Diverse polyketides from the marine endophytic Alternaria sp. LV52: Structure determination and cytotoxic activities

•Isolation and characterization of five polyketides 1–5 from the marine endophytic Alternaria sp. LV52 derived from Cystoseira tamariscifolia.•The chemical structures of compounds 1–5 were identified by extensive 1D, 2D NMR, and HR mass measurements, and by comparison with literature data.•Isolation and taxonomic characterization of the producing fungus is intensively reported on the bases of morphological and genotypic analysis.•The antimicrobial of the produced extract and derived compounds were examined against a panel of test organisms.•Compounds 2 and 4 are potentially cytotoxic against human non-small cell lung (A549) and prostate (PC3) cancer cell lines.