Preparation of ω‐¹²³I‐labelled fatty acids by ¹²³I‐for‐Br exchange: Comparison of three methods

Abstract

SUMMARYLong chain ~~~~I -l a b e l l e d fatty acids such as 16-I-hexadecanoic-, 17-I-heptadecanoic-, and 16-Ihexadec-9-enoic acid have been prepared without adding carrier by nucleOphilic in acetone, in the melt, and by use of phase transfer catalysts in non-polar solvents. While preparation in refluxing acetone required reaction times of more than 2 hours to reach saturation yields, halogen exchange in molten bromofatty acids at temperatures of about 150 C gave rise to yields of about 80% of radiochemically pure 1 7-1 231-heptadecanoic acid within only 5 minutes. Comparable yields were also obtained using Kryptofix 2 2 1 in refluxing toluene after 1 0 minutes, 231-for-Br exchange 0

No-Carrier-Added Radiohalogenation Methods with Heavy Halogens

“…3) [63,64]. [39]. The shorter reaction times and higher yield using such catalysts are contrasted with non-catalyzed iodinefor-bromine exchange in Figure 2.…”

“…Besides tetraalkylammonium salts, polyethers have also found success in catalyzing radioiodination reactions [39,53].…”

“…123 1-labeled a-iodostearic acid was performed by 123 I-for-Br exchange in a melt of the abromostearic acid and 123 1-iodide with a yield of 95% within 20 minutes [3]. A radioiodination yield of 80% for the non-isotopic exchange in ω-bromoheptadecanoic acid was achieved within 5 minutes in the melt of the compound [39]. A precursor of 0-[ l23 I]-iodo-D-alanine was labeled by the same procedure with a yield of 80% within 5 minutes [48], Another comparative study, labeling heptadecanoic acid by halogen-exchange in solution, in the melt, by tosylate substitution and by using p.…”

“…Traces of bromide lead, for example, to epimerization and a low effective specific activity when preparing 16a-125 1-iodoestradiol [32]. The importance of radiohalogenated fatty acids in nuclear medicine has resulted in the recent development of aliphatic radiohalogenation methods for their preparation [33][34][35][36][37][38][39][40][41]. The different routes used, for example, for the preparation of ω-[ 123 Ι] iodoheptadecanoic acid are illustrated in Figure 1.…”

“…labeling, the optimal conditions Based on the FINKELSTEIN method [42], halogen exchange has been used in homogeneous solutions of aprotic polar solvents to introduce iodine-123 into fatty acids [35][36][37][38][39][40][41]. Yields of up to 95% have been obtained in the appropriate solvents using nonisotopic halogen substitution on ω-and a-halogenated stearic-and heptadecanoic acids [37], Using the FINKELSTEIN method, higher yields are normally found on a macroscopic scale in iodine-forbromine substitutions as compared with the reverse reaction.…”