Three new alkaloids, hipporidine A (1), hipporidine B (2), and (−)-lobeline N-oxide (3), were discovered from the whole plant of Hippobroma longiflora
together with five known compounds (4–8). Their 2,6-disubstituted piperidine structures were established based on the HRESIMS, NMR (COSY, HMBC, HSQC, NOESY), and UV
spectroscopic data. Hipporidines A (1) and B (2) possess a rare 1,3-oxazinane moiety. Compound 3 is the N-oxide derivative of (−)-lobeline (6). Moreover,
the absolute configuration of norlobeline (5) was established by single-crystal X-ray diffraction analysis. Three major secondary metabolites (6–8) were evaluated for
their neuroprotective effect against paclitaxel-induced neurotoxicity. Consequently, pretreatment with compound 8 at a concentration of 1.0 µM displayed significant attenuation on
paclitaxel-damaged neurite outgrowth of dorsal root ganglion neurons without interfering with the cytotoxicity of paclitaxel on cervical cancer SiHa cells.
HRESIMS, IR, NMR (1H, 13C, COSY, HSQC, HMBC, and NOESY), and UV spectra of compounds 1–3, 1H and 13C NMR spectra of
compounds 5 and 7, and X-ray crystallographic data of 5 are available as Supporting Information.
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