Pyrimidine nucleoside derivatives

A similar effect occurs in the reaction of some pyrimidine nucleoside derivatives with hydroxylamine. Studies of the mechanism of this reaction with uridine derivatives340 shows that the initial point for nucleophilic attack is at C-6, and the resultant 5,6-dihydro-6-(hydroxy-amino)uridine derivative (86) is an intermediate in the conversion of the uridine derivative into the ribosylurea derivative 87 and 2-isoxazolin-5-one (88), as shown in Scheme 8. 

The use of ruthenium tetraoxide37 in a mixture of carbon tetrachloride, aqueous sodium hydrogencarbonate, and 5% aqueous sodium metaperiodate permitted the oxidation of a partially protected xylofuranosyl-adenine to the corresponding (2-keto-t/im>-pentofuranosyl)adenine,38 as well as of that of a pyrimidine nucleoside derived from L-rhamnose.39... 

III. The Structure of Pyrimidine Nucleosides Derived from Nucleic Acids.. . . 285... 

Elementary analyses indicated that the sugar moieties of pyrimidine nucleosides derived from deoxyribonucleic acid are also of the deoxypen-tosyl type. Early attempts to apply the hydrogenation procedure of Levene and LaForge60 were unsuccessful. It was generally assumed, however, that the sugar portion of the pyrimidine nucleosides of deoxyribonucleic acid is probably also of the 2-deoxy-D-ribosyl type. 

When the pyrimidine nucleoside derivative (197) was treated with potassium cyanide in iV,W-dimethylformamide, there was evidence that the totally deblocked products contained the 3-amino-3-deoxy-D-galactose nucleoside (202), as well as the 4-amino-4-deoxy-D-gulose nucleoside (199). It was suggested that the aziridine (198), formed by nitrogen participation, was a precursor of (199), and that either the oxazoline (200), formed by oxygen participation, or the anhydronucleoside (201) intervened in the formation of (202). 

Since a comprehensive summary of the vast efforts that have been expended in establishing the exact structure of the purine and pyrimidine nucleosides derived from nucleic acids has recently appeared in this Series, the details of this work will be mentioned briefly but will not be discussed here. 

Pyrimidine Nucleosides. Most of the studies of azine mercurials have been in the field of nucleosides, especially on carbosubstitution of mercurials in the 5-position in pyrimidine nucleosides derived from uracil and cytidine. 

Organomercurials are available by electrophilic substitution reactions in appropriate substrates or by metal-metal exchange reactions. Most of the studies of azine mercurials have been in the field of nucleosides, especially on carbosubstitution of mercurials in the 5-position in pyrimidine nucleosides derived from uracil and cytidine. Pyrimidine nucleosides are readily attacked by electrophiles such as Hg(II) acetate in the pyrimidine 5-position. The acetate is used for solubility reasons, but is often changed to a halide before coupling reactions <84TL2431>. 

Pyrimidines la 266,438,439 lb 32,430 Pyrimidine nucleoside derivatives lb 290 Pyrocatechol lb 170,172,185 -, 4-rerr-butyl- lb 201 Pyrocatechol derivatives lb 119 Pyrocatechol violet reagent la 398 Pyrogallol lb 383,399,400 Pyrogallol derivatives lb 312 Pyrolysis of organic substances la 92,96 a-Pyrone derivatives la 288 lb 387,388 Pyrrole lb 268,270 Pyrrole alkaloids la 66 lb 279 Pyrrole derivatives la 266.269,270 lb 63 Pyrrolidine derivatives lb 290 Pynolizidine alkaloids lb 243,246,291... 

Several factors might account for this apparent plateau elfect. Competition for phosphorylation between [ F]-FHBG and cellular thymidine is one possibility, as recently noted by Min et al. (66). Another possible cause is that tracer availability to the viral transgene was restricted in some way. For instance, [1 F]-FHBG was recently shown to accumulate much more slowly in mammalian cells expressing the wild type HSVl-tA in vitro than other radiolabeled pyrimidine nucleoside derivatives (13), and it was hypothesized that [ Fj-FHBG uptake might be limited by cell membrane transport (13). 

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