No abstract

A series of 4′-ethynyl (4′-E) nucleoside analogs were designed, synthesized, and identified as being active against a wide spectrum of human immunodeficiency viruses (HIV), including a variety of laboratory strains of HIV-1, HIV-2, and primary clinical HIV-1 isolates. Among such analogs examined, 4′-E-2′-deoxycytidine (4′-E-dC), 4′-E-2′-deoxyadenosine (4′-E-dA), 4′-E-2′-deoxyribofuranosyl-2,6-diaminopurine, and 4′-E-2′-deoxyguanosine were the most potent and blocked HIV-1 replication with 50% effective concentrations ranging from 0.0003 to 0.01 μM in vitro with favorable cellular toxicity profiles (selectivity indices ranging 458 to 2,600). These 4′-E analogs also suppressed replication of various drug-resistant HIV-1 clones, including HIV-1M41L/T215Y, HIV-1K65R, HIV-1L74V, HIV-1M41L/T69S-S-G/T215Y, and HIV-1A62V/V75I/F77L/F116Y/Q151M. Moreover, these analogs inhibited the replication of multidrug-resistant clinical HIV-1 strains carrying a variety of drug resistance-related amino acid substitutions isolated from HIV-1-infected individuals for whom 10 or 11 different anti-HIV-1 agents had failed. The 4′-E analogs also blocked the replication of a non-nucleoside reverse transcriptase inhibitor-resistant clone, HIV-1Y181C, and showed an HIV-1 inhibition profile similar to that of zidovudine in time-of-drug-addition assays. The antiviral activity of 4′-E-thymidine and 4′-E-dC was blocked by the addition of thymidine and 2′-deoxycytidine, respectively, while that of 4′-E-dA was not affected by 2′-deoxyadenosine, similar to the antiviral activity reversion feature of 2′,3′-dideoxynucleosides, strongly suggesting that 4′-Eanalogs belong to the family of nucleoside reverse transcriptase inhibitors. Further development of 4′-E analogs as potential therapeutics for infection with multidrug-resistant HIV-1 is warranted.

We examined the intracytoplasmic anabolism and kinetics of antiviral activity against human immunodeficiency virus type 1 (HIV-1) of a nucleoside reverse transcriptase inhibitor, 4-ethynyl-2-fluoro-2-deoxyadenosine (EFdA), which has potent activity against wild-type and multidrug-resistant HIV-1 strains. When CEM cells were exposed to 0.1 M

4'-C-Ethynyl-beta-D-arabino- and 4'-C-ethynyl-2'-deoxy-beta-D-ribo-pentofuranosylpyrimidine and -purine nucleosides were synthesized and evaluated for their in vitro anti-HIV activity. The key intermediate, 4-C-ethynyl- or 4-C-triethylsilylethynyl-D-ribo-pentofuranose, was prepared from D-glucose and glycosidated with various pyrimidine or purine bases. The arabinopyrimidine derivatives were prepared from the corresponding ribo derivatives via O(2),2'-anhydro nucleosides. The 2'-deoxy-ribo derivatives were synthesized by radical reduction of 2'-bromo or 2'- phenoxythiocarbonyloxy nucleosides. Among these 4'-C-ethynyl nucleosides, seven analogues proved to be potent against HIV-1 in vitro with EC(50) values ranging from 0.0003 to 0. 03 microM. These compounds also exerted activity against clinical and multi-dideoxy-nucleoside-resistant HIV-1 strains with comparable EC(50) values. Three such 4'-C-ethynyl-2'-deoxypurine analogues including 4'-C-ethynyl-2'-deoxyadenosine and 4'-C-ethynyl-2, 6-diamino-2'-deoxypurine were less cytotoxic [selectivity indices (SIs): 975-2733] than three 4'-C-ethynyl-2'-deoxycytidine analogues (SIs: 63-363). 4'-C-Ethynyl-5-fluoro-2'-deoxycytidine was least toxic (SI: >3333) and potent against all HIV strains tested.

4-Ethynyl

Certain nucleoside/nucleotide reverse transcriptase (RT) inhibitors (NRTIs) are effective against HIV-1 and HBV. However, both viruses often acquire NRTI resistance, making it crucial to develop more potent agents that offer profound viral suppression. We report here that 4′-C-cyano-2-amino-2′-deoxyadenosine (CAdA) is a novel highly potent inhibitor of both HBV (IC50=0.4 nM) and HIV-1 (IC50=0.4 nM). In contrast, the approved anti-HBV NRTI entecavir (ETV) potently inhibits HBV (IC50=0.7 nM) but is much less active against HIV-1 (IC50=1,000 nM). Similarly, the highly potent HIV-1 inhibitor 4′-ethynyl-2-fluoro-2′-deoxyadenosine (EFdA) (IC50=0.3 nM) is less active against HBV (IC50=160 nM). Southern analysis using Huh-7 cells transfected with HBV-containing plasmids demonstrated that CAdA was potent against both wild-type (IC50=7.2 nM) and ETV-resistant HBV (IC50=69.6 nM for HBVETV-RL180M/S202G/M204V), whereas ETV failed to reduce HBVETV-RL180M/S202G/M204V DNA even at 1 μM. Once daily peroral administration of CAdA reduced HBVETV-RL180M/S202G/M204V viremia (p=0.0005) in human-liver-chimeric/HBVETV-RL180M/S202G/M204V-infected mice, while ETV completely failed to reduce HBVETV-RL180M/S202G/M204V viremia. None of the mice had significant drug-related body-weight or serum human-albumin concentration changes. Molecular modeling suggests that a shallower HBV-RT hydrophobic pocket at the polymerase active site can better accommodate the slightly shorter 4′-cyano of CAdA-triphosphate (TP), but not the longer 4′-ethynyl of EFdA-TP. In contrast, the deeper HIV-1-RT pocket can efficiently accommodate the 4′-substitutions of both NRTIs. The ETV-TP’s cyclopentyl ring can bind more efficiently at the shallow HBV-RT binding pocket. Conclusion: These data provide insights on the structural and functional associations of HBV- and HIV-1-RTs and show that CAdA may offer new therapeutic options for HBV patients.

Some 4'-C-ethynyl-2'-deoxy purine nucleosides showed the most potent anti-HIV activity among the series of 4'-C-substituted 2'-deoxynucleosides whose 4'-C-substituents were methyl, ethyl, ethynyl and so on. Our hypothesis is that the smaller the substituent at the C-4' position they have, the more acceptable biological activity they show. Thus, 4'-C-cyano-2'-deoxy purine nucleosides, whose substituent is smaller than the ethynyl group, will have more potent antiviral activity. To prove our hypothesis, we planned to develop an efficient synthesis of 4'-C-cyano-2'-deoxy purine nucleosides (4'-CNdNs) and 4'-C-ethynyl-2'-deoxy purine nucleosides (4'-EdNs). Consequently, we succeeded in developing an efficient synthesis of six 2'-deoxy purine nucleosides bearing either a cyano or an ethynyl group at the C-4' position of the sugar moiety from 2'-deoxyadenosine and 2,6-diaminopurine 2'-deoxyriboside. Unfortunately, 4'-C-cyano derivatives showed lower activity against HIV-1, and two 4'-C-ethynyl derivatives suggested high toxicity in vivo.

Working hypotheses to solve the critical problems of the existing highly active anti-retroviral therapy were proposed. The study based on the hypotheses proved the validity of the hypotheses and resulted in the development of 2'-deoxy-4'-C-ethynyl-2-fluoroadenosine, a nucleoside reverse transcriptase inhibitor, with highly potent activity against all HIV-1, very favorable toxic profiles, and stability in plasma. The nucleoside will prevent or delay the emergence of drug-resistant HIV-1 variants and be an ideal therapeutic agent for both HIV-1 and HBV infections.