Methyl 2,3,6-tri- O -Benzoyl-4- O -(tert-butyldimethylsilyl)-β- D -galactopyranoside

: Methyl 2,3,6-tri- O -benzoyl-4- O -(tert-butyldimethylsilyl)-β- D -galactopyranoside was synthesized in 47% yield by the silylation of a partially benzoylated galactose derivative, prepared from methyl β- D -galactopyranoside. The product was characterized by 1 H-NMR, 13 C-NMR, IR and mass spectrometry.


Introduction
Galactose is a monosaccharide found in many glycans that cover a wide range of applications in biomedicine and in the bioeconomy [1,2]. Galectin-3, for example, plays a crucial role in many physiological processes, including cancer development and inflammation, by its recognition of βgalactoside derivatives. Thus, the synthesis of novel β-galactoside compounds as a means of inhibiting galectin-3 has been a growing area of research in recent years [3,4]. α-Galactosides are also important, such as α-galactosylceramides, which have been shown to be ligands for natural killer Tcells and to possess potent anti-tumour activity [5].
The conversion of β-glycosides to α-glycosides by anomerisation has been an interest in our group [6][7][8][9]. In the case of bioactive compounds containing a galactose monomer, improvements in the anomerisation reactions of galactose mono-and disaccharides could potentially lead to more efficient syntheses of such compounds from a wider range of starting materials. For this reason we have been exploring factors affecting reactivity to anomerisation, including the role of protecting groups, which includes the impact of silyl derivatives. In this context, we have prepared the title compound and provide the record of its synthesis and analytical data herein.
All reactions (with the exception of the deprotection step) were carried out under an inert nitrogen atmosphere using anhydrous solvents to ensure thoroughly dry reaction conditions. All reactions were monitored by TLC. Scheme 1. Synthesis of 6 from methyl β-D-galactopyranoside.

General Information
All analytical data for previously reported compounds (2-5) was found to be in accordance with data reported previously in the literature, and citations are provided. All reagents used were obtained from commercial sources and used without further purification. TLC experiments were performed using aluminium sheets pre-coated with silica gel 60 (HF254, E. Merck, Darmstadt, Germany). NMR experiments were carried out in CDCl3 using a 500 MHz spectrometer (Varian Ltd., CA, Palo Alto, USA), with the chemical shifts reported relative to internal Me4Si. NMR spectra were analysed using MestReNova software (version 11, Mestrelab Research, Santiago de Compostela, Spain). The IR spectrum was obtained using FTIR Spectrometer (Perkin Elmer Spectrum 100, Shelton, CT, USA). A mass spectrum was obtained using a Waters LCT Premier XE Spectrometer. Chromatography was performed with silica gel 60 (Sigma Aldrich, Wicklow, Ireland). Petroleum ether was the fraction with boiling point 40-60 °C.

Methyl 4,6-O-Benzylidene-2,3-di-O-benzoyl-β-D-galactopyranoside (3)
Compound 2 (1.95 g, 6.88 mmol) was dissolved in dry pyridine (10 mL) under nitrogen. 4-Dimethylaminopyridine (10 g) was added next, and the solution was then cooled to 0 °C. Benzoyl chloride (4.81 mL, 41.41 mmol) was added slowly, and the mixture was left at room temperature for 24 h. The mixture was then diluted with dichloromethane, washed with hydrochloric acid (to react with excess pyridine), dried over Na2SO4 and then concentrated to dryness under reduced pressure. Column chromatography, using a mixture of petroleum ether-EtOAc (2:1) as the mobile phase afforded 1.68 g (50%) of compound 3 as a white solid. 1 H-NMR spectroscopic data for the product was in agreement with data reported previously [14].