Rapid and unambiguous assignment of proton-deficient N-acyl amidine indole alkaloid by a combination of calculation methods

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.

Spirooxindol alkaloids from Voacanga africana: Targeting biofilm of MBLs producing Escherichia coli

Seven rarely spirooxindole alkaloids, voagafricines A-G (1-7) were isolated from the stem barks of Voacanga africana. Their structures were unambiguously elucidated by comprehensive spectroscopic data and electronic circular dichroism (ECD) analyses. 1 and 2 possess a unique indoleone system in conjugation with a 3,4'-decahydroquinoline spiral ring originating from seco-quinolhiddin core of the precursor, furthermore 1 undergo decarburization formed a novel C-3-nor monoterpenoid indole. All isolates were evaluated for their antibacterial activities against MBLs producing Escherichia coli strains. Compounds 1 and 7 were found to be potent inhibitors against E. coli 298 and 140 by targeting biofilm. Possible interaction sites of 1 and 7 with biofilm were preliminarily explored by means of molecular docking.

Phaeosphspirone (1/1'), a pair of unique polyketide enantiomers with an unusual 6/5/5/6 tetracyclic ring from the desert plant endophytic fungus Phaeosphaeriaceae sp

Phaeosphspirone, an undescribed polyketide with a unique 6/5/5/6-fused tetracyclic system, and two known analogues, herbarin and O-methylherbarin, were purified from the endophytic fungus Phaeosphaeriaceae sp. isolated from the desert plant Bassia dasyphylla. The connectivity and relative configuration of phaeosphspirone was elucidated by comprehensive HR-ESI-MS and NMR analysis together with a computer-assisted structure elucidation (CASE) method. A pair of enantiomers existing in phaeosphspirone were separated by HPLC chromatography after reacting with chiral reagents, from which the absolute configuration of phaeosphspirone was simultaneously determined based on Mosher's rule. This tandem strategy provides a useful approach for the separation and stereochemical determination of enantiomers possessing secondary hydroxyl groups. The structural feature of phaeosphspirone, herbarin and O-methylherbarin together with gene cluster analysis suggested their polyketide biosynthetic origin. Herbarin and O-methylherbarin exhibited moderate cytotoxicity against three cancer cell lines.

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