New 2-aryl-6-methyl-3,4-dihydro-β-carbolin-2-iums as potential antifungal agents: Synthesis, bioactivity and structure-activity relationship

Thirty new title compounds along with five known analogues were prepared from commercially available 2-arylhydrazin-1-ium chlorides and alpha-ketoglutaric acid. The mycelium growth rate method was used to evaluate inhibition activity against six strains of plant pathogenic fungi. Most of the compounds displayed the activity for each the fungi at 150 mu., higher than azoxystrobin, a positive drug. Compound 6-2 showed the lowest average IC50 value of 4.58 mu g/mL for all the fungi where F. solani exhibited the highest susceptibility to most of the compounds. For F. solani, some compounds were more active with IC50 values of 2.67-8.48 mu M than thiabendazole (IC50 = 9.30 mu M) and/or carbendazim (IC50 = 3.36 mu M). The SAR showed that the activity is significantly affected by substituents on the A-ring and/or D-ring along with the degree of unsaturation of the C-ring. Thus, a series of new beta-carboline compounds with potent antifungal potential were found.