*2.2. Diterpenoids*

Two new *ent*-isopimarane-type diterpenoids agallochaexcoerins D and E (**29** and **30**) [35] (Figure 9), possessing an unusual seven-membered lactone moiety, were isolated from the wood of mangrove *Excoecaria agallocha*. Notably, **29** is the first report of *ent*-3,4- secoisopimaratriene diterpenoid with a rare seven-membered ring.

**Figure 9.** Structures of compounds **29**–**31**.

Decandrinin (**31**) (Figure 9), an unprecedented C-9-spiro-fused 7,8-*seco*-*ent*-abietane, was obtained from the bark of an Indian mangrove *Ceriops decandra* (collected in the estuary of Godavari, Andhra Pradesh) [36]. The biosynthetic precursor might be the naturally more prevalent occurring 7,13-*ent*-abietadien-3*β*-ol and the plausible biosynthetic was proposed (Scheme 4). The spiro ring could be formed by oxidative cleavage and lactonization.

*ent*DELHWDGLHQ βRO

**Scheme 4.** Proposed biosynthetic pathway for compound **31** [36].

#### **3. Unusual Natural Products from Mangrove-Associated Microorganisms**

Previous chemical investigations of mangrove microbes especially mangrove-associated fungi resulted in the discovery of various bioactive secondary metabolites, including polyketides, terpenes, alkaloids, and peptides with diverse structural features.
