Solvent participation in a one-pot glycosylation strategy (SPOG) was developed on the basis of the low concentration b-selective glycosylation method. This strategy enables the production of a b-glycosidic bond in a one-pot oligosaccharide synthesis without or with minimal use of any C-2 participating function.Keywords: low concentration glycosylation; nitriles; one-pot process; reactivity-based reaction; solvent participation Oligosaccharide synthesis involves the coupling of carbohydrate units in a regio-and stereospecific manner. [1,2] This process can be accelerated by a onepot glycosylation strategy [3] and automated solidphase synthesis.[4] One-pot glycosylation refers to cascade coupling of three or more carbohydrate units in one shot.[5] A key element in these reactions is the stereochemical control of glycosidic bond formation, which often relies on traditional methods. A point in case is the use of neighbouring group participation for the construction of a 1,2-trans b-glycosidic bond. [6] However, such an approach requires the selective introduction of a C-2 participating function and it occasionally suffers from side reactions that decreases the yield of glycosylations. [7,8] Although alternative methods are available, only few of them are adapted to one-pot oligosaccharide synthesis. [9,10] Recently, a low concentration b-selective glycosylation (LCG) method was developed.[11] This method makes use of: (i) a CH 2 Cl 2 /CH 3 CN/EtCN solvent system; (ii) low substrate concentrations (10-15 mM); and (iii) low reaction temperature (À70 to À60 8C) to construct the 1,2-trans b-glycosidic bond without reliance on any C-2 participating function. A search in the literature revealed that the solvent effect on reactivity of glycosyl donors has been explored for onepot oligosaccharide synthesis, but the participation effect of an alkyl nitrile solvent on one-pot glycosylation has not been investigated. [12,13] This lack of information motivated us to develop a new one-pot glycosylation strategy on the basis of the LCG method. As the participation effect of an alkyl nitrile solvent is explored, we coin this approach as a solvent participation in one-pot glycosylation (SPOG) strategy.According to the order of solvent addition, two SPOG procedures were studied (Figure 1). In the first procedure, all glycosylation steps are performed under LCG conditions. As such, oligosaccharides with 1,2-trans b-glycosidic bonds are prepared (Figure 1 a). [10] In the second procedure, CH 2 Cl 2 and a conventional substrate concentration are employed for the first glycosylation step. Upon completion of this reaction, calculated amounts of CH 3 CN and EtCN are added to the mixture providing the LCG conditions for the next glycosylation reaction (Figure 1 b). The merit of the second procedure is to allow adjustment of the solvent mixture for the construction of a-and b-glycosidic bonds.Before exploiting the SPOG procedures, it was crucial to know if the LCG method would apply to nonthioglycoside donors. Thus, perbenzyl thiog...
Most natural 2‐acetamido‐2‐deoxyglycosides exist in a 1,2‐trans‐β‐glycosidic configuration. This study investigated the use of 2‐azido‐2‐deoxythioglycosides for 1,2‐trans‐β‐glycosidic bond formation under low‐concentration glycosylation conditions. Further application of the 2‐azido‐2‐deoxythioglycosyl substrates for one‐pot oligosaccharide synthesis was demonstrated in the synthesis of protected β‐(1→6)‐N‐acetylglucosamine trimer, core‐6–serine conjugate, and F1–α serine conjugate.
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