The preparation and use in solid phase synthesis of Na-fluorenylmethoxycarbonyl-N~-4-methoxy -2,3,6- trimethyl benzenesu Iphonyl- L-arginine is described. ... Protection of the guanidine side chain of arginine derivatives presents a continuing problem in both classical (solution) and solid phase peptide synthesis. In the latter, the introductionlJ of N "-fluorenylmethoxycarbonyl (Fmoc) amino-acids3 as alternatives to the customary t-butoxycarbonyl (Boc) deriva- tives ...