The title ternary ligand technetium-99m complex was formed as a mixture of two isomeric forms by reaction of the hydrazinonicotinamide-derivatized cyclic peptide (I) with trisodium triphenylphosphine-3,3',3''-trisulfonate (II) and tricine (III) in the presence of 99mTc pertechnetate and SnCl2. The 99Tc analogue was similarly prepared for spectroscopic characterization by using (n-Bu4N)(99TcOCl4) or (NH4)(99TcO4).
The title compound was then obtained by complexation of hydrazone (IX) with phosphine (II) and tricine (III) in the presence of Na99mTcO4 and SnCl2. Under these conditions, the hydrazone protecting group hydrolyzed to the required hydrazine. Some shortcomings caused by SnCl2 could be omitted using a non-SnCl2-containing formulation in the presence of mannitol and pluronic acid as surfactant agents.
In order to stabilize the hydrazino compound (I), a stable hydrazone derivative was prepared by two alternative procedures. Condensation of 6-hydrazinonicotinic acid (IV) with sodium 2-formylbenzenesulfonate (V) gave the hydrazone acid (VI), which was further converted to the succinimidyl active ester (VII) by treatment with N-hydroxysuccinimide and DCC. Coupling of succinimidyl ester (VII) with the aminocaproyl cyclic peptide (VIII) then gave the target hydrazone derivative (IX). Alternatively, (IX) was also prepared by condensation of the hydrazino peptide (I) with sodium 2-formylbenzenesulfonate (V).