SYNTHESIS AND RADIOIODINATION OF 3-(E)-(2-IODOVINYL)-N-ACETYL-4-CYSTEAMINYLPHENOL, A PUTATIVE TYROSINASE SUBSTRATE FOR IMAGING NEURAL CRESTTUMORS

The synthesis of 3-(E)-(2-iodovinyl)-N-acetyl-4-cysteaminylphenol (3-I V-N-Ac-4-SCAP) started from 3-iodophenol, which on condensation with c ysteamine hydrochloride gave 3-iodo-4-cysteaminylphenol (1). Acetylati on of 1 followed by selective deacetylation yielded 3-iodo-N-acetyl 4- cysteaminylphenol (3-I-N-Ac-4-SCAP; 3). The stereospecific reaction of (E)-1-trimethylsilyl-2-tri-n-butyltinethylene with 3 afforded the vin yl-TMS precursor (2-trimethylsilylvinyl)-N-acetyl-4-cysteanylphenol (3 -TMS-N-Ac-4-SCAP; 4) in high yield. This TMS vinyl precursor is a usef ul synthon for high specific activity radioiodination. Iodination of t he synthon 3-(E)-(2-trimethylsilylvinyl)-N-acetyl-4-with iodine monoch loride gave 3-IV-N-Ac-4-SCAP (5). High specific activity (no carrier a dded) 3-(E)-(2-[I-125]iodovinyl)-N-acetyl-4-cysteaminyl phenol was obt ained in 85% radiochemical yield upon a 5 min exposure of a mixture of Na[I-125]I and 3-TMS-N-Ac-4-SCAP to 2450 MHz radiation in a microwave oven.