Sesquiterpenoids from the Fruits of Alpinia oxyphylla and Their Anti‐Acetylcholinesterase Activity

Abstract Fourteen sesquiterpenoids were isolated from the fruits of Alpinia oxyphylla Miq . Their structures were elucidated based on NMR analyses ( 1 H, 13 C, DEPT, 1 H, 1 H‐COSY, HMQC, HMBC, and NOESY) and identified as 12‐nornootkaton‐6‐en‐11‐one ( 3 ), (+)‐(3 S ,4a S ,5 R )‐2,3,4,4a,5,6‐hexahydro‐3‐isopropenyl‐4a,5‐dimethyl‐1,7‐naphthoquinone ( 5 ), nootkatene ( 6 ), 9 β ‐hydroxynootkatone ( 7 ), 2 β ‐hydroxy‐ δ ‐cadinol ( 8 ), 4‐isopropyl‐6‐methyl‐1‐tetralone ( 11 ), oxyphyllone E ( 12 ), oxyphyllone D ( 13 ), oxyphyllanene B ( 15 ), oxyphyllone A ( 16 ), oxyphyllol E ( 17 ), (9 E )‐humulene‐2,3;6,7‐diepoxide ( 18 ), mustakone ( 20 ), and pubescone ( 21 ). Among them, 3 was a new norsesquiterpenoid, 8 was a new natural product, and 5, 6, 11, 20, 21 were isolated from A. oxyphylla for the first time. Twenty sesquiterpenoids, 1 – 5 and 7 – 21 , were investigated for their in vitro acetylcholinesterase (AChE) inhibitory activities, including previously isolated seven sesquiterpenoids from A. oxyphylla , (11 S )‐12‐chloronootkaton‐11‐ol ( 1 ), (11 R )‐12‐chloronootkaton‐11‐ol ( 2 ), nootkatone ( 4 ), oxyphyllenodiol A ( 9 ), oxyphyllenodiol B ( 10 ), 7‐epiteucrenone B ( 14 ), and alpinenone ( 19 ). TLC‐Bioautographic assay indicated that 1 – 4, 7, 14, 16, 18, 19 , and 21 displayed anti‐AChE activities at 10 nmol. Microplate assay confirmed that 19, 18, 16 , and 21 displayed moderate‐to‐weak anti‐AChE activities at the concentration of 100 μ M , and 19 was the most potent inhibitor with an IC 50 value of 81.6±3.5 μ M . The presence of anti‐AChE sesquiterpenoids in A. oxyphylla may partially support the traditional use of this fruit for the treatment of dementia.