**1. Introduction**

Mangrove forests are a complex ecosystem, and the microbes in mangrove sediments play an important role in the biogeochemical cycles of mangrove ecosystems [1]. The high diversity of mangrove environments has contributed to high microbial diversity, which is an important source of bioactive natural products [2–4]. Research on secondary metabolites from mangrove sediments-derived microbes has yielded many natural products with novel structures and significant pharmacological activities [5–8]. In particular, halogenated compounds obtained from mangrove-derived microbes, especially chlorine-containing metabolites, have received a grea<sup>t</sup> deal of attention [9–11].

*Mollisia* is a taxonomically neglected discomycete genus (Helotiales, Leotiomycetes) in decaying plant tissues or root soil. The natural products from the genus *Mollisia* were not well explored and were limited to few publications. Mollisinols A and B, two new metabolites were isolated from the endophytic fungus *Mollisia* sp., derived from the root bark of *Ardisia cornudentata* Mez [3]. Ophiobolin C, isolated from *Mollisia* sp. (GB5328) from the dead bark of *Tsuga canadensis*, was an inhibitor of binding with human CCR5 receptor and exhibited an IC50 value of 40 μM [12]. KS-504 compounds, three novel inhibitors of Ca2+ and calmodulin-dependent cyclic nucleotide phosphodiesterase were

**Citation:** Cai, J.; Wang, X.; Gan, X.; Zhou, Q.; Luo, X.; Yang, B.; Liu, Y.; Ratnasekera, D.; Zhou, X. New Chlorinated Metabolites and Antiproliferative Polyketone from the Mangrove Sediments-Derived Fungus *Mollisia* sp. SCSIO41409. *Mar. Drugs* **2023**, *21*, 32. https:// doi.org/10.3390/md21010032

Academic Editors: Wenhan Lin, Guoqiang Li and Jing Xu

Received: 4 December 2022 Revised: 22 December 2022 Accepted: 27 December 2022 Published: 30 December 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

isolated from *Mollisia ventosa* KAC-1 148 [13]. Mollisianitrile, a new antibiotic was isolated from *Mollisa* sp. A59–96 [14]. Benesudon, isolated from *Mollisia bensuada*, possessed antimicrobial, cytotoxic, and phytotoxic activities [15]. Mollisin, a dichloronaphthoquinone derivative produced by the fungus *Mollisia caesia* [16]. In our study, we explored potential bioactive secondary metabolites from a mangrove sediment-derived fungal strain, *Mollisia* sp. SCSIO41409, isolated from a mangrove sediment sample in Hainan Island, China. During our search for potentially diverse and bioactive secondary metabolites from mangrove fungal sources [10,17–19], two new chlorinated metabolites (**1** and **3**), and seven known polyketides (**2** and **4**–**9**) (Figure 1) were isolated and identified from a mangrove sediment-derived fungus *Mollisia* sp. SCSIO41409. These compounds were examined for antimicrobial and antiproliferative activities. Herein, we report the details of the isolation, structural elucidation, and biological evaluation of all isolated compounds.

**Figure 1.** Structures of compounds **1**–**9**.
