In an effort to obtain a more potent and specific immunotoxin for cancer therapy, we designed a series of heterobifunctional linkers characterized by a thioimidate group linked to a S-acetyl thiol (4, 5) or substituted aryldithio group (6-10). These ligands were synthesized by a Pinner-type process from the corresponding nitrile derivatives obtained by thiol-disulphide exchange reaction, reaction with