Streptochlorin is a kind of indole alkaloid derived from
marine
microorganisms. It is a promising lead compound due to its potent
bioactivity in preventing many phytopathogens, as shown in our previous
study. To explore the potential applications of this natural product,
a series of novel benzoxaborole-containing streptochlorin derivatives
were designed and synthesized through a one-step and catalyst-free
reaction in water at room temperature. All target compounds were first
screened for their antifungal profiles in vitro against six common
phytopathogenic fungi. The results of bioassay revealed that most
of the designed compounds exhibited more significant antifungal activities
against Botrytis cinrea, Gibberella zeae, Rhizoctorzia solani, Colletotrichum lagenarium, and alternaria
leaf spot under the concentration of 50 μg/mL, and this is highlighted
by compounds 4i and 5f, which demonstrated
impressive antifungal effects against G. zeae and R. solani, with their corresponding
EC50 values 0.2983 and 0.2657 μg/mL, which are obviously
better than positive control flutriafol and boscalid (5.2606 and 1.2048
μg/mL, respectively). Scanning electron microscopy on the hyphae
morphology showed that compound 5b might cause mycelial
abnormalities of G. zeae. 3D-QSAR studies
of CoMFA and CoMSIA were carried out on 29 target compounds with antifungal
activity against B. cinrea. The analysis
results indicated that introducing appropriate electronegative groups
at the 5-position of benzoxaborole and the 4,5-positions of the indole
ring could effectively improve the anti-B. cinrea activity. Moreover, compound 5b showed good antifungal
activities in vivo against Phytophthora capsici. Molecular docking was further explored to ascertain the practical
value of the active compound as a potential inhibitor of LeuRS. The
abovementioned results indicate that the designed benzoxaborole-containing
streptochlorin derivatives could be further studied as template molecules
of novel antifungal agents.
Given the importance of pyrroles in pharmaceuticals, agrochemicals and functional materials, development of efficient strategies for their construction continues to be the hot area. Here, we present a novel BF3·Et2O...
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