Synthesis of Racemic α-Amino Carboxamides via Lewis Acid-Mediated Reactions of α-Methoxyglycinamide Derivatives with Allylsilanes: Enzymatic Resolution to Optically Active α-Amino Acids

Article abstract of DOI:10.1021/jo00051a019

A short and expedient synthetic route to optically active, saturated and γ,δ-unsaturated α-amino acids is reported.The key step is a BF3*Et2O-mediated reaction of allylsilanes with N-(alkoxycarbonyl)-α-methoxyglycinamides 11-15, leading to the corresponding γ,δ-unsaturated α-aminocarboxamides.The genuine S_N1-character of this process with iminium ion 6 as intermediate is proven in the case of the glycine ester 10.Thus, reaction of enzymatically resolved 10 with ?-nucleophiles leads to racemic products.The most useful iminium precursors are the N-methoxyamides 12-14 providing good yields of coupling products.The most convenient N-protective group is the allyloxycarbonyl group.Deprotection proceeds via a Pd(O)-catalyzed transprotection to the corresponding BOC-protected analogues.Four examples of the enzymatic resolution of α-amino carboxamides, by using an L-specific aminopeptidase from Pseudomonas putida, are described in detail.Most notably, secondary N-methoxyamides are good substrates for the enzyme to provide the desired α-amino acids in high optical purity.