Two New Polyketides From Streptomyces sp. SA61: Isolation, Structure Elucidation, and Insecticidal Activity Against...

To discover novel green bio-based insecticidal lead compounds, six polyketides, including two new compounds, strekingmycin I (5) and strekingmycin J (6), together with four known analogues, were isolated and identified from the fermentation products of earthworm gut-derived Streptomyces sp. SA61. Their structures were established by comprehensive spectroscopic analysis, including NMR, HR-ESI-MS, and single-crystal x-ray diffraction. Notably, the crystallographic data of strekingmycin G (3) were obtained for the first time, which unambiguously confirmed its absolute configuration. In insecticidal activity assays against the third-instar nymphs of Bemisia tabaci, all six compounds exhibited varying degrees of toxicity. Among them, strekingmycin A (1) displayed the most potent activity, with an LC₅₀ value of 5.58 µg/mL, which was within the same concentration range as that of the positive control spirotetramat, albeit less active than the commercial standard. This study enriches the structural diversity of strekingmycin-type polyketides by reporting two new derivatives and providing the first crystallographic evidence for compound 3. Furthermore, it demonstrates for the first time the insecticidal potential of the strekingmycin family against B. tabaci, offering a scientific basis for further research on the management of piercing-sucking pests.