The substrate specificity of Escherichia coli N-acetylneuraminic acid lyase was previously switched from the natural condensation of pyruvate with N-acetylmannosamine, yielding N-acetylneuraminic acid, to the aldol condensation generating N-alkylcarboxamide analogues of N-acetylneuraminic acid. This was achieved by a single mutation of Glu192 to Asn. In order to analyze the structural changes involved and to more fully understand the basis of this switch in specificity, we have isolated all 20 variants of the enzyme at position 192 and determined the activities with a range of substrates. We have also determined five high-resolution crystal structures: the structures of wild-type E. coli N-acetylneuraminic acid lyase in the presence and in the absence of pyruvate, the structures of the E192N variant in the presence and in the absence of pyruvate, and the structure of the E192N variant in the presence of pyruvate and a competitive inhibitor (2R,3R)-2,3,4-trihydroxy-N,N-dipropylbutanamide. All structures were solved in space group P21 at resolutions ranging from 1.65 Å to 2.2 Å. A comparison of these structures, in combination with the specificity profiles of the variants, reveals subtle differences that explain the details of the specificity changes. This work demonstrates the subtleties of enzyme–substrate interactions and the importance of determining the structures of enzymes produced by directed evolution, where the specificity determinants may change from one substrate to another.

The stereochemical course of aldolase-catalysed reaction between fluoropyruvate and aldehydes is described.

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Methods for the batch scale up of DABAL-Me 3 promoted direct ester to amide synthesis have been demonstrated at 10−100 g scales using a tert-amide model compound. Procedures for 20 g scale couplings in standard laboratory glassware and up to 0.1 kg in industry-standard jacketed glass reactors in near quantitative yields are given. A derivative of the anticancer agent Imatinib (Gleevec) has been synthesized on a 26 g scale (98% yield, >98% purity) establishing DABAL-Me 3 as a potential alternative for the synthesis of amides in API scale preparations. Continuous flow methodology provides a method for larger scales (productivities of >50 g h −1 ). In addition, nitriles were coupled to primary amines and hydrazines with DABAL-Me 3 , resulting in the clean formation of free amidines (16 examples) and amidrazones.

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