Materials and Methods

Chemical Synthesis Materials. A^-ferf-Butyloxycarbonyl (r-Boc)-amino acids were obtained from the Peptide Institute, Osaka, Japan, except Ar “-r-Boc-Artm-(dinitrophenyl) histidine which was obtained from Bachem Inc., Switzerland. Tri-fluoroacetic acid was purchased glass-distilledfrom Halo-carbon Inc., North Augusta, SC, and redistilled before use. Dimethylformamide was from Burdick and Jackson, Musk-egon, MI, after selected lot numbers were pretested. Di-chloromethane was from BDH Canada, Toronto, Ontario, after selected lot numbers were pretested. Methanol was glass-distilled-grade from BDH Canada. A, A-Diisopropyl-ethylamine, A./V-dicyclohexylcarbodiimide, 1-hydroxybenzo-triazole, and the pam resins were from Applied Biosystems, Foster City, CA. Hydrogen fluoride was from Matheson Canada, Edmonton, Canada, and p-cresol, p-thiocresol, and dimethyl sulfide were from Aldrich ChemicalCo., Milwaukee, WI.