Synthetic nucleoside mimics with modified nucleobase and/or sugar moieties are of considerable importance in the search for promising candidates leads endowed with biologically interesting activity [1] . Some well-known nucleoside drugs consist of antiviral drugs ribavirin, acyclovir and zidovudine, as well as the anticancer drugs gemcitabine and cladribine. These nucleoside analogs are able to mimic natural nucleosides and as such serve as building units or inhibitors to interfere in nucleic acid synthesis or block the biological processes involving the action of nucleos(t)ides [2] -[5] . Then, they can inhibit replicating viruses and uncontrolable cancer cell proliferation, leading to potent and effective antiviral and anticancer activity, respectively. Based on the rationale to combine the special features of unnatural triazole heterocycles with those of the appended aromatic groups on the nucleobases, we have been engaged in sythesizing structurally diverse triazole nucleoside analogs bearing aromatic moieties on the triazole nucleobase with the view of identifying new structural leads exhibiting antiviral and anticancer activity. The synthesis of these nucleosides was achieved via transition metal catalyzed modern synthetic reactions, such as Suzuki coupling [6] , sonogashira reaction [7] , C-N coupling [8] and C-S coupling [9] , starting with readily available bromotriazole nucleosides intermediate, and the synthetic procedure developed is simple and easy to perform.

We report on the synthesis of an important anticancer nucleosides intermediate, using a simple and efficient condendsation procedure, giving the corresponding products in moderate yield. The intermediate can be further exploited for the synthesis of novel structural nucleoside analogues, which are currently a class of extremely important compounds in the search for anticancer drug candidates.

The synthesis of the title anticancer nucleosides intermediate 1 is shown in Scheme 1. The structures and conformations of compound 1 were further elucidated by their single crystal X-ray diffraction, as shown in Figure 1. Three-dimensional molecular-packing diagram of the title compound was shown in Figure 2.

Scheme 1. Synthesis of the anticancer nucleosides intermediate 1.

The crystals of 1 were obtained by slow evaporation of their solution in ethyl acetate/petroleum ether (3:1, v/v) mixtures. The crystal structures of 1 clearly revealed that it has well-defined geometry due to the rigidity that the fused rings confer on the molecule. Its structures and conformations were confirmed by single crystal X-ray diffraction. The molecular conformation is stabilized by N---H...O hydrogen bond; the crystal packing is governed by C---H...O and C---H...N hydrogen interactions resulting in a three-dimensional network. These values are suitable for the complexation of an aromatic ring by p-p stacking interactions.

A intermediate bromotriazole nucleoside (2R,3S,4S,5R)-2-(acetoxymethyl)-5-(3-bromo-5-(methoxycarbonyl)- 1H-1,2,4-triazol-1-yl)tetrahydrofuran-3,4-diyl diacetate has been synthesised. The structure and conformation were confirmed by single crystal X-ray diffraction and ¹H NMR. Novel triazole nucleoside analogs bearing aromatic systems on the nucleobase have been synthesised from this intermediate. They have great potential to bind aromatic guest molecules. Further studies on their binding properties are in progress.

We thank the Shaanxi provincial Department of Education (Grant No. 2013JK0659) and Shaanxi University of Technology (SLGQD13-2) for financial support, the Hubei provincial Department of Education (Grant No. D20112503), Hubei Key Laboratory of Pollutant Analysis & Reuse Technology (Grant No. KL2013G06).