Methyl 2-naphthoates from a traditional Chinese herb Morinda officinalis var. officinalis

Abstract Fifteen methyl 2-naphthoate derivatives ( 1 – 15 ), including 11 previously undescribed ones ( 1 – 10 and 13 ), have been isolated from the roots of a well-known Chinese herb, Morinda officinalis var. officinalis . The structures of these isolates were determined on the basis of detailed spectroscopic analyses, and 12 of them were identified as six pairs of enantiomers ( 1 – 12 ). While the relative configurations of 1 and 5 were confirmed by X-ray crystallographic analysis and calculated 13 C NMR data, respectively, the absolute configurations of 1 – 12 were established via interpretation of experimental and computed ECD data. Compounds 1 – 4 possessed a novel heterocylic bridge ring system incorporating a 2,6-dioxabicyclo[3.2.1]oct-3-ene motif. Our biological evaluations revealed that (−)-mornaphthoate E ( 9 ) showed significant cytotoxicity against a panel of human cancer cell lines (MDA-MB-231, MCF-7 and A549, IC 50 1–10 μM), while (−)-mornaphthoate A ( 2 ) displayed mild inhibition against butyrylcholinesterase (IC 50 37.98 ± 1.98 μM).