Solid-phase synthesis of N,N'-unsymmetrically substituted ureas: Application to the synthesis of carbaza peptides

Abstract

The synthesis of Boc- or Fmoc-monoprotected propylenediamine derivatives is reported starting from N-protected α-amino acids. The introduction of these building blocks on solid support via the formation of a urea moiety leads to a new pseudopeptide family (C(α)-CH2-CH2-N(α)(R)-CO-NH-C(α)). Two carbonylating reagents, i.e N,N'-carbonyldiimidazole and triphosgene, as well as different coupling procedures, have been tested to optimize the Boc and Fmoc solid-phase synthesis of a model peptide incorporating this isosteric replacement.