A New Synthetic Method for Dipeptides Containing α,β-Didehydroamino Acids Utilizing an α-Tosylglycine Residue

The reaction of peptides containing an N-Boc- or N-Z-α-tosylglycine residue at the N-terminus with a variety of excess nitro compounds under basic conditions to give the nitro compound-adducts in good yields, followed by the elimination of nitrous acid from the adducts to afford the corresponding dipeptide containing α,β-didehydroamino acids with (Z)-configuration predominantly. Treatment of the same starting materials with aldehydes in the presence of base and tributylphosphine also gave a dipeptide containing α,β-didehydroamino acids with high (Z)-selectivity in satisfactory yields. The present method can be successfully applied to the synthesis of a protected leucine enkephalin analog