Cyclonucleosides synthesis

Several examples of the synthesis of cyclonucleoside derivatives by radical ring-closure reactions are also available <1996T9496, 1999J(P1)1257, 2000T8689, 2002CBC534, 2005EJ04640>. 

M. Ikebara and H. Miki, Studies of nucleosides and nucleotides. LXXXH Cyclonucleosides. (39). Synthesis and Properties of 2 -halogeno-2 -deoxyadenosines, Chem. Pharm Butt. 26 2449 (1978). 

The formation of the cyclonucleosides shown below (for their synthesis see Ro-mieu et al. 1999b) shows that the addition of the C(5 ) radical can also add to the C(5)-C(6) Thy double bond [the corresponding Cyd case has been discussed... 

Synthesis of 2 -Deoxy-2 -oc-fluoro Pyrimidine Nucleosides via Cleavage of Cyclonucleosides... 

The synthesis of 2 -deoxy-2 -a-fluoro purine nucleosides via cleavage of purine O-cyclo-nucleosides (see Scheme 7.2) has not been reported, presumably for the following reasons [18] (i) the synthesis of purine O-cyclonucleosides is not so easy as that of pyrimidine O-cyclonucleosides (ii) the glycosyl bond of purine nucleosides is rather unstable under severe reaction conditions such as the use of HF and (iii) it is not easy to remove the... 

Ikehara, M. and Maruyama, T. (1975) Studies of nucleosides and nucleotides - LXV Purine cyclonucleosides-26 a versatile method for the synthesis of purine O-cyclo-nucleosides. The... 

Ikehara, M. and Imura, J. (1981) Studies on nucleosides and nucleotides. LXXXVII. Purine cyclonucleosides. XLII. Synthesis of 2 -deoxy-2 -fluoroguanosine. Chem. Pharm. Bull., 29, 1034-1038. 

Analogous structures were established for the 2 -deoxynucleosides.They were not oxidized by periodate18 and could be converted into cyclonucleosides,1920 thus showing the (3 configuration. In addition the ribonucleoside uridine was converted into 2 -deoxyuridine,21 obtained by deamination of the naturally occurring 2 -deoxycytidine, via 02,2 -cyclouridine,22,23 a versatile intermediate exploited in Cambridge and elsewhere for the synthesis of 3-/I-D-arabinofuranosyl uracil (spongouridine) and other nucleosides.24 This and other cyclonucleosides are capable of a remarkable number of useful transformations. 

In a report describing the synthesis of D-ribofuranose glycone-containing cyclonucleosides, Ewing et al. found potassium hydroxide in DMF... 

The oxazolinone 107, a new recoverable chiral auxiliary that gives a high level of asymmetric induction in model aldol reactions and Diels-Alder cycloadditions (in which the reactant is connected to the auxiliary by -acylation), has been synthesized from L-gulonic acid. The key step in its synthesis was the thermal intramolecular nitiene insertion shown in Scheme 21. The formation of oxazolinethiones on hydrolysis of isothiocyanato-sugar derivatives is covered in detail in Chapter 9, section 3.3. Base-catalysed reaction of StS-O-isopropylidene-D-xylofuranosylamine with P-isothiocyanato-alkanals led to tricyclic derivatives such as 108, considered as cyclonucleoside analogues. ... 

Approaches to nucleoside synthesis by additions to suitably activated N-glycosides continue to receive attention. Ribofuranosyl purines have been prepared by addition of the imidazole derivative (7) to the glycosyl iminoether (8). Both a- and /3-ribosyl hypoxanthines and the corresponding 6-thio analogues were prepared in this manner. Addition of diketene to the amino-oxazoline derivative (9) gave a cyclonucleoside which was hydrolysed to the nucleoside analogue (10). Cyclization of ribopyranosyldiaminomaleonitrile... 

Novel types of cyclonucleosides have been obtained from the 3 ,5 -0-TIPDS derivative of 2 -ketouridine. Reaction with hydroxylamine gave a mixture of E and Z-oximes together with a cyclonucleoside from which (21) could be prepared by acidic methanolysis. Reduction of the deprotected oxime to the arai ino-hydroxylamine also led to cyclization to the cyclonucleoside (22).40 a full account has been given of the synthesis of CHoOH... 

A photochemical cyclisation was used as a key step in the synthesis of a novel type of cyclonucleoside, , 5 -anhydroadenosine-8-phosphoric acid (14) (Scheme 4). ... 

OUgoribonucleotides modified in the 2 position (120-122) as well as ohgomers of cyclonucleoside phosphates (123,124) have been of interest for conformational studies. The first preparations of a-anomeric oligonucleotides were also done by solution phosphotriester synthesis (125), although solid-phase phosphoramidite chemistry was used for longer sequences. 

Ikehara, M, Uesugi, S and Shida, T. (1980) Polynucleotides. LV. Synthesis and properties of dinucleoside monophosphates derived from adenine 8,2-S- and uracil 6,2 -0-cyclonucleosides Further support for the left-handed stacking of oligonucleotides giving high-anti base torsion angles. Chem Pharm Bull. 28, 189-197... 

Nagyvary, J. (1966) Studies on the specific synthesis of the natural inter-nucleotide linkage by the use of cyclonucleosides I. The utilization of unprotected nucleotides Biochemistry 5, 1316-1322. 

M. Ikehara, A. Hasegawa, J. Imura, Studies of nucleosides and nucleotides LXXXV. Purine cyclonucleosides 41. A new synthesis of 2 -deoxy-2-fluoro-adenosine by the use of tetrahydropyranyl protecting group. J. Carbohyd. Nucleosides Nucleotides 7 131 (1980). 

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