*Article* **New Thiodiketopiperazine and 3,4-Dihydroisocoumarin Derivatives from the Marine-Derived Fungus** *Aspergillus terreus*

**Jing-Shuai Wu 1,2, Xiao-Hui Shi 1,2, Guang-Shan Yao 1,2,3, Chang-Lun Shao 1,2, Xiu-Mei Fu 1,2, Xiu-Li Zhang 1,2, Hua-Shi Guan 1,2,\* and Chang-Yun Wang 1,2,\***


Received: 7 February 2020; Accepted: 24 February 2020; Published: 26 February 2020

**Abstract:** *Aspergillus terreus* has been reported to produce many secondary metabolites that exhibit potential bioactivities, such as antibiotic, hypoglycemic, and lipid-lowering activities. In the present study, two new thiodiketopiperazines, emestrins L (**1**) and M (**2**), together with five known analogues (**3**–**7**), and five known dihydroisocoumarins (**8**–**12**), were obtained from the marine-derived fungus *Aspergillus terreus* RA2905. The structures of the new compounds were elucidated by analysis of the comprehensive spectroscopic data, including high-resolution electrospray ionization mass spectrometry (HRESIMS), one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR), and electronic circular dichroism (ECD) data. This is the first time that the spectroscopic data of compounds **3**, **8**, and **9** have been reported. Compound **3** displayed antibacterial activity against *Pseudomonas aeruginosa* (minimum inhibitory concentration (MIC) = 32 μg/mL) and antifungal activity against *Candida albicans* (MIC = 32 μg/mL). In addition, compound **3** exhibited an inhibitory effect on protein tyrosine phosphatase 1 B (PTP1B), an important hypoglycemic target, with an inhibitory concentration (IC)50 value of 12.25 μM.

**Keywords:** marine-derived fungus; *Aspergillus terreus*; thiodiketopiperazines; dihydroisocoumarins
