Volume 21, Issue 5 - Kyoichi A. Watanabe Commemorative issue

Ribavirin, a broad-spectrum antiviral agent is used in the clinic alone or in combination with other antivirals and/or interferons. Numerous structural analogues of ribavirin have been developed, among them tiazofurin, which is inactive against viruses but is a potent anticancer drug. Tiazofurin was found to inhibit nicotinamide adenine dinucleotide (NAD)-dependent inosine monophosphate dehydrogenase (IMPDH) after metabolic conversion into tiazofurin adenine dinucleotide (TAD), which binds well but could not serve as IMPDH cofactor. TAD showed high selectivity against human IMPDH vs. other cellular dehydrogenases. Mycophenolic acid (MPA) was even more specific, binding at the cofactor-binding domain of IMPDH. Ribavirin adenine dinucleotide, however, did not show any significant inhibition at the enzymatic level. We synthesized numerous NAD analogues in which natural nicotinamide riboside was replaced by tiazofurin, MPA moiety, or benzamide riboside, and the adenosine moiety as well as the pyrophosphate linker were broadly modified. Some of these compounds were found to be low nanomolar inhibitors of the enzyme and sub-micromolar inhibitors of cancer cell line proliferation. The best were as potent as tyrosine kinase inhibitor gleevec heralded as a ‘magic bullet’ against chronic myelogenous leukemia. In recent years, ribavirin was rediscovered as a potential anticancer agent against number of tumors including leukemia. It was clearly established that its antitumor activity is related to the inhibition of an oncogene, the eukaryotic translation initiation factor (eIF4E).

5′-Norcarbocyclic analogues of furano[2,3- d ]pyrimidine nucleosides as well as 5-bromo and 5-iodouracil derivatives were synthesized to evaluate their potential antitumor activity. The halogenated derivatives display no cytotoxicity with respect to all tested cells: KB-3-1 (human epidermoid carcinoma), HeLa (human cervical epithelioid carcinoma), HuTu-80 (human duodenal cancer), B16 (mouse melanoma), and MDCK (normal epithelial). The cytotoxicity of the non-halogenated furano[2,3- d ]pyrimidine derivatives increases with the lengthening of the alkyl chain of the substituent from 45 to 60 μ m for octyl to from 3 to 10 μ m for dodecyl.

3′-Deoxy-3-azidothymidine (AZT, zidovudine) is a nucleoside-analog reverse transcriptase inhibitor, successfully used against the human immunodeficiency virus (HIV). Its structure contains an azide function, which makes it a useful substrate for 1,2,3-triazole synthesis, using the copper-catalyzed azide-alkyne cycloaddition, the flagship reaction of ‘click chemistry’. Herein we present the synthesis and spectral characterization of its 1,2,3-triazole derivative containing a fluorenylmethyloxycarbonyl (fmoc) fluorescent fragment. The preparation and characteristics of a novel fluorescent probe, 9 H -fluoren-9-ylmethyl prop-2-yn-1-yl carbonate (propargyl-fmoc) is also presented.

New 4,7-bis(arylamino)-2-tetra- O -acetyl-β-d-glucopyranosylimino-1,3,5,6-dithiadiazepines were synthesized via reaction of N -tetra- O -acetyl-β-d-glucopyranosyl isocyanodichloride with 1,6-diaryl-2,5-dithio-bis-ureas without using any catalyst. Thus, the synthesis of 7-membered heterocycles containing two sulfur and two nitrogen atoms through carbon-sulfur bond formation was explored. The chemical structures of these new compounds were elucidated by IR, 1 H NMR, 13 C NMR, mass spectral, and elemental analyses.

A series of new 8-alkoxy-1,3-dimethyl-2,6-dioxopurin-7-yl-substituted acetohydrazides and butanehydrazides 6 – 12 was synthesized and evaluated for the analgesic activity in two in vivo models: the writhing syndrome and the hot-plate tests. Among the investigated derivatives, compounds with N ′-arylidenehydrazide moiety 9 – 12 show analgesic activity significantly higher than that of acetylsalicylic acid, which may indicate the importance of this structural element for analgesic properties. The lack of the activity in the hot-plate test may suggest that the analgesic activity of the newly synthesized compounds is mediated by a peripheral mechanism. The selected compounds 7 and 12 inhibit tumor necrosis factor α production in a rat model of lipopolysaccharide-induced endotoxemia, similarly to theophylline, which may confirm their anti-inflammatory properties.

A series of 3,5-diarylisoxazoles (1–9) underwent reaction with N -bromosuccinimide in acetic acid to yield the corresponding 3.5-diaryl-4-bromoisoxazoles (1Br–9Br) in low to moderate yield. The X-ray structure of 3-(4-chlorophenyl)-5-phenyl-4-bromoisoxazole showed torsion angles of ~40° and ~36° between the 3- and 5-aryl groups and the central ring system, respectively. Molecular modeling studies predicted the 3,5-phenylisoxazole ring system to be essentially coplanar and the 3,5-diphenyl groups of the 4-bromoisoxazole derivative to be twisted with torsional angles of 50° and 37°, respectively. Carbon-13 nuclear magnetic resonance ( 13 C NMR) data of the 3,5-diaryl-4-bromoisoxazoles were obtained in dimethyl sulfoxide- d 6 (DMSO- d 6 ) at 50°C. Plots of the C 4 chemical shift data for isoxazoles (1–9) vs. those for 4-bromoisoxazoles (1Br – 9Br) showed a good linear correlation ( r 2 = 0.974) with a slope of 0.96. Substitution on the 3-aryl group had essentially no effect on the chemical shift for C 4 of the 4-bromoisoxazole, whereas that on the 5-aryl group showed an excellent correlation with σ + values. Despite the predicted torsion angle differences, distal transmission of substituent effects in the 4-bromo ring system was essentially analogous to that in the planar 3,5-diarylisoxazoles.

Pyridine O- galactosides 3 , 4 , and 2-(4′-fluorobenzoyloxy)pyridine derivatives 5 were prepared by simple nucleophilic substitution reactions. These nucleosides were studied as anti-proliferating agents of human promyelotic leukemia (HL-60) cells. Compound 5a shows the highest anti-proliferative activity (77% at 100 μ m ) among the synthesized compounds.

The synthesis and isolation of 3′- O -aminothymidine oximes have been optimized. Synthesized compounds were characterized by NMR and UV spectral and analytical data. A mixture of previously not reported syn and anti isomers of acetaldoximes was assessed for anti-HIV activity and the prevention of syncytia formation caused by HIV-1 infection.

An effective method of synthesis of 5,5′-modified 2′,5′-dideoxyuridine derivatives is based on sequential 5′-iodination and azidation of 5-[4-(1-decyl)-1,2,3-triazol-1-yl]methyl-2′-deoxyuridine followed by 1,3-dipolar cycloaddition of the intermediate azide with an olefin under the catalysis of Cu(I) resulting in 75–85% yield of 5′-[4-substituted (1,2,3-triazol-1-yl]-5-[4-(1-decyl)-1,2,3-triazol-1-yl]methyl-2′,5′-dideoxyuridine. The compounds were shown to possess low cytotoxicity in Vero , A549 cells and Jurkat cell cultures and did not demonstrate noticeable antimicrobial activity.

Tris-(hydroxymethyl)phosphine oxide (THPO) to a certain extent resembles a part of 2′-deoxyribofuranose, although it exists in an acyclic form only and the oxygen atom at the THPO phosphorus center provides additional hydration site or acceptor of hydrogen bonds. After proper protection of hydroxyl groups, THPO was functionalized with nucleobases and converted into phosphoramidite monomers suitable for incorporation into growing oligonucleotide chains within the solid phase synthesis protocol. The resultant THPO-DNA analogs show reduced affinity to complementary DNA strands, and are resistant towards snake venom and calf spleen exonucleases.

The synthesis of new 2,6-disubstituted purine 2′,3′-dideoxy-2′,3′-difluoro-D-arabino nucleosides is reported. Their ability to block HIV and HCV replication along with their cytotoxicity toward Huh-7 cells, human lymphocyte, CEM and Vero cells was also assessed. Among them, β-2,6-diaminopurine nucleoside 25 and guanosine derivative 27 demonstrate potent anti-HIV-1 activity (EC 50 = 0.56 and 0.65 μ m ; EC 90 = 4.2 and 3.1 μ m ) while displaying only moderate cytotoxicity in primary human lymphocytes.