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.
A series of ergoline derivatives, analogues of Pergolide 1 and Lysergol 6, were synthesized, radiolabeled with '=I or 75Se, and evaluated for their ability to cross the Blood Brain Barrier of rats, for potential use as radiopharmaceuticals for imaging the brain. Introduction of the radiolabel was either at the 17-position (attached to the SB-methylene) or at the 2-position of the indole portion of the ergoline moie Of the 8 radiolabeled compounds tested, two pergolide analogues, SB-(methyl%eseleno)-methyl-6-propyl ergoline 5 and 8B-['~I]-iodomethyl-6-propyl ergoline 2f showed the highest uptake in the brain, adrenal and heart with good organ to blood ratios. This work has shown that analogues of pergolide, a dopamine agonist, if labeled with '=I may yield a clinically useful brain imaging radiopharmaceutical. 1 2 5 , 9 J [O;I H,,, C H 2 7 6 S e [ 4cH2c 2 z. cn,i
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