The introduction of on-line solid-phase extraction (SPE)
in HPLC-NMR has dramatically enhanced the sensitivity
of this technique by concentration of the analytes in a
small-volume NMR flow cell and by increasing the amount
of the analyte by multiple peak trapping. In this study,
the potential of HPLC-DAD-SPE-NMR hyphenation was
demonstrated by structure determination of complex
constituents of flower, leaf, root, and stem extracts of an
African medicinal plant Kanahia laniflora. The technique
was shown to allow acquisition of high-quality
homo- and heteronuclear 2D NMR data following analytical-
scale HPLC separation of extract constituents. Four
flavonol glycosides [kaempferol 3-O-(6-O-r-L-rhamnopyranosyl)-
â-D-glucopyranoside; kaempferol 3-O-(2,6-di-Or-
L-rhamnopyranosyl)-â-D-glucopyranoside; quercetin 3-O-
(2,6-di-O-r-L-rhamnopyranosyl)-â-D-glucopyranoside(rutin);
and isorhamnetin, 3-O-(6-O-r-L-rhamnopyranosyl)-â-Dglucopyranoside]
and three 5r-cardenolides [coroglaucigenin
3-O-6-deoxy-â-D-allopyranoside; coroglaucigenin 3-O-
(4-O-â-D-glucopyranosyl)-6-deoxy-â-D-glucopyranoside; 3¢-
O-acetyl-3¢-epiafroside] were identified, with complete
assignments of 1H and 13C resonances based on HSQC
and HMBC spectra whenever required. Confirmation of
the structures was provided by HPLC-MS data. The
HPLC-DAD-SPE-NMR technique therefore speeds up the
dereplication of complex mixtures of natural origin significantly,
by characterization of individual extract components
prior to preparative isolation work.