Optimized conventional synthesis of ``RGD{''} and ``RGDS{''} peptides and their sarcosine mimics as integrin GP IIb/IIIa antagonists

Synthetic arginyl-glycyl-alpha-aspartyl ``RGD{''} and arginyl-glycyl-alpha-aspartyl-serinyl ``RGDS{''} peptide sequences, which are originally located in matrix proteins, are confirmed to be as versatile integrin GP IIb/IIIa antagonists. Since integrins, as cell surface glycoprotein receptors are implicated in several physiological mechanisms, these peptides are recently specially considered in the design of new therapeutics. Replacing glycine by sarcosine, as its more lipophilic isomer, in RGD peptides seemed, accordingly, interesting in revealing some structural/biological activity relationships. To render ``RGD{''} peptides more conveniently available, an ameliorated quasi-gram yield conventional synthesis in solution of the parent ``RGD{''} and ``RGDS{''} {[}8, Scheme 1A \& 15, Scheme 1B] and their sarcosine analogues, {[}8', Scheme 1A \& 15', Scheme 1B] respectively, is herein described. A compilation of the mild hydrogenolysis removable Z and NO2 groups and/or the acidiolytic removable Boc group were manipulated for the amino temporary protecting steps. Both the DCCI/HOBt and MA methodologies served well as peptide coupling methods.