**4. Conclusions**

In summary, five new compounds (**1**–**5**) and two previously reported metabolites (**6** and **7**) were isolated from the mangrove-derived endophytic fungus *C. cladosporioides* MA-299. The structures of **3** and **6** were confirmed by single-crystal X-ray diffraction analysis and this is the first time for reporting the crystal structures of the two compounds. Compound **4** showed potent inhibitory activity against plant-pathogenic fungi (*G*. *cingulate* and *F.oxysporum* f. sp. *cucumerinum*), each with MIC value of 1.0 μg/mL, while **7** showed potent inhibitory activity against aquatic bacterium (*E. ictarda*) and plant-pathogenic fungus (*G*. *cingulate*), with MIC values of 4.0 and 1.0 μg/mL respectively. Compound **3** exhibited moderate inhibitory activity against human pathogenic bacterium *S. aureus* with MIC value of 8.0 μg/mL and acetylcholinesterase inhibitory activity with IC50 value of 40.26 μM.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-3397/17/5/296/s1, 1D and 2D NMR spectra and ECDs of compounds **1**–**5** as well as crystal packing of compounds **3** and **6**.

**Author Contributions:** F.-Z.Z. performed the experiments for the isolation, structure elucidation, and antimicrobial evaluation; and prepared the manuscript; X.-M.L. performed the 1D and 2D NMR experiments; X.L. contributed to part of the structure determination; S.-Q.Y. contributed the optimization of fermentation; L.-H.M contributed to part of the structure determination and jointly supervised the research; B.-G.W. supervised the research work and revised the manuscript.

**Funding:** Financial support from the Natural Science Foundation of China (81673351 and 31600267) and from the Natural Science Foundation of Shandong Province, China (ZR2016BQ17), is gratefully acknowledged. Bin-Gui Wang acknowledges the support of Taishan Scholar project from Shandong province.

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