Nucleoside cyclic 3 ,5 -phosphates, preparation

The sugar configuration about the T, 2, 3, and 4 positions can be changed by synthesis. A variety of pyrimidine nucleoside cyclic phosphates have been made. Ukita et al. (425) prepared -D-lyxo-uridine 2 3 -cyclic phosphate (Fig. 21a). The configuration about the 2 and 3 positions is inverted and the two OH groups are now cis to the base rather than trans as in the D-ribose series. No hydrolysis at all of this compound was observed in the presence of RNase. However, both the cyclic phosphate and the free 2 (3 )-nucleotides inhibit the enzyme. The... 

Silicon containing analogues of nucleoside cyclic phosphates are also readily prepared by reaction of the nucleoside with di-/-butylsilicon diesters (Equation (6)) <90CL97>. 

Other substrates for spleen exonuclease are the p-nitrophenyl esters of nucleoside-3 -phosphates and bis(p-nitrophenyl) phosphate, which is split only very slowly. These substrates are also split by enzymes having quite different natural substrates (Table I) (80-87). In fact, not only phosphodiesterases, in a broad sense, such as acid DNase, micrococcal nuclease, spleen and venom exonucleases, and cyclic phosphodiesterase but also enzymes such as nucleoside phosphoacyl hydrolase and nucleoside polyphosphatase split these substrates. As pointed out by Spahr and Gesteland (86), this may be explained by the fact that these substrates are not true diesters but rather mixed phosphoanhydrides because of the acidic character of the phenolic OH. It is evident that the use of the synthetic substrates, advocated by Razzell (3) as specific substrates for exonucleases, may be very misleading. Table II shows the distinctive characters of three spleen enzymes active on bis(p-nitrophenyl) phosphate which are present in the crude extracts from which acid exonuclease is prepared. 

It must be emphasized that much of the information on the enzyme to date comes from partially purified preparations. Even though it seems uniquely specific for nucleoside 3, 5 -cyclic phosphates, the possibility cannot be excluded that in some tissues more than one diesterase may be present. In fact, Hardman and Sutherland (64) have shown that a second 3, 5 -cyclic phosphate diesterase exists in heart muscle which is primarily specific for uridine 3, 5 -cyclic phosphate. This enzyme was found to be more sensitive to inhibition by theophylline and to activation by imidazole. Further studies are needed to clarify its precise status other such enzymes may be discovered in the future. 

Ribonucleoside 2 3 -cyclic phosphate are far more liable toward alkali and acid than are the noncyclic phospho-diesters. Hydrolysis of ribonucleoside 2 3 -cyclic phosphate produces a mixture of 2 - and 3 -phos-phates in approximately equal amoimts. Acid- and alkali-catalyzed alcoholysis of these cyclic phosphates also produces a mixture of the 2 -and 3 -alkyl phosphates, - - and the reactions are apparently reversible. " This behavior is a rather general characteristic of five-mem-bered, cyclic phosphates. [[Six-membered, cyclic phosphates, namely (25), (28), and (28a), are relatively more stable. Phosphodiesterases have been employed for the convenient preparation of specific nucleoside 2 - or 3 -phosphates by selective cleavage of a particular 0-P linkage in nucleoside 2 3 -cyclic phosphates. ... 

Cyclic phosphates of nucleosides containing sugars other than D-ribose have been prepared. Ukita and Hayatsu phosphorylated l-(5-0-benzoyl-... 

Nucleoside 5 phosphates show no tendency to isomerise, and the 2 and 3 isomers are stable under alkaline conditions. Cyclic 2, 3 ribonucleoside phosphates can be prepared from either the 2 or 3 isomers using a dehydrating agent such as dicyclohexyl dicarbodiimide. The latter reagent can be used to prepare cyclic 3, 5 nucleoside phosphates from nucleoside 5 phosphates. 

These cyclic phosphates are intermediates in the enzymic and alkaline degradation of ribonucleic acids, and may be the activated intermediates for the enzymic synthesis of ribonucleic acids from the nucleotides 175), Enzymes specific for the hydrolysis of nucleoside 2,3-cyclic phosphates to the monoesters have been prepared from snake venom, spleen, and intestinal mucosa. (See Chapter VIII.)... 

Treatment of nucleoside 5 -phosphates with sodium cyclotriphosphate gives 2 ,5 - and 3 ,5 -diphosphates and 2 ,3 -cyclic-5 -diphosphates, with the product distribution dependent on pH, reaction temperature and reaction time. 191 3, 5 -Diphosphates of labile deoxynucleosides can be prepared by the action of phosphoryl tetrakis-triazole, followed by hydrolysis.192... 

Phosphorus oxychloride is very useful in the preparation of nucleoside 5 -phosphates (eq 19) given appropriate mixtures of POCI3, pyridine, and water. The primary hydroxy (5 ) is sufficiently reactive for there to be minimal formation of cyclic phosphates at the 2,3-positions of nucleosides. The intermediate phosphorodichloridate can be converted to the corresponding triphosphate by treatment with inorganie phosphate in a convenient one-pot fashion. 

Modification other atoms or groups. Besides fluorine atoms, other atoms (such as C, N and O) and groups are also used to produce novel sugar-modified nucleoside monophosphates. 2-C-Methyl nucleosides are potential candidates with activity against Hepatitis C virus. Leisvuori et al ° prepared 3,5-cyclic phosphates (25a) and 3,5-cyclic thiophosphates (25h) of 2-C-methyl ribonucleosides as potential antiviral drugs. 

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