Synthesis of racemic .alpha.-amino carboxamides via Lewis acid-mediated reactions of .alpha.-methoxyglycinamide derivatives with allylsilanes: enzymic resolution to optically active .alpha.-amino acids
摘要:
A short and expedient synthetic route to optically active, saturated and gamma,delta-unsaturated alpha-amino acids is reported. The key step is a BF3.OEt2-mediated reaction of allylsilanes with N-(alkoxycarbonyl)-alpha-methoxyglycinamides 11-15, leading to the corresponding gamma,delta-unsaturated alpha-aminocarboxamides. The genuine S(N)1-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 pi-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(0)-catalyzed transprotection to the corresponding BOC-protected analogues. Four examples of the enzymatic resolution of alpha-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 a-amino acids in high optical purity.
Synthesis of racemic .alpha.-amino carboxamides via Lewis acid-mediated reactions of .alpha.-methoxyglycinamide derivatives with allylsilanes: enzymic resolution to optically active .alpha.-amino acids
摘要:
A short and expedient synthetic route to optically active, saturated and gamma,delta-unsaturated alpha-amino acids is reported. The key step is a BF3.OEt2-mediated reaction of allylsilanes with N-(alkoxycarbonyl)-alpha-methoxyglycinamides 11-15, leading to the corresponding gamma,delta-unsaturated alpha-aminocarboxamides. The genuine S(N)1-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 pi-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(0)-catalyzed transprotection to the corresponding BOC-protected analogues. Four examples of the enzymatic resolution of alpha-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 a-amino acids in high optical purity.
Palladium-Catalyzed Transprotection of Allyloxycarbonyl-Protected Amines: Efficient One-Pot Formation of Amides and Dipeptides
作者:Eric C. Roos、Pablo Bernabe、Henk Hiemstra、W. Nico Speckamp、Bernard Kaptein、Wilhelmus H. J. Boesten
DOI:10.1021/jo00111a035
日期:1995.3
The synthetic utility of the N-(allyloxycarbonyl) (Alloc) substituent in alpha-amino acid derivatives is substantially extended beyond its well-known function as an amine protecting group. When the palladium-catalyzed deprotection is carried out by using tributyltin hydride as nucleophile (the Guibe method) in the presence of an active acylating agent a new acyl group is introduced on nitrogen. Successful acylating agents include carboxylic acid anhydrides, acid chlorides, and activated esters. A useful example of this methodology is the removal of the Alloc group in the presence of tert-butyl dicarbonate, which in essence amounts to a ''transprotection'' to a Boc-protected alpha-amino acid derivative. More importantly, the use of activated N-protected alpha-amino ester derivatives (e.g., pentafluorophenyl esters) leads to dipeptides. This new method for peptide coupling proceeds very fast under mild conditions, in good to excellent yields, and without noticeable racemization.
Palladium-catalyzed synthesis of amides and peptides
作者:Eric C. Roos、Pablo Bernabé、Henk Hiemstra、W.Nico Speckamp、Bernard Kaptein、Wilhelmus H.J. Boesten
DOI:10.1016/0040-4039(91)80241-w
日期:1991.11
When the Pd(0)-catalyzed hydrostannolysis of the N-allyloxycarbonyl group is carried out in the presence of an activated carbonyl compound, a coupling product is formed. This new method appears to be applicable to the synthesis of a wide range of amides and peptides.
Synthesis of racemic .alpha.-amino carboxamides via Lewis acid-mediated reactions of .alpha.-methoxyglycinamide derivatives with allylsilanes: enzymic resolution to optically active .alpha.-amino acids
作者:Eric C. Roos、Hendrik H. Mooiweer、Henk Hiemstra、W. Nico Speckamp、Bernard Kaptein、Wilhelmus H. J. Boesten、Johan Kamphuis
DOI:10.1021/jo00051a019
日期:1992.12
A short and expedient synthetic route to optically active, saturated and gamma,delta-unsaturated alpha-amino acids is reported. The key step is a BF3.OEt2-mediated reaction of allylsilanes with N-(alkoxycarbonyl)-alpha-methoxyglycinamides 11-15, leading to the corresponding gamma,delta-unsaturated alpha-aminocarboxamides. The genuine S(N)1-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 pi-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(0)-catalyzed transprotection to the corresponding BOC-protected analogues. Four examples of the enzymatic resolution of alpha-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 a-amino acids in high optical purity.