Synthesis of salicyl-peptides and their effect on human platelet aggregationin vitro

A series of leucine dipeptide amides containing at their N-terminal amino group the salicyl-residue [(o)-RO-C6H4-CO-, where R=H or CH3CO] have been synthesized by conventional solution techniques and tested for their inhibitory activity on human platelet aggregationin vitro induced by collagen, ADP or adrenaline. The salicyl-peptide (o)-HO-C6H4-CO-Leu-Asp(OBzl)-NH2 was found to exert strong inhibitory activity on platelet aggregation induced by collagen with an IC50 value 4.5 mM. The corresponding dipetide H2N-Leu-Asp(OVzl)-NH2 was also examined and was found to be less active, indicating that the presence of the lipophilicβ-benzyl ester group in combination with the salicyl group enhance the inhibitory activity. All the other salicyl-peptides examined either didn't show any inhibitory or aggregatory activity or a slight inhibition at the concentration of 9–10 mm.