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

The eicosapeptide (Gly88,90) 82-101 hCG-beta was synthesized by the fragment condensation of the nonapeptide (Gly88,90) 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. Antipeptide 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-beta or ARCM hCG-beta, suggesting that the conformational epitopes of hCG-beta in the region 82-101 may not be accessible to antibodies.