*4.2.4 Ecology*

The volatile compounds play an important role in the inter- and intraspecies chemical communication in marine algae. They act as pheromones [97] or allelochemicals, chemical defenses against herbivores [132, 133], and inhibition of bacterial and fungal biofilms [134]. The genus *Dictyopteris* produce a high amount of C11 hydrocarbons, some of which act as pheromones that stimulate gamete release or attract sperm during sexual reproduction [96]. The first male-attracting metabolite was elucidated as ectocarpene (54) [135] which shows a moderate activity at 10 mM. A subsequent study revealed that the real pheromone used by the female gamete was pre-ectocarpene (62) which is active at 5 pM. In fact, the alga produces pre-ectocarpene which undergoes a thermal rearrangement (Cope rearrangement)

**15**

*Algae Essential Oils: Chemistry, Ecology, and Biological Activities*

to lead to ectocarpene [136]. The Cope rearrangement occurs between the time of the releasing and attraction of the pheromone; the sigmatropic transformation serves as a natural control mechanism for deactivation of the pheromone [136]. The genus *Dictyopteris* produces significant amounts of C11-sulfur compounds which

In green algae, the volatile compounds, such as (Z)-8- heptadecane, act also as allochemicals [61]. In the genus *Caulerpa*, the caulerpenyne is the most abundant cytotoxic sesquiterpene produced by *C. taxifolia* and *C. racemosa* [138, 139]. It is involved either in the chemical defense of the plant against herbivore or within the framework of interspecific competition as antifeedant and/or antifouling activities [140]. In red algae, the halogenated organic compounds are produced, probably, to be involved in the defense system against microorganism infection [141], herbivore attack [141], space competitors [142], and harmful fouling by different types of epiphytes [142].

There are several reports of secondary metabolites, among them are numerous volatile compounds, derived from macroalgae which exhibit a broad range of

The essential oil of *D. membranacea* has shown a strong antibacterial activity against *Staphylococcus aureus* and *Agrobacterium tumefaciens*, which is translated by an MIC of 1519 μg/mL [106]. The volatile oil of *P. pavonica* possesses a moderate antimicrobial activity against *Staphylococcus aureus* and *Candida albicans* [144]; antifungal against *Macrophomina phaseolina*, *Rhizoctonia solani*, and *Fusarium solani* [145]; cytotoxicity against KB cells [146]; and antitumor activity against lung and human carcinoma cell lines [147]. On the other hand, the volatile of *H. clathratus* showed a pronounced antimicrobial activity against *S. cerevisiae* compared with

*DOI: http://dx.doi.org/10.5772/intechopen.91672*

are involved in chemical defense [137].

*Halogenated sesquiterpenes from red the genus* Laurencia*.*

biological activities such as antibiotics [40, 143].

Canesten as reference material [148].

*4.2.5 Biological activities*

**Figure 8.**

*Algae Essential Oils: Chemistry, Ecology, and Biological Activities DOI: http://dx.doi.org/10.5772/intechopen.91672*

*Essential Oils - Bioactive Compounds, New Perspectives and Applications*

*Monoterpenes isolated Santa Cruz* Plocamium cartilagineum*.*

*Monoterpenes isolated from* Plocamium cartilagineum *(Chile).*

Rhodomelaceae is elatol (103); it is isolated from *L. elata* [128] and from several other species of *Laurencia* [129]. An exhaustive literature review has described the chemical structure data and biological activities of the halogenated sesquiterpenes

The volatile compounds play an important role in the inter- and intraspecies chemical communication in marine algae. They act as pheromones [97] or allelochemicals, chemical defenses against herbivores [132, 133], and inhibition of bacterial and fungal biofilms [134]. The genus *Dictyopteris* produce a high amount of C11 hydrocarbons, some of which act as pheromones that stimulate gamete release or attract sperm during sexual reproduction [96]. The first male-attracting metabolite was elucidated as ectocarpene (54) [135] which shows a moderate activity at 10 mM. A subsequent study revealed that the real pheromone used by the female gamete was pre-ectocarpene (62) which is active at 5 pM. In fact, the alga produces pre-ectocarpene which undergoes a thermal rearrangement (Cope rearrangement)

**14**

of red algae [130, 131].

*4.2.4 Ecology*

**Figure 7.**

**Figure 6.**

**Figure 8.** *Halogenated sesquiterpenes from red the genus* Laurencia*.*

to lead to ectocarpene [136]. The Cope rearrangement occurs between the time of the releasing and attraction of the pheromone; the sigmatropic transformation serves as a natural control mechanism for deactivation of the pheromone [136]. The genus *Dictyopteris* produces significant amounts of C11-sulfur compounds which are involved in chemical defense [137].

In green algae, the volatile compounds, such as (Z)-8- heptadecane, act also as allochemicals [61]. In the genus *Caulerpa*, the caulerpenyne is the most abundant cytotoxic sesquiterpene produced by *C. taxifolia* and *C. racemosa* [138, 139]. It is involved either in the chemical defense of the plant against herbivore or within the framework of interspecific competition as antifeedant and/or antifouling activities [140]. In red algae, the halogenated organic compounds are produced, probably, to be involved in the defense system against microorganism infection [141], herbivore attack [141], space competitors [142], and harmful fouling by different types of epiphytes [142].

#### *4.2.5 Biological activities*

There are several reports of secondary metabolites, among them are numerous volatile compounds, derived from macroalgae which exhibit a broad range of biological activities such as antibiotics [40, 143].

The essential oil of *D. membranacea* has shown a strong antibacterial activity against *Staphylococcus aureus* and *Agrobacterium tumefaciens*, which is translated by an MIC of 1519 μg/mL [106]. The volatile oil of *P. pavonica* possesses a moderate antimicrobial activity against *Staphylococcus aureus* and *Candida albicans* [144]; antifungal against *Macrophomina phaseolina*, *Rhizoctonia solani*, and *Fusarium solani* [145]; cytotoxicity against KB cells [146]; and antitumor activity against lung and human carcinoma cell lines [147]. On the other hand, the volatile of *H. clathratus* showed a pronounced antimicrobial activity against *S. cerevisiae* compared with Canesten as reference material [148].

The cytotoxicity is the most common activity observed for halogenated organic compounds isolated from the family Rhodomelaceae. A large number of these compounds were shown to be cytotoxic to a wide range of cancer cell lines [115].

Among many of the halogenated sesquiterpenes evaluated for their in vitro cytotoxic effects against HeLa and HEP-2 cancer cell lines, and against nontumoral VERO cells, during both lag- and log-phase cell growth [149], elatol (103) turned out the most active compound with IC50 values of 4.1 and 1.3 μM to HeLa, 2.4 and 2.0 μM to HEP-2, and 2.3 and 25.0 μM to VERO cells, in lag- and log-phase, respectively [150]. Further studies were carried on the evaluation of the cytotoxicity against several tumor cell lines of chamigrane [150] and Laurane- and Cuparane-type sesquiterpenes and were found to display a wide range of potency levels [151, 152]. Other activities of halosesquiterpenes such as antibacterial activity [153], antifungal activity [154], and antiviral activity [155] were investigated and conducted to promising results.
