2-Deoxy-3’-guanosine monophosphate

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. 

Acyclovir is an acyclic guanosine derivative that requires three phosphorylation steps for activation. Conversion to the monophosphate is carried out by the virus thymidine kinase, and conversion to the di- and triphosphate is carried out by host kineases. The active nucleotide triphosphate inhibits viral replication by competing with the viral deoxy-GTP for the viral DNA polymerase. Thus, acyclovir triphosphate is inserted into the growing viral DNA, leading to irreversible chain termination. Reduced susceptibility to acyclovir is due to altered viral thymidine kinase. Because the MOA of ganciclovir is similar to that of acyclovir, HSV that is resistant to acyclovir is also resistant to ganciclovir. 

Chemical Synthesis.—Purine nucleoside 5 -monophosphates enriched with or 0 on the phosphate group are conveniently prepared by treating phosphorus pentachloride in dry triethyl phosphate with one equivalent of the appropriately labelled water to give PO]- or P 0]P0Cl3, which is not isolated but mixed with adenosine or guanosine in the same solvent. Work-up of the resulting 5 -phos-phorodichloridate in similarly labelled water permits the formation of pO]-or P 0]AMP (or GMP) in fair yield with good enrichment. The 5 -monophos-phates of the 5 -C-methyl uridines derived from 6-deoxy-D-allose and 6-deoxy-L-talose have been prepared via phosphorylation of the 2, 3 -0,0-ethoxymethyl-idene derivative of the nucleosides (1) with -cyanoethyl phosphate and DCC or TPS-Cl. The same method has been used to phosphorylate iV -benzoylated 2, 3 -0,C -isopropylidene derivatives of various 5 -C-alkyladenosine species (2) and also 4 -allyladenosine (3) as part of a study in which derivatives of AMP... 

Nucleosides. Nucleotides, and Derivatives.- 2, 3 ,5 -Trl-0 -acetyl-adenosine and -guanosine, 4- -ethyl-thymidlne, N -methyl-2 -deoxyadenoslne, 5-raethoxymethyl-2 -deoxy-urldlne and its 0-D-threo-isomer, 5-fluoroarablnosylcytoslne, the 2 -deoxynucleo-side (17), cls-thymldine 3 ,5 -cyclic methyl phosphonate and the corresponding 3, 5 -cycllc N,N-dlmethylphosphoramldate,a cobalt(II) complex with 2 -deoxyinosine 5 -monophosphate,... 

Generally, UV absorption spectra can be utilized to determine the family to which an unknown base, nucleoside, or nucleotide belongs. Indeed, the chro-mophore of the nucleosides or nucleotides is typical of the purine or pyrimidine structvu-e, with different maximum absorption wavelengths in the adenosine, guanosine, cytosine, or thymidine series. For example, it is possible to differentiate readily the UV absorption spectra of guanosine (G), G-monophosphate (GMP), deoxy GMP (dGMP), G-diphosphate (GDP), and G-triphosphate (GTP), from those of adenosine (A), AMP, dAMP, ADR, and ATP. 

Closely related to ATP, and present in biological systems, are a number of other nucleoside triphosphates and their corresponding diphosphates and monophosphates. These are uridine triphosphate (UTP), cytidine triphosphate (CTP), guanosine triphosphate (GTP), and thymidine triphosphate (TTP), all of which have about the same free energy of hydrolysis as ATP (11.29). In addition there are the deoxy nucleoside triphosphates (Chapter 10.4). 

There have been a number of reports on phosphonate analogues of nucleoside monophosphates, including a further paper on 2, 3 -dideoxy-3 -phosphonomethyl analogues (see Vol. 18, p.203) which reports the guanosine compound (176) for the first time.23i Phosphonoformate esters of anti-HIV nucleosides, such as (177), have been prepared,232 as has the 5 -0-phosphonomethyl compound (178), by alkylation of the unsaturated nucleoside, protection of the uracil NH being necessary.23 3 xhe isosteric phosphonates of type (179) have also been made, as outlined in Scheme 23, with the unsaturated thymidine member being a potent antiretroviral agent.234,235 x e phosphonomethyl derivative (180) of 3 -deoxy-3 -... 

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