Abstract
The use of bifunctional catalysts in organic synthesis finds inspiration in the selectivity of enzymatic catalysis which arises from the specific interactions between basic and acidic amino acid residues and the substrate itself in order to stabilize developing charges in the transition state. Many enzymes act as bifunctional catalysts using amino acid residues at the active site as Lewis acids and Lewis bases to modify the substrate as required for the given transformation. They bear a clear advantage over non-biological methods for their ability to tackle problems related to the synthesis of enantiopure compounds as chiral building blocks for drugs and agrochemicals. Moreover, enzymatic synthesis may offer the advantage of a clean and green synthetic process in the absence of organic solvents and metal catalysts. In this work the reaction mechanism of norcoclaurine synthase is described. This enzyme catalyzes the Pictet-Spengler condensation of dopamine with 4-hydroxyphenylacetaldehyde (4-HPAA) to yield the benzylisoquinoline alkaloids central precursor, (S)-norcoclaurine. Kinetic and crystallographic data suggest that the reaction mechanism occurs according to a typical bifunctional catalytic process.
Highlights
Enzymatic Bifunctional CatalysisAcid-base bifunctional catalysis is considered an efficient and reliable strategy in small molecule asymmetric catalysis
The use of bifunctional catalysts in organic synthesis finds inspiration in the selectivity of enzymatic catalysis which arises from the specific interactions between basic and acidic aminoacid residues and the substrate itself in order to stabilize developing charges in the transition state [1]
For this reason many organic chemists have recently focused their attention in the use of enzymes as bifunctional catalysts, widely recognized as practical alternatives to traditional organic synthesis [3]
Summary
Acid-base bifunctional catalysis is considered an efficient and reliable strategy in small molecule asymmetric catalysis. Lipases, whose role in nature is to catalyse the hydrolysis of triacyl glycerides, have been successfully used as transesterification catalysts for stereoselective acylation and kinetic resolution of alcohols [9] All these enzymes represent a new class of chiral catalysts useful for a broad range of selective organic transformations. They bear a clear advantage over non-biological methods for their ability to tackle problems related to the synthesis of enantiopure compounds as chiral building blocks for drugs and agrochemicals. To this purpose screening for novel enzymes capable of catalyzing new enantioselective reactions is constantly needed. The discovery of new enzymes will provide clues for designing new green chemistry processes
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