A new efficient route for synthesis of R,R- and S,Shexamethylpropyleneamine oxime for labeling with technetium-99m

[99mTc]Tc-Hexamethylpropylene amine oxime (HMPAO) is currently used as a regional cerebral blood flow imaging agent for single photon emission computed tomography (SPECT). The HMPAO ligand exists in two isomeric forms: d,l and meso showing different properties in vivo. Later studies indicated that brain uptake patterns of 99mTc-complexes formed from separated enantiomers differed. Separation of enantiomers is difficult by fractional crystallizations method. Usually, the substance is obtained in low chemical yield in a time-consuming procedure. Furthermore, the final product still contains some impurity. So we have developed new efficient route for synthesis of R,R - and S,S -HMPAO enantiomeric compounds in 6-steps. Nucleophilic substitution (SN2) reactions of 2,2-dimethylpropane-1,3-diamine either with S- (1a) or R-methyl-2-chloropropanoate (1b) were performed to produce compounds R,R- (2a) or S,S -isomer (2b) derivatives protected with benzylchloroformate (Cbz), respectively. And then Weinreb amide and methylation reaction using Grignard reagent, oxime formation with ketone group and deprotectiion of Cbz group by hydrogenolysis gave S,S- (7a) or R,R-HMPAO (7b), respectively. Entaniomeric compounds were synthesied with high yield and purity without any undesired product. The 7a or 7b kits containing 10 µg SnCl2-2H2O were labeled with 99mTc with high radiolabeling yield (90%).