NITROACETYL GROUP AS A PEPTIDE SYNTHON - SYNTHESIS OF DIPEPTIDES WITH AN ALPHA,ALPHA-BISALLYLGLYCINE RESIDUE AT THE N-TERMINUS

N-Nitroacetyl derivatives of L-proline, L-valine, and L-phenylalanine esters were prepared in two steps under mild conditions (Scheme 2). Regiospecific mono- and bis-allylation of these nitroacetyl derivatives were accomplished in presence of a Pd(0) catalyst. The bis-allyl derivatives 7-9 were obtained in 40-75% yield. The tertiary NO2 group in these compounds could be transformed into an acetylamino group by Zn/AcOH/AC2O. The final products 11-13 are dipeptides in which the N-terminal glycine residue bears two alpha-allyl substituents.