Construction and agrochemical efficacy of novel indolo[2,3-b]andrographolide derivatives

To find new pesticide candidates, by using of a natural product andrographolide as the precursor, a series of novel indolo[2,3-b]andrographolide derivatives were semisynthesized by Fischer-indole rearrangement reaction. Their structures were identified by ¹H NMR, IR, mp, and HRMS, and the steric configuration of compound Ic was further determined on single-crystal analysis. Compounds If and IIb showed 5.9 and 7.0 times potent acaricidal activity compared to andrographolide against Tetranychus cinnabarinus. Compound Ib displayed 4.2 folds higher aphicidal activity compared to andrographolide against Eriosoma lanigerum. In addition, the pronounced insecticidal activity of compound IIc against Aphis citricola was 4.2 folds of that of andrographolide. Scanning electron microscopy revealed that compound IIb can destroy the epidermis of T. cinnabarinus. These results can provide a basis for future research on botanical agrochemicals.