Solid phase synthesis of oligoureas using O-succinimidyl-(9H-fluoren-9-ylmethoxycarbonylamino)ethylcarbamate derivatives as activated monomers

An efficient stepwise synthesis of oligoureas (up to the nonamer) on solid support using O-succinimidyl-(9H-fluoren-9-ylmethoxycarbonylamino)ethylcarbamate derivatives as activated monomers is described. These building blocks were readily prepared starting from N-Fmoc-protected β3-amino acids via Curtius rearrangement of the corresponding acyl azides and treatment of the resulting isocyanate with N-hydroxysuccinimide.