[(2R,3S,5R)-3-Acetoxy-5-(5-formyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-yl)-2,3,4,5-tetrahydrofuran-2-yl]methyl acetate

In the two independent but very similar molecules (A and B) of the title compound, C14H16N2O8, both six-membered pyrimidine rings are nearly planar [maximum deviations = 0.010 (3) Å in A and 0.028 (3) Å in B]. The five-membered furanose ring in molecule A adopts an envelope conformation, while the same ring in molecule B has a twisted conformation. In the crystal, the A molecules are linked via a pair of intermolecular N—H⋯O hydrogen bonds, forming dimers. Each A molecule is further linked to a B molecule via a second N—H⋯O hydrogen bond. There are also a number of C—H⋯·O interactions present, leading to the formation of a three-dimensional network.

In the two independent but very similar molecules (A and B) of the title compound, C 14 H 16 N 2 O 8 , both six-membered pyrimidine rings are nearly planar [maximum deviations = 0.010 (3) Å in A and 0.028 (3) Å in B]. The five-membered furanose ring in molecule A adopts an envelope conformation, while the same ring in molecule B has a twisted conformation. In the crystal, the A molecules are linked via a pair of intermolecular N-HÁ Á ÁO hydrogen bonds, forming dimers. Each A molecule is further linked to a B molecule via a second N-HÁ Á ÁO hydrogen bond. There are also a number of C-HÁ Á ÁÁO interactions present, leading to the formation of a three-dimensional network.   Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 2; Ày; z; (ii) x À 1 2 ; Ày þ 1 2 ; Àz; (iii) x; y; z þ 1; (iv) x þ 1 2 ; Ày þ 1 2 ; Àz.

Comment
Many pyrimidine nucleosides with modification on the 5-position of the pyrimidine ring have drawn much attention due to their interesting pharmacological properties, such as antitumor, antiviral, and antimicrobial activities (De Clercq et al., 2005;Agrofoglio et al., 2003, Lee et al., 2009. The title compound has been used as a powerful synthon for the preparation of a variety of nucleoside derivatives due to the rich and extensive chemistry of the aldehyde carbonyl (Fan et al., 2006a(Fan et al., , 2006b(Fan et al., , 2010(Fan et al., , 2011Zhang et al., 2009). However, its crystal structure has not been reported as yet.
The absolute structure of the title compound is known because the synthetic procedure does not affect stereogenic atoms of the starting compound. In the two independent (A & B) but very similar molecules of the title compound ( Fig. 1) all the bond lengths and bond angles are within normal ranges. In molecule A the O1-C4 bond is a little longer than bond O1-C1, as is bond O16-C15 compared to bond O16-C18 in molecule B. This is similar to the situation in 2'-deoxy-3',5'-di-O-acetyluridine (Luo et al., 2007), but different to that in 2,3,5-triacetyluridine (Low & Wilson, 1984). The atoms connected directly with the pyrimidine ring and the atoms in the aldehyde carbonyl group in the 5-position of the pyrimidine ring are coplanar with the pyrimidine ring, which means there is an exstensive conjugated system in each molecule. The five-membered furanose ring in molecule A adopts an envelope conformation with atom C2 at the flap, while in molecule B the five-membered ring is twisted on bond C15-C16.
In the crystal, two A molecules form a pseudosymmetric dimer connected via N-H···O hydrogen bonds, involving the N atom of the pyrimidine base and the adjacent carbonyl O atom of the pyrimidine base. Each A molecule is further connected to a B molecule via an N-H···O hydrogen bond involving the N atom of the pyrimidine base and carbonyl O atom of the acetoxy groups in the 3'-position of the furanose ring (see Table 1 and Fig. 2 for details). There are also a number of C-H···O interactions present leading to the formation of a three-dimensional network (Table 1).

Experimental
The title compound was synthesized following the previously reported procedure (Fan, et al., 2006b). Single crystals, suitable for X-ray diffraction analysis, were obtained by slow evaporation of the solvents from a dichloromethane-petroleum ether (1:1 v/v) solution of the title compound.