Preparation of Carbon-14 Labeled 2-(2-Mercaptoacetamido)-3-phenylpropanoic Acid as Metallo-beta-lactamases Inhibitor (MBLI), for Coadministration with Beta-lactam Antibiotics

Aim and Objective: Bacteria could become resistant to beta-lactam antibiotics through production of beta-lactamase enzymes like metallo-beta-lactamase. 2-(2-mercaptoacetamido)-3-phenylpropanoic acid was reported as a model inhibitor for this enzyme. In order to elucidate the mechanism of action in the body's internal environment, preparation of a labeled version of 2-(2-mercaptoacetamido)-3-phenylpropanoic acid finds importance. In this regard, we report a convenient synthetic pathway for preparation of carbon-14 labeled 2-(2-mercaptoacetamido)-3-phenylpropanoic acid. Materials and Methods: This study was initiated by using non-radioactive materials. Then, necessary characterization was performed after each of the reactions. Finally, the synthesis steps were continued to produce the target labeled product. For labeled products, the process was started from benzoic acid-[carboxyl-C-14] which has been prepared from barium C-14-carbonate. Chromatography column and NMR spectroscopy were used for purifications and identification of desired products, respectively. Barium [C-14]carbonate was purchased from Amersham Pharmacia Biotech and was converted to [C-14] benzyl bromide. Radioactivity was determined using liquid scintillation spectrometer. Results: We used [C-14]PhCH2Br which was previously prepared from [C-14]BaCO3, H2SO4, PhMgI, LAH and HBr, respectively. To neutralize the [C-14]phenylalanine in acidic condition and to reach an isoelectric point of phenylalanine (pH = 5.48), Pb(OH)(2) was used. Next, thioacetic acid and bromo acetic acid were used to prepare (acetylthio) acetic acid. A peptide coupling reagent was used in this stage to facilitating amide bond formation reaction between [C-14]methyl-2-amino-3-phenyl propanoate hydrochloride and (acetylthio) acetic acid. Conclusion: Carbon-14 labeled 2-(2-mercaptoacetamido)-3-phenylpropanoic acid via radioactive phenylalanine was obtained with overall chemical yield 73% and radioactivity 65.3 nCi. The labeled target product will be used for in vivo pharmacological studies.