**4. Conclusions**

To summarize, based on the OSMAC culture strategy, four new indole-diterpenoids were isolated from the marine-derived fungus *Penicillium* sp. KFD28 secondary metabolites. The absolute configurations of new compounds **1**–**3** were determined by spectroscopic methods coupled with experimental and calculated ECD. New compound **4** showed mild cytotoxicity against the human cervical cancer cell line HeLa. Notably, compound **9** exhibited strong cytotoxic activity against the human liver cancer cell line BeL-7402 with IC50 values of 5.3 μM, indicating that compound **9** deserves further study for its therapeutic potential to develop new anti-hepatoma drugs. Compound **7** showed pronounced antibacterial activity against *Bacillus subtilis* with MIC values of 16 μg/mL, which had the potential to become an antibiotic. However, the mechanisms causing cytotoxicity and bacteria restraint were unknown and require further study. In general, this study expanded the application of the OSMAC method to increase the chemical and biological diversity of natural products isolated from the *Penicillium* sp. KFD28.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/md19110613/s1, Figures S1–S38: 1D NMR, 2D NMR, IR, and HRESIMS spectra of the new compounds **1**–**4**; Figure S39: the picture of strain *Penicillium* sp. KFD28; Figure S40: Separation flow chart of fungus *Penicillium* sp. KFD28 secondary metabolites extract; Figure S41: HPLC chromatograms of the EtOAc extracts monitored at wavelengths of 230 nm and 274 nm; Figure S42: HPLC chromatograms of the EtOAc extracts using Rice solid medium with L-tryptophan, and compounds **6**, **12**, **14**, **8**, and **11** monitored at wavelengths of 230 nm and 274 nm; Figure S43: ECD curve for compound **4** and computation section of compounds **1**–**3**.

**Author Contributions:** L.-T.D. contributed to fungal fermentation, compounds purification, and structural elucidation. L.Y. and F.-D.K. were responsible for chemical computation and preparation of the paper. Q.-Y.M. and Q.-Y.X. contributed to the bioassays and identified the fungal strain. H.-F.D. revised the paper. Z.-F.Y. and Y.-X.Z. designed the work and revised the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Natural Science Foundation of Hainan Province (2019CXTD411), Financial Fund of the Ministry of Agriculture and Rural Affairs, P.R. of China (NFZX2021), China Agriculture Research System of MOF and MARA (CARS-21), Central Publicinterest Scientific Institution Basal Research Fund for Chinese Academy of Tropical Agricultural Sciences (1630052017002, 1630052021019).

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

**Conflicts of Interest:** The authors declare no conflict of interest.
