The benzoyl-protected ligand (IV) was prepared as follows. Acylation of triglycine (I) with chloroacetyl chloride (II) produced the chloroacetamide (III). Subsequent treatment of chloride (III) with sodium thiobenzoate yielded thioester (IV). The title 99technetium complex was prepared by in situ hydrolysis of the thiobenzoate ester (IV) to mercaptoacetyl triglycine (V) in the presence of a solution of [99mTc]pertechnetate, SnCl2 as the technetium reducing species, and gluconate or tartrate as intermediate Tc complexing agents.
The protected ligand (IV) was also prepared by a related method. The acylation of thioglycolic acid (V) with benzoyl chloride (VI) under Schotten-Baumann conditions afforded S-benzoyl thioglycolic acid (VII). After activation of (VII) as the corresponding succinimidyl ester (VIII) with N-hydroxysuccinimide and DCC, coupling with triglycine (I) furnished compound (IV).
Other S-protecting groups for mercaptoacetyl triglycine have been reported. The S-benzyl derivative (X) was prepared by condensation of triglycine (I) with (benzylthio)acetyl chloride (IX). Alternatively, the S-benzamidomethyl compound (XII) was prepared as follows. Thioglycolic acid (V) was condensed with benzamidomethanol under acidic conditions to give S-(benzamidomethyl)thioglycolic acid (XI), which was then coupled to triglycine (I) using DCC/HOBt. Deprotection in the presence of 99Tc pertechnetate under the same conditions as above furnished the title Tc complex.