Browsing by Author "Mulani, Shaheen"

Now showing 1 - 2 of 2

Iterative One-Pot alpha-Glycosylation Strategy: Application to Oligosaccharide Synthesis
(2012-11-01)
Liu, Chih-Yueh Ivan
;
Mulani, Shaheen
;
Mong, Kwok-Kong Tony
;
應用化學系
;
Department of Applied Chemistry
Based on the combined use of dimethylformamide (DMF) modulation and neighboring group participation, three iterative one-pot a-glycosylation methods, i.e., one-pot (a,a)-, one-pot (beta,a)-, and one-pot (a,beta)-glycosylations, were developed. These methods are applicable to a range of thioglycosyl donors, confer stereocontrol in a-/beta-glycosidic bond formation, and thus provide for rapid access to oligosaccharides with various permutations of anomeric configurations. The utility of these one-pot glycosylation methods is demonstrated in the synthesis of eight non-natural and natural oligosaccharide targets, including the core 1 serine conjugate, core 8 serine conjugate, the D-Gal-a(1?3)-D-Glc-a(1?3)-L-Rha trisaccharide unit of the cell wall component in Streptococcus pneumoniae, and the D-Glc-a(1?2)-D-Glc-a(1?3)-D-Glc trisaccharide terminus of the N-linked glycan precursor. Confirmation of the anomeric configurations of these oligosaccharides is evidenced by 1H, 13C, 13C-non-proton decoupling, and heteronuclear correlation 2D NMR experiments. Global deprotection of selected oligosaccharide targets is illustrated.
Neighboring-Group Participation by C-2 Ether Functions in Glycosylations Directed by Nitrile Solvents
(2011-10-01)
Chao, Chin-Sheng
;
Lin, Ching-Yu
;
Mulani, Shaheen
;
Hung, Wei-Cheng
;
Mong, Kwok-kong Tony
Ether-protecting functions at C-2 hydroxy groups have been found to play participating roles in glycosylations when the reactions are conducted in nitrile solvent mixtures. The participation mechanism is based on intramolecular interaction between the lone electron pair of the oxygen atom of the C-2 ether function and the nitrile molecule when they are positioned in a cis configuration. A 1,2-cis glycosyl oxazolinium intermediate is formed. This participation, in conjunction with the anomeric effect of the glycosyl donor, confers high 1,2-trans selectivities on glycosylations. Further application of this concept has led to efficient preparations of alpha-(1 -> 5)-arabinan oligomers.