Journal of Organic Chemistry p. 6769 - 6778 (1992)
Update date:2022-07-30
Topics:
Roos, Eric C.
Mooiweer, Hendrik H.
Hiemstra, Henk
Speckamp, W. Nico
Kaptein, Bernard
et al.
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 SN1-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.
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