Synthesis of Silacyclic Dipeptides: Peptide Elongation at Both N- and C-Termini of Dipeptide.

A new type of peptide bond formation utilizing silacyclic amino acids or peptides is described. This work has the following advantages: (1) imidazolylsilane is a highly fascinating coupling reagent for dipeptide synthesis from N-,C-terminal unprotected amino acids with amino acid tert -butyl esters; (2) deprotection of the tert -butyl ester at the C-terminus and cyclization sequentially proceed depending on reaction conditions to afford novel silacyclic dipeptides; (3) the cyclized products show a remarkable capacity as substrates of peptide elongation because the silacyclic compounds can act as both nucleophiles and electrophiles, and this capacity lead to one-pot site-selective tetra- and oligopeptide syntheses. These innovative advantages will help to simplify classical peptide synthesis significantly.