| Carbohydrate chemistry and glycobiology have received much attention in recent years. Carbohydrate and glycoconjugates play an important role of life activities. As the polyhydroxy characteristics of carbohydrate, its structure is very complex and heterogeneous, and thus it is very difficult to separate from the living body for biological research. Chemical synthesis method can solve this problem. In this thesis, we proposed a new strategy of selective removal of the trimethylsilyl(TMS) protecting group at C-6position from per-O-trimethylsilylated sugars in the presence of ammonium acetate. The technology was successful extended to sphingosine, and the primary O-TMS was removed in good yield to afford9b, a useful intermediate for the preparation of a-GalCer.1. The selective removal of O-TMS protecting group at C-6position(1) As a model system, per-O-trimethylsilylated a-D-galactose was treated with ammonium acetate varying the quantity of catalyst and reaction solvent at different temperature. It was observed that the use of2.0equivalent of NH4OAc in co-solvent of CF2Cl2and CH3OH (v/v=1/1) at r.t. give6-detrimethylsilylated galactose in good to excellent yield. This method provided several advantages such as mild reaction conditions, high regioselectivity, high yields and convenient post-processing.(2) In the reaction conditions of (1), this methodology was extended to per-O-trimethylsilylated monosaccharides and disaccharides.(3) After the free C-6hydroxyl of the galactose and galactoside protected by acetyl and trichloroacetonitrile, they were treated with ammonium acetate, but there was no product detected by TLC.2. efficient synthesis of a-galactosylceramide intermediates(1) the primary O-TMS protecting group of per-O-trimethylsilylated phyto-sphingosine (9a) was selectively removed in the presence of ammonium acetate in high yield to afford9b.(2) per-O-trimethylsilylated a-galactosyl iodide was coupled with activated sphingosine acceptors(9b), the silyl groups are readily removed upon methanolysis. This three step, one-pot synthetic platform provides rapid access to an important molecule of a-galactosylceramide intermediates(10). |
