Kenji Kitano

4′-Ethynyl Nucleoside Analogs: Potent Inhibitors of Multidrug-Resistant Human Immunodeficiency Virus Variants In Vitro

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.

Potential of 4'-C-substituted nucleosides for the treatment of HIV-1.

Extensive efforts have been made to identify nucleoside reverse transcriptase inhibitors (NRTIs). Eight NRTIs have now been approved for clinical use; however, variants of HIV-1 resistant to these antiviral agents have emerged in patients even when they are treated with combinations [highly active antiretroviral therapy (HAART)]. Thus, the development of novel compounds that are active against drug-resistant HIV-1 variants and that prevent or delay the emergence of resistant HIV-1 variants is urgently needed. Previously, 4′-C-substituted nucleosides (4′-SNs) were designed as new types of NRTIs. They were synthesized and examined as potential therapeutic agents against HIV infection. Among them, several 4′-substituted-2′-deoxynucleosides (4′-SdNs), especially those that bear an ethynyl group, were shown to be active against various laboratory and clinical HIV-1 strains including known drug-resistant variants. These results were recently reported by our collaborators. In this review, we summarize the design, synthesis and demonstrations of the anti-HIV activity of 4′-SNs, and then consider 4′-SNs as potential therapeutic agents for HIV-1.

Synthesis of 4′-C-fluoromethylnucleosides as potential antineoplastic agents

Abstract 2-Deoxy- d -erythro-, ribo-, and arabino-pentofuranosylcytosines, which have a fluoromethyl group at the 4′-position, were synthesized. Introduction of fluorine was achieved by DAST treatment of 4-C- hydoxymethyl- d -ribofuranose , the key intermediate of 4′-C-methylnucleosides. Among these nucleosides, the 2′-deoxy derivative exhibited potent antineoplastic activity in vitro.

Design, efficient synthesis, and anti-HIV activity of 4'-C-cyano- and 4'-C-ethynyl-2'-deoxy purine nucleosides.

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.

Synthesis and Biological Activities of 2′-Modified 4′-Thionucleosides

Abstract We have synthesized 4′-thioDMDC, 4′-thiogemcitabine, and 4′-thioarabinonucleosides, as potential antitumor and antiviral agents, originated from D-glucose. Biological activities of these compounds are also described.

Synthesis of 4′-C-ethynyl and 4′-C-cyano purine nucleosides from natural nucleosides and their anti-HIV activity

Abstract Purine 2′-deoxynucleosides bearing an ethynyl or a cyano group at C-4′ of the sugar moiety were synthesized from the corresponding 2′-deoxynucleosides. These compounds exhibited very potent anti-HIV activity, and remained active against drug resistant HIV strains.