Inspired
by the widely antiphytopathogenic application of diversified
derivatives from natural sources, cryptolepine and its derivatives
were subsequently designed, synthesized, and evaluated for their antifungal
activities against four agriculturally important fungi Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, and Sclerotinia sclerotiorum. The results obtained from in vitro assay indicated that compounds a1–a24 showed great fungicidal property against B. cinerea (EC50 < 4 μg/mL); especially, a3 presented significantly prominent inhibitory activity with an EC50 of 0.027 μg/mL. In the pursuit of further expanding
the antifungal spectrum of cryptolepine, ring-opened compound f1 produced better activity with an EC50 of 3.632
μg/mL against R. solani and an
EC50 of 5.599 μg/mL against F. graminearum. Furthermore, a3 was selected to be a candidate to
investigate its preliminary antifungal mechanism to B. cinerea, revealing that not only spore germination
was effectively inhibited and the normal physiological structure of
mycelium was severely undermined but also detrimental reactive oxygen
was obviously accumulated and the normal function of the nucleus was
fairly disordered. Besides, in vivo curative experiment
against B. cinerea found that the therapeutic
action of a3 was comparable to that of the positive control
azoxystrobin. These results suggested that compound a3 could be regarded as a novel and promising agent against B. cinerea for its valuable potency.