SYNTHESIS AND RADIOIODINATION OF A STANNYL OLIGODEOXYRIBONUCLEOTIDE

Synthesis and radioiodination of a stannyl oligodeoxyribonucleotide we re undertaken to evaluate a gamma ray emitting ODN ligand for thrombus imaging in vivo. Synthesis of the ODN was based on modified automated beta-cyanoethyl phosphoramidite chemistry with an organotin nucleosid e (dU) coupled to a thrombin binding aptamer sequence to give d(U*GGT TGGTGTGGTTGG). The synthesis accommodated dU, which is destannylated by iodine or acids. Fourteen standard synthesis cycles were followed b y one 'stannyl synthesis cycle', distinguished by Fmoc protection, omi ssion of capping, oxidation by an organic peroxide and cleavage by amm onium hydroxide, The organotin nucleoside phosphoramidite tyl-stannylv inyl]-2'-deoxyuridine-3'-(2-cyanoethyl N,N-di-isopropyl phosphoramidit e)} was prepared from 5-iodo-2'-deoxyuridine. A customized mild rapid workup included deprotection with methylamine, and reverse phase HPLC with CH3CN/triethylammonium bicarbonate, Pure stannyl ODN was highly r etained by reverse phase HPLC, Radioiodination of stannyl ODN (100 mu g) provided I-123-labeling yields up to 97%. Five alternative oxidants were effective, High specific activity [I-123]-ODN (15000 Ci/mmol) wa s recovered, separated from unlabeled isomers, Excellent reverse phase HPLC resolution of ODN isomers (alternatively I, Cl, H or Br in vinyl deoxyuridine) was essential, The affinity of the iodovinyl aptamer an alog (K-d = 36 nM) for human alpha-thrombin was similar to the native aptamer (K-d = 45 nM).