Abstract
The title compounds are a class of structurally simple analogues of quaternary benzo[c]phenanthridine alkaloids (QBAs). In order to develop novel QBA-like antifungal drugs, in this study, 24 of the title compounds with various substituents on the N-phenyl ring were evaluated for bioactivity against seven phytopathogenic fungi using the mycelial growth rate method and their SAR discussed. Almost all the compounds showed definite activities in vitro against each of the test fungi at 50 μg/mL and a broad antifungal spectrum. In most cases, the mono-halogenated compounds 2–12 exhibited excellent activities superior to the QBAs sanguinarine and chelerythrine. Compound 8 possessed the strongest activities on each of the fungi with EC50 values of 8.88–19.88 µg/mL and a significant concentration-dependent relationship. The SAR is as follows: the N-phenyl group is a high sensitive structural moiety for the activity and the characteristics and position of substituents intensively influence the activity. Generally, electron-withdrawing substituents remarkably enhance the activity while electron-donating substituents cause a decrease of the activity. In most cases, ortha- and para-halogenated isomers were more active than the corresponding m-halogenated isomers. Thus, the title compounds emerged as promising lead compounds for the development of novel biomimetic antifungal agrochemicals. Compounds 8 and 2 should have great potential as new broad spectrum antifungal agents for plant protection.
Highlights
Fungal plant diseases are one of the important concerns to agricultural production and food safety worldwide [1]
We expected that the structural similarity between the designed compounds and their model compounds can lead to discovery of new compounds with higher bioactivity than the model compounds
As a part of our ongoing program for the development of quaternary benzo[c]phenanthridine alkaloids (QBAs)-like isoquinoline drugs, we report the evaluation of the antifungal activity of compounds 1–24 against various plant pathogenic fungi and the establishment of their structure-activity relationships
Summary
Fungal plant diseases are one of the important concerns to agricultural production and food safety worldwide [1]. Most natural antifungal compounds are not suitable for direct or extensive application as agricultural fungicides because of their lower activity than that of artificial antimicrobial agents, limited sources or higher cost, they have been considered as ideal leads or model compounds for the development of new environmentally acceptable antimicrobial agents. QBAs-like compounds, i.e., 2-aryl-3,4-dihydroisoquinolin-2-iums (1–24, Figure 1), based on a structural biomimetic strategy. The compounds have approximate equal molecular length to QBAs. We expected that the structural similarity between the designed compounds and their model compounds can lead to discovery of new compounds with higher bioactivity than the model. As a part of our ongoing program for the development of QBAs-like isoquinoline drugs, we report the evaluation of the antifungal activity of compounds 1–24 against various plant pathogenic fungi and the establishment of their structure-activity relationships. There has been no information on the antifungal activity of the title compounds in the literature until now
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