Nucleoside Analogues for Positron Emission Tomography Imaging and to Study Radiation Mediated Generation of Radicals from Azides

Nitrogen-Centered Radicals Derived from Azidonucleosides

“…The formation of (i) RNH• (64) from 60, (ii) R=N• (65) from 61, and (iii) RN 3 • − (66) from 62, after gamma-irradiation at 77 K, was observed. Moreover, tetrazolocytidine 63 (a cylic derivative of 62), upon irradiation, also produced azide anion radical 67 [94,95].…”

“…The formation of (i) RNH• from 60, (ii) R=N• (65) from 61, and (iii) RN3• − (66) from 62, after gamma-irradiati 77 K, was observed. Moreover, tetrazolocytidine 63 (a cylic derivative of 62), upon ir ation, also produced azide anion radical 67 [94,95]. The proposed mechanism for the electrochemical reduction of dAAzP 69b on mer surface involves the one-electron reduction of the azido-group to nitrene anion radica accompanied by dinitrogen release.…”

“…Photolabile N-hydroxypyrid-2(1H)one or thione 86 were also used for guanine radical generation [107,108]. It is noteworthy that preliminary results on the addition of a radiation-produced electron to 2-azido-2′deoxyinosine produces the complex EPR signals, and subsequent UV photoexcitation leads to the mixture of radicals, including the possible formation of sugar radicals rather than the elusive guanyl aminyl radical 82 [95]. The Greenberg's group reported the photochemical generation of σ-iminyl radical 2′deoxycytidin-4-N-yl 88 from a nitrophenyl oxime precursor 87 and the synthesis of oligonucleotides containing 87 for DNA incorporation (Figure 16) [109].…”

“…The tautomerization of syn-aminyl radical also leads to the iminyl σ-radical 88 [111,112]. Interestingly, contrary to these findings, [109][110][111] the one-electron reduction (conditions for DEA) of azide precursors at the C4 positions of pyrimidine bases (62 or 63) led to the formation of anion radicals 66 or 67 (see Figure 11) [94,95]. One-electron oxidation and ESR studies of 1-methylcytosine and 2 ′ -deoxycytidine 91 showed that the cytidine cation radical 92 preferentially deprotonates to form an aminyl radical 94 syn to the carbonyl moiety (Figure 17).…”

“…The tautomerization of syn-aminyl radical also leads to the iminyl σ-radical 88 [111,112]. Interestingly, contrary to these findings, [109][110][111] the one-electron reduction (conditions for DEA) of azide precursors at the C4 positions of pyrimidine bases (62 or 63) led to the formation of anion radicals 66 or 67 (see Figure 11) [94,95].…”