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Versatile synthesis and mechanism of activation of S-benzoxazolyl glycosides.

ABSTRACT: As a part of a program for developing new efficient procedures for stereoselective glycosylation, a range of S-benzoxazolyl (SBox) glycosides have been synthesized. The mechanistic aspects of the SBox moiety activation for glycosylation via a variety of conceptually different pathways in the presence of thiophilic, electrophilic, or metal-based promoters have been investigated.

SUBMITTER: Kamat MN

PROVIDER: S-EPMC2535574 | biostudies-literature | 2007 Aug

REPOSITORIES: biostudies-literature

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Versatile synthesis and mechanism of activation of S-benzoxazolyl glycosides.

Kamat Medha N MN Rath Nigam P NP Demchenko Alexei V AV

The Journal of organic chemistry 20070804 18

As a part of a program for developing new efficient procedures for stereoselective glycosylation, a range of S-benzoxazolyl (SBox) glycosides have been synthesized. The mechanistic aspects of the SBox moiety activation for glycosylation via a variety of conceptually different pathways in the presence of thiophilic, electrophilic, or metal-based promoters have been investigated. ...[more]

PMID: 17676918

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Project description:Stereoselective manipulations at the C1 anomeric position of saccharides are one of the central goals of preparative carbohydrate chemistry. Historically, the majority of reactions forming a bond with anomeric carbon has focused on reactions of nucleophiles with saccharide donors equipped with a leaving group. Here, we describe a novel approach to stereoselective synthesis of C-aryl glycosides capitalizing on the highly stereospecific reaction of anomeric nucleophiles. First, methods for the preparation of anomeric stannanes have been developed and optimized to afford both anomers of common saccharides in high anomeric selectivities. We established that oligosaccharide stannanes could be prepared from monosaccharide stannanes via O-glycosylation with Schmidt-type donors, glycal epoxides, or under dehydrative conditions with C1 alcohols. Second, we identified a general set of catalytic conditions with Pd2(dba)3 (2.5 mol%) and a bulky ligand (JackiePhos, 10 mol%) controlling the ?-elimination pathway. We demonstrated that the glycosyl cross-coupling resulted in consistently high anomeric selectivities for both anomers with mono- and oligosaccharides, deoxysugars, saccharides with free hydroxyl groups, pyranose, and furanose substrates. The versatility of the glycosyl cross-coupling reaction was probed in the total synthesis of salmochelins (siderophores) and commercial anti-diabetic drugs (gliflozins). Combined experimental and computational studies revealed that the ?-elimination pathway is suppressed for biphenyl-type ligands due to the shielding of Pd(II) by sterically demanding JackiePhos, whereas smaller ligands, which allow for the formation of a Pd-F complex, predominantly result in a glycal product. Similar steric effects account for the diminished rates of cross-couplings of 1,2-cis C1-stannanes with aryl halides. DFT calculations also revealed that the transmetalation occurs via a cyclic transition state with retention of configuration at the anomeric position. Taken together, facile access to both anomers of various glycoside nucleophiles, a broad reaction scope, and uniformly high transfer of anomeric configuration make the glycosyl cross-coupling reaction a practical tool for the synthesis of bioactive natural products, drug candidates, allowing for late-stage glycodiversification studies with small molecules and biologics.

Dataset Information

Versatile synthesis and mechanism of activation of S-benzoxazolyl glycosides.

Publications

Versatile synthesis and mechanism of activation of S-benzoxazolyl glycosides.

Similar Datasets

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