Synthesis, structural modification, and biological activity of a novel bisindole alkaloid iheyamine A

Diseases caused by plant viruses and pathogens pose a serious threat to crop yield and quality. Traditional pesticides have gradually developed drug resistance and brought certain environmental safety issues during long-term overuse. There is an urgent need to discover new candidate compounds to address these issues. In this study, we achieved the efficient synthesis of iheyamine A and its derivatives, and discovered their excellent antiviral activities against tobacco mosaic virus (TMV). Most compounds displayed higher antiviral activities against TMV than commercial ribavirin at 500 μg/mL, with compounds 3a (Inactive effect IC₅₀: 162 µg/mL), 3d (Inactive effect IC₅₀: 249 µg/mL), 6p (Inactive effect IC₅₀: 254 µg/mL), and 7a (Inactive effect IC₅₀: 234 µg/mL) exhibiting better antiviral activities than ningnanmycin at 500 μg/mL (Inactive effect IC₅₀: 269 µg/mL). Meanwhile, the structure–activity relationships of this type of compounds were systematically studied. We chose 3a for further antiviral mechanism research and found that it can directly act on viral coat protein (CP). The interaction of 3a and CP was further verified via molecular docking. These compounds also showed broad-spectrum fungicidal activities against 8 plant pathogenic fungi, especially for P. piricola. This study provides a reference for the role of iheyamine alkaloids in combating plant pathogenic diseases.