Chemical synthesis and immunological properties of a cyclic eicosapeptide (Gly88,90) 82–101 of the beta subunit of human chorionic gonadotrophin

The eicosapeptide (Gly^88,90) 82–101 hCG-β was synthesized by the fragment condensation of the nonapeptide (Gly^88,90) 82–90 and the undecapeptide 91–101 followed by iodine oxidation to make the disulfide loop. Intramolecularity of the disulfide linking cysteines at 93 and 100 was confirmed. Anti-peptide antibodies were elicited in rabbits upon immunization with a conjugate of the peptide with tetanus toxoid. The repertoire of these antibodies was directed solely against the undecapeptide 91–101. These antibodies showed no recognition for hCG, hCG-β or ARCM hCG-β, suggesting that the conformational epitopes of hCG-β in the region 82–101 may not be accessible to antibodies.