**6. Sulfer containing metabolites**

#### **6.1 Polysulfides and alkylsulfides**

Sulfur atom rarely found among the marine organism. Ascidians belonging to the genus *Lissoclinum (didemnidae)* had shown resistant towards Plasmodium chemical scaffolds, some of them with unique antiviral activity against mammalian erythrocytes. Among these metabolites, several structurally intriguing antimicrobial polysulfides have activity comparable to the commercially available antimalarials chloroquine and quinine shows activity against bacteria, fungi and other infective agents. Antifungal properties of benzopentathiepin varacin isolated from *L.perforatum*. Due to its antifungal properties, they paved the way for the isolation of.

Lissoclinotoxins A and B. Toxins isolated from *L.vareau* showed activity against *Candida albicans* with a 14 mm zone of inhibition. Polysufides showed an activity of strong cytotoxicity, being 100times more potent than 5 against *Staphylococcus aureus.* Having a minimum inhibitory concentration IC90 of 0.05ug/ml against human colon cancer HCT 116. Role of ascidian associated microorganism, showed activity against *Aeromonas salmonicida* and *Vibrio anguillarium*. Role played by the ascidian associated microorganism in the synthesis and cytotoxic activity was tested against the *Aeromonas salmonicida* and *Vibrio anguillarium* by the zonal inhibition assays of their secondary metabolites reported by the discovery of analogues lissoclinotoxin B. It is a potent inhibitor of bacteria, mainly against the *Aeromonas salmonicidia*. Varacin isolated from the colonial ascidian exhibited antimicrobial properties. It had moderate cytotoxic effects against the Polycitor species. Varacin showed active resistance towards the strain Plasmodium isolated and also exhibited strong activity in vitro against the *Candida albicans*. On the other hand, this peptide exhibited a lower IC 50 value at 296 nM towards the Gram-positive *Bacillus subtilis* [42]. Further, three polysulfites isolated from the colonial ascidian, was isolated as acetates, 4-Trichosporon metagrophytes and it showed resistance to *Candida albicans* with an MIC of 20 and 40 μg/mL.

### **6.2 Bengacarboline**

A beta-carboline alkaloid derived from the ascidian *Didemnin* species, known to contain cytotoxic effect on in vitro A26 human tumor cell line and inhibit topoisomerase II activity [43].

#### **6.3 Ihenyamines A-B**

A derivative from the ascidian, *Polycitorella* species containing compounds exhibiting moderate cytotoxicity towards in-vitro cell line studies. Alkaloids of *Staurosporine*, studied on the MONO-MAC-6 cell lines, successfully inhibited the cancer growth and are known to be strong inhibitors of Protein kinase [44]. Pibocin B isolated from the Japan ascidian *Eudistoma* species, has a unique strucrtural species of N-O methylindole alkaloid and known to produce moderate cytotoxic [45] (Makarieva et al.,) effect towards mouse *Ehrlich* carcinoma cells with an ED50 25 μg/mL (**Figure 5**).

*Antimicrobial Peptides Derived from Ascidians and Associated Cyanobacteria DOI: http://dx.doi.org/10.5772/intechopen.99183*

**Figure 5.** *Showing image of ascidian* Eudistoma *species.*
