CYCLO(-ARGINYL-SARCOSYL-ASPARTYL-PHENYLGLYCYL-)(2) - SIMPLE SYNTHESISOF AN RGD-RELATED PEPTIDE WITH INHIBITORY ACTIVITY FOR PLATELET-AGGREGATION

The dimerization-cleavage of the tetrapeptide precursor bound to the b enzophenone oxime resin afforded cyclo[-Arg(Tos)-Sar-Asp(OcHex)-Phg-]( 2), a cyclic analogue of the RGD peptide. The yield and the selectivit y between the tetra-/octa-peptide formed through the cyclization-cleav age depended on the sequence of the tetrapeptide. The ratio of tetra-/ octa-peptide also depended on the substitution Level of the oxime resi n with the peptide segment. The cyclic octapeptide was also synthesize d through the solution-phase dimerization-cyclization from the linear tetrapeptide precursor. The solution-phase dimerization-cyclization wa s very efficiently mediated with BOP/HOBt as the condensation reagent. 1(H) NMR and CD spectra suggested that the cyclic octapeptide was of some restricted conformation, which might be involved in the preferred formation of the octapeptide in both solid- and solution-phase synthe ses. The octapeptide showed potent inhibitory activity toward platelet aggregation; however, it showed no activity toward cell adhesion.