Radical Dehalogenation And Purine Nucleoside Phosphorylase E. Coli: How Does An Admixture Of 2 ',3 '-Anhydroinosine Hinder 2-Fluoro-Cordycepin Synthesis

During the preparative synthesis of 2-fluorocordycepin from 2-fluoroadenosine and 3 '-deoxyinosine catalyzed by E. coli purine nucleoside phosphorylase, a slowdown of the reaction and decrease of yield down to 5% were encountered. An unknown nucleoside was found in the reaction mixture and its structure was established. This nucleoside is formed from the admixture of 2 ',3 '-anhydroinosine, a byproduct in the preparation of 3-' deoxyinosine. Moreover, 2 ',3 '-anhydroinosine forms during radical dehalogenation of 9-(2 ',5 '-di-O-acetyl-3 '-bromo- -3 '-deoxyxylofuranosyl)hypoxanthine, a precursor of 3 '-deoxyinosine in chemical synthesis. The products of 2 ',3 '-anhydroinosine hydrolysis inhibit the formation of 1-phospho-3-deoxyribose during the synthesis of 2-fluorocordycepin. The progress of 2 ',3 '-anhydroinosine hydrolysis was investigated. The reactions were performed in D2O instead of H2O; this allowed accumulating intermediate substances in sufficient quantities. Two intermediates were isolated and their structures were confirmed by mass and NMR spectroscopy. A mechanism of 2 ',3 '-anhydroinosine hydrolysis in D2O is fully determined for the first time.