, the enzymatic process is not enantioselective and only simple aliphatic aldehydes, such as propanal and hexanal, had been used. Generally, practical lipase-catalysed aldol reactions hadn't been developed in organic synthesis. To the best of our knowledge, other lipase-catalysed aldol additions, especially asymmetric aldol reactions have never been reported.
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