## 4 Bioactivity of Monoterpenes in Macroalgae
Further studies should be performed to develop further modifications for the enhancement of their activity. However, [PERSON] et al. (2017) observed that the cytotoxic activity of halogenated monoterepenes (**5**, **113-118**) from _Plozanium subrui_ [PERSON] and _Plozanium cornutum_ (Turner) [PERSON] was higher when compared to the known anticancer drug _cis_-platin. [PERSON] et al. (2017) showed that Delocalides A-C (**52**-57), poly halogenated monoterepenes from _Plozanium corallortiza_, exhibited good activity against human esophageal cancer cell lines when compared to the commonly used _cis_-platin. It can be observed that the genus _Plozanium_ produces a great variety of polyhalogenated monoterepenes with various anticancer activities (Table 2). [PERSON] et al. (2019) isolated one new halogenated monoterepene (**119**) from _P. cartilagineum_ collected from South Africa. It showed good cytotoxic activity against the cells of human lung cancer and mouse neuro-2a cell lines. Halomon **102** along with the compounds **120-124** isolated from _Portieria hornemannii_ were good inhibitors against DNA methyltransferase-1 isoform, which represents the enzyme responsible for tumor growth (2018). [PERSON] et al. (2017) showed that halogenated monoterepenes could have selective activity against certain cancer cell lines. Among isolated compounds (**30**, **125**, **126**, **127-132**) from _P. cartilagineum_, the most potent activity exhibited the compounds **30**, **125**, **126**, and **128** with notably selective cytotoxicity against colon and cervical adenocarcinoma cells. Halogenated monoterepenes **62** and **63** isolated from _Plozanium maxillum_ were tested against MDA-MB-231 metastatic breast carcinoma cell line and showed moderate antiproliferative activity ([PERSON] _et al._, 2017). This level of activity of both of the compounds **62** and **63** is comparable with the previously reported activities of halogenated monoterepenes (**54**, **55**, **58**, **60**, **104-109**) against the same cancer cell lines ([PERSON] _et al._, 2017). Geographical variation, except on anticancer activity, showed also an influence on antiplasmodial activity of halogenated monoterepenes isolated from _Plozanium cornutum_([PERSON] _et al._, 2017). [PERSON] et al. (2017) also emphasized the importance of dichloromethyl moiety at position 7 when considering the higher antiplasmodial activity of halogenated monoterepenes. They observed that two novel compounds **134** and **135** containing 7-dichloromethyl moiety showed significantly higher activity toward strains of _Plasmodium falciparum_ compared with already known compounds **53**, **58**, **133-135**, **138**, and **139**. Furthermore, two novel cyclohexane polyhalogenated monoterepenes **140** and **141** and fluorolcamioid C (**30**) reported earlier ([PERSON] _et al._, 2017) were very efficient repellents and antifeedants, as well as selective insect cell toxicants depending on the number of halogenated substituents, as well as halogen type. Strong antifeedant activity was observed when five halogen substituents were present in monoterepene skeleton, but when compared to six halogen substituents the activity was significantly decreased. The substitution of Br atom showed higher activity of the molecule when compared with C-1 atom ([PERSON] _et al._, 2017). According to [PERSON] et al. [83], red algae belonging to the genus _Plocanium_ exhibit strong insecticidal activities (Table 2). They studied two polyhalogented monoterepenes, aplysiaterpenoid A (**142**) and telfairine (**143**), isolated from _Plocanium telfairiae_ ([PERSON] and [PERSON]) [PERSON] ex Kutzing and tested their insecticidal activities against _Blattella germanica_ and _Anopheles gambiae_. Aplysiaterpenoid A (**142**) and telfairine (**143**) possess cyclodie-type insecticidal mode of action due to the orientations of the sterically bulky regions and electronegative centers in monoterepenes.