Withanolides from Datura ceratocaula and Datura discolor and their acetylcholinesterase inhibitory activity.

The investigation of the chemical constituents of Datura ceratocaula and D. discolor allowed to isolate three new withanolides, datucerolide A (1) from the first species, and datudiscolides A (8) and B (9) from the second. In addition, seven known withanolides and five ubiquitous compounds were isolated from these plants, along with 27-O-β-d-glucopyranosyl dinnoxolide A (5), which was obtained as the tetraacetyl derivative 4. All the structures were elucidated by analyses of their spectroscopic and spectrometric data and that of dinnoxolide A (6) was confirmed by X-ray diffraction analysis. The structure 4 was assigned earlier to daturametelin G-Ac and that of 5 to datinolide B, therefore, it will be discussed whether these assignments are correct. On the other hand, the structure of datudiscolide A (8) was previously assigned to the aglycone of dinoxin B (14), however, a revision of its reported NMR data showed inconsistencies with the proposed structure. The inhibitory activity of withanolides 2, 3, 6-8, 12, and 13 against acetylcholinesterase enzyme (AChE) was evaluated. Compounds 6, 7, 12, and 13 exhibited the best activity with IC values ranging from 2.8 to 21.5 μM.