Radioiodine labelling of a small chemotactic peptide, utilizing two different prosthetic groups: a comparative study

• Published in: Journal of labelled compounds & radiopharmaceuticals Vol. 51; no. 1; pp. 48 - 53
• Main Author: Rossouw, Daniel D.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.01.2008; Wiley
• Subjects: 123 I; Biochemical Research Methods; Biochemistry & Molecular Biology; Biological and medical sciences; Chemistry; Chemistry, Analytical; Chemistry, Medicinal; conjugates; Contrast media. Radiopharmaceuticals; iodovinyl; Life Sciences & Biomedicine; Medical sciences; peptide; Pharmacology & Pharmacy; Pharmacology. Drug treatments; Physical Sciences; Science & Technology; iodovinyl; REAGENT; peptide; conjugates; BIOLOGICAL BEHAVIOR; I-123; BACTERIAL-INFECTION; Iodine 123; 123I; Radiolabelling; Prosthetic group; Iodine Isotopes; Conjugated compound; Chemotactic peptide; Comparative study
• ISSN: 0362-4803; 1099-1344
• DOI: 10.1002/jlcr.1471

The use of iodobenzoates as pre‐labelled prosthetic groups in the radioiodination of peptides is becoming increasingly popular. The utilization of an iodovinyl ester unit as an alternative conjugation agent for the preparation of a radioiodinated peptide conjugate (peptide‐[123I]I‐PEA) was investigated in this study. A pre‐labelled unit, containing a tetrafluorophenyl ester group, was purified on a small C18 column and the dimethylformamide eluate was used directly in the conjugation step. Similar methodology was applied for a comparative radiosynthesis of an iodobenzoate analogue (peptide‐[123I]IB), using a succinimidyl ester. The influences of various reaction parameters on conjugation yields were investigated while maintaining a fixed amount of peptide. At high activity levels (more than 200 MBq) the conjugation yield of peptide‐[123I]I‐PEA was very sensitive to relatively large reaction volumes and increased amount of base. By optimizing these parameters, the formation of radiochemical impurities was minimized. Under similar conditions, peptide‐[123I]I‐PEA formed much faster than peptide‐[123I]IB. Sep‐Pak C18 purification afforded conjugates with radiochemical purities both in excess of 98% and free from unreacted peptide. Recovered conjugation yields of peptide‐[123I]I‐PEA in 50% ethanol were in excess of 60%, while those for peptide‐[123I]IB were less than 40%. Copyright © 2008 John Wiley & Sons, Ltd. Radiolabelled iodovinyl‐ and iodobenzene‐peptide conjugates were prepared using 123I as the radioisotope and a slightly different methodology to that previously reported. Under the conditions used, the iodovinyl analogue formed at a faster rate and was obtained with a higher radiochemical yield under optimal conditions. Both conjugates were purified on Sep‐Pak C18 mini‐columns and had radiochemical purities in excess of 98%. Copyright © 2008 John Wiley & Sons, Ltd.