Biocatalytic asymmetric synthesis of unnatural amino acids using C-N lyases

Abstract

Optically pure functionalized aspartic acid derivatives are highly valuable as core structures in pharmaceuticals, nutraceuticals, and agrochemicals. Despite their broad applications, the direct asymmetric synthesis of functionalized aspartic acids remains a challenge. The aim of the research described in the PhD thesis of Haigen Fu was to develop novel and efficient biocatalytic methodologies for the direct stereoselective synthesis of chiral functionalized aspartic acids. The first part of the thesis describes chemoenzymatic synthesis of C-3 substituted aspartic acids using an engineered variant of methylaspartate ammonia lyase (MAL-L384A). This enzyme catalyzes the stereoselective addition of ammonia to a range of fumarate derivatives, providing a powerful synthetic tool for the preparation of valuable 3-substituted aspartic acids that function as potent glutamate transporter inhibitors. Moreover, an efficient, 9-step chemoenzymatic route towards enantiopure L-TFB-TBOA, a highly potent inhibitor of glutamate transporters, was achieved at multigram scale. Based on this enzyme technology, a series of glutamate transporter inhibitors with photo-controlled activity were prepared, enabling the remote, reversible, and spatiotemporally controlled regulation of transport. In the second part of the thesis, the biocatalytic asymmetric synthesis of N-substituted aspartic acids using ethylenediamine-N,N'-disuccinic acid lyase (EDDS lyase) as biocatalyst is reported. EDDS lyase has a remarkably broad nucleophile scope, accepting a wide variety of structurally distinct amines for stereoselective addition to fumarate, providing enzymatic access to various aminocarboxylic acids including the natural product aspergillomarasmine A, N-cycloalkyl-substituted aspartic acids, as well as difficult N-arylated aspartic acids and chiral pyrazolidin-3-ones. These characterized native and engineered carbon-nitrogen lyases nicely complement the rapidly expanding biocatalytic toolbox for asymmetric synthesis of noncanonical amino acids.