Antifouling Compounds from Marine Invertebrates

In this review, a comprehensive overview about the antifouling compounds from marine invertebrates is described. In total, more than 198 antifouling compounds have been obtained from marine invertebrates, specifically, sponges, gorgonian and soft corals.


Terpenoids from Corals
The principal terpenoids elaborated by gorgonian and soft corals are sesquiterpenes and diterpenes. The representative structures of diterpenoids by carbon skeleton class from corals included briarane type, cembrane type, eunicellan type, xenicane type, pseudopterosin type, dilophol type, etc. Many of these diterpenoids were reported to have AF activity against marine invertebrate larvae.

Terpenoids from Corals
The principal terpenoids elaborated by gorgonian and soft corals are sesquiterpenes and diterpenes. The representative structures of diterpenoids by carbon skeleton class from corals included briarane type, cembrane type, eunicellan type, xenicane type, pseudopterosin type, dilophol type, etc. Many of these diterpenoids were reported to have AF activity against marine invertebrate larvae.

Alkaloids
Many types of AF alkaloids, especially brominated alkaloids, have been isolated from marine sponges.

Alkaloids
Many types of AF alkaloids, especially brominated alkaloids, have been isolated from marine sponges.

Other Kinds of Compounds
Besides the above characteristic terpenoids, alkaloids and steroids, there were many other kinds of AF compounds isolated from marine invertebrates, such as polyacetylenes, butenolides, phenol derivatives, and peptides.

Other Kinds of Compounds
Besides the above characteristic terpenoids, alkaloids and steroids, there were many other kinds of AF compounds isolated from marine invertebrates, such as polyacetylenes, butenolides, phenol derivatives, and peptides.

Conclusions
Totally, over 198 AF compounds have been obtained from marine invertebrates, especially, sponges, gorgonian and soft corals. These compounds covered isocyanoterpenoids, sesquiterpenes, diterpenes, sesterterpenes, triterpenoids, alkaloids (including bromotyrosine-derived, pyrrole-derived, pyridine-derived and indole-derived compounds), steroids, polyacetylenes, butenolides, peptides, and phenol derivatives, which played important chemical defense roles in the marine invertebrates. In here, the AF activities of 198 compounds towards microfouling and macrofouling were summarized in Table 1. It is thought that AF compounds have medium to high bioactivity with a threshold of EC 50 < 15 µg/mL, and AF compounds having high LC 50 /EC 50 ratios (>15) are potentially good candidate antifoulants [14]. From Table 1, we can see that some of these compounds are potent antifoulants with low/non-toxicity, such as some of the isocyanoterpenoids, briarane-type diterpenoids, cembrane-type diterpenoids, and indole alkaloids. However, little was known about their mode of actions and AF activities in fields, because of the serious problems of the supplies from these marine invertebrates, which restricted the development of these potent AF compounds in antifouling paints. Although some studies about the total synthesis of several isocyanoterpenoids, briarane-type diterpenoids, and cembrane-type diterpenoids have been done, too many steps of these synthetic routes with low yields limited their applications. To overcome the problems, more studies about the organic syntheses of these potent AF compounds as models are needed. In addition, scientists have paid more attention to AF compounds from marine microorganisms, especially sponge-derived and gorgonian-derived microorganisms in recent years.