Title: Biomimetic oxidative decarboxylation of amino acids by H2O2 using a tungstate based heterogeneous catalyst
Authors: Claes, Laurens
Matthessen, Roman
Stassen, Ivo
De Baerdemaeker, Trees
De Vos, Dirk
Issue Date: 10-Mar-2014
Conference: Netherlands' Catalysis and Chemistry Conference edition:15 location:Noordwijkerhout, the Netherlands date:10-12 March 2014
Article number: P24
Abstract: Oxidative decarboxylation of α-amino acids is generally mediated by hypobromite (‘Br+’) species, which are produced from organic reagents like N-bromosuccinimide[1] or by NaOCl induced oxidation of NaBr.[2] However, large amounts of (in)organic waste products are generated. On the other hand, it has been shown that the enzyme vanadium chloroperoxidase is able to perform the oxidative decarboxylation of L-glutamic acid and L-phenylalanine with hydrogen peroxide (H2O2).[3] Based on previous work on olefin epoxidation[4], a tungstate-exchanged layered double hydroxide (LDH) has been developed as a heterogeneous mimic of the enzyme’s active site: electrostatically immobilized tungstate ions are transformed in situ by H2O2 into peroxotungstate species, which in turn oxidize bromide ions to hypobromite species. A catalytic system containing LDH and NH4Br in an organic solvent or even water allows selective oxidative decarboxylation of α-amino acids into nitriles, whereas in enzyme-catalyzed reactions selectivity is often reduced due to aldehyde formation. H2O2 is added in a controlled way to increase oxidant efficiency. In this way, phenylalanine can be transformed into phenylacetonitrile with 88% yield using 8 equivalents of H2O2. The catalyst material is stable under reaction conditions and recycling is easy.

The substrate scope has been extended to other α-amino acids. Alanine, valine, leucine, isoleucine and norleucine were converted into aliphatic nitriles with 88-100% yield. Moreover, the system is compatible with alcohol and amide moieties. For carboxylic acids, amines and guanidines, neutralization with respectively NaOH or HBr prior to decarboxylation is recommended; nitrile yields are often > 90%. Methionine has been transformed in two steps into its nitrile-sulfone derivative.
Publication status: published
KU Leuven publication type: IMa
Appears in Collections:Centre for Surface Chemistry and Catalysis

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