Stereoselective synthesis of novel 4′-methylsulfanyl-pyrimidine ribonucleosides by means of nucleophilic substitution of the 4′-benzoyloxy leaving group
Kazuhiro Haraguchi; Yasuaki Kimura; Hiroshi Abe; Hiroki Kumamoto; Hiromichi Tanaka
Tetrahedron, Jul. 2025, [Reviewed]

Deviated binding of anti-HBV nucleoside analog E-CFCP-TP to the reverse transcriptase active site attenuates the effect of drug-resistant mutations
Yoshiaki Yasutake; Shin-ichiro Hattori; Hiroki Kumamoto; Noriko Tamura; Kenji Maeda; Hiroaki Mitsuya
Scientific Reports, 08 Jul. 2024, [Reviewed]
Abstract

While certain human hepatitis B virus-targeting nucleoside analogs (NAs) serve as crucial anti-HBV drugs, HBV yet remains to be a major global health threat. E-CFCP is a 4′-modified and fluoromethylenated NA that exhibits potent antiviral activity against both wild-type and drug-resistant HBVs but less potent against human immunodeficiency virus type-1 (HIV-1). Here, we show that HIV-1 with HBV-associated amino acid substitutions introduced into the RT’s dNTP-binding site (N-site) is highly susceptible to E-CFCP. We determined the X-ray structures of HBV-associated HIV-1 RT mutants complexed with DNA:E-CFCP-triphosphate (E-CFCP-TP). The structures revealed that exocyclic fluoromethylene pushes the Met184 sidechain backward, and the resultant enlarged hydrophobic pocket accommodates both the fluoromethylene and 4′-cyano moiety of E-CFCP. Structural comparison with the DNA:dGTP/entecavir-triphosphate complex also indicated that the cyclopentene moiety of the bound E-CFCP-TP is slightly skewed and deviated. This positioning partly corresponds to that of the bound dNTP observed in the HIV-1 RT mutant with drug-resistant mutations F160M/M184V, resulting in the attenuation of the structural effects of F160M/M184V substitutions. These results expand our knowledge of the interactions between NAs and the RT N-site and should help further design antiviral NAs against both HIV-1 and HBV.

Regio- and Stereoselective Synthesis of 2′-Deoxy-4′-thioguanine Nucleosides: Evaluation of Anti-Hepatitis B Virus Activity and ­Cytotoxicity Leading to Improved Selectivity Index by 4′-C-Cyanation
Kazuhiro Haraguchi; Hiroki Kumamoto; Shuhei Imoto; Nobuyo Kuwata-Higashi; Hiroaki Mitsuya
Synlett, 05 Dec. 2023, [Reviewed]
Abstract

An N 9-regio- and β-anomer-selective 4′-thioglycosidation of purine bases has been developed. The reaction between a 2-deoxy-2-iodo-4-thioribofuranosyl glycosyl donor and N-(6-chloro-9H-purin-2-yl)-2-methylpropanamide gave the corresponding 2′-deoxy-4′-thiopurine nucleoside in 87% yield along with its N 7-regioisomer in 6% yield, without the formation of the α-anomer. By using a derivative obtained from 17, a practical chemical synthesis of 2′-deoxy-4′-thioguanosine was developed. 4′-α-C-Cyano-2′-deoxy-4′-thioguanosine was synthesized, starting from a 4-(acetoxymethyl)-2-deoxy-2-iodo-4-thioribofuranose derivative as a glycosyl donor. An evaluation of the anti-hepatitis B virus (HBV) activity and the cytotoxicity toward the host cell revealed that 4'-C-cyano-2'-deoxy-4'-thioguanosine exhibited about 100 times more potent anti-HBV activity than 2′-deoxy-4′-thioguanosine with a comparative cytotoxicity, resulting in the identification of a novel molecule having better selectivity index value than that of 2′-deoxy-4′-thioguanosine. This finding might provide a guideline for the development of the next generation of anti-HBV agents.

A Novel Anti-HBV Agent, E-CFCP, restores Hepatitis B virus (HBV)-induced Senescence-associated Cellular Markers Perturbation in Human Hepatocytes.
Yuki Takamatsu; Sanae Hayashi; Hiroki Kumamoto; Shuhei Imoto; Yasuhito Tanaka; Hiroaki Mitsuya; Nobuyo Higashi-Kuwata
Virus research, 16 Mar. 2023, [Reviewed]
Cellular senescence is a cellular state with a broad spectrum of age-related physiological conditions that can be affected by various infectious diseases and treatments. Therapy of hepatitis B virus (HBV) infection with nucleos(t)ide analogs (NAs) is well established and benefits many HBV-infected patients, but requires long-term, perhaps lifelong, medication. In addition to the effects of HBV infection, the effects of NAs administration on hepatocellular senescence are still unclear. This study investigated how HBV infection and NAs treatment influence cellular senescence in human hepatocytes and humanized-liver chimeric mice chronically infected with live HBV. HBV infection upregulates or downregulates multiple cellular markers including senescence-associated β-galactosidase (SA-β-Gal) activity and cell cycle regulatory proteins (e.g., p21CIP1) expression level in hepatocellular nuclei and humanized-mice liver. A novel highly potent anti-HBV NA, E-CFCP, per se did not have significant disturbance on markers evaluated. Besides, E-CFCP treatment restored HBV-infected cells as physiological phenotypes that are comparable to the HBV-uninfected cells. The results reported here demonstrate that, regardless of the mechanism(s), chronic HBV infection perturbates multiple senescence-associated markers in human hepatocytes and humanized-mice liver, but E-CFCP can restore this phenomenon.

Synthesis of novel entecavir analogues having 4′-cyano-6′′-fluoromethylenecyclopentene skeletons as an aglycone moiety as highly potent and long-acting anti-hepatitis B virus agent
Hiroki Kumamoto; Nobuyo Higashi-Kuwata; Sanae Hayashi; Debananda Das; Haydar Bulut; Ryoh Tokuda; Shuhei Imoto; Kengo Onitsuka; Yuka Honda; Yuki Odanaka; Satoko Shimbara-Matsubayashi; Kazuhiro Haraguchi; Yasuhito Tanaka; Hiroaki Mitsuya
RSC Advances, 2023, [Reviewed]
Encouraged by our recent findings that 4′-cyano-deoxyguanosine (2), entecavir analogues 4 and 5 are highly potent anti-hepatitis B virus (HBV) agents, we designed and synthesized 6 having a hybridized structure of 4 and 5.

DAST-Mediated Fluorination of 1-[4-Thio-β-d-arabinofuranosyl]uracil: Investigation of Thiolane vs Thietane Formation and Stereoselective Synthesis of 4′-ThioFAC
Kazuhiro Haraguchi; Noyori Hannda; Mizuki Wakasugi; Madoka Maruyama; Hirokazu Ishii; Daisuke Nagano; Hiroki Kumamoto
Synthesis, 23 Sep. 2022, [Reviewed]
Abstract

The unprecedented DAST-mediated (DAST = diethylaminosulfur trifluoride) deoxygenative fluorination of benzoyl-, TBDPS-, and Bn-protected 1-(β-d-4-thioarabinofuranosyl)uracil at the sugar portion was examined. Three kinds of nucleoside (Ns) products were formed: target thiolane Ns, ring-contracted thietane Ns, and anhydro Ns products. The reaction pathway was determined by the electronic effect of the protecting groups at the sugar and base moieties. The benzoylated uracil starting material gave the 2,2′-anhydronucleoside (anhydro Ns) as a major product, whereas the silylated and benzylated starting materials furnished the corresponding fluorinated products, in which the ring-contracted thietanes predominantly formed. The desired thiolane Ns could be obtained as major product by the addition of a pyridine derivative as an additive. Upon reacting N 3-benzoylated 1-(β-d-4-thioarabinofuranosyl)uracil with DAST in the presence of 2,4,6-collidine, the target 2′-deoxy-2′-β-fluoro-4′-thiouracil nucleoside could be obtained in 72% isolated yield along with the corresponding thietane Ns (7%) and anhydro Ns (3%) (thiolane Ns/thietane Ns/anhydro Ns = 10.3:1.00:0.43), with recovery of the starting material (12%). In this study, the first stereoselective synthesis of the β-anomer of 1-(2-deoxy-2-fluoro-4-thio-β-d-arabino-pentofuranosyl)cytosine (4′-thioFAC) has been developed.

4-Thiofuranoid Glycal: Versatile Glycosyl Donor for the Selective Synthesis of β-anomer of 4'-thionucleoside and its Biological Activities.
Kazuhiro Haraguchi; Hiroki Kumamoto; Hiromichi Tanaka
Current medicinal chemistry, 2022, [Reviewed]
The first highly diastereoselective synthesis of β-anomers of 4'-thionucleosides has been carried out by means of electrophilic glycosidation utilizing 3,5-O-(di-tertbutylsilylene) (DTBS)-4-thiofuranoid glycal as a glycosyl donor. The resulting glycosides were transformed into ribo-, 2'-deoxy-, and arabinofuranosyl nucleosides through a chemical transformation of the 2'-substituent. The additive Pummerer reaction of the glycal Soxide gave 1,2-di-O-acetyl-3,5-O-DTBS-4-thioribofuranose. The utility of the DTBSprotected 4-thioribofuranose has been demonstrated by the preparation of 4'-thio analogues of pyrimidine- and purine-4'-thioribonucleosides based on the Vorbrüggen glycosidation. Synthesis of 4'-thio-counterpart of C-nucleoside antibiotic tiazofurin has also been carried out. α-Face selective hydroboration of 1-C-aryl- or 1-C-heteroaryl-glycals obtained by cross-coupling of 1-tributylstannylglycal has furnished the respective β- anomer of 4'-thio-C-ribonucleosides, including 4'-thio analogue of nucleoside antibiotic pseudouridine and 9-deazaadenosine. On the basis of lithiation chemistry, 1-C- and 2-Ccarbon- carbon-substituted 3,5-O-(1,1,3,3-tetraisopropyldisiloxane-1,3- diyl) (TIPDS)- 4- thiofuranoid glycal were synthesized. These glycals enabled us to prepare 1'-C- and 2'-β- C-carbon-substituted 2'-deoxy-4'-thionucleosides, including thio-counterpart of antitumor nucleoside antibiotic angustmycin C. Furthermore, 1'-C-methyl-4'-thiothymidine emerged as a potent inhibitor of angiogenesis. In addition, 1'-C-methyl-4'-thiothymidine exhibited more potent inhibitory activity against thymidine kinase-deficient mutant of herpes virus than that of ganciclovir. Among the 4'-substituted 4'-thiothymidines, the 4'- C-cyano- and 4'-C-ethynyl derivatives inhibited replication of HIV variant resistant to 3TC (HIVM184V) as potently as HIV-1IIIB. In terms of the value of selectivity index (SI), 4'-C-cyano-4'-thiothymidine showed a 3-fold selective index (SI) than that of the corresponding thymidine derivative. Furthermore, 4'-C-ethynyl-2'-deoxy-4'-thioguanosine has a 20-fold better value (>18,200) than that of 2'-deoxyguanosine counterpart (933). Furthermore, 4'-azido-4'-thiothymidine emerged as a selective and potent anti-EBV agent. In terms of antineoplastic activity, 4'-azido- and 4'-C-fluoromethyl-2'-deoxy-4'-thiocytidine inhibited proliferation of human B-cell (CCRF-SB) and T-cell leukemia (Molt-4) cell lines, although the parent compound 2'-deoxy-4'-thiocytidine did not exhibit any cytotoxicity up to 100 μM. These facts concerning the biological activities suggested that replacement of the furanose oxygen with a sulfur atom is a promising approach for the development of less toxic antiviral and antineoplastic nucleoside antimetabolites. 4'- Thionucleoside also acts as a monomer for oligonucleotides (ONs) therapeutics, exhibiting superior biological properties. Therefore, this review provides a wide range of potential monomers for antisense ON and siRNA.

Identification of a novel long-acting 4'-modified nucleoside reverse transcriptase inhibitor against HBV.
Nobuyo Higashi-Kuwata; Sanae Hayashi; Hiroki Kumamoto; Hiromi Ogata-Aoki; Debananda Das; David Venzon; Shin-Ichiro Hattori; Haydar Bulut; Mai Hashimoto; Masaki Otagiri; Nobutoki Takamune; Naoki Kishimoto; David A Davis; Shogo Misumi; Masakazu Kakuni; Yasuhito Tanaka; Hiroaki Mitsuya
Journal of hepatology, May 2021, [Reviewed]
BACKGROUND & AIMS: While certain nucleos(t)ide reverse transcriptase inhibitors (NRTIs) are efficacious in treating HBV infection, their effects are yet to be optimized and the emergence of NRTI-resistant HBV variants is an issue because of the requirement for lifelong treatment. The development of agents that more profoundly suppress wild-type and drug-resistant HBVs, and that have a long-acting effect, are crucial to improve patient outcomes. METHODS: Herein, we synthesized a novel long-acting 4'-modified NRTI termed E-CFCP. We tested its anti-HBV activity in vitro, before evaluating its anti-HBV activity in HBV-infected human-liver-chimeric mice (PXB-mice). E-CFCP's long-acting features and E-CFCP-triphosphate's interactions with the HBV reverse transcriptase (HBV-RT) were examined. RESULTS: E-CFCP potently blocked HBVWTD1 production (IC50qPCR_cell=1.8 nM) in HepG2.2.15 cells and HBVWTC2 (IC50SB_cell=0.7 nM), entecavir (ETV)-resistant HBVETV-RL180M/S202G/M204V (IC50SB_cell=77.5 nM), and adefovir-resistant HBVADV-RA181T/N236T production (IC50SB_cell=14.1 nM) in Huh7 cells. E-CFCP profoundly inhibited intracellular HBV DNA production to below the detection limit, but ETV and tenofovir alafenamide (TAF) failed to do so. E-CFCP also showed less toxicity than ETV and TAF. E-CFCP better penetrated hepatocytes and was better tri-phosphorylated; E-CFCP-triphosphate persisted intracellularly for longer than ETV-triphosphate. Once-daily peroral E-CFCP administration over 2 weeks (0.02~0.2 mg/kg/day) reduced HBVWTC2-viremia by 2-3 logs in PXB-mice without significant toxicities and the reduction persisted over 1-3 weeks following treatment cessation, suggesting once-weekly dosing capabilities. E-CFCP also reduced HBVETV-RL180M/S202G/M204V-viremia by 2 logs over 2 weeks, while ETV completely failed to reduce HBVETV-RL180M/S202G/M204V-viremia. E-CFCP's 4'-cyano and fluorine interact with both HBVWT-RT and HBVETV-RL180M/S202G-M204 -RT via Van der Waals and polar forces, being important for E-CFCP-triphosphate's interactions and anti-HBV potency. CONCLUSION: E-CFCP represents the first reported potential long-acting NRTI with potent activity against wild-type and treatment-resistant HBV. LAY SUMMARY: Although there are currently effective treatment options for HBV, treatment-resistant variants and the need for lifelong therapy pose a significant challenge. Therefore, the development of new treatment options is crucial to improve outcomes and quality of life. Herein, we report preclinical evidence showing that the anti-HBV agent, E-CFCP, has potent activity against wild-type and treatment-resistant variants. In addition, once-weekly oral dosing may be possible, which is preferrable to the current daily dosing regimens.

Design and Synthesis of 4'-Cyano Dideoxy Isonucleosides and Their Activity against HIV-1 and HBV
Shuhei Imoto; Kengo Onitsuka; Kakeru Yamaguchi; Ryoh Tokuda; Nobuyo Higashi-Kuwata; Shunsuke Kuwahara; Hiroki Kumamoto; Kenji Maeda; Kazuhiro Haraguchi; Hiroaki Mitsuya
HETEROCYCLES, 2020, [Reviewed]

An alternative method for the synthesis of 2'-halogeno-1',2'-unsaturated uridine derivatives through syn-elimination of pivalic acid of 2'-halogeno- 2'-deoxy-1'-pivaloyloxyuracil nucleoside: preparation of its 2'-C-branched nucleosides.
Kazuhiro Haraguchi; Eisen Gen; Hiroki Kumamoto; Yoshiharu Itoh; Hiromichi Tanaka
Nucleosides, nucleotides & nucleic acids, 2020, [Reviewed]
An alternative method for the preparation of 2'-bromo- (5b) and 2'-iodo- (5c) 1',2'-unsaturated uracil nucleosides has been developed. The protocol was on the basis of the syn-elimination of pivalic acid from 2'-bromo-(7a,b) and 2'-iodo-(9a,b) 1'-pivaloyloxy-2'-deoxyuridine derivatives, which were derived from the halo-pivaloyloxylation of 3',5'-bis-O-TBDMS-1',2'-unsaturated uridine 1. Compounds 5b and 5c were shown to serve as versatile synthons for the respective 2'-C-branched 1',2'-unsaturated uracil nucleosides, through palladium-catalyzed cross-coupling or halogen-lithium exchange reactions.

Synthesis and evaluation of the anti-hepatitis B virus activity of 4'-Azido-thymidine analogs and 4'-Azido-2'-deoxy-5-methylcytidine analogs: structural insights for the development of a novel anti-HBV agent.
Kengo Onitsuka; Ryoh Tokuda; Nobuyo Kuwata-Higashi; Hiroki Kumamoto; Manabu Aoki; Masayuki Amano; Satoru Kohgo; Debananda Das; Kazuhiro Haraguchi; Hiroaki Mitsuya; Shuhei Imoto
Nucleosides, nucleotides & nucleic acids, 2020, [Reviewed]
Hepatitis B virus (HBV) infection is a major worldwide health problem that requires the development of improved antiviral therapies. Here, a series of 4'-Azido-thymidine/4'-Azido-2'-deoxy-5-methylcytidine derivatives (6, 10-15) were synthesized, and their anti-HBV activities evaluated. Compounds 10-15 were synthesized via an SNAr reaction of 18, in which the 4-position of the thymine moiety was activated as the 2,4,6-triisopropylbenzenesulfonate. Compounds 11-15 showed no antiviral activity. However, 4'-Azido thymidine (6) and 4'-Azido-2'-deoxy-5-methylcytidine (10) displayed significant anti-HBV activity (EC50 = 0.63 and 5.99 µM, respectively) with no detectable cytotoxicity against MT-2 cells up to 100 µM.

Synthesis of 4′-substituted 2′-deoxy-4′-thiocytidines and its evaluation for antineoplastic and antiviral activities
Kazuhiro Haraguchi; Hiroki Kumamoto; Kiju Konno; Hideki Yagi; Yutaka Tatano; Yuki Odanaka; Satoko Shimbara Matsubayashi; Robert Snoeck; Graciela Andrei
Tetrahedron, 16 Aug. 2019, [Reviewed]

Synthesis, Anti-HBV, and Anti-HIV Activities of 3'-Halogenated Bis(hydroxymethyl)-cyclopentenyladenines.
Hiroki Kumamoto; Shuhei Imoto; Masayuki Amano; Nobuyo Kuwata-Higashi; Masanori Baba; Hiroaki Mitsuya; Yuki Odanaka; Satoko Shimbara Matsubayashi; Hiromichi Tanaka; Kazuhiro Haraguchi
ACS Medicinal Chemistry Letters, 13 Dec. 2018, [Reviewed]
Synthesis of 3'-halogeno analogues (5a-d) of 9-[c-4,t-5-bis(hydroxymethyl)-cyclopent-2-en-r-1-yl]-9H-adenine (BCA, 3) was accomplished by means of dual utilization of the vinyl sulfone functional moieties in both 10 and 16 utilizing a SN2' conjugate-addition reaction and a sulfur-extrusive stannylation, respectively. Evaluation of the antiviral activities of 5a-d revealed that introduction of a halogeno-substituent into the 3'-position of (-)-BCA diminished its anti-HIV-1 activity but increased the inhibitory activity for the reverse transcriptase of HBV in that the 3'-fluorinated BCA 5d exhibited the highest activity without significant cytotoxicity.

A novel entecavir analogue constructing with a spiro[2.4]heptane core structure in the aglycon moiety: Its synthesis and evaluation for anti-hepatitis B virus activity.
Hiroki Kumamoto; Misato Fukano; Shuhei Imoto; Satoru Kohgo; Yuki Odanaka; Masayuki Amano; Nobuyo Kuwata-Higashi; Hiroaki Mitsuya; Kazuhiro Haraguchi; Kiyoshi Fukuhara
Nucleosides, nucleotides & nucleic acids, 03 Jul. 2017, [Reviewed]
Synthesis of a novel 2'-deoxy-guanine carbocyclic nucleoside 4 constructed with spiro[2.4]heptane core structure in the aglycon moiety was carried out. Radical-mediated 5-exo-dig mode cyclization and following cyclopropanation proceeded efficiently to furnish the spiro alcohol 10. Subsequent Mitsunobu-type glycosylation between 13 and 14, deoxygenation of the 2'-hydroxyl group of 16 and deprotection of 17 gave the title compound 4. Compound 4 demonstrated moderate anti-HBV activity (EC50 value of 0.12 ± 0.02 µM) and no cytotoxicity against HepG2 cells was observed up to 100 µM.

Pyrolysis of UR-144, a synthetic cannabinoid, augments an affinity to human CB1 receptor and cannabimimetic effects in mice.
Asuka Kaizaki-Mitsumoto; Kyoko Hataoka; Masahiko Funada; Yuki Odanaka; Hiroki Kumamoto; Satoshi Numazawa
The Journal of toxicological sciences, 2017, [Reviewed]
Drug abusers most often smoke 'herbal incense' as a cigarette or inhale it using a smoking tool. Smoking may cause pyrolysis of the drug and produce decomposed products of which biological effect has never been investigated. The synthetic cannabinoid UR-144 is known to undergo thermal degradation, giving a ring-opened isomer, so-called UR-144 degradant. The present study demonstrates by using UR-144 as a model drug that the smoke of burned UR-144 contains the UR-144 degradant. The UR-144 degradant showed approximately four fold higher agonist activity to human CB1 receptor and augmented hypothermic and akinetic actions in mice compared to UR-144. These results indicate that smoking behavior may increase psychological actions of the certain synthetic cannabinoids.

Diastereoselective Synthesis of 6″-(Z)- and 6″-(E)-Fluoro Analogues of Anti-hepatitis B Virus Agent Entecavir and Its Evaluation of the Activity and Toxicity Profile of the Diastereomers.
Hiroki Kumamoto; Misato Fukano; Tomohiko Nakano; Keito Iwagami; Chiaki Takeyama; Satoru Kohgo; Shuhei Imoto; Masayuki Amano; Nobuyo Kuwata-Higashi; Manabu Aoki; Hiroshi Abe; Hiroaki Mitsuya; Kiyoshi Fukuhara; Kazuhiro Haraguchi
The Journal of organic chemistry, 01 Apr. 2016, [Reviewed]
A method for the diastereoselective synthesis of 6″-(Z)- and 6″-(E)-fluorinated analogues of the anti-HBV agent entecavir has been developed. Construction of the methylenecyclopentane skeleton of the target molecules has been accomplished by radical-mediated 5-exo-dig cyclization of the selenides 6 and 15 having the phenylsulfanylethynyl structure as a radical accepting moiety. In the radical reaction of the TBS-protected precursor 6, (Z)-anti-12 was formed as a major product. On the other hand, TIPS-protected 15 gave (E)-anti-12. The sulfur-extrusive stannylation of anti-12 furnished a mixture of geometric isomers of the respective vinylstannane, whereas benzoyl-protected 17 underwent the stannylation in the manner of retention of configuration. Following XeF2-mediated fluorination, introduction of the purine base and deoxygenation of the resulting carbocyclic guanosine gave the target (E)- and (Z)-3 after deprotection. Evaluation of the anti-HBV activity of 3 revealed that fluorine-substitution at the 6″-position of entecavir gave rise to a reduction in the cytotoxicity in HepG2 cells with retention of the antiviral activity.

Three 25-NBOMe-type drugs, three other phenethylamine-type drugs (25I-NBMD, RH34, and escaline), eight cathinone derivatives, and a phencyclidine analog MMXE, newly identified in ingredients of drug products before they were sold on the drug market
Asuka Kaizaki-Mitsumoto; Naoki Noguchi; Saki Yamaguchi; Yuki Odanaka; Satoko Matsubayashi; Hiroki Kumamoto; Kiyoshi Fukuhara; Masahiko Funada; Kiyoshi Wada; Satoshi Numazawa
FORENSIC TOXICOLOGY, Jan. 2016, [Reviewed]

Design, Synthesis, and Evaluation of Anti-HBV Activity of Hybrid Molecules of Entecavir and Adefovir: Exomethylene Acycloguanine Nucleosides and Their Monophosphate Derivatives.
Shuhei Imoto; Satoru Kohgo; Ryoh Tokuda; Hiroki Kumamoto; Manabu Aoki; Masayuki Amano; Nobuyo Kuwata-Higashi; Hiroaki Mitsuya; Kazuhiro Haraguchi
Nucleosides, nucleotides & nucleic acids, 2015, [Reviewed]
Exomethylene acycloguanine nucleosides 4, 6 and its monophosphate derivatives 5, 7, and 8 have been synthesized. Mitsunobu-type coupling of 2-N-acetyl-6-O-diphenylcarbamoylguanine (11) with primary alcohols proceeded regioselectively to furnish the desired N(9)-substituted products in moderate yield. Evaluation of 4-8 for anti-HBV activity in HepG2 cells revealed that the phosphonate derivative 8 was found to exhibit moderated activity (EC50 value of 0.29 μM), but cytotoxicity (CC50 value of 39 μM) against the host cells was also observed.

From the chemistry of epoxy-sugar nucleosides to the discovery of anti-HIV agent 4'-ethynylstavudine-Festinavir.
Kazuhiro Haraguchi; Shingo Takeda; Yutaka Kubota; Hiroki Kumamoto; Hiromichi Tanaka; Takayuki Hamasaki; Masanori Baba; Elijah Paintsil; Yung-Chi Cheng
Current pharmaceutical design, 2013, [Reviewed]
Branched sugar nucleosides have attracted much attention due to their biological activities. We have demonstrated that epoxysugar nucleosides serve as versatile precursor for the stereo-defined synthesis of these nucleoside derivatives on the basis of its ring opening with organoaluminum or organosilicon reagents. In this review article, novel methods for the synthesis of nucleoside analogues branched at the 1' and 4'-position will be described. During this study, we could discover an anti-HIV agent, 4'-ethynylstavudine (Festinavir). Festinavir showed more potent anti-HIV activity than the parent compound stavudine (d4T). Other significant properties of Festinavir are as follows: 1) much less toxic to various cells and also to mitochondorial DNA synthesis than d4T, 2) better substrate for human thymidine kinase than d4T, 3) resistant not only to chemical glycosidic bond cleavage but also to catabolism by thymidine phosphorylase, 4) the activity improves in the presence of a major mutation, K103N, associated with resistance to non-nucleoside reverse transcriptase inhibitors. Detailed profile of the antiviral activities, biology and pharmacology of Festinavir are also described.

Tuning efficiency of the 4-exo-trig cyclization by the electronic effect: ring closure of 3,3-difluoro-4-pentenyl carbon radicals and synthesis of a gem-difluorocyclobutane nucleoside.
Hiroki Kumamoto; Sachiko Kawahigashi; Hiromi Wakabayashi; Tomohiko Nakano; Tomoko Miyaike; Yasuyuki Kitagawa; Hiroshi Abe; Mika Ito; Kazuhiro Haraguchi; Jan Balzarini; Masanori Baba; Hiromichi Tanaka
Chemical communications (Cambridge, England), 18 Nov. 2012, [Reviewed]
4-exo-trig Cyclization reaction of a 4-pentenyl carbon radical containing the gem-difluoromethylene moiety adjacent to a radical accepting α,β-unsaturated ester was found to proceed efficiently to furnish a novel gem-difluorocyclobutane derivative. The cyclized product could be transformed into a gem-difluoromethylene analogue of oxetanocin T.

Synthesis of the 5′-Fluoro-2′β-methyl Analogues of Neplanocin
Hiroki Kumamoto; Marina Kobayashi; Nobuyuki Kato; Jan Balzarini; Hiromichi Tanaka
European Journal of Organic Chemistry, May 2011, [Reviewed]

Preparation of CarbocyclicC-Nucleosides from α-Chlorooxime Precursor
Ugo Pradere; Hiroki Kumamoto; Vincent Roy; Luigi A. Agrofoglio
European Journal of Organic Chemistry, Feb. 2010, [Reviewed]

ヌクレオシドの合成化学から抗ウイルス剤の創生へ　　　　　　　　　　　　　　　
2010, [Reviewed]

抗ウイルス剤の創製を目指した新規炭素環ヌクレオシド類の合成　　　　　　　　　　　　　　　
2010, [Reviewed]

Radical-mediated stannylation of vinyl sulfones: access to novel 4′-modified neplanocin A analogues
Hiroki Kumamoto; Kazuki Deguchi; Tadashi Wagata; Yuu Furuya; Yuki Odanaka; Yukio Kitade; Hiromichi Tanaka
Tetrahedron, Sep. 2009

Synthesis of (±)-4′-ethynyl-5′,5′-difluoro-2′,3′-dehydro-3′-deoxy- carbocyclic thymidine: a difluoromethylidene analogue of promising anti-HIV agent Ed4T
Hiroki Kumamoto; Kazuhiro Haraguchi; Mayumi Ida; Kazuo T. Nakamura; Yasuyuki Kitagawa; Takayuki Hamasaki; Masanori Baba; Satoko Shimbara Matsubayashi; Hiromichi Tanaka
Tetrahedron, Sep. 2009

Click Azide-Alkyne Cycloaddition for the Synthesis of D-(-)-1,4-Disubstituted Triazolo-Carbanucleosides
Julie Broggi; Hiroki Kumamoto; Sabine Berteina-Raboin; Steven P. Nolan; Luigi A. Agrofoglio
European Journal of Organic Chemistry, 26 Feb. 2009

Synthesis of 4'-substituted cordycepins via benzenesulfenylation at the 4'-position as a key step.
Yutaka Kubota; Mariko Ehara; Hiroki Kumamoto; Hisashi Shimada; Kazuhiro Haraguchi; Hiromichi Tanaka
Nucleic acids symposium series (2004), 2009
With an aim to synthesize 4'-substituted cordycepins, the 4'-phenylthio precursor 4 was prepared from adenosine through an electrophilic addition to the 3',4'-unsaturated derivative 2 by using NIS/PhSH system. Nucleophilic substitution of 4 with a series of alcohols in the presence of NBS gave the respective 4'-alpha-alkoxy cordycepins 6 as the major stereoisomer. Use of DAST, in stead of alcohol in this reaction, gave the 4'-fluoro analogue 7. The 4'-sulfone derivative 8 obtained by m-CPBA oxidation of 4 was employed for the reaction with organoaluminum reagents. These reactions furnished various types of the 4'-carbon-substituted cordycepins 9.

Synthesis of 5'-fluoro-2'-beta-methylneplanocin analogues.
Hiroki Kumamoto; Marina Kobayashi; Hiromichi Tanaka
Nucleic acids symposium series (2004), 2009
Synthesis of 5'-fluoro-2'-beta-methylneplanocin analogues (5) was carried out. The cyclopentenone 16 was prepared from methyl mannopyranoside by using ring closing metathesis, stereoselective introduction of methyl group, and seleno cyclization as representative steps. Introduction of a fluorine atom was conducted by electrophilic fluorination. Antiviral activity of 5 will also be presented.

Preparation of acyclo nucleoside phosphonate analogues based on cross-metathesis
Hiroki Kumamoto; Dimitri Topalis; Julie Broggi; Ugo Pradère; Vincent Roy; Sabine Berteina-Raboin; Steven P. Nolan; Dominique Deville-Bonne; Graciela Andrei; Robert Snoeck; Daniel Garin; Jean-Marc Crance; Luigi A. Agrofoglio
Tetrahedron, Apr. 2008

Synthesis of (±)-9-[c-4, t-5-bis(hydroxymethyl)cyclopent-2-en-r-1-yl]-9H-adenine (BCA) derivatives branched at the 4′-position based on intramolecular SH2′ cyclization
Hiroki Kumamoto; Nonoko Takahashi; Tomomi Shimamura; Hiromichi Tanaka; Kazuo T. Nakamura; Takayuki Hamasaki; Masanori Baba; Hiroshi Abe; Masahiko Yano; Nobuyuki Kato
Tetrahedron, Feb. 2008

Synthesis and antiviral evaluation of (+/-)-4'-ethynyl-5'-difluorocarbocyclic-d4T analogue.
Hiroki Kumamoto; Kazuhiro Haraguchi; Mayumi Ida; Hiromichi Tanaka; Takayuki Hamasaki; Masanori Baba
Nucleic acids symposium series (2004), 2008
Synthesis of (+/-)-4'-ethynyl-5'-difluorocarbocyclic-d4T analogue 8, in which the furanose ring oxygen of usual nucleosides is replaced with a geminal-difluoromethylidene group, was carried out. Electrophilic fluorination with Selectfluor was applied to construct a gem-difluorocyclopentenone system to give 12. Regioselective introduction of thymine base was performed under the Mitsunobu conditions by employing the 4-methoxycarbonyl derivative 13. Antiviral evaluation of 8 was also examined.

Nucleotide binding to human UMP-CMP kinase using fluorescent derivatives -- a screening based on affinity for the UMP-CMP binding site.
Dimitri Topalis; Hiroki Kumamoto; Maria-Fernanda Amaya Velasco; Laurence Dugué; Ahmed Haouz; Julie Anne C Alexandre; Sarah Gallois-Montbrun; Pedro Maria Alzari; Sylvie Pochet; Luigi André Agrofoglio; Dominique Deville-Bonne
The FEBS journal, Jul. 2007
Methylanthraniloyl derivatives of ATP and CDP were used in vitro as fluorescent probes for the donor-binding and acceptor-binding sites of human UMP-CMP kinase, a nucleoside salvage pathway kinase. Like all NMP kinases, UMP-CMP kinase binds the phosphodonor, usually ATP, and the NMP at different binding sites. The reaction results from an in-line phosphotransfer from the donor to the acceptor. The probe for the donor site was displaced by the bisubstrate analogs of the Ap5X series (where X = U, dT, A, G), indicating the broad specificity of the acceptor site. Both CMP and dCMP were competitors for the acceptor site probe. To find antimetabolites for antivirus and anticancer therapies, we have developed a method of screening acyclic phosphonate analogs that is based on the affinity of the acceptor-binding site of the human UMP-CMP kinase. Several uracil vinylphosphonate derivatives had affinities for human UMP-CMP kinase similar to those of dUMP and dCMP and better than that of cidofovir, an acyclic nucleoside phosphonate with a broad spectrum of antiviral activities. The uracil derivatives were inhibitors rather than substrates of human UMP-CMP kinase. Also, the 5-halogen-substituted analogs inhibited the human TMP kinase less efficiently. The broad specificity of the enzyme acceptor-binding site is in agreement with a large substrate-binding pocket, as shown by the 2.1 A crystal structure.

Synthesis of 5'-branched neplanocin A analogues based on radical-mediated sulfur-extrusive stannylation.
Hiroki Kumamoto; Hiromichi Tanaka
Nucleic acids symposium series (2004), 2007
An approach was developed for the synthesis of 5'-branched neplanocin A, as potential inhibitors against S-adenosyl-L-homocysteine hydrolase. The vinyl-stannane system of the key synthetic intermediate (14) in the present study, was prepared by radical-mediated sulfur-extrusive stannylation.

Looking for new pyrimidine acyclic nucleotide analogues designed for phosphorylation by human UMP-CMP kinase.
Dimitri Topalis; Hiroki Kumamoto; Julie A C Alexandre; Laurence Dugué; Sylvie Pochet; Sabine Berteina-Raboin; Luigi A Agrofoglio; Dominique Deville-Bonne
Nucleosides, nucleotides & nucleic acids, 2007
Human UMP-CMP kinase is involved in the phosphorylation of nucleic acid precursors and also in the activation of antiviral analogues including cidofovir, an acyclic phosphonate compound that mimicks dCMP and shows a broad antiviral spectrum. The binding of ligands to the enzyme was here investigated using a fluorescent probe and a competitive titration assay. At the acceptor site, the enzyme was found to accommodate any base, purine and pyrimidine, including thymidine. A method for screening analogues based on their affinity for the UMP binding site was developed. The affinities of uracil vinylphosphonate derivatives modified in the 5 position were found similar to (d)UMP and (d)CMP and improved when compared to cidofovir.

Cross-metathesis mediated synthesis of new acyclic nucleoside phosphonates.
Vincent Roy; Hiroki Kumamoto; Sabine Berteina-Raboin; Steven P Nolan; Dimitri Topalis; Dominique Deville-Bonne; Jan Balzarini; Johan Neyts; Gracelia Andrei; Robert Snoeck; Luigi A Agrofoglio
Nucleosides, nucleotides & nucleic acids, 2007
With the commercial availability of well-defined ruthenium metathesis catalysts which combine high stability and broad functional group compatibility, olefin metathesis is now routinely integrated in various syntheses. We will report here the overwhelming power and scope of cross-metathesis in the area of new acyclic nucleoside phosphonates. Scope and limitations of this approach, and especially the E/Z stereocontrol, are discussed on selected examples from our drug discovery group.

Synthesis of novel 4'-modified neplanocin A analogues and their inhibitory activity against S-adenosyl-L-l-homocysteine hydrolase.
Hiroki Kumamoto; Kazuki Deguchi; Nonoko Takahashi; Hiromichi Tanaka; Yukio Kitade
Nucleosides, nucleotides & nucleic acids, 2007
A new approach was developed for the synthesis of 4'-modified neplanocin A analogues, as potential inhibitors against S-adenosyl-L-homocysteine hydrolase. The vinylstannane 13, a key intermediate in the present approach, was prepared by radical-mediated sulfur-extrusive stannylation.

Synthesis and anti-human immunodeficiency virus activity of 4'-branched (+/-)-4'-thiostavudines.
Hiroki Kumamoto; Takahito Nakai; Kazuhiro Haraguchi; Kazuo T Nakamura; Hiromichi Tanaka; Masanori Baba; Yung-Chi Cheng
Journal of medicinal chemistry, 28 Dec. 2006
Motivated by our recent finding that 4'-ethynylstavudine (4) is a promising anti-human immunodeficiency virus type 1 (HIV-1) agent, we synthesized its 4'-thio analogue, as well as other 4'-thiostavudines having a carbon substituent at the 4'-position, as racemates in this study. Methyl 3-oxo-tetrahydrothiophen-2-carboxylate (5) was used as a starting material to construct the requisite 4-thiofuranoid glycal (13). Introduction of a thymine base was carried out by an electrophilic addition reaction to 13 using N-iodosuccinimide (NIS) and bis(trimethylsilyl)thymine. The desired beta-anomer (16beta) obtained as a major product in this reaction underwent ready elimination with activated Zn to give the 4'-carbomethoxy derivative (18). By using 18 as a common intermediate, 4'-carbon-substituted (CH2OH, CO2Me, CONH2, CH=CH2, CN, and C(triple bond)CH) 4'-thiostavudines were prepared. Among these six compounds, 4'-cyano (28) and 4'-ethynyl (29) analogues were found to show inhibitory activity against HIV-1 with ED50 values of 7.6 and 0.74 microM, respectively. The activity of 29 was comparable to that of stavudine, but 29 was not as active as 4. Optical resolution of 29 was briefly examined.

Cross-metathesis in the synthesis of bioactive phosphonates　　　　　　　　　　　　　　　
Agrofoglio, L. A; Kumamoto, H; Roy, V
Chimica Oggi., 2006, [Reviewed]

3'-Carbon-substituted pyrimidine nucleosides having a 2',3'-dideoxy and 2',3'-didehydro-2',3'-dideoxy structure: synthesis and antiviral evaluation.
Hiroki Kumamoto; Sayoko Onuma; Hiromichi Tanaka; Ginger E Dutschman; Yung-Chi Cheng
Antiviral chemistry & chemotherapy, 2006
The bis(tributylstannyl) derivative of 2',3'-didehydro-2',3'-dideoxyuridine (d4U) underwent an anionic 5'-O-->3'-C stannyl migration to yield the 3'-tributylstannyl-d4U. This compound, with its vinylstannane structure, allowed ready access to the preparation of 3'-carbon-substituted analogues through the Stille reaction. A conventional transformation of the uracil moiety of these d4U analogues led to the corresponding 2',3'-didehydro-2',3'-dideoxycytidine (d4C) counterparts. Some 2',3'-dideoxycytidine (ddC) analogues were also synthesized. Antiviral evaluation revealed that none of these analogues showed activity against HIV, hepatitis B virus, herpes simplex virus-1 (HSV-1) and HSV-2.

Synthesis of novel 4'-carbon-substituted BCA derivatives based on radical cyclization.
Hiroki Kumamoto; Nonoko Takahashi; Tomomi Shimamura; Hiromichi Tanaka
Nucleic acids symposium series (2004), 2006
Synthesis of (+/-)-4'-carbon-substituted BCA analogues (3) was carried out. Stereospecific construction of the cis-disposed 4'-carbon-substituent and 5'-hydroxy-methyl group was secured by employing the bicyclo-[3.3.0]lactone 11 as a key intermediate, which was prepared by radical-mediated 5-exo-trig cyclization of the phenylselenomethyl ester 10. After manipulation of the double bond of 11, 6-chloropurine was introduced based on the Mitsunobu reaction of the allyl alcohol 15. Ammonolysis of the resulting carbocyclic nucleoside led to the adenine derivative 16. Saponification of the bicylic lactone furnished the 4'-carboxylic acid 17 which serves as a precursor for other 4'-carbon-substituted analogues.

Anti-human immunodeficiency virus type 1 activity and resistance profile of 2',3'-didehydro-3'-deoxy-4'-ethynylthymidine in vitro.
Takao Nitanda; Xin Wang; Hiroki Kumamoto; Kazuhiro Haraguchi; Hiromichi Tanaka; Yung-Chi Cheng; Masanori Baba
Antimicrobial agents and chemotherapy, Aug. 2005
2',3'-Didehydro-3'-deoxy-4'-ethynylthymidine (4'-Ed4T) has been identified as a novel nucleoside analog with potent and selective anti-human immunodeficiency virus type 1 (HIV-1) activity and weak cytotoxicity in cell cultures. 4'-Ed4T proved to be 5- to 10-fold more active than its structurally related compound, stavudine (d4T). However, the drug resistance profile of 4'-Ed4T was different from those of d4T and other existing HIV-1 nucleoside reverse transcriptase inhibitors (NRTIs). Approximately 6- to 11-fold decreases in susceptibility to 4'-Ed4T were observed for HIV-1 carrying NRTI-associated mutations (D67N, K70R, T215F, and K219Q) or the lamivudine (3TC)-resistant mutation M184V. In contrast, the susceptibility of the virus carrying the K65R mutation or the multidrug-resistant mutation with the Q151M complex (A62V, V75I, F77L, F116Y, and Q151M) was not altered. Furthermore, the activity of 4'-Ed4T appeared to be enhanced in the presence of K103N, a major nonnucleoside reverse transcriptase inhibitor-resistant mutation. Although 4'-Ed4T was 4.5- to 17.5-fold less active against multidrug-resistant clinical isolates than against a reference strain isolated from a treatment-naïve patient, it was still inhibitory to these isolates at low concentrations. Analysis of 4'-Ed4T-resistant HIV-1 obtained through in vitro selection revealed that the virus was also resistant to 3TC and had two amino acid mutations (P119S and T165A) in addition to the M184V mutation. Since 4'-Ed4T has increased anti-HIV-1 activity, decreased cytotoxicity, and a different resistance profile, it should be considered for further development as a new member of NRTIs.

5-Exo versus 6-endo cyclization of nucleoside 2-sila-5-hexenyl radicals: reaction of 6-(bromomethyl)dimethylsilyl 1',2'-unsaturated uridines.
Junko Ogamino; Hideaki Mizunuma; Hiroki Kumamoto; Shingo Takeda; Kazuhiro Haraguchi; Kazuo T Nakamura; Hiroshi Sugiyama; Hiromichi Tanaka
The Journal of organic chemistry, 04 Mar. 2005
The mode of cyclization of 2-sila-5-hexen-1-yl radicals generated from 6-(bromomethyl)dimethylsilyl-1',2'-unsaturated uridines was investigated. In contrast to the case of the 2'-unsubstituted 6-silicon-tethered substrate (4), which undergoes exclusive 6-endo-cyclization, reactions of the 2'-substituted (Me, CO2Me, OBz, and Cl) derivatives (14, 20, 22, and 24) uniformly proceeded in preferential or exclusive 5-exo-mode. The Tamao oxidation of the resulting cyclized products was also carried out to synthesize the corresponding 1'-C-hydroxymethyl derivatives.

Synthesis of (+/-)-4'-ethynyl and 4'-cyano carbocyclic analogues of stavudine (d4T).
Hiroki Kumamoto; Kazuhiro Haraguchi; Hiromichi Tanaka; Takao Nitanda; Masanori Baba; Ginger E Dutschman; Yung-Chi Cheng; Keisuke Kato
Nucleosides, nucleotides & nucleic acids, 2005
The synthesis of (+/-)-4'-ethynyl (8) and 4'-cyano (9) carbocyclic analogues of the anti-HIV agent stavudine (5, d4T) is reported. The carbocyclic unit (16) was constructed from readily available beta-keto ester 10. The ethynyl or cyano group of 8 and 9 were prepared, after the introduction of thymine base to 16, by manipulation of the ester function. Evaluation of the anti-HIV activity of 8 and 9 was also carried out.

4'-Ethynylstavudine (4'-Ed4T) has potent anti-HIV-1 activity with reduced toxicity and shows a unique activity profile against drug-resistant mutants.
Hiromichi Tanaka; Kazuhiro Haraguchi; Hiroki Kumamoto; Masanori Baba; Yung-Chi Cheng
Antiviral chemistry & chemotherapy, 2005
A nucleoside analogue 4'-ethynylstavudine (4'-Ed4T) was recently synthesized during chemical studies directed towards the development of a new route to 4'-carbon-substituted nucleosides. This compound was found to be more anti-HIV-1 active than the parent compound stavudine (d4T) and much less toxic to various cells and also to mitochondrial DNA synthesis. It became apparent that 4'-Ed4T is a better substrate for human thymidine kinase than d4T, and very much more resistant to catabolism by thymidine phosphorylase. The study of 4'-Ed4T against various drug-resistant HIV-1 mutants has disclosed its unique activity profile.

Reaction of the 2'-silyl and 2'-stannyl derivatives of 6-(bromomethyl)dimethylsilyl-1',2'-unsaturated uridine under radical conditions.
Junko Ogamino; Hideaki Mizunuma; Hiroki Kumamoto; Kazuhiro Haraguchi; Hiromichi Tanaka
Nucleosides, nucleotides & nucleic acids, 2005
The mode of cyclization (5-exo versus 6-endo) of 2-sila-5-hexen-1-yl radicals generated from 2'-tributylstannyl- and 2'-trimethylsilyl-6-(bromomethyl)dimethylsilyl-1',2'-unsaturated uridines (8 and 9) was investigated. Although the actual structure of the reaction products differ from each other reflecting the ease of elimination of the 2'-substituent, it was found that both substrates prefer the 5-exo-cyclization pathway.

Lithiation at the 6-position of uridine with lithium hexamethyldisilazide: crucial role of temporary silylation.
Yuichi Yoshimura; Hiroki Kumamoto; Ayuka Baba; Shingo Takeda; Hiromichi Tanaka
Organic letters, 27 May 2004
Lithium hexamethyldisilazide (LiHMDS) can mediate silylation at the 6-position of uridine, although LiHMDS alone is not able to generate the C-6-lithiated uridine. Experimental results showed that temporary silylation of O-4 (or N-3) of the uracil ring triggers the C-6 lithiation with LiHMDS. This finding allowed us to develop an efficient intramolecular alkylation of 5'-deoxy-5'-iodouridine to furnish 6,5'-C-cyclouridine. [reaction--see text]

Sulfur extrusion with tin radical: synthesis of 4',5'-didehydro-5'-deoxy-5'-(tributylstannyl)adenosine, an intermediate for potential inhibitors against S-adenosyl homocysteine hydrolase.
Hiroki Kumamoto; Sayoko Onuma; Hiromichi Tanaka
The Journal of organic chemistry, 09 Jan. 2004
A new approach has been developed for the synthesis of potential inhibitors of S-adenosyl-l-homocysteine (AdoHcy) hydrolase. The key intermediate 9-[2,3-bis-O-(tert-butyldimethylsilyl)-5-(Z)-(tributylstannyl)-5-deoxy-beta-d-erythro-pent-4-enofuranosyl]adenine (12) was prepared by sulfur extrusion reaction of 4',5'-didehydro-5'-deoxy-5'-(phenylthio)adenosine (11) with tributyltin radical. It was found that this reaction proceeds stereoselectively, forming 12 irrespective of the geometry of 11. Compound 12 readily underwent iodination, bromination, and chlorination with retention of configuration, whereas fluorination gave both (Z)- and (E)-isomers of vinyl fluoride. Because of the susceptibility of 12 to protodestannylation, the (Z)-vinyl iodide (13), prepared in quantitative yield from 12, was used as a substrate for C-C bond formation. Various types of carbon substituents (phenyl, vinyl, trifluorovinyl, ethynyl, and cyano) were introduced to the 5'-position of the 5-deoxy-beta-d-erythro-pent-4-enofuranosyl structure to open up a new route to potential inhibitors of AdoHcy hydrolase.

Synthesis of novel 4'-modified neplanocin A analogues based on radical-mediated sulfur-extrusive stannylation.
Hiroki Kumamoto; Kazuki Deguchi; Nonoko Takahashi; Hiromichi Tanaka
Nucleic acids symposium series (2004), 2004
A new approach was developed for the synthesis of 4'-modified neplanocin A, as potential inhibitors against S-adenosyl-L-homocysteine hydrolase. Vinylstannane derivative 5, a key intermediate in the present approach, was prepared by radical-mediated sulfur-extrusive stannylation.

Synthesis of carbocyclic analogues of 4'-ethynyl- and 4'-cyano-d4T.
Hiroki Kumamoto; Keisuke Kato; Kazuhiro Haraguchi; Hiromichi Tanaka; Takao Nitanda; Masanori Baba; Ginger E Dutschman; Yung-Chi Cheng
Nucleic acids symposium series (2004), 2004
Synthesis of carbocyclic analogues of 4'-ethynyl and cyano-d4T (4 and 5) was investigated. The ethynyl or cyano group was constructed by conversion of the ester function of key intermediate 13. The carbocyclic unit 12 was prepared from readily available beta-keto ester 6.

Stannylation Approach to the Synthesis of 2′- and 3′-Substituted Analogues of 2′,3′-Didehydro-2′,3′-dideoxynucleosides
Hiroki Kumamoto; Sayoko Onuma; Hiromichi Tanaka
Nucleosides, Nucleotides and Nucleic Acids, Oct. 2003

Development of radioiodinated nucleoside analogs for imaging tissue proliferation: comparisons of six 5-iodonucleosides.
Jun Toyohara; Akio Hayashi; Mikiko Sato; Akie Gogami; Hiromichi Tanaka; Kazuhiro Haraguchi; Yuichi Yoshimura; Hiroki Kumamoto; Yoshiharu Yonekura; Yasuhisa Fujibayashi
Nuclear medicine and biology, Oct. 2003
The aim of this study was to determine the most suitable iodonucleoside analogs for use in tissue proliferation imaging by means of single photon emission tomography (SPECT). In this study, 5-[ (125)I]iodo-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl)uracil ([ (125)I]FITAU, 1E) and 5-[ (125)I]iodo-1-methyl-(2-deoxy-2-bromo-beta-D-arabinofuranosyl)uracil ([ (125)I]IMBAU, 1F) were synthesized and their biological data were compared with previously published results regarding 4'-thio nucleoside analogs and the reference compound 5-[ (125)I]iodo-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil ([ (125)I]FIAU, 1D). 5-Iodo-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil (FIAU, 2D), 5-iodo-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl)uracil (FITAU, 2E), and 5-iodo-1-methyl-(2-deoxy-2-bromo-beta-D-arabinofuranosyl)uracil (IMBAU, 2F) were successfully labeled with (125)I and their in vitro cytosolic thymidine kinase (TK(1)) phosphorylation, recombinant thymidine phosphorylase enzymatic catabolism, TK(1)-dependent cell uptake, and in vivo biodistribution in normal mice were evaluated. Five compounds (1B, 1C, 1D, 1E, and 1F) were stable against C-N glycoside degradation induced by recombinant thymidine phosphorylase. However, 5-[ (125)I]iodo-2'-deoxyuridine ([ (125)I]IUdR, 1A) was not shown to be stable against such degradation. The TK(1) assay showed that [ (125)I]FIAU (1D) expressed 16% of the phosphorylation potential of [ (125)I]IUdR (1A). Furthermore, [ (125)I]FITAU (1E) was shown to have reduced phosphorylation potential, in comparison with that of [ (125)I]IUdR (1A) (<0.01). [ (125)I]IMBAU (1F) did not show any phosphorylation. In vitro cell uptake and in vivo proliferation-selective uptake of each nucleoside was largely dependent on its potential as a TK(1) substrate. Neither [ (125)I]FITAU (1E) nor [ (125)I]IMBAU (1F) were shown to have distinct TK(1)-dependent cell uptake and retention in the proliferating tissues. From these results, we concluded that [ (125)I]FITAU (1E) and [ (125)I]IMBAU (1F) are not effective as imaging agents of cell proliferation. The biological data obtained with these nucleosides were compared, and requirements for the design of pharmaceutically useful radioiodinated nucleoside analogs were also considered.

Stereo-defined synthesis of 5'-(Z)-substituted 4',5'-unsaturated adenosines and evaluation of their inhibitory activity against S-adenosyl homocysteine hydrolase.
Hiroki Kumamoto; Sayoko Onuma; Hiromichi Tanaka; Yukio Kitade
Nucleic acids research. Supplement (2001), 2003
A new approach was developed for the synthesis of 5'-(Z)-substituted 4',5'-unsaturated adenosines, potential inhibitors against S-adenosyl-L-homocysteine hydrolase (SAHase). A highly stereoselective radical-mediated sulfur-extrusive stannylation was employed as a key step in the present approach. Inhibitory activity of the compounds against SAHase is also presented.

Study on the reaction mechanism of C-6 lithiation of pyrimidine nucleosides by using lithium hexamethyldisilazide as a base.
Yuichi Yoshimura; Hiroki Kumamoto; Ayuka Baba; Shingo Takeda; Hiromichi Tanaka
Nucleic acids research. Supplement (2001), 2003
The reaction mechanism of C-6 lithiation of uridine mediated by lithium hexamethyldisilazide (LiHMDS) has been investigated. LiHMDS alone dose not lithiate at C-6 of uridine. However, in the presence of an appropriate silylating agent, e.g. trimethylsilyl chloride, the reaction of 1 with LiHMDS allowed to lithiate at C-6 and gave the corresponding C-6 silylated product 2. The experimental results shown below revealed that O-4 (N-3) of uracil moiety may be temporarily masked by silylation, which triggers the C-6 lithiation by lowering the pKa of H-6. The reaction could efficiently be applied to the synthesis of 6,5'-C-cyclouridine, a nucleoside analogue fixed in a specific glycosyl torsion angle by a carbon-carbon bridge.

Nucleophilic addition of benzenethiol to 1',2'-unsaturated nucleosides: 1'-C-phenylthio-2'-deoxynucleosides as anomeric radical precursors.
Hiroki Kumamoto; Miki Murasaki; Kazuhiro Haraguchi; Aki Anamura; Hiromichi Tanaka
The Journal of organic chemistry, 23 Aug. 2002
The addition reaction of benzenethiol to the glycal portion of 1',2'-unsaturated uridine proceeds efficiently in the presence of Et(3)N. The mechanism involves nucleophilic attack of thiolate at the anomeric position in the rate-determining step, wherein conjugation between the nucleobase and the glycal portion is crucial. The derivative having a methyl group either at the 2'- or 6-position did not undergo this addition reaction, due to their sterically prohibited coplanarity. The 1',2'-unsaturated derivatives of thymine and adenine can also be used as substrates for this addition reaction. It was also shown that the resulting 1'-C-phenylthio-2'-deoxynucleosides serve as precursors for radical-mediated C-C bond formation at the anomeric position.

SULFOXIDE-METAL EXCHANGE FOR THE SYNTHESIS OF THE 2′-TRIBUTYLSTANNYL DERIVATIVE OF 2′,3′-DIDEHYDRO-2′,3′-DIDEOXYURIDINE (d4U): A GENERAL ENTRY TO 2′-CARBON-SUBSTITUTED ANALOGUES OF d4U
Hiroki Kumamoto; Sayoko Onuma; Kumiko Tsuchiya; Yuko Egusa; Hiromichi Tanaka; Tsuyoshi Satoh
Nucleosides, Nucleotides and Nucleic Acids, Jul. 2002

Simple entry to 3'-substituted analogues of anti-HIV agent stavudine based on an anionic O --> C stannyl migration.
Hiroki Kumamoto; Hiromichi Tanaka
The Journal of organic chemistry, 31 May 2002
Reaction of 5'-O-protected derivatives of the anti-HIV agent stavudine (d4T) with LTMP was investigated with the aim to lithiate the vinylic hydrogens (H-3' and H-2'). When the lithiation of the 5'-O-tert-butyldiphenylsilyl derivative 5 was carried out in the presence of HMPA, an anionic silyl migration took place to give the 3'-C-silylated product 4a. The stannyl version of this reaction was found to be also possible, which has disclosed a highly simple entry to the d4T analogues variously substituted at the 3'-position by manipulating the 3'-C-stannyl d4T as a common intermediate.

A versatile intermediate for the synthesis of 3′-substituted 2′,3′-didehydro-2′,3′-dideoxyadenosine (d4A): preparation of 3′-C-stannyl-d4A via radical-mediated desulfonylative stannylation
Sayoko Onuma; Hiroki Kumamoto; Misono Kawato; Hiromichi Tanaka
Tetrahedron, Mar. 2002

ithiation-based silylation and stannylation for nucleoside synthesis　　　　　　　　　　　　　　　
Kumamoto, H; Kato, K; Tanaka, H
Recent Advances in Nucleosides; Chemistry and Chemotherapy, 2002

New Aspects in the Lithiation Chemistry of Nucleosides: Anionic Migration of Silyl and Stannyl Groups.
Hiroki Kumamoto; Hiromichi Tanaka
Journal of Synthetic Organic Chemistry, Japan, 2002

Radical-mediated furanose ring reconstruction from 2′,3′- seco -uridine
Hiroki Kumamoto; Junko Ogamino; Hiromichi Tanaka; Hisaki Suzuki; Kazuhiro Haraguchi; Tadashi Miyasaka; Tsutomu Yokomatsu; Shiroshi Shibuya
Tetrahedron, Apr. 2001

Stereo- and regioselective radical cyclization of 6-(bromomethyl)dimethylsilyl-1´,2´-unsaturted uracil nucleosides: synthesis of 1´--hydroxy-methyl nucleosides　　　　　　　　　　　　　　　
Oganmino, J; Kumamoto, H; Mizunuma. H; Takeda, S; Haraguchi, K; Tanaka, H
Nucleic Acid Res. Suppl., 2001

LITHIATION-STANNYLATION CHEMISTRY FOR NUCLEOSIDE SYNTHESIS
Hiromichi Tanaka; Hiroki Kumamoto
Main Group Metal Chemistry, Jan. 2001

An Intramolecular Anionic Migration of a Stannyl Group from the 6-Position of 1-(2-Deoxy- d - erythro -pent-1-enofuranosyl)uracil to the 2′-Position: Synthesis of 2′-Substituted 1′,2′-Unsaturated Uridines
Hiroki Kumamoto; Satoru Shindoh; Hiromichi Tanaka; Yoshiharu Itoh; Kazuhiro Haraguchi; Eisen Gen; Atsushi Kittaka; Tadashi Miyasaka; Masato Kondo; Kazuo T Nakamura
Tetrahedron, Jul. 2000

Lithiation study on d4T　　　　　　　　　　　　　　　
Kumamoto, H; Tanaka, H
Nucleic Acids Symp. Ser., 2000

First Evident Generation of Purin-2-yllithium:  Lithiation of an 8-Silyl-Protected 6-Chloropurine Riboside as a Key Step for the Synthesis of 2-Carbon-Substituted Adenosines
Hiroki Kumamoto; Hiromichi Tanaka; Ryota Tsukioka; Yumiko Ishida; Akiko Nakamura; Satoe Kimura; Hiroyuki Hayakawa; Keisuke Kato; Tadashi Miyasaka
The Journal of Organic Chemistry, 01 Oct. 1999

Synthesis of 3´--carbon-substituted 2´,3´-dideoxynucleosides from naturally occurring nucleosides　　　　　　　　　　　　　　　
Kumamoto, H; Tanaka, H; Ogamino, J; Suziki, H; Haraguchi, K; Miyasaka, T
Nucleic Acids Symp. Ser., 1999

Lithiation-stannylation chemistry of nucleosides
Tanaka, H; Kumamoto, H; Shindoh, S; Hayakawa, H; Kato, K; Miyasaka, T
Nucleosides Nucleotides, 1999, [Reviewed]

Stannyl migration from the base to the sugar portion of 1′,2′-unsaturated uridine: the first example of substitution at the 2′-position
Hiroki Kumamoto; Satoru Shindoh; Hiromichi Tanaka; Eisen Gen; Kazuhiro Haraguchi; Atsushi Kittaka; Tadashi Miyasaka
Tetrahedron Letters, May 1998

Synthesis of 2´-substitued 1´,2´-unsaturaterd uridines　　　　　　　　　　　　　　　
Kumamoto, H; Shindoh, S; Tanaka, H; Miyasaka, T
Nucleic Acids Symp. Ser., 1998

Synthesis of 2-alkynylcordycepins and evaluation of their vasodilating activity
Kumamoto, H; Hayakawa, H; Tanaka, H; Shindoh, S; Kato, K; Miyasaka, T; Endo, K; Machida, H; Matsuda, A
Nucleosides Nucleotides, 1998, [Reviewed]

A New Entry to 2-Substituted Purine Nucleosides Based on Lithiation-Mediated Stannyl Transfer of 6-Chloropurine Nucleosides
Keisuke Kato; Hiroyuki Hayakawa; Hiromichi Tanaka; Hiroki Kumamoto; Satoru Shindoh; Satoshi Shuto; Tadashi Miyasaka
The Journal of Organic Chemistry, 01 Oct. 1997

Lithiation-mediated CC silyl and stannyl migrations observed in 6-chloro-9-(β-d-ribofuranosyl)purine
Keisuke Kato; Hiroyuki Hayakawa; Hiromichi Tanaka; Hiroki Kumamoto; Tadashi Miyasaka
Tetrahedron Letters, Sep. 1995

Lithiation based silylation andstannylation of 6-chloro-9-(-D-ribofuranosyl)purine　　　　　　　　　　　　　　　
Kato, K; Hayakawa, H; Tanaka, H; Kumamoto, H; Miyasaka, T
Nucleic Acids Symp. Ser., 1995

Synthesis of novel entecavir analogues having cyano group and fluorine; Evaluation of their anti-HBV activity
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