Uridine, hydrolysis

These were originally prepared by Khorana as selective protective groups for the 5 -OH of nucleosides and nucleotides. They were designed to be more acid-labile than the trityl group because depurination is often a problem in the acid-catalyzed removal of the trityl group. Introduction of p-methoxy groups increases the rate of hydrolysis by about one order of magnitude for each p-methoxy substituent. For 5 -protected uridine derivatives in 80% AcOH, 20°, the time for hydrolysis was... 

Bu4N F , THF, "2 min. The TBDS group is less reactive toward tri-ethylammonium fluoride than is the TIPDS group. It is stable to 2 M HCl, aq. dioxane, oyemight. Treatment with 0.2 MNaOH, aq. dioxane leads to cleavage of only the Si—O bond at the 5 -position of the uridine derivative. The TBDS derivative is 25 times more stable than the TIPDS derivative to basic hydrolysis. 

For 5 -protected uridine derivatives in 80% AcOH, 20°, the times for hydrolysis were as follows... 

A study comparing the half-lives for hydrolysis of a variety of esters of 5 -0-acyl-uridines gave the following results ... 

If it is desired to isolate only the pyrimidine nucleosides, hydrolysis of the nucleic acid may be carried out in acid medium.6 This process, however, entails extensive deamination of cytidine to uridine. The pyrimidine... 

Alkaline hydrolysis splits the nucleotide into its phosphate and sugar-base residues. The sugar-base is known as a nucleoside. The nucleosides are named according to the type of base present. If a purine base is present it will end -osine, e.g. adenosine, while if a pyrimidine is present the name will end -idine, e.g. uridine. 

Hampel and Burke observed that protection of hammerhead backbone sites in Mg + solutions required assembly of the full ribozyme-substrate complex. In other words, testing of ribozyme or substrate separately in the hydroxyl footprinting assay showed essentially complete hydrolysis of all nucleotides (Figure 2B of reference 56). In contrast, the fully assembled ribozyme-substrate complex showed protection of nucleotides structurally near the densely packed three-helix junction of hammerhead constructs HH16, HHal, and RNA 6. Two of the ribozyme group of protected nucleotides (Gs, Ae) are part of the conserved uridine U-turn seen in all known hammerhead constructs. (See Figures 6.10,6.11, and 6.12.) The footprinting results are collected in Table 6.5. 

This enzyme [EC S.5.4.5], also called cytidine aminohy-drolase, catalyzes the hydrolysis of cytidine to produce uridine and ammonia. 

Thie enzyme [EC 3.2.2.1], also known as inosine-uridine preferring nucleoside hydrolase and lU-nucleoside hydrolase, catalyzes the hydrolysis of an A-o-ribosylpurine to produce a purine and D-ribose. 

Mild, acidic hydrolysis of the derivative 41 gave uridine 5 -pyrophosphate, 2-acetamido-2-deoxy-D-glucose 6-phosphate, and D-galactose. Alkaline degradation leads to uridine 5 -(2-acetamido-2-deoxy-a-D-glucopyranosyl pyrophosphate) and a-D-galactopyranosyl phosphate, among other products. 

Oligosaccharide derivatives of uridine 5 -pyrophosphate are probably present in higher plants. Cellobiose and a disaccharide composed of a glucose and an arabinose were identified among products of enzymic hydrolysis of a uridine diphosphate sugar fraction from larch wood.20... 

Alkaline hydrolysis of uridine 5 - (a - D- glucopyranosyl pyrophosphate) results in the formation of uridine 5 -phosphate and a-D-glu-copyranose 1,2-cyclic phosphate24 (81). The reaction reaches completion after 30 min at 0° in concentrated aqueous ammonia, or after 2 min at 100° and pH 8.5. Partial conversion of the cyclic phosphate (81) into a-D-glucopyranosyl phosphate and D-glucose 2-phosphate occurs under conditions of elevated temperature. 

It remains unclear whether or not the rate of cleavage of the gly-cosyl bond in sugar nucleotides depends upon the structure of the nucleotide residue, and the same uncertainty is true for other reactions that affect the glycosyl group no systematic kinetic studies have been reported. However, it may be noted that there appears to be no essential difference between the rates of acidic hydrolysis of the 5 -(a-D-glucopyranosyl pyrophosphates) of uridine and N3-methyluridine, 331... 

Hydrolysis of sugar nucleotides with unspecific pyrophosphatases has already been mentioned (Section 11,1, p. 310). A similar reaction is catalyzed by a bacterial enzyme specific for adenosine 5 -(a-D-glucopyranosyl pyrophosphate).459 The specific conversion of uridine 5 -(a-D-glucopyranosyl pyrophosphate) into a-D-glucopyranosyl phosphate, uridine, and inorganic phosphate was observed with an enzyme from Escherichia colt 459,460 a preparation from Bacillus subtilis can act in a similar manner461 on different sugar nucleotides. ... 

The less basic purines generate different adducts. Both a C-8 adduct 107 and an 0-6 adduct 108 are produced in the presence of I, while the exclusive product of the reaction of A with 75n and 75o is the unique benzene imine 109. ° These purines also exhibit lower selectivity for trapping of the nitre-nium ions (Table 3). The pyrimidine nucleosides thymidine (T), uridine (U), and cytosine (C) showed negligible reactivity with these two nitrenium ions. ° The selectivity ratios for T, U, and C given in Table 3 are upper limits based on the decrease in the yield of the hydrolysis products at high nucleoside concentration (ca. 50mM). ° Since no adducts were isolated it is not clear that these selectivities represent nucleophilic trapping by the pyrimidines. 

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