*3.1. Polyketides*

Polyketides (PKs) are a large family of secondary metabolites with prominent structural diversity and various biological activities, isolated from diverse organisms. Polyketide synthases (PKSs) catalyze the sequential decarboxylative condensations of acyl-CoA thioesters to form structurally diverse PKs [37]. We direct readers to the fantastic reviews for more information on PKSs [38–41]. An even-increasing number of PKs from the mangrove-associated microorganisms are being reported.

#### 3.1.1. Coumarins and Isocoumarins

Naturally occurring coumarins and isocoumarins are an essential class of benzopyrene derivatives and are present in remarkable amounts in plants, while only a few are found in microorganisms and animal sources.

Up to now, 12 new coumarin and 102 new isocoumarin derivatives have been obtained from mangrove-associated fungi [42,43]. Among them, Peniisocoumarin A and B (**32** and **33**, Figure 10), a pair of unusual dimeric isocoumarin-type diastereoisomers containing a symmetric four-membered core at C-9/9- and C-10/10- were obtained from the fermentation of *Penicillium commune* QQF-3 (isolated from fresh fruit of the mangrove plant *Kandelia candel*) [44]. The structures of **32** and **33** were unanimously defined by X-ray diffraction analysis using Cu K*α* radiation. In 2015, Darsih et al., discovered penicilliumolide A (**34**) (Figure 10), an unusual tetracyclic isocoumarin containing a *γ*-lactone ring fused with a unique spiro framework, from the mangrove endophytic fungus *Penicillium chermesinum* HLit-ROR2 [45].

**Figure 10.** Structures of compounds **32**–**34**.
