A 21-residue, two disulfide-containing peptide has been synthesized on solid phase. Three alternative protection schemes, based on Boc/benzyl chemistry and combinations of the 4- methylbénzyl with either acetamidomethyl, 9-fluorenylmethyl or 3-nitro-2-pyridylsulfenyl groups for pairs of cysteine residues have been examined. The most successful route involved formation of the first disulfide on the resin via 9-fluorenylmethylcysteine ...