Synthetic Study of Peptide Aldehydes

Some of the leupeptin Ac-LL analogs, in which the argininal moiety was replaced by aromatic aminoaldehydes, were synthesized starting from benzyloxycarbonyl-α-amino-aldehyde semicarbazones derived from benzyloxycarbonyl amino acid esters by the reduction with diisobutylaluminum hydride. The racemization of the aldehyde part of the purified analogs was examined using the analytical ion exchange chromatography of diastereomers produced by the condensation of L-aspartic acid with aminoalcohols, which were obtained by the sodium borohydride reduction of the synthesized peptide aldehydes followed by acid hydrolysis. The results demonstrate that racemization occurs only to a limited extent, when these starting materials are used and careful purifications of the products are carried out.