Synthesis And Biological Activity Of Novel Nucleosides Analogues

Nucleoside reverse transcriptase inhibitors (NRTIs) are the backbone of current antiretroviral drugs in treatment of HIV and hepatitis. There are 7 NRTIs drugs which have been approved by FDA for the therapy of AIDS. The disadvantages of these drugs are tolerability and adverse effects in current therapy, so it is necessary to find out new drugs with little side effects to inhibit the drug-resistant HIV variants.All the 7 NRTIs belong to the family of 2’,3’-dideoxy nucleosides (ddN), the difference between ddN and natural nucleosides is the lack of 3’-OH, and this maybe the key why HIV can discriminate ddN and does not accept them as substrate for the viral DNA replication. In this article, some 4’-substituted nucleosides are synthesized and the conformation of these compounds has been investigated.First, a series of novel 4’-substituted nucleosides are designed and synthesized. These compounds belong to 2’-deoxynucleosides (dN) just like natural nucleosides and distinguish from the 7 NRTIs drugs by the existence of 3’-OH. All of them show potent anti-HIV activity and compound 25 has potent anti-HBV and anti-tumor activity.Second, crystal structure of compound 25 shows the exo configuration of C-3’. 1H NMR represent the similar coupling constants between compound 1a,2 and 25. Calculations on the dihedral angles, using the 3JH-1’,H-2’and 3JH-2,H-3’ values and Altona-Haasnoot’s equations, show the dihedral angles between H-1’ and H-2’ to be about 7°, and those between H-2’ and H-3’ to be about 155°. These results and the observed NOEs between H-6 and H-3’ indicate C-3’ should be the endo (North type) conformation in solution. In addition, the difference between compound 2,25 and their hydrochloride salt were discussed. The evidence of compound 26 protonated at N3 rather than amino group was confirmed by 1H and 13C NMR.Third, the in vitro anti-HIV activity of compounds 1a, 1b, and 2 was evaluated by anti-HIV (wild type) replication assay, and compound 2 was found to be extremely potent against HIV-1 wild-type strain without obvious cytotoxicity. The anti-HIV activity of 25 and 26 was first evaluated in vitro according to standard procedures using efavirenz (EFV) and zidovudine (AZT) as controls. Compounds 25 and 26 exhibited extremely potent antiviral activity with IC50 values of 0.3 and 0.13 nM, respectively. In HBV-transfected HepG2.2.15 cells, compound 25 exhibited a potent inhibitory activity on HBsAg and HBeAg secretion, with IC50 values of 45.4 nM and 48.9 nM on day 9 respectively. These results showed that inhibitory effect of 25 on HBsAg and HBeAg secretion was better than that of 3TC.25 was also effective in suppressing DHBV replication of DHBV-infected duck models. The in vivo anti-HBV activity was confirmed by histopathological improvement.Fourth, we studied the activity of compound 25 in a number of cancer cells in vitro and in vivo.25 potently inhibited cell proliferation with an IC50 of 0.95-4.55μM in a variety of aggressive human cancer cell lines including B-cell non-Hodgkin’s lymphomas, lung adenocarcinoma and acute myeloid leukemia. Mouse xenograft models of hepatocarcinoma (H22), sarcoma (S180) and gastric carcinoma (SGC7901) demonstrated that 25 had significant tumor growth inhibition activity in a dose-dependent manner with low toxicity.Finally, N3-methyl thymidine (3-meT) was synthesized and the crystal structure of FTO in complex with it was reported. FTO comprises an amino-terminal AlkB-like domain and a carboxy-terminal domain with a novel fold. In contrast with the structures of other AlkB members, FTO possess an extra loop covering one side of the conserved jelly-roll motif. Structural comparison shows that this loop selectively competes with the unmethylated strand of the DNA duplex for binding to FTO, suggesting that it has an important role in FTO selection against double-stranded nucleic acids. The ability of FTO to distinguish 3-meT or 3-meU from other nucleotides is conferred by its hydrogen-bonding interaction with the two carbonyl oxygen atoms in 3-meT or 3-meU. Taken together, these results provide a structural basis for understanding FTO substrate-specificity, and serve as a foundation for the rational design of FTO inhibitors. Future studies are needed to determine how they contribute to substrate recognition by FTO. Nevertheless, our structural information provides a starting point for the successful development of FTO inhibitors that holds promise for developing therapeutic agents to treat obesity or even diabetes.