7-Aminocephalosporanic acid (I) was converted to tert-butyl ester (II) by treatment with isobutylene and sulfuric acid. Subsequent diazotization, followed by reaction with methanol and rhodium catalyst, provided the 7-methoxy derivative (IIIa-b) as a diastereomeric mixture. The desired 7S-isomer was then deprotected with trifluoroacetic acid in anisole, yielding carboxylic acid (IV). Coupling of acid (IV) with 3-iodobenzylamine (VI) via activation as the mixed anhydride (V) with ethyl chloroformate gave rise to amide (VII). The sulfide group of (VII) was finally converted into the title sulfone by oxidation with oxone.

The synthesis of the 125I-labeled compound is shown in Scheme 2. Carboxylic acid (IV) was coupled with 3-(tri-n-butylstannyl)benzylamine (VIII) via the mixed anhydride (V) to produce amide (IX). Subsequent oxidation with oxone afforded the sulfone (X). Finally, iododestannylation of (X) employing Na125I and chloramine-T furnished the radiolabeled compound.