ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComplete kinetic isotope effect description of transition states for acid-catalyzed hydrolyses of methyl .alpha.- and .beta.-glucopyranosidesAndrew J. Bennet and Michael L. SinnottCite this: J. Am. Chem. Soc. 1986, 108, 23, 7287–7294Publication Date (Print):November 1, 1986Publication History Published online1 May 2002Published inissue 1 November 1986https://pubs.acs.org/doi/10.1021/ja00283a025https://doi.org/10.1021/ja00283a025research-articleACS PublicationsRequest reuse permissionsArticle Views824Altmetric-Citations131LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
The homoallylically substituted alcohols (1-OH and 3-OH) of the sterically congested alkene adamanylideneadamantane (1-H) react with acid catalysis in a solvent of 50% v/v acetic acid:50% v/v aqueous sulfuric acid at 110 degrees C to give a saturated ketone 5, the structure of which has been characterized by (1)H and (13)C NMR spectroscopy and by single-crystal X-ray diffraction. Isotopic labeling studies demonstrate that the reaction involves a stereospecific protonation of the double bond and an intramolecular 1,4-hydride transfer from the secondary alcohol C-H to the other carbon of the olefin. The rearrangement reaction exhibits a kinetic isotope effect (KIE) of 2.34 +/- 0.17 for the intramolecular hydride transfer reaction and a competitive isotope effect of 1.2 for protonation of the olefin. These results are consistent with a two-step reaction in which the protonation of the double bond, a potentially reversible process, is followed by the rate-determining, intramolecular 1,4-hydride transfer.
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The modification of nucleocytoplasmic proteins with O-linked N-acetylglucosamine (O-GlcNAc) plays diverse roles in multicellular organisms. Inhibitors of O-GlcNAc hydrolase (OGA), the enzyme that removes O-GlcNAc from proteins, lead to increased O-GlcNAc levels in cells and are seeing widespread adoption in the field as a research tool used in cells and in vivo. Here we synthesize and study a series of tight binding carbohydrate-based inhibitors of human OGA (hOGA). The most potent of these 2'-aminothiazolines binds with a sub-nanomolar Ki value to hOGA (510 ± 50 pM) and the most selective has greater than 1 800 000-fold selectivity for hOGA over mechanistically related human lysosomal β-hexosaminidase. Structural data of inhibitors in complex with an hOGA homologue reveals the basis for variation in binding among these compounds. Using linear free energy analyses, we show binding of these 2'-aminothiazoline inhibitors depends on the pKa of the aminothiazoline ring system, revealing the protonation state of the inhibitor is a key driver of binding. Using series of inhibitors and synthetic substrates, we show that 2'-aminothiazoline inhibitors are transition state analogues of hOGA that bind to the enzyme up to 1-million fold more tightly than the substrate. These collective data support an oxazoline, rather than a protonated oxazolinium ion, intermediate being formed along the reaction pathway. Inhibitors from this series will prove generally useful tools for the study of O-GlcNAc. The new insights gained here, into the catalytic mechanism of hOGA and the fundamental drivers of potency and selectivity of OGA inhibitors, should enable tuning of hOGA inhibitors with desirable properties.
The solvolysis of α-d-glucopyranosyl fluoride in hexafluoro-2-propanol gives two products, 1,1,1,3,3,3-hexafluoropropan-2-yl α-d-glucopyranoside and 1,6-anhydro-β-D-glucopyranose. The ratio of these two products is essentially unchanged for reactions that are performed between 56 and 100 °C. The activation parameters for the solvolysis reaction are as follows: ΔH(++) = 81.4 ± 1.7 kJ mol(-1), and ΔS(++) = -90.3 ± 4.6 J mol(-1) K(-1). To characterize, by use of multiple kinetic isotope effect (KIE) measurements, the TS for the solvolysis reaction in hexafluoro-2-propanol, we synthesized a series of isotopically labeled α-d-glucopyranosyl fluorides. The measured KIEs for the C1 deuterium, C2 deuterium, C5 deuterium, anomeric carbon, ring oxygen, O6, and solvent deuterium are 1.185 ± 0.006, 1.080 ± 0.010, 0.987 ± 0.007, 1.008 ± 0.007, 0.997 ± 0.006, 1.003 ± 0.007, and 1.68 ± 0.07, respectively. The transition state for the solvolysis reaction was modeled computationally using the experimental KIE values as constraints. Taken together, the reported data are consistent with the retained solvolysis product being formed in an S(N)i (D(N)(++)*A(Nss)) reaction with a late transition state in which cleavage of the glycosidic bond is coupled to the transfer of a proton from a solvating hexafluoro-2-propanol molecule. In comparison, the inverted product, 1,6-anhydro-β-D-glucopyranose, is formed by intramolecular capture of a solvent-equilibrated glucopyranosylium ion, which results from dissociation of the solvent-separated ion pair formed in the rate-limiting ionization reaction (D(N)(++) + A(N)). The implications that this model reaction have for the mode of action of retaining glycosyltransferases are discussed.
A series of isotopically labeled natural substrate analogues (phenyl 5-N-acetyl-α-d-neuraminyl-(2→3)-β-d-galactopyranosyl-(1→4)-1-thio-β-d-glucopyranoside; Neu5Acα2,3LacβSPh, and the corresponding 2→6 isomer) were prepared chemoenzymatically in order to characterize, by use of multiple kinetic isotope effect (KIE) measurements, the glycosylation transition states for Vibrio cholerae sialidase-catalyzed hydrolysis reactions. The derived KIEs for Neu5Acα2,3LacβSPh for the ring oxygen (18V/K), leaving group oxygen (18V/K), C3-S deuterium (DV/KS) and C3-R deuterium (DV/KR) are 1.029 ± 0.002, 0.983 ± 0.001, 1.034 ± 0.002, and 1.043 ± 0.002, respectively. In addition, the KIEs for Neu5Acα2,6βSPh for C3-S deuterium (DV/KS) and C3-R deuterium (DV/KR) are 1.021 ± 0.001 and 1.049 ± 0.001, respectively. The glycosylation transition state structures for both Neu5Acα2,3LacβSPh and Neu5Acα2,6LacβSPh were modeled computationally using the experimental KIE values as goodness of fit criteria. Both transition states are late with largely cleaved glycosidic bonds coupled to pyranosyl ring flattening (4H5 half-chair conformation) with little or no nucleophilic involvement of the enzymatic tyrosine residue. Notably, the transition state for the catalyzed hydrolysis of Neu5Acα2,6βSPh appears to incorporate a lesser degree of general-acid catalysis, relative to the 2,3-isomer.
The 13th International Conference on Biology and Chemistry of Sialic Acids will be held at the Kongresshotel Potsdam, Potsdam, Germany.The program of Sialoglyco 2010 is dedicated to address and integrate all aspects of (poly)sialoglycochemistry and -biology.Internationally recognized experts will meet with junior scientists to establish a vivid and stimulating discussion platform.Please feel cordially invited to actively participate in fruitful discussions and enjoy both the scientifically inspiring atmosphere of the conference and the delightful environment of a truly European city.
The 13th International Conference on Biology and Chemistry of Sialic Acids will be held at the Kongresshotel Potsdam, Potsdam, Germany.The program of Sialoglyco 2010 is dedicated to address and integrate all aspects of (poly)sialoglycochemistry and -biology.Internationally recognized experts will meet with junior scientists to establish a vivid and stimulating discussion platform.Please feel cordially invited to actively participate in fruitful discussions and enjoy both the scientifically inspiring atmosphere of the conference and the delightful environment of a truly European city.
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
