Two efficient routes for rapid assembly of the tumor-associated carbohydrate antigen Globo-H hexasaccharide 2 by the pre-activation based iterative one pot strategy are reported. The first method involves the sequential coupling of four glycosyl building blocks, leading to the desired hexasaccharide in 47% overall yield in one-pot. Although model study on constructing the challenging Gal-α-1,4-Gal linkage in Gb3 trisaccharide yielded the desired α linkage almost exclusively, similar approach to assemble the hexasaccharide led to formation of significant amount of β anomer. As an alternative, the second synthesis utilizes three components in one pot with the Gal-α-1,4-Gal linkage pre-formed, producing the desired hexasaccharide in a similar overall yield as the four component approach. Both methods demonstrate that oligosaccharides containing α and β linkages within the same molecule can be constructed in one pot via the pre-activation based approach with higher glyco-assembly efficiencies than the automated solid phase synthesis strategy. Furthermore, because glycosylations can be carried out independent of anomeric reactivities of donors, it is not necessary to differentiate anomeric reactivities of building blocks through extensive protective group adjustment for chemoselective glycosylation. This confers great flexibilities in building block design allowing matching of the donor with the acceptor leading to improved overall yield.
Gangliosides have attracted much attention due to their important biological properties. Herein, we report the first chemoenzymatic syntheses of two globo series of ganglioside oligosaccharides, Globo-H 1 and stage-specific embryonic antigen-4 (SSEA-4) 2. The common precursor SSEA-3 pentasaccharide for these two compounds was assembled rapidly using the pre-activation based one-pot glycosylation method. The stereoselectivity in forming the 1,2-cis linkage in SSEA-3 was attributed to a steric buttressing effect of the donor rather than electronic properties of the glycosyl donors. SSEA-3 was then successfully fucosylated by the fucosyltransferase WbsJ and sialylated by sialyltransferases CST-I and PmST1 producing Globo-H and SSEA-4 respectively.
The DoE (Design of Experiments)-based calibration method that incorporates models is called MBC (Model Based Calibration) and accomplishes modeling and optimization with MATALAB Toolbox-MBC Model Fitting and MBCOptimization. This methodology is provided with less calibration time as well as identical accuracy of measurement. This paper presents a DoE-based experiment to investigate the effects of the injection timing, rail pressure, pilot injection timing and pilot injection quantity on performance and emissions of a common rail heavy duty diesel, find out the optimal combination of such parameters.
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