Browsing by Author "Chen, Min-Chun"

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Low-Concentration 1,2-trans beta-Selective Glycosylation Strategy and Its Applications in Oligosaccharide Synthesis
(2009)
Chao, Chin-Sheng
;
Li, Chen-Wei
;
Chen, Min-Chun
;
Chang, Shih-Sheng
;
Mong, Kwok-Kong Tony
This study develops an operationally easy, efficient, and general 1,2-trans beta-selective glycosylation reaction that proceeds in the absence of a C2 acyl function. This process employs chemically stable thioglycosyl donors and low substrate concentrations to achieve excellent beta-selectivities in glycosylation reactions. This method is widely applicable to a range of glycosylsubstrates irrespective of their structures and hydroxyl-protecting functions. This low-concentration 1,2-trans beta-selective glycosylation in carbohydrate chemistry removes the restriction of using highly reactive thioglycosides to construct 1,2-trans beta-glycosidic bonds. This is beneficial to the design of new strategies for oligosaccharide synthesis, as illustrated in the preparation of the biologically relevant beta-(1 -> 6)-glucan trisaccharide, beta-linked Gb(3) and isoGb(3) derivatives.
Tandem One-Pot Acetalation-Acetylation for Direct Access to Differentially Protected Thioglycosides and O-Glycosides with p-Toluenesulfonic Acid
(2009-03-03)
Mong, Kwok-Kong Tony
;
Chao, Chin-Sheng
;
Chen, Min-Chun
;
Lin, Chun-Wei
;
應用化學系
A new tandem one-pot acetalation-acetylation procedure is reported which streamlines routine protecting-group manipulation of carbohydrate molecules in production of differentially protected 0- and thioglycosides. This new procedure eliminates the use of highly toxic pyridine, and p-toluenesulfonic acid is employed as catalyst for acetalation and acetylation. Synthetic utility of the new procedure is demonstrated in the expeditious preparation of differentially protected glycosides from a wide variety of carbohydrate substrates including unprotected O-glycosides, thioglycosides, and N-acetyl neuraminic acid ester.
Versatile acetylation of carbohydrate substrates with bench-top sulfonic acids and application to one-pot syntheses of peracetylated thioglycosides
(2008-04-07)
Chao, Chin-Sheng
;
Chen, Min-Chun
;
Lin, Shih-Che
;
Mong, Kwok-Kong T.
;
應用化學系
Inexpensive and readily available sulfonic acids, p-toluenesulfonic acid, and sulfuric acid are versatile and efficient catalysts for the peracetylation of a broad spectrum of carbohydrate substrates in good yield and in a practical time frame. Three appealing features in sulfonic acid-catalyzed acetylation of free sugars were explored including (1) suppression of furanosyl acetate formation for D-galactose and L-fucose; (2) high yielding chemoselective acetylation of sialic acid under appropriate conditions; and (3) peracetylation of amino sugars with different amino protecting functions. Simple one-pot two step acetylation-thioglycosidation methods for the expeditious synthesis of p-tolyl per-O-acetyl thioglycosides were also delineated. (C) 2008 Elsevier Ltd. All rights reserved.