Crystal structure of 3-C-(N-benzyloxycarbonyl)aminomethyl-3-deoxy-1,2:5,6-di-O-isopropylidene-α-d-allofuranose

The title compound consists of a substituted 2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxolane skeleton. The furanose ring adopts a conformation close to C 3-exo. Both dioxolane rings adopt envelope conformations with an O atom as the flap in each case. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, forming chains propagating along the b-axis direction.

The synthesis of sugar amino acids and their properties and applications have been reported on by Rjabovs et al. (2015), and reviewed by  and Risseeuw et al. (2013). The title compound can be used as a precursor for the syntheses of imino sugars and 10-aza-C-nucleosides (Filichev & Pedersen, 2001). The syntheses and biological properties of imino sugars have been reviewed by Ló pez et al. (2012), while the syntheses and biological properties of aza-nucleosides have been reported on by Romeo et al. (2010) and Merino (2006). ISSN 2056-9890

Structural commentary
The title compound, Fig. 2, consists of a tetrahydrofuran core fused with a dioxolane ring and substituted with dioxolane and (N-benzyloxycarbonyl)aminomethyl moieties. The furanose ring adopts a conformation close to C 3 -exo. On the other hand, the furanose ring may be viewed as an envelope, where atom C3 deviates from the mean plane through atoms O1/C1/ C2/C4 by 0.567 (2) Å . The fused dioxolane ring also adopts an envelope conformation, where O14 deviates from the mean plane through the four near planar atoms (O12/C1/C2/C13) by 0.422 (2) Å . The dihedral angle between the planar fragments of these rings is 67.1 (1) . The five-membered ring of the 2,2-dimethyl-1,3-dioxolan-4-yl group also adopts an envelope conformation, with atom O7 deviating from the mean plane through the four planar atoms (O9/C5/C6/C8) by 0.519 (1) Å .

Supramolecular features
In the crystal, molecules are linked by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, forming chains propagating along the b-axis direction ( Fig. 3 and Table 1).

Figure 2
The molecular structure of compound (1), with atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 3
The crystal packing of compound (1), viewed along the a axis. Hydrogen bonds are shown as dashed lines (see Table 1 for details). For clarity only H atoms involved in these interactions have been included. Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x; y þ 1; z; (ii) x; y À 1; z.

Synthesis and crystallization
The two methods for the synthesis of compound (1) are illustrated in Fig. 1. From compound (2): A mixture of nitromethyl compound (2) (5.00 g, 16.5 mmol, 1 equiv.) and 10% Pd/C (1.00 g) in MeOH (200 ml) was hydrogenated under 40 atm pressure at 313 K overnight (TLC control). The resulting reaction mixture was filtered through celite and the filtrate was evaporated under reduced pressure. The residue was dissolved in THF (60 ml) and a solution of K 2 CO 3 (2.50 g, 18.1 mmol, 1.1 equiv.) in water (35 ml) was added. The resulting mixture was cooled to 273 K and N-(benzyloxycarbonyloxy)succinimide (4.50 g, 18.1 mmol, 1.1 equiv) was added portion-wise. The reaction mixture was stirred at 273 K for 4 h (TLC control). Solid K 2 CO 3 (1 g) was added and the formed layers were separated. The organic phase was washed with saturated aqueous solution of NaHSO 4 (50 ml) while the aqueous phase was extracted with a mixture of hexanes and CH 2 Cl 2 (3 Â 100 ml, 8:2 v/v). The combined organic phase was washed with brine (2 Â 100 ml), dried over Na 2 SO 4 , filtered and evaporated under reduced pressure. Crude product (1) was obtained as a yellow oil (6.60 g, 98% crude) and used further without additional purification.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.