Anti-Helicobacter pylori metabolites from Heterotheca inuloides (Mexican arnica).

Abstract Preparations of the plant known as “Mexican arnica” ( Heterotheca inuloides ) have been traditionally used for the treatment of several ailments including stomach ulcers and for relief of colic. To find possible biologically active components against these ailments, we tested the acetone extract as well as different metabolites biosynthesized by this species, including cadinane-type sesquiterpenoids, triterpenes, phytosterols and flavonoids, against Helicobacter pylori . Among these compounds, sesquiterpenes 7-hydroxy-3,4-dihydrocadalene ( 3 ) and 7-hydroxy-cadalene ( 4 ) exhibited strong anti- H. pylori activity with MICs values of 1.95 and 3.91 μg/mL, respectively. HPLC-UV/DAD analyses revealed that both substances together with related compounds 7 , 8 and 9 were the major constituents of the acetone extract. Enzymatic assays and docking studies showed that unlike quercetin ( 10 ), a secondary metabolite also isolated from this species, compounds 3 and 4 did not inhibit the activity of urease, a potent virulence factor of H. pylori . Additionally, two new C 1 -C 9 secocadinanes ( 1 and 2 ) were isolated from the aerial parts of this species. Their structures were determined by extensive NMR and HRESIMS spectroscopic data analyses.