Thiated derivatives of 2′,3′-dideoxy-3′-fluorothymidine: Synthesis, in vitro anti-HIV-1 activity and interaction with recombinant drug resistant HIV-1 reverse transcriptase forms

Triphosphate Prodrugs of the Anti-HIV-Active Compound 3'-Deoxy-3'-fluorothymidine (FLT)

3'-Fluoro-3'-deoxythymidine (FLT) was identified as one of the most potent inhibitors of human immunodeficiency virus (HIV) replication. However, FLT also showed severe toxicity so that it was abundant as a potential chemotherapeutic agent. Here, we describe various triphosphate prodrugs of FLT aiming for (a) a bypass of all phosphorylation steps needed to convert the nucleoside analogue into its triphosphate (TP) form, (b) an intracellular delivery of hydrolytically and enzymatically stable triphosphate derivatives, and (c) increasing the selectivity for HIV-RT vs three cellular DNA polymerases including the mitochondrial DNA polymerase γ. γ-Alkylated FLTTP compounds fulfill all of these requirements because these compounds proved highly resistant to dephosphorylation and showed strong selectivity for HIV-RT. Moreover, a prodrug form of these compounds proved to be nontoxic in CEM cells.

Enzymatic synthesis and phosphorolysis of 4(2)-thioxo- and 6(5)-azapyrimidine nucleosides by E. coli nucleoside phosphorylases

The trans-2-deoxyribosylation of 4-thiouracil (4SUra) and 2-thiouracil (2SUra), as well as 6-azauracil, 6-azathymine and 6-aza-2-thiothymine was studied using dG and E. coli purine nucleoside phosphorylase (PNP) for the in situ generation of 2-deoxy-α-D-ribofuranose-1-phosphate (dRib-1P) followed by its coupling with the bases catalyzed by either E. coli thymidine (TP) or uridine (UP) phosphorylases. 4SUra revealed satisfactory substrate activity for UP and, unexpectedly, complete inertness for TP; no formation of 2'-deoxy-2-thiouridine (2SUd) was observed under analogous reaction conditions in the presence of UP and TP. On the contrary, 2SU, 2SUd, 4STd and 2STd are good substrates for both UP and TP; moreover, 2SU, 4STd and 2'-deoxy-5-azacytidine (Decitabine) are substrates for PNP and the phosphorolysis of the latter is reversible. Condensation of 2SUra and 5-azacytosine with dRib-1P (Ba salt) catalyzed by the accordant UP and PNP in Tris∙HCl buffer gave 2SUd and 2'-deoxy-5-azacytidine in 27% and 15% yields, respectively. 6-Azauracil and 6-azathymine showed good substrate properties for both TP and UP, whereas only TP recognizes 2-thio-6-azathymine as a substrate. 5-Phenyl and 5-tert-butyl derivatives of 6-azauracil and its 2-thioxo derivative were tested as substrates for UP and TP, and only 5-phenyl- and 5-tert-butyl-6-azauracils displayed very low substrate activity. The role of structural peculiarities and electronic properties in the substrate recognition by E. coli nucleoside phosphorylases is discussed.

Synthesis of activated 3'-amino-3'-deoxy-2-thio-thymidine, a superior substrate for the nonenzymatic copying of nucleic acid templates

We present a scalable synthesis of 3'-amino-3'-deoxy-2-thio-thymidine-5'-phosphoro-2-methylimidazolide, an activated monomer that can copy adenosine residues in nucleic acid templates rapidly without a polymerase. The sulfur atom substitution enhances the rate of template copying by 5-fold compared with the 3'-amino-3'-deoxy-T monomer, while the 3'-amino monomers exhibit a 2- to 30-fold enhancement compared with their ribonucleotide counterparts.