Design, synthesis and evaluation of 3-arylidene azetidin-2-ones as potential antifungal agents against Alternaria solani Sorauer.

A new concise and facile method was explored to synthesize a collection of new 3-arylidene azetidin-2-ones, which could be regarded as the derivatives of the hybrid scaffold of bioactive natural cinnamamide and heterocycle azetidi-2-one. The structures of the synthesized compounds were characterized by 1H, 13C NMR, and MS; and their antifungal activity were evaluated against Alternaria solani Sorauer. These antifungal data were subjected to a quantitative structure-activity relationship (QSAR) analysis using Codessa software on the basis of the results from B3LYP/6-31G(d,p) quantum calculations. The best regressive model revealed that potentially more active compounds should have low dipole moments and QC-min (minimal net atomic charge for a C atom), and high QO-max (maximal net atomic charge for an O atom) and QN-min (minimal net atomic charge for an N atom). The most potent compound 7k could lead to intracellular accumulation of reactive oxygen species, dissipation of mitochondrial transmembrane potential, and an autophagy-like cell death process in A. solani Sorauer. Taken together, these results laid the foundation for further design of improved crop-protection agents based on this hybrid scaffold.

Natural α-methylenelactam analogues: Design, synthesis and evaluation of α-alkenyl-γ and δ-lactams as potential antifungal agents against Colletotrichum orbiculare.

In our continued efforts to improve the potential utility of the α-methylene-γ-lactone scaffold, 62 new and 59 known natural α-methylenelactam analogues including α-methylene-γ-lactams, α-arylidene-γ and δ-lactams, and 3-arylideneindolin-2-ones were synthesized as the bioisosteric analogues of the α-methylenelactone scaffold. The results of antifungal and cytotoxic activity indicated that among these derivatives compound (E)-1-(2, 6-dichlorobenzyl)-3-(2-fluorobenzylidene) pyrrolidin-2-one (Py51) possessed good selectivity with the highest antifungal activity against Colletotrichum orbiculare with IC50 = 10.4 µM but less cytotoxic activity with IC50 = 141.2 µM (against HepG2 cell line) and 161.2 µM (against human hepatic L02 cell line). Ultrastructural change studies performed by transmission electron microscope showed that Py51 could cause important cell morphological changes in C. orbiculare, such as plasma membrane detached from cell wall, cell wall thickening, mitochondria disruption, a dramatic increase in vacuolation, and eventually a complete loss in the integrity of organelles. Significantly, mitochondria appeared one of the primary targets, as confirmed by their remarkably aberrant morphological changes. Analysis of structure-activity relationships revealed that incorporation of the aryl group into the α-exo-methylene and the N-benzyl substitution increased the activity. Meanwhile, the α-arylidene-γ-lactams have superiority in selectivity over the 3-arylideneindolin-2-ones. Based on the results, the N-benzyl substituted α-(2-fluorophenyl)-γ-lactam was identified as the most promising natural-based scaffold for further discovering and developing improved crop-protection agents.