A new diterpene from the fungal mycelia of Hericium erinaceus

•Six compounds (1–6) were isolated from the fungal mycelia of Hericium erinaceus.•One of two new compounds (1 and 2) is a diterpene (1).•Compound (3) showed strong antibacterial activity against Helicobacter pylori.•The diterpene (1) showed moderate antibacterial activity against H. pylori.•The diterpene (1) showed good cytotoxicity activity against two human cancer cell lines.