## 2 Biological Activities of Monoterpenes
### Acyclic Monoterpenes
The anticancer activity of the essential oil from _Ocimum forskolei_ Benth with 28-10% of linalool has been reported [37]. The oil's IC\({}_{50}\) values were shown to be close to 17, 7, 5, and 25 \(\upmu\)g/mL for MCF7, HT29, HCT116, and MRC5 respectively. A recent study done found that linalool displays antiproliferation effects on breast cancer cell lines MCF-7 and MDA-MB-231. This research demonstrated that at 100 \(\upmu\)M concentration of linalool there was approximately 55 and 65 % cell viability for MCF7 and MDA-MB-231 respectively after 24 h [35]. The determined IC\({}_{50}\) values of linalool were a mild 588 and 480 \(\upmu\)M for MDA-MB-231 and MCF7 respectively [35]. Unfortunately, no data was provided for normal cells, which calls for further studies to experimentally determine therapeutic index and its potential as anticancer agent. Linalool has demonstrated antioxidative properties in a study from _Plumeria alba_[38]. The essential oils from this plant have been shown to have antioxidant properties. Gas Chromatography-Mass Spectroscopy studies identified that linalool composes about 24%of the active essential oil. The samples prepared from the plants flowers gave IC\({}_{50}\) values of 370, 1014, and 1943 \(\upmu\)g/mL for the H\({}_{2}\)O\({}_{2}\) scavenging assay, DPPH radical scavenging assay, and thiobarbituric acid reactive substances (TBARS) assay respectively [38]. In addition, in vivo studies in hemiparkinsonian rat models indicated neuroprotective effects. Linalool treatment demonstrated neuroprotection in the form of anti-inflammatory and antioxidative action in dosages as low as 50 mg/kg [39]. Through the observed behavioral and neurochemical effects linalool indicated neuroprotective activity presumably through its antioxidative properties [39]. Linalyl acetate (**3b**, Figure 3) has been well documented to have favorable bioactivities. Anticancer properties have been associated with essential oils from _Lavandula angustifolia_, _Lavandula officinalis_, _Lavandula latifolia_, and bergamot [40; 41; 42; 43; 44], all of which contain linalyl acetate in concentrations as high as 44%. A study conducted on the lavender essential oils from _Lavandula angustifolia_ demonstrated an IC\({}_{50}\) values of 0.36% (\(v/v\)) against HaCaT cell line in an MTT assay [43]. Additionally, there have been reports of linalyl acetate associated antioxidant activity in essential oils of _Salvia sclarea_, and _Myrtus nivelei_, across different regions [45; 46]. The essential oil attained from _Myrtus nivelei_ demonstrated an IC\({}_{50}\) value of 2.25 mg/mL [46]. Myrcene (**4**, Figure 3) has been shown to display anticancer bioactivities when used as a mixture in the essential oils from _Mentha spicata_, _Matricaria chamomilla_, and _Citrus pseudolimon_[47; 48]. The IC\({}_{50}\) values of the essential oil from _Matricaria chamomilla_ were demonstrated to be between 200 and 320 \(\upmu\)g/mL for cancer cell lines A549, MCF, and PC3. Meanwhile the IC\({}_{50}\) values for the _Mentha spicata_ essential oils were 672, 708, and 206 \(\upmu\)g/mL for cell lines A549, MCF, and PC3 respectively [47]. It has been documented that plant essential oils with high concentrations of myrcene have antioxidant potential in biological systems. Essential oils from _Hedlyosmum purpurascens_, _Pinus tulareis_, _Salvia officinalis_, _Cymbopgon citratus_, _Piper eriopadon_, and _Pranges trifida_, all having high concentrations of myrcene, have demonstrated antioxidant activities [49; 50; 51; 52; 53]. Myrcene has been demonstrated to inhibit oxidative stress by down regulating pro-inflammatory cytokines and inflammatory mediators [54]. This compound's ability to decrease the oxidative stress induced by rotenone was demonstrated by the significant reduction of pro-inflammatory cytokines upon myrcene-rotenone co-treatment. While monitoring expression levels of inflammatory markers a dramatic decrease in expression was noted in iNOS and COX-2 [54].