2-[ lZ5I ]iodobenzyl)benzylmethylselenonium tetraf luoroborate (L) and(0-[ 1251]iodobenzyl)dibenzylselenonium tetrafluor b rate (2) were synthesized by methylation and benzylation of ~-[PzPI]iodobenzyl benzyl selenide respectively. The starting compound 2-iodobenzyl benzyl selenide was radioiodinated with sodium [ 1251]iodide by melt-exchange in a sealed ampoule maintained at 75OC for 12 hours, with subsequent chromatographic purification yielding the pure compound in a radiochemical yield of 33.0% and specific activity of at least 68.0 mCi/mmol. Tissue distribution studies of compounds 1 and 2, performed i n rats, showed that the labelled compounds accumulated rapidly in the heart. The maximum heart-to-blood ratios for compounds 1 and 2 were 4.2:l and G.4:1 compared to that of 2.0:l for previously synthesized [75Se]Trimethylselenonium Iodide (2). The search for a better myocardial imaging agent to supersede the cyclotronproduced [201Tl]thallous chloride has centered upon a number of lipophilic cationic complexes labeled with isotopes having better physical properties. 3 Investigations with radiolabelled phosphonium monocations such as [ HItetraphenyl phosphonium bromide, [3H]methyl triphenyl phosphonium bromide, [ iodomethyl ammoniums have shown promising myocardial uptake (3). 11 Clmethyl triphenyl phosphonium bromide (1,2), and a series of radioiodinated Previous studies in our laboratory with the cation [75Se]trimethylselenonium iodide (2) showed relatively low myocardial uptake with the maximum uptake A . S. Purikh eta/. i n k i d n e y s , a s p r e d i c t e d , due t o t h e h y d r o p h i l i c n a t u r e o f t h e compound ( 4 ) . The p u r p o s e of t h i s s t u d y was t o s u b s t i t u t e o n e or more m e t h y l g r o u p ( s ) from [ S e ] t r i m e t h y l s e l e n o n i u m i o d i d e w i t h b e n z y l g r o u p ( s ) . r a d i o i o d i n a t e a n d e v a l u a t e t h e r e s u i t i n g l i p o p h i l i c compounds (g-[1251]iodobenzyl)benzylmethyls e l e n o n i u m t e t r a f l u o r o b o r a t e (1) a n d (2-[ 1251]iodobenzyl)dibenzylselenonium tetraf l u o r o b o r a t e (2) f o r u s e a s p o t e n t i a l m y o c a r d i a l p e r f u s i o n a g e n t s ( F i g . 1).
75F i g u r e 1. Selenonium S a l t s 1 , 2. 3.
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