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@article{1585757,
author = {Sychrovsky, V. and Saman, D. and Fiala, Radovan and Humpa, Otakar and Sykora, J. and Kessler, P. and Blechta, V. and Dobrev, P. and Schraml, J.},
article_location = {HOBOKEN},
article_number = {12},
doi = {http://dx.doi.org/10.1002/mrc.4890},
keywords = {C-13 NMR; C-13-C-13 coupling constants; C-13-H-1 coupling constants; H-1 NMR; H-1-H-1 coupling constants; natural product; NMR; NOE; rotamers; stereochemistry},
language = {eng},
issn = {0749-1581},
journal = {Magnetic Resonance in Chemistry},
title = {Ascorbigen A-NMR identification},
url = {http://dx.doi.org/10.1002/mrc.4890},
volume = {57},
year = {2019}
}
TY - JOUR
ID - 1585757
AU - Sychrovsky, V. - Saman, D. - Fiala, Radovan - Humpa, Otakar - Sykora, J. - Kessler, P. - Blechta, V. - Dobrev, P. - Schraml, J.
PY - 2019
TI - Ascorbigen A-NMR identification
JF - Magnetic Resonance in Chemistry
VL - 57
IS - 12
SP - 1084-1096
EP - 1084-1096
PB - John Wiley & Sons
SN - 07491581
KW - C-13 NMR
KW - C-13-C-13 coupling constants
KW - C-13-H-1 coupling constants
KW - H-1 NMR
KW - H-1-H-1 coupling constants
KW - natural product
KW - NMR
KW - NOE
KW - rotamers
KW - stereochemistry
UR - http://dx.doi.org/10.1002/mrc.4890
L2 - http://dx.doi.org/10.1002/mrc.4890
N2 - The connectivities of all atoms in ascorbigen A, an important metabolite, were determined unambiguously for the first time. The connectivity between carbon atoms was established by 2D INADEQUATE, and one-bond C-13-C-13 coupling constants were determined for all pairs of directly connected carbon atoms except for two strongly coupled carbon pairs. The C-13-C-13 coupling in one of the pairs was proved by a modification of standard INADEQUATE; however, the signals from the other pair were too weak to be observed. The connectivity within the two strongly coupled C-C pairs was confirmed by a combination of COSY and gHSQC; the latter experiment also identified all C-H bonds. The proton nuclear magnetic resonance (H-1 NMR) spectra in dry dimethyl sulfoxide allowed identification and assignment of the signals due to NH and OH protons. The derived structure, 3-((1H-indol-3-yl)methyl)-3,3a,6-trihydroxytetrahydrofuro[3,2-b]furan-2(5H)-one, agrees with the structure suggested for ascorbigen A in 1966. The density functional theory (DFT) calculations showed that among 16 possible stereoisomers, only two complied with the almost zero value of the measured (3)J(H6-H6a). Of the two stereoisomers, 3S,3aS,6S,6aR and 3R,3aR,6R,6aS, the latter was excluded on synthetic grounds. The nuclear Overhauser effect measurements unveiled close proximity between H2 ' proton of the indole and the H6a proton of the tetrahydrofuro[3,2-b]furan part. Detailed structural interpretation of the measured NMR parameters by means of DFT NMR was hampered by rotational flexibility of the indole and tetrahydrofuro[3,2-b]furan parts and inadequacy of Polarizable Continuum Model (PCM) solvent model.
ER -
SYCHROVSKY, V., D. SAMAN, Radovan FIALA, Otakar HUMPA, J. SYKORA, P. KESSLER, V. BLECHTA, P. DOBREV and J. SCHRAML. Ascorbigen A-NMR identification. \textit{Magnetic Resonance in Chemistry}. HOBOKEN: John Wiley \&{} Sons, 2019, vol.~57, No~12, p.~1084-1096. ISSN~0749-1581. Available from: https://dx.doi.org/10.1002/mrc.4890.
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