The hydroxynitrile lyases (HNLs) from Prunus amygdalus (PaHNL), Manihot esculenta (MeHNL), and Hevea brasiliensis (HbHNL) were successfully immobilized in sol-gels. The cross-linked enzyme aggregate (CLEA) of HbHNL was also prepared. These immobilized enzymes and the commercial PaHNL-and MeHNL-CLEAs were employed for the enantioselective synthesis of cyanohydrins. The sol-gels were highly efficient at low catalyst loading and particularly stable towards the organic solvent (diisopropyl ether) and substrate/product deactivation. The stabilization effect was inconsistent for CLEAs of different HNLs and significant deactivation of PaHNL-and HbHNL-CLEAs in diisopropyl ether was observed. In contrast commercial MeHNL-CLEA proved to be a remarkably robust and efficient biocatalyst in diisopropyl ether.

An immobilized form of the hydroxynitrile lyase from Linum usitatissimum (LuHNL) as crosslinked enzyme aggregate (CLEA) with high specific activity (303.5 U/g) and recovery (33%) was developed. Molecular imprinting using 2-butanone as additive in the immobilization process improved the synthetic activity of the biocatalyst. LuCLEA could be partially recycled for the synthesis of (R)-2-butanone cyanohydrin on a preparative scale over two batches. The enantioenriched cyanohydrin obtained was further hydrolyzed to give (R)-2-hydroxy-2-methylbutyric acid in 85% yield (from 2-butanone) and 87% ee.

The development of a scalable asymmetric route to a new calcitonin gene-related peptide (CGRP) receptor antagonist is described. The synthesis of the two key fragments was redefined, and the intermediates were accessed through novel chemistry. Chiral lactam 2 was prepared by an enzyme mediated dynamic kinetic transamination which simultaneously set two stereocenters. Enzyme evolution resulted in an optimized transaminase providing the desired configuration in >60:1 syn/anti. The final chiral center was set via a crystallization induced diastereomeric transformation. The asymmetric spirocyclization to form the second fragment, chiral spiro acid intermediate 3, was catalyzed by a novel doubly quaternized phase transfer catalyst and provided optically pure material on isolation. With the two fragments in hand, development of their final union by amide bond formation and subsequent direct isolation is described. The described chemistry has been used to deliver over 100 kg of our desired target, ubrogepant.