Novel seco-dammarane triterpenes with antimicrobial activity against plant pathogens from Ailanthus altissima petioles

Abstract

There is a growing demand for effective, environmentally friendly pesticides due to increasing environmental awareness and stricter regulations on chemical use. Natural products, including secondary metabolites of the invasive tree of heaven ( Ailanthus altissima ), could represent promising sources for biopesticide development. A bioassay-guided isolation workflow involving thin-layer chromatography (TLC)– Bacillus subtilis bioassay, TLC–high-resolution mass spectrometry (HRMS), and preparative flash column chromatography yielded three antimicrobial seco -dammarane triterpenes from the methanolic extract of A. altissima petioles, namely the known shoreic acid ( 1 ), and the previously undescribed foveolin C ( 2 ), and (20 S ,24 R )-epoxy-25-hydroxy-A-homo-4-oxadammaran-3-one ( 3 ). Their structures were elucidated by nuclear magnetic resonance (NMR) spectroscopy, supported by high-resolution tandem mass spectrometry (HRMS/MS) and polarimetry. The presence of the hydroxylated, polyunsaturated fatty acids 13-hydroxy-9,11-octadecadienoic acid (13-HODE, 4 ) and 9-hydroxy-10,12-octadecadienoic acid (9-HODE, 5 ), previously isolated from A. altissima bark, was also confirmed in the petioles by high-performance liquid chromatography (HPLC)–HRMS/MS. To the best of our knowledge, compounds 2 and 3 are reported here as new natural products, while compounds 1 , 4 , and 5 were detected in A. altissima petioles for the first time. In microdilution assays, compounds 1 – 5 showed antimicrobial activity against B. subtilis , the plant pathogenic bacteria Curtobacterium flaccumfaciens pv. flaccumfaciens , Clavibacter michiganensis , and Rhodococcus fascians , as well as the plant pathogenic fungus Fusarium graminearum . Compound 1 exhibited the strongest antibacterial activity, especially against C. michiganensis and R. fascians , with minimal inhibitory concentration (MIC) values two-fold lower than those of the positive control neomycin. Compounds 2 – 5 were the most effective against R. fascians , with MIC values the same as or two-fold higher than those of neomycin. These results indicate that A. altissima petioles represent a promising source of antimicrobial phytochemicals. After proper structure optimization, they could serve as lead compounds for the development of novel antimicrobial agents against certain phytopathogens.