Discovery of Cadinane-Type Sesquiterpenoids from the Infected Stems of Hibiscus tiliaceus as Potential Agrochemical Fungicides.

Ten new cadinane-type sesquiterpenoids, named hibisceusins I-R ( 1 - 10 ), along with 14 known sesquiterpenoids ( 11 - 24 ), were acquired from the tainted stems of Hibiscus tiliaceus . Their structures were identified via spectroscopic analysis, one-dimensional (1D) and two-dimensional (2D) NMR, and computer-assisted structure elucidation techniques, including infrared (IR) and mass spectrometry (MS) data. Additionally, subsequent DP4/DP4+ probability methods were used to resolve 3 's relative configurations by comparing their experimental values to the predicted NMR data. The absolute configurations of compounds 1 - 4 were measured through electronic circular dichroism (ECD) spectra. The ability of all isolates to inhibit the growth of five phytopathogenic fungi ( Rhizopus stolonifer , Verticillium dahliae Kleb., Thanatephorus cucumeris , Fusarium oxysporum Schltdl., and F. oxysporum HK-27) was evaluated. Aldehydated sesquiterpenoids ( 1 , 6 - 9 , 11 , 12 , and 22 ) and a known sesquiterpenoid quinine ( 18 ) exhibited significant inhibitory activities against V. dahliae , T. cucumeris , F. oxysporum , and F. oxysporum HK-27 with minimum inhibitory concentration (MIC) values of 2.5-50 μg/mL, but all isolates remained inactive against R. stolonifer . Moreover, the effects of the isolates on the mycelial morphology were watched through scanning electron microscopy. This study revealed that aldehydated cadinane-type sesquiterpenoids could be used as novel antifungal molecules to develop agrochemical fungicides in plant protection.