Green Synthesis of α,β- and β,β-Dipeptides under Solvent-Free Conditions

The reactivity of N-tert-butyloxycarbonyl-N-carboxyanhydrides derived from beta-alanine, (S)-beta(3-)homophenylglycine, and (S)-beta(3)-carboxyhomoglycine with different alpha- and beta-amino ester hydrochlorides was examined under ball-milling activation. In particular, good to excellent yields of several relevant alpha,beta- and beta,beta-dipeptides were obtained. An illustrative application of this methodology consisted in the high-yield synthesis of the mammalian alpha,beta-dipeptide N-Boc-L-carnosine-OMe.