Acid-base equilibria of 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid and its labeling with technetium-99m

Abstract

The acid-base equilibria of a novel hepatobiliary imaging agent, 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid (DIIODIDA) were studied. The potentiometrically determined acidity constants of the second carboxylic group, amino and amide groups were pK2 = 2.52 ± 0.02; pK3 = 5.86 ± 0.06 and pK4 = 10.9 ± 0.1. The determinations were performed at 25 ºC and an ionic strength of 0.1 mol/dm3 (NaCl). The acidity constants (pK1 = 1.3 ± 0.4) corresponding to the first carboxylic group was determined indirectly, on the basis of equilibrium constants obtained in a heterogeneous system, at 25 ºC and an ionic strength 1 mol/dm3 (HCl, NaCl). DIIODIDA was labeled with technetium-99m, and the influence of pH on the yield of labeling was investigated. It was found that labeling within the pH range from 5.5 to 6.5 provided a radiopharmaceutical of high radiochemical purity (>98 %).

Ispitane su kiselinsko-bazne ravnoteže novog hepatobilijarnog agensa, 2,4-dijod- 6-metilfenilkarbamoilmetil iminodisirćetne kiseline. Kiselinske konstante koje odgovaraju drugoj karboksilnoj grupi, amino i amidnoj grupi određene su potenciometrijski: pK2 = 2.52 ± 0.02; pK3 = 5.86 ± 0.06 I pK4 = 10.9 ± 0.1. Određivanja su izvedena na 25 ºC i pri konstantnoj jonskoj sili 0,1 mol/dm3 (NaCl). Kiselinska konstanta prve karboksilne grupe (pK1 = 1,3_0,4) određena je indirektno na osnovu ravnotežnih konstanti određenih u heterogenom sistemu, na 25 ºC i jonskoj sili 1 mol/dm3 (HCl, NaCl). DIIODIDA je obeležena tehnecijumom-99m i ispitan je uticaj pH na prinos obeležavanja. Utvrđeno je da se obeležavanjem u pH opsegu 5,5-6,5 dobija radiofarmaceutik visoke radiohemijske čistoće (> 98 %).