acid and lyophilized the peptide product was purified by hplc on a 700 ml column of 15 20 u03bcm 300 u00e5 vydac c 18 reverse phase packing the separations group hesperia calif using a 0 50 gradient in acetonitrile 0 1 tfa fractions containing product as ascertained by analytical hplc were pooled and lyophilized to afford about 1 0 gram of pure tetrapeptide from 10 grams of resin substantially similar synthesis procedures were used for the solid phase synthesis of other peptide derivatives of this invention by substituting equivalent amounts of other boc tyrosine derivatives for the boc tyrosine methyl ether and or des amino arginine homoarginine or acetyl arginine for arginine in the above example the peptide derivatives prepared in example 1 were tested for their platelet binding inhibitor activity by the following standard protocol platelet preparation 60 ml of whole blood is freshley drawn and anticoagulated with 1 10th volume of ccd 100 mm na citrate and 136 mm glucose ph 6 5 with hcl at room temperature rt the blood is divided into 2 disposable 60 ml plastic centrifuge tubes and centrifuged for 3 minutes at 1000 u00d7 g allowing the centrifuge to coast to a stop no brake the platelet rich plasma prp is withdrawn being careful that no white cells are taken and is placed in a 60 ml centrifuge tube the tube is immediately placed on ice for.