New 7-Chloro-9-methyl-2-phenyl-3,4-dihydro-β-carbolin-2-iums as Promising Fungicide Candidates: Design, Synthesis, and Bioactivity.

As our further research, a series of new 7-chloro-9-methyl-2-phenyl-3,4-dihydro-β-carbolin-2-iums were designed and synthesized. Twelve compounds were found with excellent inhibition activity on three to five out of six phytopathogenic fungi, superior to standard drugs thiabendazole and/or azoxystrobin. Especially, displayed the highest activity against three out of the fungi and the highest comprehensive activity for all of the fungi. The test revealed that at 50 μg/mL was able to completely control infections in apples over 8 days. Scanning/transmission electron microscopic observations found that could damage the hyphal integrity and cell membrane structure of . The safety evaluation showed that had no effect on the germination rate of cowpea seed at ≤200 μg/mL. The SAR revealed that the combination of 7-Cl and 2'- or 4'-alkyl is conducive to improvement of the activity. Thus, 7-chloro-9-methyl-2-phenyl-3,4-dihydro-β-carbolin-2-ium is a promising antifungal lead scaffold.