Donor Preactivation-Based Glycosylation:An Efficient Strategy for Glycan Synthesis

Carbohydrates have gained a lot of appreciation in the past few decades due to their important roles in numerous biological events.Acquiring a structurally well-defined carbohydrate compound is essential for the understanding of its functions.Although some innovative methods have been developed for the synthesis of complex oligosaccharides,glycan synthesis is in general still a time-consuming and difficult work.Herein,we will introduce the preactivation-based glycosylation strategy,which is an efficient protocol independent of the reactivity of glycosyl donor.This review will focus on summarizing the versatile applications of preactivation strategy in stereoselective glycosylation and one-pot assembly of biologically important oligosaccharides and even polysaccharides。

Controlled synthesis of CO_2-diol from renewable starter by reducing acid value through preactivation approach

Synthesis of polyols from carbon dioxide（CO2） is attractive from the viewpoint of sustainable development of polyurethane industry;it is also interesting to adjust the structure of the CO2-polyols for versatile requirement of polyurethane.However,when renewable malonic acid was used as a starter,the copolymerization reaction of CO2 and propylene oxide（PO） was uncontrollable,since it proceeded slowly（13 h） and produced 40.4 wt%of byproduct propylene carbonate（PC） with a low productivity of 0.34kg/g.A careful analysis disclosed that the acid value of the copolymerization medium was the key factor for controlling the copolymerization reaction.Therefore,a preactivation approach was developed to dramatically reduce the acid value to 0.6mg（KOH）/gby homopolymerization of PO into oligo-ether-diol under the initiation of malonic acid,which ensured the controllable copolymerization,where the copolymerization time could be shortened by 77%from 13 to 3 h,the PC content was reduced by 76%from 40.4 wt%to 9.4 wt%,and the productivity increased by 61%from 0.34 to 0.55 kg/g.Moreover,by means of preactivation approach,the molecular weight as well as the carbonate unit content in the CO2-diol was also controllable.

A five-component one-pot synthesis of phosphatidylinositol pentamannoside(PIM_5)

A practical and efficient synthesis of phosphatidylinositol pentamannoside （PIM5） was achieved based on a five-component one-pot sequential glycosylation protocol with exclusive regio- and stereo-selectivity. Two regioselective sequential glycosylations on inositol and p-tolyl thioglycosides as the sole type of building blocks made this protocol to avoid the tedious protective group manipulations. This synthetic strategy provides access to other important glycolipids with similar structures.