SIDE REACTION DURING THE DEPROTECTION OF CYS(ACM)-CONTAINING PEPTIDESWITH IODINE - SYNTHESIS OF DISULFIDE FRAGMENTS FROM CATHEPSIN-D STRUCTURE

Peptides H-TPPQC(Acm)FTV-NH2 (I) and H-VSVPC(Acm)QSASSAS-NH2 (III) wer e prepared by the solid phase method. Their oxidation with iodine affo rded hexadecapeptide II tetracosapeptide IV and eicosapeptide VI. The disulfide peptides II, IV and VI are designed according to the sequenc e of the processing loop in human cathepsin D. The purity of the pepti des was determined by analytical HPLC and capillary zone electrophores is. In addition to the expected [M + H](+) ion, FAB MS of HPLC-pure te tracosapeptide IV exhibited a molecular ion with the same relative mol ecular mass as the starting dodecapeptide III, in spite of clean HPLC separation of III and IV Free-flow zone electrophoresis of IV separate d peptide V isomeric with III. Mass spectra, amino acid analysis and E dman sequencing revealed that the peptide V is a product of iodine-med iated S-->O shift of Acm group in the serine-rich peptide III. Daughte r-ion spectra of protonated molecules, recorded after collision-induce d dissociation, have shown that the Acm moiety is bonded to Ser 9 or S er 10.