Building units for N-backbone cyclic peptides. Part 4. Synthesis of protected N^α-functionalized alkyl amino acids by reductive alkylation of natural amino acids

A new method for the synthesis of protected N^α-(ω-Y-alkyl) amino acids (Y is a thio, amino or carboxy group) and related compounds by reductive alkylation of natural amino acids is reported. These new amino acids serve as building units for the synthesis of backbone-cyclic peptides. They are orthogonally protected at the α-amino position by butoxycarbonyl (Boc) or 9-fluorenylmethoxycarbonyl (Fmoc), using trimethylsilyl temporary protection, to allow for their incorporation into peptides by solid phase peptide synthesis.