Stereoselective 1,2-cis glycosylation of 2-O-allyl protected thioglycosides.
The technique of intramolecular aglycon delivery (IAD), whereby a glycosyl acceptor is temporarily appended to a hydroxyl group of a glycosyl donor is an attractive method that can allow the synthesis of 1,2-cis glycosides in an entirely stereoselective fashion. 2-O-Allyl protected thioglycoside donors are excellent substrates for IAD, and may be glycosylated stereoselectively through a three-step reaction sequence. This sequence consists of quantitative yielding allyl bond isomerisation, to produce vinyl ethers that can then undergo N-iodosuccinimide mediated tethering of the desired glycosyl acceptor, and subsequent intramolecular glycosylation, to yield either alpha-glucosides or beta-mannosides accordingly. Although attempted one-pot tethering and glycosylation is hampered by competitive intermolecular reaction with excess glycosyl acceptor, this problem can be simply overcome by the use of excess glycosyl donor. Allyl mediated IAD is a widely applicable practical alternative to other IAD approaches for the synthesis of beta-mannosides, that is equally applicable for alpha-gluco linkages. It is advantageous in terms of both simplicity of application and yield, and in addition has no requirement for cyclic 4,6-protection of the glycosyl donor.
Aloui
Mahmoud
M
Dyson Perrins Laboratory, Oxford University, South Parks Road, Oxford, OX1 3QY, UK.
Chambers
David J
DJ
Cumpstey
Ian
I
Fairbanks
Antony J
AJ
Redgrave
Alison J
AJ
Seward
Christopher M P
CM
D003432:Cross-Linking Reagents / Q000737:chemistry; D004187:Disaccharides / Q000138:chemical synthesis / Q000737:chemistry; D006031:Glycosylation; D009844:Oligosaccharides / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D013388:Succinimides / Q000737:chemistry; D013865:Thioglycosides / Q000737:chemistry*
D003432:Cross-Linking Reagents; D004187:Disaccharides; D009844:Oligosaccharides; D013388:Succinimides; D013865:Thioglycosides; C008155:N-iodosuccinimide