A predictive tool for assessing ¹³C NMR chemical shifts of flavonoids

Abstract

Herein are presented the (1)H and (13)C NMR data for seven monohydroxyflavones (3-, 5-, 6-, 7-, 2'-, 3'-, and 4'-hydroxyflavone), five dihydroxyflavones (3,2'-, 3,3'-, 3,4'-, 3,6-, 2',3'-dihydroxyflavone), a trihydroxyflavone (apigenin; 5,7,4'-trihydroxyflavone), a tetrahydroxyflavone (luteolin; 5,7,3',4'-tetrahydroxyflavone), and three glycosylated hydroxyflavones (orientin; luteolin-6C-beta-D-glucoside, homoorientin; luteolin-8C-beta-D-glucoside, vitexin; apigenin-8C-beta-D-glucoside). When these NMR spectra are compared, it is possible to assess the impact of flavone modification and to elucidate detailed structural and electronic information for these flavonoids. A simple predictive tool for assigning flavonoid (13)C chemical shifts, which is based on the cumulative differences between the monohydroxyflavones and flavone (13)C chemical shifts, is demonstrated. The tool can be used to accurately predict (13)C flavonoid chemical shifts and it is expected to be useful for rapid assessment of flavonoid (13)C NMR spectra and for assigning substitution patterns in newly isolated flavonoids.

Empirically predicted 13C NMR chemical shifts for 8‐hydroxyflavone starting from 7,8,4′‐trihydroxyflavone and from 7,8‐dihydroxyflavone

“…The 13 C chemical shifts reported by Ares et al [5] have been assigned on a matching basis Recently, Park et al [6] published the 1 H NMR and 13 C chemical shifts for flavone and 19 substituted flavones among which was 7,8,4 -trihydroxyflavone; the solvent was dimethylsulphoxide-d 6 . The predictive tool of Burns et al [4] can be operated in reverse to obtain the 13 C chemical shifts for 8-hydroxyflavone using the measured values of 13 C chemical shifts for 7,8,4 -trihydroxyflavone, 7-hydroxyflavone, and 4 -hydroxyflavone. This procedure was accomplished in the following manner:…”

“…As a result of this work, a predictive tool was developed for assessing 13 C NMR chemical shifts of flavonoids. [4] This simple tool is based upon the cumulative differences between the 13 C chemical shifts for carbon atoms in monohydroxyflavones and those for the corresponding carbon atoms in flavone. The purpose of this tool is to predict rapidly 13 C NMR spectra of flavonoids and to assign substitution patterns in newly isolated flavonoids.…”

Secondary Metabolites from an Infusion of Lippia gracilis Schauer Using the LC‑DAD-SPE/NMR Hyphenation Technique

“…The substitution of formic acid aqueous solution 0.5% (v/v) as eluent (A) for TFA solution affected the retention times of both peaks and they elluted before 30 min. The gradient profile of the organic modifier MeOH (B) was, thus, adjusted in order to trap orientin (1, t R = 27.0 min, 600 µg), 31,32 and isoorientin (2, t R = 29.0 min, 500 µg) 31,32 flavonoids. For the second section of the original chromatographic profile with compounds that eluted after 50 minutes, 26 the exchange of methanol as the modifier for acetonitrile led to higher resolution which improved the trapping process.…”

“…31,32 To further furnish insight in the chemical structures of compounds 1 and 2 they were also submitted to analysis by (-)ESI-ITMS 2 (electrospray ionization-ion trap tandem mass spectrometry). -, which are representative of 0,3 X and 0,2 X glucose cross-ring cleavage.…”

Flavone 8‐C‐Glycosides from Haberlea rhodopensisFriv. (Gesneriaceae)

“…The sugar moiety was identified by a careful analysis of vicinal coupling patterns as b-glucopyranose, with a J(1'',2'') value of 10.1 Hz confirming b-linkage. The chemical shift of C(1'') (d(C) 74.5) was indicative of a C-glycosidic linkage [4] [12]. Analysis of 1 H-NMR spectra confirmed that ring A was fully substituted (Table).…”