Structurally restricted conjugates of the beta-subunit of the human chorionic gonadotropin to produce antisera

Structurally restricted conjugates, beta-hCG(-NH2)4(-NHC-NH-NH2)11(-C-O-TT)1-11, were synthesized by protecting the amino and guanidino functional groups of the beta-subunit of the human chorionic gonadotropin (beta-hCG) with t-Boc groups; then, the carboxyl groups of the protected intermediate were coupled by carbodiimide reagents with basic groups of tetanus toxoid (TT). After removal of the t-Boc groups, the immunogen has a total of fifteen amino and guanidino functional groups, which may be superior to carboxyl groups, for immunologic recognition. Conjugates, prepared in non-polar and aqueous systems, had ratios of beta-hCG to TT of 13:1 and 7:1, respectively. Immunization of rabbits yielded antisera which showed an inhibition of 50% for 41-62 ng/ml, beta-hCG, at final dilution ratios of up to 1:80,000.