Preparation of Cyclonucleosides

Unprecedented formation of 8(R),5′-O-cycloribonucleosides through a triflation reaction of purine ribonucleosides

“…The N-3 of purine nucleosides is well known to readily displace 5 0 -activating groups (e.g., tosyl, mesyl, iodo, O-sulfonamide), yielding N 3 ,5 0 -anhydronucleoside salts. 20 We assumed that the presence in 4 of a chlorine atom at the 6-position of the purine contributed to the reduction in nucleophilicity of N-3 and prevented N 3 ,5 0 -O-cyclization, as previously reported for acylation of the N6 amino group in adenosine derivatives. 21 Additionally, the replacement of 2 0 ,3 0 -O- isopropylidene protecting groups by TBS groups was reported to decrease N 3 ,5 0 -cyclonucleoside formation.…”

“…The chemical structure of these cyclonucleosides, including the absolute configuration at C8, was established by NMR and X-ray diffraction analysis. Many cyclonucleosides (from synthetic routes or natural sources) has been described in the literature, 20 including 8,5 0 -imino-cyclonucleosides from C-8 halogenation 24 and purine 5 0 ,8-cyclo-2 0 -deoxyribonucleosides via C-5 0 radical formation. 25 The formation of these 7,8-dihydro-8(R),5 0 -O-cyclonucleosides may be explained through an intermolecular triflyl migration from O-5 0 to N-7, never described so far.…”

3-Phenyl-5,6,7,8-tetrahydropyrimido[4,5-c]pyridazin-7-one as nucleobase substitute in DNA: synthesis of the 2′-deoxyribonucleoside, cyclonucleoside formation, and base pairing in oligonucleotides

“…10b We refer to a review covering details of the preparation of cyclonucleosides. 11 In order to shed more light on this matter we studied the formation of the 8-azapurine cyclonucleoside 8 reported by Goldman and Kalman 12 as 8 shows structural analogy to the cyclonucleoside 6 with respect to the pyrimidine and sugar moiety. We confirmed this work and collected additional data of compound 3.…”

Synthesis of purine homo-N-nucleosides modified with coumarins as free radicals scavengers*

“…The CM reaction of derivative 2a with the 4-allyloxycoumarin (8) 53 by treatment with the catalyst 5 (14 mol% in two portions) under MW irradiation resulted to the product 9 (63%). This product seems to be the E-isomer since in the 13 C-NMR spectrum the shift is only at 69.1 ppm, but nothing at 65.1 ppm as expected for the possible Z-isomer 45 .…”