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Ascorbigen A—NMR identification

SYSNO ASEP	0507455
Document Type	J - Journal Article
R&D Document Type	Journal Article
Subsidiary J	Článek ve WOS
Title	Ascorbigen A—NMR identification
Author(s)	Sychrovský, Vladimír (UOCHB-X)_{RID, ORCID} Šaman, David (UOCHB-X)_{RID, ORCID} Fiala, R. (CZ) Humpa, O. (CZ) Sýkora, Jan (UCHP-M)_{RID, ORCID, SAI} Kessler, P. (DE) Blechta, Vratislav (UCHP-M)_{RID, ORCID, SAI} Dobrev, Petre (UEB-Q)_{RID, ORCID} Schraml, Jan (UCHP-M)_{RID, ORCID, SAI}
Source Title	Magnetic Resonance in Chemistry. - : Wiley - ISSN 0749-1581 Roč. 57, č. 12 (2019), s. 1084-1096
Number of pages	13 s.
Language	eng - English
Country	GB - United Kingdom
Keywords	13C NMR ; 13C–13C coupling constants ; 13C–1H coupling constants ; 1H NMR ; 1H–1H coupling constants ; natural product ; NMR ; NOE ; rotamers ; stereochemistry
Subject RIV	CF - Physical ; Theoretical Chemistry
OECD category	Physical chemistry
Subject RIV - cooperation	Institute of Chemical Process Fundamentals - Physical ; Theoretical Chemistry
R&D Projects	GA15-12719S GA ČR - Czech Science Foundation (CSF)
	GA16-10948S GA ČR - Czech Science Foundation (CSF)
	GA19-13436S GA ČR - Czech Science Foundation (CSF)
Method of publishing	Limited access
Institutional support	UOCHB-X - RVO:61388963 ; UCHP-M - RVO:67985858 ; UEB-Q - RVO:61389030
UT WOS	000473987100001
EID SCOPUS	85068378971
DOI	10.1002/mrc.4890
Annotation	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 13C–13C coupling constants were determined for all pairs of directly connected carbon atoms except for two strongly coupled carbon pairs. The 13C–13C 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 (1H 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 3J(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.
Workplace	Institute of Organic Chemistry and Biochemistry
Contact	asep@uochb.cas.cz ; Kateřina Šperková, Tel.: 232 002 584 ; Viktorie Chládková, Tel.: 232 002 434
Year of Publishing	2020
Electronic address	https://onlinelibrary.wiley.com/doi/abs/10.1002/mrc.4890

Number of the records: 1