Hexaricins, Pradimicin-like Polyketides from a Marine Sediment-Derived Streptosporangium sp. and Their Antioxidant Effects

Seven pradimicin-like polyketides were isolated from the dichloromethane extract of the marine sediment-derived Streptosporangium sp. CGMCC 4.7309, including five new hexaricins, D–H ( 1 – 5 ), and known hexaricins A ( 6 ) and C ( 7 ). Their structures were determined by HRESIMS, 1D and 2D NMR, and other spectroscopic analyses. The absolute configurations of compounds 1 – 5 were determined on the basis of circular dichroism and specific rotation data. All isolated compounds 1 – 7 were tested for their antioxidant capacities by DPPH • scavenging, • OH scavenging, and • O 2 ̅ scavenging assays. Compounds 3 and 4 displayed stronger antioxidant activities than the positive control ( tert -butylhydroquinone). The relationship between structure and antioxidant activity is discussed. These compounds could be effective natural antioxidants with considerable pharmaceutical value.