Deoxynucleoside

All NRTIs, as exemplified for AZT (Fig. 7), act in a similar fashion following their uptake by the cells, they are phosphorylated successively to their 5 -monophosphate, 5 -diphosphate, and 5 -triphosphate form (De Clercq 2002). Unlike the first phosphorylation step in the metabolic pathway of the acyclic guanosine analogues (see above), which is carried out by a virus-encoded enzyme (thymidine kinase), the first as well as the subsequent phosphorylations of the 2, 3 -dideoxynucleosides are carried out by cellular enzymes, that is, a 2 -deoxynucleoside (e.g., dThd) kinase, a 2 -deoxynucleotide (e.g., dTMP) kinase, and a (2 -deoxy)nucleoside 5 -diphosphate (NDP) kinase. 

Chattopadhayaya,. An NMR conformational smdy of the complexes of C/ H double-labeled 2 -deoxynucleosides and deoxycytidine kinase (dCK)./. Chem. Soc. Perkin. 

Weinert, E. E. Rokita, S. E. Kinetic and trapping studies of 2 -deoxynucleoside alkylation by a quinone methide. Chem. Res. Toxicol. 2005, 18, 1970-1970. 

K. Mizutani, T. Electronic and structural requirements for metabolic activation of butylated hydroxytoluene analogs to their quinone methides, intermediates responsible for lung toxicity in mice. Biol. Pharm. Bull. 1997, 20, 571-573. (c) McCracken, P. G. Bolton, J. L. Thatcher, G. R. J. Covalent modification of proteins and peptides by the quinone methide from 2-rm-butyl-4,6-dimethylphenol selectivity and reactivity with respect to competitive hydration. J. Org. Chem. 1997, 62, 1820-1825. (d) Reed, M. Thompson, D. C. Immunochemical visualization and identification of rat liver proteins adducted by 2,6-di- m-butyl-4-methylphenol (BHT). Chem. Res. Toxicol. 1997, 10, 1109-1117. (e) Lewis, M. A. Yoerg, D. G. Bolton, J. L. Thompson, J. Alkylation of 2 -deoxynucleosides and DNA by quinone methides derived from 2,6-di- m-butyl-4-methylphenol. Chem. Res. Toxicol. 1996, 9, 1368-1374. 

Angle, S. R. Yang, W. Nucleophilic addition of 2 -deoxynucleosides to the o-quinone methides lO-(acetyloxy) and 10-methoxy-3,4-dihydro-9(2T/)-anthracenone. J. Org. Chem. 1992, 57, 1092-1097. 

Solomon JJ, Fedky J, Mukai F, et al. 1985. Direct alkylation of 2 - deoxynucleosides and DNA following irLviiro reaction with acrylamide. Cancer Res 45 3465- 3470. 

Deoxy-a-D-ribosyl-l-phosphate 20, a key substrate in the preparation of 2 -deoxynucleosides, was stereoselectively prepared by crystallization-induced asymmetric transformation in the presence of an excess of ortho-phosphoric acid and tri( -butyl)amine under strictly anhydrous conditions (Scheme 2).7 Initial Sn2 displacement of Cl in ot-glycosyl chloride 16 by phosphoric acid resulted in a 1 1 a/p anomeric mixture of 17 and 18 due to the rapid anomerisation of the a-chloride in polar solvents. Under acidic conditions, in the presence of an excess of H3P04, an equilibration between the a and p anomers gradually changed in favour of the thermodynamically more stable a-counterpart. By selective crystallization of the mono tri( -butyl)ammonium salt of the a-phosphate from the mixture, the equilibrium could be shifted towards the desired a-D-ribosyl phosphate 18 (oc/p = 98.5 1.5), which was isolated as bis-cyclohexylammonium salt 19 and deprotected to furnish compound 20. 

This enzyme [EC 2.7.1.77] catalyzes the reaction of a nucleotide with a 2 -deoxynucleoside to produce a nucleoside and a 2 -deoxynucleoside 5 -monophosphate. The nucleotide substrate can be substituted with phenyl phosphate and nucleoside 3 -phosphates, although they are not as effective. 

NUCLEOSIDE PHOSPHOTRANSFERASE 2 -Deoxynucleoside 5 -monophosphate, NUCLEOSIDE PHOSPHOTRANSFERASE (DEOXY)NUCLEOSIDE MONOPHOSPHATE KINASE... 

Regulation of ribonucleotide reductase by both positive feedback from ATP and negative feedback by various 2 -deoxynucleoside triphosphates (eg, dATP) is tightly coupled to the need for DNA synthesis. 

By far, 2-fluoro-2-deoxyfuranoses have been the most studied compounds. Indeed, at a structural level they are the closest analogues of 2-deoxynucleosides. Due to its electronic effect, the fluorine atom in the 2 position inhibits development of a positive charge on the anomeric carbon (which is responsible for the hydrolytic cleavage of nucleosides). In order to enhance the stability of 2-deoxynucleosides in acidic medium, and thus make oral administration of an antiviral compound easier, introduction of a fluorine atom in the 2 position is a commonly used strategy. The resulting protective effect toward proteolysis has been well demonstrated, as exemplified by the fluorinated analogues of ddl and ddA (cf. Chapter 3, Figure 3.13). However, the presence of this fluorine atoms often induces modifications in the antiviral properties of the molecule. ... 

Fluoro-2-deoxynucleosides and 3-fluoro-3-deoxynucleosides are generally prepared either by coupling between the fluorodeoxyfuranose and the base, or by fluorinating the nucleoside (the nucleophilic fluorination reactions are sometimes compatible with the presence of the base). ... 

As shown in Figure 6.5, two lipases-CalB and PS-showed a remarkable complementary selectivity toward the hydroxyl groups of different 2 -deoxynucleosides. Specifically, CalB acylated the expected C-5 OH, whereas lipase PS directed its action toward the secondary C-3 OH. In this way, several monoesters were prepared in high yields [77]. Moreover, the same selectivity was... 

ATP -I- 2 -deoxynucleoside = ADP + 2 -deoxynucleoside 5 -phosphate (<1>, compulsory ordered steady-state reaction mechanism with formation of a ternary complex with the phosphate donor and acceptor [2] the enzyme from embryonic cells of Drosophila melanogaster differs from other deoxynucleoside kinases [EC 2.7.1.76 (deoxyadenosine kinase) and EC 2.7.1.113 (deoxyguanosine kinase)] in its broad specificity for all four common deoxynucleosides)... 

An example is given in Fig. 1, where normalized total fluorescence decays are shown for 2 -deoxynucleosides and 2 -deoxynucleotides. In contrast to previous findings our work revealed that the fluorescence decays are complex and cannot be described by single exponentials. They consist of an ultrafast component (< 200 fs) and a slower one (ranging from about 0.4 ps for 2 -deoxyadenosine up to 1.4 ps in the case of 2 -deoxycytidine monophosphate). 

Fig. 1. Total fluorescence decays are shown for 2x1 O 3 M aqueous solutions of 2 -deoxynucleosides (filled circles) and 2 -deoxynucleotides (open circles) recorded at 330 nm. The excitation wavelength was 267 nm.

It is worth noting that the fluorescence decays and quantum yields are the same for 2 -deoxynucleosides and 2 -deoxynucleotides in the case of purines (dA/dAMP and dG/dGMP) while for the pyrimidines (dC/dCMP and dT/TMP), the fluorescence quantum yields of nucleotides are higher and the fluorescence decays slower as compared to those of the corresponding nucleosides. This shows that the phosphate moiety does affect the excited state relaxation to a certain extent. 

M. J. Robins, J. S. Wilson, and F. Hansske, Nucleic acid related compounds. 42. A general procedure for the efficient deoxygenation of secondary alcohols. Regiospecific and stereoselective conversion of ribonucleosides to 2 -deoxynucleosides, J. Am Chem Soc. 105 4059 (1983). 

Deoxygenation of sec-alcohols.1 2 -Deoxynucleosides (1) can be deoxygen-ated efficiently to 2 3 -dideoxynucleosides (3) by reaction with N,N -thiocarbonyl-diimidazole in DMF (80°) to form imidazolides, which on reaction with methanol are converted into methylthionocarbonates (2). These crystalline derivatives are reduced by Bu3SnH to 3. 

Table 10.4. G (base release) (unit 10-7 mol J-1) from some pyrimidine nucleosides and 2 -deoxynucleosides induced by the S04 radical [G(S04 ) = 3.3 x 10-7 mol J"1) at different dose rates pulsed electron-beam irradiation ( 6 Gy per 2 ps pulse, high dose rate) and y-irradiation (0.013 Gy s-1, low dose rate Aravindakumar et al. 2003) ...

Table 10.30. y-Radiolysis of N20/02-saturated aqueous solutions of 2 -deoxynucleosides (2 x 10-3 mol dm-3). G(base release) (unit 10-7 mol J-1) immediately after irradiation and after heating for 3h at 60 °C. (Wagner and von Sonntag, unpubl. results) ... 

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