**Teratopyrones A–C, Dimeric Naphtho-**γ**-Pyrones and Other Metabolites from** *Teratosphaeria* **sp. AK1128, a Fungal Endophyte of** *Equisetum arvense*

**Ya-Ming Xu 1, A. Elizabeth Arnold 2, Jana M. U**- **Ren 2, Li-Jiang Xuan 3, Wen-Qiong Wang <sup>3</sup> and A. A. Leslie Gunatilaka 1,\***


Academic Editors: Muhammad Ilias and Dhammika Nanayakkara Received: 12 October 2020; Accepted: 26 October 2020; Published: 30 October 2020

**Abstract:** Bioassay-guided fractionation of a cytotoxic extract derived from a solid potato dextrose agar (PDA) culture of *Teratosphaeria* sp. AK1128, a fungal endophyte of *Equisetum arvense*, afforded three new naphtho-γ-pyrone dimers, teratopyrones A–C (**1**–**3**), together with five known naphtho-γ-pyrones, aurasperone B (**4**), aurasperone C (**5**), aurasperone F (**6**), nigerasperone A (**7**), and fonsecin B (**8**), and two known diketopiperazines, asperazine (**9**) and isorugulosuvine (**10**). The structures of **1**–**3** were determined on the basis of their spectroscopic data. Cytotoxicity assay revealed that nigerasperone A (**7**) was moderately active against the cancer cell lines PC-3M (human metastatic prostate cancer), NCI-H460 (human non-small cell lung cancer), SF-268 (human CNS glioma), and MCF-7 (human breast cancer), with IC50s ranging from 2.37 to 4.12 μM while other metabolites exhibited no cytotoxic activity up to a concentration of 5.0 μM.

**Keywords:** endophytic fungus; *Teratosphaeria*; teratopyrones; naphtho-γ-pyrones; nigerasperone A
