## 2 Sesquiterpenals and Their Bioactivities
### Acyclic Sesquiterpenals  
Acyclic sesquiterpenals are defined as open chain sesquiterpenal compounds, with representative examples including nerolidol and farnesol (Table 1, Figure 1). Nerolidol exists as a colorless to pale yellow viscous oil, and is characterized by its delicate sweet floral aroma, which includes nuances of rose, lily-of-the-valley, and apple blossom [10]. This compound is primarily derived from plant sources, such as _Melaleuca viridiflora_, _Zin-giber officinal_, _Myroxylon balsamum_, and _Myroxylon peruiferum_, and trace quantities can be detected in premium _Roman chamonile_ essential oils [10]. Nerolidol exhibits diverse bioactivities, including antimicrobial [11], anti-biofilm [12], antioxidant [13], antiparasitic [14], transdermal permeation-enhancing [15], antinociceptive [16], and anticancer [17] properties. Farnesol, a colorless hydrophobic liquid with limited aqueous solubility but high miscibility in organic solvents, such as ethanol, is renowned for its sweet floral fragrance. It is ubiquitously distributed in essential oils of diverse botanical species, notably _Aniba roseadora_, _Ahelmoschus moschatus_, _Cananga adorata_, _Acacia farnesiana_, _Myroxylon balsamum_, _Cymbopogon martini_, _Polianthes tuberosa_, _Jasminum grandiflora_, and _Citrus aurantium_[18]. In addition to plant systems, farnesol is present in animal and microbial organisms, where it plays crucial roles in intercellular signaling, quorum sensing modulation, and apoptosis regulation [19]. These distinctive characteristics support its extensive applications as a cosmetic fragrance component, a natural acaricidal agent, and a precursor in anticancer drug development [19].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Classification** & **Sesquiterpenol** & **Functions and Applications** & **References** \\ \hline \multirow{6}{*}{acyclic} & \multirow{3}{*}{nerolidol} & antimicrobial, anti-biofilm, antioxidant, antiparassitic, & \multirow{3}{*}{[11; 12; 13; 14; 15; 16; 17]} \\  & & transdermal permeation-enhancing, antinociceptive, & & \\  & & and anticancer properties & \\ \cline{2-4}  & & & essential oils, intercellular signaling, quorum sensing & \\  & & modulation, apoptosis regulation & & \\ \hline \multirow{6}{*}{monocyclic} & \multirow{3}{*}{(-)-\(\alpha\)-bisabolol} & \multirow{3}{*}{\
\begin{tabular}{c} ulcer healing, gallstone dissolution, analgesia, \\ anti-inflammatory, bacteriostasis, anti-genotoxic, \\ melanin inhibition \\ \end{tabular} } & \multirow{3}{*}{[9; 20]} \\  & & elemol & fragrance formulation, personal care products, laundry & \\  & & detergents, household commodities & & [21] \\ \hline \multirow{6}{*}{bicyclic} & \multirow{3}{*}{\(\tau\)-cadinol} & \multirow{3}{*}{
\begin{tabular}{c} pest-repellent, nutritional substrate, membrane \\ stabilizer, energy metabolism modulator, smooth \\ muscle relaxation, antidiararheffects, calcium \\ channel antagonism, phyto germination regulation, \\ acaricidal action, insect repellency \\ \end{tabular} } & \multirow{3}{*}{[23; 24; 25; 26]} \\  & & & woody aroma, cosmetics and household products, \\  & & anti-angial activity, arrhythmia suppression, & \\  & & antihypertensive effects & \\ \cline{2-4}  & & & antitumor, antimicrobial, antibacterial prophylaxis, & [28; 29; 30; 31] \\ \cline{2-4}  & & & virucidal activity, antioxidant properties & \\ \cline{2-4}  & & & cedrol & oriental fragrance formulations & [32; 33; 34] \\ \cline{2-4}  & & & anticancer, antimicrobial, antifungal, antiviral, \\  & & anti-inflammatory & & [35] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Functions of different sesquiterpenols.  
Figure 1: Applications, biological activities and structures of sesquiterpenols.