2,3,4,6-Tetra-O-benzoyl-4-nitrophenyl-1-thio-α-d-mannopyranoside–dichloromethane–diethyl ether mixed solvate (1/0.53/0.38)

The title compound, C40H31NO11S·0.53CH2Cl2·0.38C4H10O, was synthesized in two steps from mannose pentaacetate and single crystals were grown by slow evaporation. The structure was determined by single-crystal X-ray diffraction, confirming the α-configuration of the anomeric thioaryl substituent. The asymmetric unit contains two crystallographically distinct molecules of the carbohydrate. The central pyranose rings of these are geometrically similar, but there are differences in the orientations of the benzoate substituents.

The title compound, C 40 H 31 NO 11 SÁ0.53CH 2 Cl 2 Á0.38C 4 H 10 O, was synthesized in two steps from mannose pentaacetate and single crystals were grown by slow evaporation. The structure was determined by single-crystal X-ray diffraction, confirming the -configuration of the anomeric thioaryl substituent. The asymmetric unit contains two crystallographically distinct molecules of the carbohydrate. The central pyranose rings of these are geometrically similar, but there are differences in the orientations of the benzoate substituents.

Comment
Thioglycosides are extremely useful and versatile glycoside donors for the synthesis of oligosaccharides, which may be activated by a wide range of electrophiles and also by electrochemical methods (France et al., 2004). The nature of an aromatic substituent of an aryl thioglycoside has a strongly modulating effect on the reactivity of such a thioglycoside; strongly electron withdrawing substituents greatly reduce their reactivity towards electrophiles (Roy et al., 1992) and also increase their oxidation potentials. Such 'disarmed' (Mootoo et al., 1988) thioglycosides may themselves therefore be used as acceptors for the glycosylation of more reactive 'armed' thioglycoside donors. The title compound was obtained by a trans-esterification sequence from the corresponding peracetylated thioglycoside, itself synthesized from mannose penta-acetate by treatment with 4-nitrothiophenol and boron trifluoride etherate in dichloromethane, by Zemplen deacetylation followed by reaction with benzoyl chloride in pyridine in the presence of N,N-dimethylaminopyridine (DMAP).
Experimental 1,2,3,4,6-Penta-O-acetyl-D-mannopyranoside (2.17 g, 3.55 mmol) and 4-nitrothiophenol (1.75 g, 11.26 mmol) were suspended in anhydrous dichloromethane (15 ml), under an atmosphere of argon, the mixture was cooled to 0°C, and boron trifluoride diethyl etherate (3.3 ml, 26 mmol) was added dropwise. The reaction mixture was then stirred at room temperature until after 66 h, t.l.c. (petroleum ether/ethyl acetate, 1:1) indicated complete consumption of the starting material, and the formation of a single product (Rf 1/2). The reaction was quenched by the addition of triethylamine (10 ml), and the mixture was then partitioned between water (200 ml) and dichloromethane (200 ml supplementary materials sup-2 4-Nitrophenyl 2,3,4,6-tetra-O-acetyl-1-thio-α-D-mannopyranoside, as prepared above, (1.66 g, 3.43 mmol) was dissolved in methanol (26 ml) and sodium methoxide (0.20 g, 3.80 mmol) was added. The reaction mixture was then stirred at 22°C and, after 45 min, t.l.c. (petroleum ether/ethyl acetate, 1:1) indicated complete consumption of the starting material (Rf 0.6) and the formation of a single product (Rf 0.1). Cation exchange resin IR-120 was then added until neutral pH was attained, and then the mixture was filtered and the solvent was removed under reduced pressure. Azeotropic evaporation with toluene (15 ml) furnished the crude product, which was used in the next step without further purification. The residue was dissolved in pyridine (10 ml) and the mixture was cooled to 0°C. Benzoyl chloride (2.5 ml, 21.52 mmol), and N,N-dimethylaminopyridine (97 mg, 0.79 mmol) were added and the reaction mixture was stirred at room temperature for 24 h after which time, t.l.c.

Refinement
A single-crystal (approximately 0.24 x 0.28 x 0.34 mm) was mounted on a glass fibre using perfluoropolyether oil and cooled rapidly to 150 K in a stream of cold N 2 using an Oxford Cryosystems CRYOSTREAM unit (Cosier and Glazer, 1986). Diffraction data were measured using an Enraf-Nonius KappaCCD diffractometer (graphite-monochromated Mo Kα radiation, λ = 0.71073 Å). Intensity data were processed using the DENZO-SMN package (Otwinowski and Minor, 1997).
The structure was solved in the space group P 2 1 using the direct-methods program SIR92 (Altomare et al., 1994), which located all ordered non-hydrogen atoms. Subsequent full-matrix least-squares refinement was carried out using the CRYSTALS program suite (Betteridge et al., 2003). Coordinates and anisotropic thermal parameters of all non-hydrogen atoms were refined.

supplementary materials sup-3
A difference Fourier map showed the presence of several peaks of electron density located within a small cavity within the lattice. These were identified as the non-hydrogen atoms of a disordered mixture of CH 2 Cl 2 and Et 2 O. The coordinates, isotropic thermal parameters and site occupancies of these were refined. The C-Cl distances were restrained to 1.77 (2) Å, the C-O distances to 1.44 (2) Å and the C-C distances to 1.50 (2) Å. Bond angles were restrained to 112 (2)° and similarity restraints applied to the thermal parameters of directly-bonded atoms.

Special details
Refinement. Geometric restraints were applied to the disordered solvent. The C-Cl bond lengths of the dichloromethane were restrained to 1.77 (2) Å and the Cl-C-Cl angle t0 112 (2) °. The C-O bond lengths of the diethyl ether were restrained to 1.44 (2) Å, the C-C bond lengths to 1.50 (2) Å and athe C-O-C and C-C-O angles to 112 (2) °. Similarity restraints were applied to the displacement parameters of directly-bonded atoms.