New mild acid-labile protecting groups for the guanidino function of Nα-fluorenylmethoxycarbonyl-l-arginine in solid-phase peptide synthesis: 10, 11-dihydro-5H-dibenzo[a,d]. cyclohepten-5-yl, 2-methoxy-10, 11-dihydoro-5H-dibenzo[a,d]. cyclohepten-5-yl and 5H-dibenzo[a,d]. cyclohepten-5-yl groups

10, 11-Dihydro-5H-dibenzo[a, d]. cyclohepten-5-yl [5-dibenzosuberyl]. and 5H-dibenzo[a, d]. -cyclohepten-5-yl [5-dibenzosuberenyl]. groups have been found to be useful protecting groups for the guanidino function of arginine in solid-phase peptide synthesis on Fmoc chemistry. The arginine derivatives ( 4a, b, c ) derivatized with these groups were easily deprotected with mild acid (less than 30 min with 25% trifluoroacetic acid). Tryptophan-containing peptide sequences, two hexapeptides ( 6 ) and (8), were synthesized in good yield by mild acid treatment (50% trifluoroacetic acid in 1 h) of the peptide resins ( 5a, c-f and 7a, c, d ) assembled via 4a, b, c using benzotriazol-1 -yl-oxy-tris-(pyrrolidino)-phosphonium hexafluorophosphate-1-hydroxybenzotriazole mediated coupling.