THE NON PROTONABLE REDUCED AZA-PEPTIDE FRAGMENT

The reduced aza-peptide fragment (C-alpha-CH2-NH-N(alpha)R-CO-NH-C-alp ha) is obtained by reduction of the semicarbazone moiety (C-alpha-CH=N -N(alpha)R-CO-NH-C-alpha) in an imino aza-peptide. It differs from the aminomethylene link (C-alpha-CH2-NH-C(alpha)HR-CO-NH-C-alpha) found i n the reduced peptides by the absence of protonation in water in the 2 -12 pH range. The reduced aza-analogue of the Pro-Ala dipeptide has be en studied in solution by H-1-NMR and IR spectroscopy, and in the soli d state by X-ray diffraction. Its structure is quite similar to that o f the neutral reduced dipeptide analogue in solution. (C) 1997 Elsevie r Science Ltd.