Abstract
In nature, the D-enantiomers of amino acids (D-AAs) are not used for protein synthesis and during evolution acquired specific and relevant physiological functions in different organisms. This is the reason for the surge in interest and investigations on these “unnatural” molecules observed in recent years. D-AAs are increasingly used as building blocks to produce pharmaceuticals and fine chemicals. In past years, a number of methods have been devised to produce D-AAs based on enantioselective enzymes. With the aim to increase the D-AA derivatives generated, to improve the intrinsic atomic economy and cost-effectiveness, and to generate processes at low environmental impact, recent studies focused on identification, engineering and application of enzymes in novel biocatalytic processes. The aim of this review is to report the advances in synthesis of D-AAs gathered in the past few years based on five main classes of enzymes. These enzymes have been combined and thus applied to multi-enzymatic processes representing in vitro pathways of alternative/exchangeable enzymes that allow the generation of an artificial metabolism for D-AAs synthetic purposes.
Highlights
D-amino acids (D-AAs) are still considered the “unnatural” enantiomers of amino acids because they are not used in protein synthesis [1]
The aim of this review is to report the advances in synthesis of D-enantiomers of amino acids (D-AAs) gathered in the past few years based on five main classes of enzymes
The aim of this review is to report the advances in enzymatic synthesis of D-AAs reported in the past few years
Summary
D-amino acids (D-AAs) are still considered the “unnatural” enantiomers of amino acids because they are not used in protein synthesis [1]. A number of enzymes producing or metabolizing D-AAs have been discovered and devised to produce D-AAs [8,9] While each of these methods are useful, they often suffer from various drawbacks including modest yields and enantioselectivity, low reaction rates, low titer of starting material, and the demand for multiple steps. These weaknesses represented the driving force that pushed numerous research groups worldwide to identify, engineer and apply enzymes in novel biocatalytic processes aimed to generate D-AAs by more-sustainable processes. The presentation is based on the five main classes of enzymes used, even if they have been frequently applied jointly in cascade, multi-enzymatic processes
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