**4. Conclusions**

In summary, 23 secondary metabolites, including six new isocoumarin derivative talaromarins A-F (**1**–**6**) and 17 known analogues (**<sup>7</sup>**–**23**) were obtained from the mangrovederived fungus *Talaromyces flavus* TGGP35. Compounds **6**–**11**, **17**–**19** and **22** exerted similar or better antioxidant activity than the positive control trolox (IC50 = 0.29 mM), with IC50 values ranging from 0.009 to 0.27 mM. Compounds **10**, **18**, **21** and **23** exhibited strong inhibitory activities against *α*-glucosidase with IC50 values ranging from 0.10 to 0.62 mM, while the IC50 value of positive control acarbose was 0.5 mM. All compounds showed no antibacterial or anti-phytopathogenic activity at the concentrations of 50 μg/mL and 1 mg/mL, respectively. Their plausible biosynthetic pathway and structure–activity relationships were also explored. Therefore, these findings demonstrate the potential of these active compounds as lead compounds for developing antioxidants and as diabetes control agents.

**Supplementary Materials:** The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/md20060361/s1, D, 2D NMR and MS data of new compounds **1**–**6**.

**Author Contributions:** J.C. and X.-C.Z. performed the experiments for the isolation, structure elucidation and prepared the manuscript; W.-N.Z. and B.W. contributed to the antioxidant activity and antimicrobial evaluation; Y.-P.L. contributed to part of the structure determination; J.L., M.-J.C. and G.-Y.L. organized documents and performed basic experiments; G.-L.H. and G.-Y.C. contributed the optimization of fermentation; C.-J.Z. and J.X. supervised the research work and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by Key Science and Technology Program of Hainan Province (No. ZDKJ202008), the National Natural Science Foundation of China (Nos. 32160108, 41866005, 82160675 and 81973229), Key Research and Development Program of Hainan Province (No. ZDYF2021SHFZ270 and ZDYF2021SHFZ108), Hainan Provincial Natural Science Foundation of China (No. 220RC593), the Innovation Platform for Academicians of Hainan Province Specific Research Fund of The Innovation Platform for Academicians of Hainan Province (No. YSPTZX202030).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available in this article and Supplementary Material.

**Conflicts of Interest:** The authors declare no competing financial interest.
