Specific Application in the Synthesis of Non-natural Amino Acids

Specific Application in the Synthesis of Non-natural Amino Acids 

Because of its efficiency and broad substrate tolerance with regard to the alkyl halide, organocatalytic asymmetric alkylation has been applied to the synthesis of several unusual amino acids. These non-natural amino acids are often key intermediates in the synthesis of biologically active peptides and other compounds of pharmaceutical importance. 

The Imperiali group also reported the preparation of analogous optically active a-amino acids bearing a cyanoanthracene and a substituted pyridyl group, respec- 

A limitation of the organocatalytic alkylation reaction was, however, discovered by Pirrung et al. when applying the method to the synthesis of (S)-/ -cyclooctate-traenylalanine [49]. Although high yields were obtained, the resulting product was racemic. 

The Maruoka group have reported further application of N-spiro phase-transfer catalysts of type 29 to the diastereoselective a-alkylation of N-terminal di-, tri-, and tetrapeptides [52]. The reactions proceed with high diastereoselectivity, furnishing a diastereomeric ratio (d.r.) of up to 99 1 for the resulting dipeptide products. 

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