**5. Conclusion**

Terpenes represent one of the largest and most diverse classes of natural products. They have numerous roles ranging from defense repellents against herbivores or pathogens through animal attract hormones to agents designed to help disperse seeds and pollen. Monoterpenoids and sesquiterpenoids are obviously the major constituents of EOs, while in some oils the occurrence of diterpenoids was observed as quite minor constituents when present. In an ecological context, mono- and

**95**

**Author details**

more detailed studies.

Cameroon

Fongang Fotsing Yannick Stephane1

\*Address all correspondence to: fongangfys@yahoo.fr

provided the original work is properly cited.

Maroua, Maroua, Cameroon

\* and Bankeu Kezetas Jean Jules2

1 Department of Chemistry, Higher Teachers Training College, University of

2 Department of Chemistry, Faculty of Science, University of Bamenda, Bambili,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Terpenoids as Important Bioactive Constituents of Essential Oils DOI: http://dx.doi.org/10.5772/10.5772/intechopen.91426*

sesquiterpenes play an important role in the relations between organisms, for example, as attractants of pollinators or deterrents of herbivores. The enormous diversity of terpenoids and wide spectrum of biological activities make them attractive for many industries, and new areas of application still have not been discovered. Despite their rich and complex composition, the use of EOs remains limited to the cosmetics and perfumery domains. It is worthy to develop a better understanding of their chemistry and biological properties as well as that of their individual components for new and valuable applications in human health.

Despite their well-recognized bioactivities, EOs have been misused with regard to their level of toxicity. Some EOs or their major constituents have been recorded to be much toxic with bad side effects including convulsions, irritation, and photodermatosis. Literature review of the available data shows that serious accidents, most of which involve young children, are due to a small number of EOs, ingested in large amount. The development and the expansion of therapies using EOs and the evaluation of their acute toxicity have become more important to avoid their abusive use. The most common adverse events are eye, mucous membrane, and skin irritation and sensitization particularly to oils containing aldehydes and phenols. Despite all, no well-defined studies have proved that these EOs are harmful, but this deserves

## *Terpenoids as Important Bioactive Constituents of Essential Oils DOI: http://dx.doi.org/10.5772/10.5772/intechopen.91426*

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

described [156].

humans and animals [159].

ing their use as flavoring and antioxidant agents [104].

aldehydes > ketones > alcohols > esters > hydrocarbons [156].

sesquiterpene hydrocarbons (24.0%) [114].

myrcene, and camphene [161].

nabinoids are odorless [162].

**5. Conclusion**

as the mevalonate pathway and the phosphatidylcholine biosynthesis, which results in cell growth inhibition, cell cycle arrest occurring at the G0/G1 interphase, and increased apoptosis [155]. Antibacterial and antifungal activities of oils with high levels of sesquiterpenes as cadinene, spathulenol, and selinene were

Cristiani and coworkers have reported the antimicrobial activity of four monoterpenes (*p*-cymene, *γ*-terpinene, carvacrol, and thymol) against the Gram-positive bacterium *S. aureus* and the Gram-negative bacterium *E. coli*. They concluded that thymol was considerably more toxic against *S. aureus* than the other three terpenes, while carvacrol and *p*-cymene were the most active against *E. coli* [157]. Germacrene D with its three double bonds as electron-rich centers demonstrated good ability to scavenge superoxide radical anions [156]. However, linalool and nerolidol may also display pro-oxidant activity. Carvacrol and thymol are reported to be the main constituents of volatile oils from *Origanum* species in general [158, 159]. With limonene, citronellol, myrtenol, linalool, and carvacrol are among monoterpenes showing in vitro and in vivo cardiovascular effects in both

Monoterpenes, sesquiterpenes, and oxygenated derivatives extracted from EOs have shown strong inhibitory activities against pathogenic bacteria, hence suggest-

Alzheimer's disease is by far the most prevalent of all known forms of dementia. Wojtunik-Kulesza and collaborators showed that three monocyclic monoterpenes (carvone, pulegone, and γ-terpene) possess acetylcholinesterase (AchE) inhibitory activity. Among the investigated terpenes, the three later were recognized as compounds with promising activities in the development of multi-target directed ligands [160]. The lipophilic character of terpene skeleton combined with the hydrophobic character of the functional group is essential for activity. Thus, a rank of activity has been proposed as follows:

In 2010, Conti and coworkers measured the insect repellent activity of three EOs. They found that at lowest dose (0.001%), the OE of *Hyptis suaveolens* exhibited a significant higher repellent effect compare to *Hyptis spicigera* and *Lavandula angustifolia*. After chemical analyses of the OE of *H. suaveolens*, monoterpene hydrocarbons were the most represented class of volatiles (64.1%), followed by

In EOs, the components found in higher concentrations and related to antimicrobial activity are phenolic compounds such as linalool, sabinene, menthol,

Sesquiterpenes have anti-inflammatory and anti-allergic properties. The antiinflammatory activities of some medicinal plants are due to the presence of one or more sesquiterpene lactones [26]. Above all, terpenes are responsible for the smell and flavor typical of the different varieties of *Cannabis sativa*, whereas phytocan-

Terpenes represent one of the largest and most diverse classes of natural products. They have numerous roles ranging from defense repellents against herbivores or pathogens through animal attract hormones to agents designed to help disperse seeds and pollen. Monoterpenoids and sesquiterpenoids are obviously the major constituents of EOs, while in some oils the occurrence of diterpenoids was observed as quite minor constituents when present. In an ecological context, mono- and

**94**

sesquiterpenes play an important role in the relations between organisms, for example, as attractants of pollinators or deterrents of herbivores. The enormous diversity of terpenoids and wide spectrum of biological activities make them attractive for many industries, and new areas of application still have not been discovered. Despite their rich and complex composition, the use of EOs remains limited to the cosmetics and perfumery domains. It is worthy to develop a better understanding of their chemistry and biological properties as well as that of their individual components for new and valuable applications in human health.

Despite their well-recognized bioactivities, EOs have been misused with regard to their level of toxicity. Some EOs or their major constituents have been recorded to be much toxic with bad side effects including convulsions, irritation, and photodermatosis. Literature review of the available data shows that serious accidents, most of which involve young children, are due to a small number of EOs, ingested in large amount. The development and the expansion of therapies using EOs and the evaluation of their acute toxicity have become more important to avoid their abusive use. The most common adverse events are eye, mucous membrane, and skin irritation and sensitization particularly to oils containing aldehydes and phenols. Despite all, no well-defined studies have proved that these EOs are harmful, but this deserves more detailed studies.
