Neuroprotective compounds from the resinous heartwood of Aquilaria sinensis

Six undescribed compounds, including three sesquiterpenoids [(4S,5S,7S,8S,11R)-7-hydroxyguai-1(10)-en-8,12-olide, aquilarisinone, and 2Z,7(13),9E-humulatrien-12-ol-5-one], one diphenylpentanone [1-(2-hydroxyphenyl)-5-phenylpentan-3-one], and two 2-(2-phenylethyl)chromones (6-epiagarotetrol and triepoxyhexahydrochromone A), along with 15 known compounds, were isolated from the resinous heartwood of Aquilaria sinensis (Thymelaeaceae). Their structures were determined by mass (MS) and nuclear magnetic resonance (NMR) spectroscopic data. The absolute configuration of (4S,5S,7S,8S,11R)-7-hydroxyguai-1(10)-en-8,12-olide was confirmed by X-ray diffraction analysis, and the configurations of (4S,7S,8S,10R,11R)-7,10-epoxyguai-1(5)-en-8,12-olide, aquilarisinone, 6-epiagarotetrol, and triepoxyhexahydrochromone A were confirmed by electronic circular dichroism (ECD) calculations. The neuroprotective activities of the compounds were evaluated using models of BACE1 inhibition and PC12 cells with corticosterone- and 1-methyl-4-phenylpyridine ion (MPP⁺)-induced damage. At concentrations of 1, 2, and 5 μM, triepoxyhexahydrochromone A, (+)-(7R,10R)-selina-4,11(13)-diene-12,15-dial, (-)-(5R,7R,10R)-12,15-dioxo-α-selinene, and (+)-(1R,4S,5R)-1β-hydroxyeremophila-7(11),9-dien-8-one exerted significant protective effects (p < 0.01) on PC12 cell injury induced by corticosterone, while triepoxyhexahydrochromone A and (-)-(5R,7R,10R)-12,15-dioxo-α-selinene exerted significant protective effects (p < 0.01) on MPP⁺-induced PC12 cell injury at concentrations of 1, 2, and 5 μM. No compounds produced significant inhibitory effects on BACE1, with inhibition rates of less than 20% observed at a concentration of 20 μM.