Cultivation of locust associated rare actinobacteria, Amycolatopsis sp. HCa4, has provided five unusual macrolactams rifamorpholines A-E. Their structures were determined by interpretation of spectroscopic and crystallographic data. Rifamorpholines A-E possess an unprecedented 5/6/6/6 ring chromophore, representing a new subclass of rifamycin antibiotics. The biosynthetic pathway for compounds 1-5 involves a key 1,6-cyclization for the formation of the morpholine ring. Compounds 2 and 4 showed potent activities against methicillin-resistant Staphylococcus aureus (MRSA) with MICs of 4.0 and 8.0 μM, respectively.
Two novel enediyne-derived natural products, amycolamycins A and B (1 and 2), were characterized from a locust-associated actinomycete Amycolatopsis sp. HCa4. Amycolamycins A and B contain a unique 2-(cyclopenta[a]inden-5-yl)oxirane core with suspected enediyne polyketide biosynthetic origin. Sequencing and analysis of the acm biosynthetic gene cluster allowed us to propose the biosynthetic pathway of 1 and 2. Moreover, amycolamycin A (1) was selectively cytotoxic to the M231 breast cancer cell line.
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