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Oxazolinium ion

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An oxazolinium ion is the species that is formed by anchimeric assistence in the glycosidic bond-cleaving reaction of a 2-deoxy-2-acetamido glycoside [1]. Solution studies have shown that the 2-acetamido N-acetyl group enhances spontaneous hydrolysis, of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside relative to methyl α-D-glucopyranoside, by more than 1000-fold [2]. An oxazolinium ion can be deprotonated to give an oxazoline, which is a stable and isolable species. Oxazolinium ions are common intermediates in the neighboring group participation mechanism of glycoside hydrolases, including glycoside hydrolases from families GH18, GH20, GH25, GH56, GH84, and GH85.

Oxazolinium ion.png
Mechanism for conversion of a 2-acetamido-2-deoxy-β-D-glycoside to an oxazolinium ion and oxazoline.


Anchimeric assistance can occur with modified 2-acetamido groups, such as 2-glycolylamido groups, affording hydroxymethyl substituted oxazolinium ion intermediates, such as that demonstrated for the glycoside hydrolases of GH84 [3].

See also

References

  1. Tews, I., Terwisscha van Scheltinga, A.C., Perrakis, A., Wilson, K.S., and Dijkstra, B.W. J. Am. Chem. Soc. 1997, 119, 7954-7959. [Tews1997]
  2. Piszkiewicz, D.; Bruice, T. C. J. Am. Chem. Soc. 1968, 90, 5844-5848. [Piszkeiwicz1968]
  3. Macauley MS, Chan J, Zandberg WF, He Y, Whitworth GE, Stubbs KA, Yuzwa SA, Bennet AJ, Varki A, Davies GJ, and Vocadlo DJ. Metabolism of vertebrate amino sugars with N-glycolyl groups: intracellular β-O-linked N-glycolylglucosamine (GlcNGc), UDP-GlcNGc, and the biochemical and structural rationale for the substrate tolerance of β-O-linked β-N-acetylglucosaminidase. J Biol Chem. 2012 Aug 17;287(34):28882-97. DOI:10.1074/jbc.M112.363721 | PubMed ID:22692202 | HubMed [Macauley2012]
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