Isolation, structural characterisation and nematocidal activity of two new sixteen-membered macrolides from mutant Streptomyces avermitilis NEAU1069-6

Two new sixteen-membered macrolactones, 6, 8a-seco-6, 8a-dihydroxy doramectin (1) and 13α-O-α-L-oleandrosyl-23-α-hydroxy-25-isopropyl milbemycin β3 (2), were isolated from the fermentation broth of mutant Streptomyces avermitilis NEAU1069-6. Their structures were established by extensive spectroscopic analysis including 1D and 2D NMR, HRESIMS data and comparison with data from the literature. Bioactivity assays revealed that 1 exhibited weak nematocidal activity, while 2 demonstrated moderate nematocidal activity with LC50 of 60.1 μg mL−1.