Phenyl 2,3,4-tri-O-benzyl-1-thio-α-d-mannopyranoside monohydrate

In the title compound, C33H34O5S·H2O, the mannopyranoside ring adopts a chair conformation with the 2-α-thiophenyl group occupying an axial position. One of the pendant benzyl groups is disordered over two sets of sites in a 0.5:0.5 ratio. In the crystal, the water molecule makes two O—H⋯O hydrogen bonds to an adjacent sugar molecule with the O atoms of the primary alcohol and ether groups acting as acceptors. At the same time, the OH group of the sugar makes a hydrogen bond to a water molecule.

In the title compound, C 33 H 34 O 5 SÁH 2 O, the mannopyranoside ring adopts a chair conformation with the 2--thiophenyl group occupying an axial position. One of the pendant benzyl groups is disordered over two sets of sites in a 0.5:0.5 ratio. In the crystal, the water molecule makes two O-HÁ Á ÁO hydrogen bonds to an adjacent sugar molecule with the O atoms of the primary alcohol and ether groups acting as acceptors. At the same time, the OH group of the sugar makes a hydrogen bond to a water molecule.

Related literature
For background to the synthesis and properties of mannopyranosides, see: Boons (1991); Szurmai et al. (1994); Caravano et al. (2003); Grizot et al. (2006); Dohi et al. (2008). For ring conformation analysis, see: Cremer & Pople (1975 strategies for the regioselective transformations of monosaccharides to achieve glycosylation reactions or further functionalizations are of paramount importance. Furthermore, the knowledge of the conformations of carbohydrates alone or bound to protein gives access to key informations that can be exploited to understand biocatalytic processes or stereoelectronic effects (Caravano et al., 2003).
Numerous strategies of protections of mannopyranosides have been described in the litterature (e.g. Boons, 1991;Szurmai et al., 1994) in order to derivatise the primary alcohol. The title compound is also a key intermediate for the synthesis of heptosyl transferase inhibitors (Dohi et al., 2008;Grizot et al., 2006).
Crystal structure of the title compound confirms the expected relative stereochemistry : C1 R, C2 S, C3 S, C4 R, C5 R.
The 2-alpha-thiophenyl group on C1 and the O-benzyl group on C2 occupy an axial position, the two other O-benzyl groups (on C3 and C4) and carbon atom C6 occupying an equatorial position.
Thiophenyl-2,3,4-O-tri-benzyl-alpha-D-mannopyranoside co-crystallized with one water molecule (O W ). This water molecule is part of a H bond network involving the primary alcohol O6 and also secondary alcohol O2 (Table 1). Packing is further reinforced by van der Waals interactions involving the aromatic rings.

Experimental
The title compound was obtained by a six-step synthetic route that will be described in details elsewhere. Overall yield is 70%. Colourless prisms of (I) were obtained by evaporation of a solution in ethyl acetate.

Refinement
Disorder of the benzyl C(21) > C(27) moiety substituting oxygen O(4) was included in the refinement (0.5 occupacy for both parts that were restrained to have similar bond lengths and angles). H atoms on water oxygen atom O W and on alcohol oxygen atom O(6) were located by Fourier difference maps and allowed to ride on their parent O atoms.
All other H atoms were placed at idealized positions and allowed to ride on their parent atoms, with C-H = 0.97 Å and U iso (H) = 1.2U eq (C) for methylene groups, C-H = 0.93 Å and U iso (H) = 1.2U eq (C) for aromatic carbons, and C-H = 0.96 Å and U iso (H) = 1.5U eq (C) for the methyl group. Fig. 1. The molecular structure of (I): C-bound H atoms are omitted and disorder is not presented for clarity. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 Rfactors(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.