13C-labeled N-acetyl-neuraminic acid in aqueous solution: detection and quantification of acyclic keto, keto hydrate, and enol forms by 13C NMR spectroscopy

Journal of the American Chemical Society
Thomas KlepachAnthony S Serianni

Abstract

Aqueous solutions of N-acetyl-neuraminic acid (Neu5Ac, 1) labeled with (13)C at C1, C2, and/or C3 were analyzed by (13)C NMR spectroscopy to detect and quantify the acyclic forms (keto, keto hydrate, enol) present at varying pHs. In addition to pyranoses, solutions contained the keto form, based on the detection of C2 signals at approximately 198 ppm (approximately 0.7% at pH 2). Spectra of [2-(13)C] and [3-(13)C] isotopomers contained signals arising from labeled carbons at approximately 143 and approximately 120 ppm, respectively, which were attributed to enol forms. Solution studies of [1,2,3-(13)C3] 1 substantiated the presence of enol (approximately 0.5% at pH 2). Enol was not detected at pH > 6.0. A C2 signal observed at approximately 94 ppm was identified as C2 of the keto hydrate (approximately 1.9% at pH 2), based partly on its abundance as a function of solution pH. Density functional theory (DFT) calculations were used to study the effect of enol and hydrate structure on J(CH) and J(CC) values involving C2 and C3 of these forms. Solvated DFT calculations showed that (2)J(C2,H3) in cis and trans enols have similar magnitudes but opposite signs, making this J-coupling potentially useful to distinguish enol configuratio...Continue Reading

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Citations

Sep 13, 2012·The Journal of Organic Chemistry·Wenhui ZhangAnthony S Serianni
Jun 27, 2015·Critical Reviews in Food Science and Nutrition·Christoph H RöhrigNigel Baldwin
Jan 4, 2013·Magnetic Resonance in Chemistry : MRC·A CanalesM Martín-Pastor
Jul 10, 2019·Magnetic Resonance in Chemistry : MRC·Leonid B Krivdin
Jul 25, 2017·EFSA Journal·UNKNOWN EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA)Henk van Loveren
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Aug 20, 2016·Angewandte Chemie·Mohamed I HassanChristopher N Boddy
Dec 21, 2019·Bioorganic & Medicinal Chemistry Letters·Takahiko MatsushitaKoji Matsuoka
Nov 11, 2020·Molecules : a Journal of Synthetic Chemistry and Natural Product Chemistry·Weiwei ZhuJianming Yao
Apr 9, 2010·Inorganic Chemistry·Martín Regueiro-FigueroaCarlos Platas-Iglesias
Apr 26, 2021·The Journal of Biological Chemistry·Takfarinas KentacheEmile Van Schaftingen
Aug 14, 2010·The Journal of Organic Chemistry·Pietro AlleviMario Anastasia

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