Enantioselective Enzymatic Hydroaminations for the Production of Functionalised Aspartic Acids

The enzyme EDDS lyase can be readily produced and purified, with about 60 mg being obtained from 1 L of cell culture. After initial freezing in liquid nitrogen, the enzyme can be stored at −20 ∘C in a concentration of 8.7 mg.mL−1 (in 20 mM Na2HPO4 buffer, pH 8.5) for at least 6 months without significant loss of catalytic activity. We have showcased how EDDS lyase can accept the non-natural amine substrates 5a,b in the enantioselective hydroamination of fumarate, yielding the corresponding N-heterocycloalkyl-substituted L-aspartic acids 6a,b with high conversions (84−91%), good isolated yields (41−67%) and excellent stereoselectivity (>99% ee) (Table 5.1). In addition, we previously reported that EDDS lyase can accept a panel of homo- and heterocycloalkyl amines (comprising four-, five- and six-membered rings) in the selective addition to fumarate, giving the corresponding N-(hetero)cycloalkyl-substituted L-aspartic acids with excellent optical purity (>99% ee in all cases) [9]. Except for the broad cycloalkylamines scope, we recently demonstrated that EDDS lyase can also accept a wide variety of structurally distinct amines for stereoselective addition to fumarate, providing (chemo)enzymatic access to various aminocarboxylic acids, including the natural product toxin A and aspergillomarasmine A [12], difficult-to-synthesise N-arylated aspartic acid derivatives [13] and substituted pyrazolidin-3-ones [13]. As such, EDDS lyase, with its remarkably broad amine scope, nicely complements the biocatalytic toolbox for the synthesis of noncanonical amino acids