Submonomer synthesis of aza-peptides featuring regioselective alkylation of peptide-bound aza-Gly residues provided ten aza-analogues of the Growth Hormone Releasing Peptide-6 (GHRP-6) in 15-42% yield and purity generally >or=90%. Circular dichroism demonstrated that azaPhe-peptide 7a induced a beta-turn conformation which may be responsible for its 1000-fold improvement in GHRP-6 selectivity for the CD36 receptor. This versatile method for making aza-peptides avoids solution-phase hydrazine synthesis and is well suited for studying side-chain-activity relationships of biologically active peptides.

Aza-peptides have been used as tools for studying SARs in programs aimed at drug discovery and chemical biology. Protected aza-dipeptides were synthesized by a solution-phase submonomer approach featuring alkylation of N-terminal benzophenone semicarbazone aza-Gly-Xaa dipeptides using different alkyl halides in the presence of potassium tert-butoxide as base. Benzophenone protected aza-dipeptide tert-butyl ester 31c was selectively deprotected at the C-terminal ester or N-terminal hydrazone to afford, respectively, aza-dipeptide acid and amine building blocks 36c and 40c, which were introduced into longer aza-peptides. Alternatively, removal of the benzophenone semicarbazone protection from aza-dipeptide methyl esters 29a-c led to intramolecular cyclization to produce aza-DKPs 39a-c. In light of the importance of aza-peptides and DKPs as therapeutic agents and probes of biological processes, this diversity-oriented solution-phase approach may provide useful tools for studying peptide science.