Phosphorylation, nucleosides

The RNA world hypothesis caused prebiotic phosphate chemistry to become an attractive research area again unfortunately, no clear evidence for a realistic nucleotide synthesis under the simplified conditions of a primitive Earth has yet appeared. Important work on nucleoside phosphorylation has, however, been done. It is important to distinguish between ... 

Following phosphorylation using the Yoshikawa procedure, the reaction of pyrophosphate with the intermediate phosphorodichloridate followed by aqueous work-up provides a convenient one-pot synthesis for triphosphates. With slight modification to this procedure, thiophosphoryl chloride can be used in place of phosphoryl chloride to give 5 -( 1 -thio)triphosphates as a mixture of two diaste-reoisomers (.S p and Rp). Both procedures require the prior preparation of the DMF-soluble, bis(tri-n-butylammonium) salt of pyrophosphate. This is prepared as a 0.5 M solution, can be stored in the fridge and is converted to its terrafcis(tri-n-butylammonium) salt immediately prior to reaction. Rates of nucleoside phosphorylation vary considerably and it is necessary to monitor the formation of the phosphorodichloridate during the Yoshikawa procedure in order... 

Ponnamperuma C, Mack R. Nucleotide Synthesis under Possible Primitive Earth Conditions. Science 1965 48 1221-1223. Lohrmann R, Orgel LE. Urea-inorganic phosphate mixtures as prebiotic phosphorylating agents. Science 1971 171 490-494. Reimann R, Zubay G. Nucleoside phosphorylation a feasible step in the prebiotic pathway to RNA. Orig. Life Evol. Biosph. 1999 29 229-247. 

Greenberg, N., Schumm, D.E., and Wehh, T.E. (1977) Uridine kinase activities and pyrimidine nucleoside phosphorylation in fluoropyrimidine-sensitive and -resistant cell lines of the Novikoff hepatoma. The Biochemical Journal, 164 (2), 379-387. 

Use of PC13 for the phosphonylation of nucleosides Phosphorylation of ribonudeosides with phosphorus trichloride (a) Honjo, M., Marumoto,... 

Nucleotidyltransferases are all enzymes that catalyze the simple transfer of a nucleoside phosphoryl group from a donor substrate to an acceptor. They differ... 

Acetylation of hydroxyl groups and esterification of carboxyl groups have been observed ia a limited number of cases but, ia geaeral, have ao preparative advantage over chemical methods. By comparison, phosphorylation has been useful ia the preparatioa of modified purine and pyrimidine mononucleotides from their corresponding nucleosides, eg, 6-thioguanosiae [85-31-4] (51) (97). 

Showdomycin. Showdomycin (2-p-D-ribofuranosyhnaleimide) (7) is a maleimide C-nucleoside antibiotic synthesi2ed by S. showdoensis-, isoshowdomycin (8) and maleimycin (9) have also been isolated (1—6). Showdomycin is not phosphorylated by nucleoside kinase and is not a substrate for nucleoside phosphorylase. Once (7) enters the cell, it blocks the uptake of glucose and other nutrients. 

Amino-5-iodo-2, 5 -dideoxyuridine [56045-73-9] (13) C2H22IN2O4, was synthesized ia 1975 (27) and was found effective against herpes keratitis ia rabbits (28). This compound is markedly less cytotoxic than IdU, iadicating that it may have a safer and more specific mode of antiviral activity. A potential limitation of this group of nucleosides is their specificity, for they fail to inhibit all strains of herpes vimses. The specific antiviral activity of (13) is considered to be a result of the incorporation of the 5 -Ai-phosphate into both viral and host DNA in infected cells, but not into the DNA of normal cells. Phosphorylation of (13) occurs only in herpes vims-infected cells, brought about by a vims-induced thymidine kinase (29). 

Basically, AZT is anabohcaHy phosphorylated to AZT mono-, di-, and tri-phosphates by various enzymes (kinases) of a target ceU (159). AZT-triphosphate competes with other phosphorylated pyrimidine nucleosides for incorporation into HIV DNA by the viral reverse transcriptase. Incorporation of the AZT-triphosphate into reverse transcriptase results in viral DNA chain termination. Reverse transcriptase is essential in the repHcative cycle of HIV. 

Another dideoxypyrimidine nucleoside active against human immunodeficiency vims is 3 -azido-2/3 -dideoxyuridine [84472-85-5] (AZDU or CS-87, 64) C H N O. Since its synthesis, (167) CS-87 has been identified as a promising antiHIV agent (168) and is currentiy undergoing phase I clinical trials in patients with AIDS and AIDS-related complex. It appears to be less potent than AZT against HIV in a peripheral blood mononuclear (PBM) cell screening system and in MT-4 cell lines. This lower activity in PBM cells appears to be related to a lower affinity of CS-87 for the enzyme responsible for its initial phosphorylation (169). However, CS-87 has significantly lower toxicity on bone marrow cells than AZT (170) and penetration of the CNS as a 5 -dihydropyridine derivative. 

Decitabine (5-aza-deoxycytosine) is an analog of the nucleoside 2 -deoxycytidine. It is believed to exert its antineoplastic effects after phosphorylation and direct incorporation into DNA and by inhibition of the enzyme DNA methyltransferase, causing hypomethylation of DNA and cellular differentiation or apoptosis. DNA hypomethylation is achieved at concentrations below those required to significantly inhibit DNA synthesis, which may promote restoration of function to genes associated with control of cellular differentiation and proliferation. Cytotoxicity in rapidly dividing cells may also result from covalent adducts between DNA methyltransferase and decitabine. 

Tli is immunosuppressive drug, which is only marketed in Japan, is a nucleoside analog. Its phosphorylated form, mizoribine-5-phosphate, is a potent inhibitor of IMPDH activity. 

From this observation of the inhibition by adenosine, and other observations, Newell and Tucker suspected the existence of a common synthetic pathway for adenosine and thiamine, and proved (with the help of a collection of mutants) that the bifurcation occurred after the 5-amino- l-(P-D-ribofura-nosyl)imidazole 5 -phosphate (46) step (Scheme 23). Finally, they found that 5-amino-l-(0-D-ribofuranosyl)imidazole (47), labeled with l4C in the imidazole ring, was incorporated into pyramine without significant loss of molar radioactivity by a mutant that is able to use this nucleoside (presumably after phosphorylation).53,54... 

However, acyclic nucleotide analogs (acyclic nucleoside phosphonates) have been developed, which carry one phosphonate moiety and require only the two subsequent phosphorylation steps (De Clercq et al. 1978). Independent of virus-encoded kinases, they display a broader spectrum of efficacy. This class comprises important drugs against HIV (tenofovir) and HBV (adefovir, tenofovir), as well as cidofovir, which is approved for use against CMV retinitis, but also displays an exceptionally broad efficacy profile against many herpesviruses, adenovirus, poxviruses, and papillomaviruses (De Clercq and Holy 2005). 

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