Browsing by Author "Pradhan, Tapan Kumar"

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(2-Ketulosonyl)onate 2,3-O-thionocarbonate donors for the synthesis of KO and KDO alpha-glycosides and a one-pot glycosylation method for 2-keto acid donors
(2020-08-21)
Mong, Kwok-Kong Tony
;
Pradhan, Tapan Kumar
;
Chiu, Cheng-Hsin
;
Hung, Wei-Cheng
;
Chen, Chao-Ju
We report a short synthetic strategy for direct preparation of (2-ketulosonyl)onate donors. These donors feature a cyclic thionocarbonate group at the C2 and C3 positions, which plays a multitude of chemical roles. It protects the C2 and C3 hydroxyls during building block preparation. In glycosylation, the thionocarbonate can be activated by a sulfenylating promoter and serves as a leaving group. Because of its beta-configuration, it also plays the role of a stereo-directing group during the formation of the alpha-glycosidic bond. In addition, the thionocarbonate donors can couple with thioglycoside acceptors. This orthogonal property was used for the development of the first one-pot glycosylation method for 2-keto acid sugars.
Formal Synthesis of 3-Deoxy-D-manno-Octulosonic Acid (KDO) and 3-Deoxy-D-arabino-2-heptulosonic Acid (DAH)
(2013-01-01)
Pradhan, Tapan Kumar
;
Lin, Chun Cheng
;
Mong, Kwok Kong Tony
;
應用化學系
;
Department of Applied Chemistry
Practical synthetic routes to 3-deoxy-D-manno-octulo-sonic acid (KDO) and 3-deoxy-D-arabino-2-heptulosonic acid (DAH) from common sugar substrates are reported. Chain homologation of the sugar substrates was accomplished by Wittig olefination and Corey-Fuchs alkynylation. A new cyclization strategy was investigated to access the desired pyranosyl isomer of the KDO target.
Glycosylation Chemistry of 3-Deoxy-D-manno-Oct-2-ulosonic Acid (Kdo) Donors
(2015-04-01)
Pradhan, Tapan Kumar
;
Mong, Kwok Kong Tony
;
交大名義發表
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National Chiao Tung University
3-Deoxy-D-manno-Oct-2-ulosonic acid (Kdo)-containing oligosaccharides are a conserved carbohydrate component in lipopolysaccharides ( LPSs) of the outer membrane of Gram-negative bacteria, and they are also present in capsular polysaccharides ( CPSs) of bacteria and plant cells. The association of the bacterial LPS with the pathophysiology of bacterial infection have long been recognized. Structure-pathophysiology studies of bacterial infection need to use pure and homogeneous LPS fragments. Such a requirement can be fulfilled by the synthesis of Kdo glycosides and related Kdo-oligosaccharide conjugates. This article provides an overview of the glycosylation chemistries of the synthesis of Kdo alpha-/beta-glycosides, oligosaccharides with Kdo units such as LPS core oligosaccharides, and lipid A derivatives.
Preparation of a Protected 3-Deoxy-D-manno-oct-2-ulosonate Glycal Donor for the Synthesis of beta-KDO-Containing Oligosaccharides
(2014-03-07)
Pradhan, Tapan Kumar
;
Lin, Chun Cheng
;
Mong, Kwok-Kong Tony
;
應用化學系
;
Department of Applied Chemistry
A practical method for the synthesis of KDO glycal donors was developed. The prepared KDO donors exhibited excellent disastereoselectivity of glycosylation in a CH2Cl2-CH3CN solvent mixture, which was found to be associated with the isopropylidene protection at the C-4 and C-5 hydroxyls. The synthetic use of the KDO donor was demonstrated in the preparation of beta-KDO-containing oligosaccharides.
Total Synthesis of a Glycoglycerolipid from Meiothermus taiwanensis through a One-Pot Glycosylation Reaction and Exploration of its Immunological Properties
(2013-12-01)
Ghosh, Bhaswati
;
Lai, Yen-Hsun
;
Shih, Yu-Yin
;
Pradhan, Tapan Kumar
;
Lin, Chun-Hung
The total synthesis of a glycoglycerolipid isolate of Meiothermus taiwanensis and its truncated structural analogues is reported. Our synthesis employed DMF-modulated and low-concentration glycosylation reactions for the construction of - and -glycosidic bonds in the absence of participating protecting groups. Further simplification of the synthesis was achieved by employing a low-concentration one-pot glycosylation procedure. Preliminary immunological studies showed that one of the truncated structural analogues suppressed the cytokine production of THP-1 monocytes.