## 2 The Phytochemistry of _Artemisia annua_ L. (Qinghao)
### Monoterpenoids
#### 2.5.1 Regular Acyclic Monoterpenes  
A cDNA for (3\(R\))-linaloid synthase, which converts GPP to (3\(R\))-linaloid (**250**) by ionization of the pyrophosphate group, has been described recently from _A. annua_[110]. Most of the regular acyclic monoterepenes reported in Table 23 can be derived by further functional group modifications (dehydration, reduction or oxidation) of \(\;\)linaloid (**250**) or its isomers, geraniol (**244**) and nervl (**248**). Figure 2: Structures of isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP), nervl pyrophosphate (NPP) and linaloyl pyrophosphate (LPP) which are all possible precursors to monoterepenes from _A. annua_. \begin{table}
\begin{tabular}{|l|l|l|l|} \hline
**Name** & **Alternative Name(s)** & **CAS number** & **References** \\ \hline Citronellolol (**242**) & 3,7-Dimethyl-6-octation-1-ol & [106-22-9] & [24] \\ Citronellal (**243**) & 3,7-Dimethyl-6-octation & [106-23-0] & [28] \\ Geraniol (**244**) & (E)-3,7-Dimethyl-2,6-octation-1-ol & [106-24-1] & [22] \\ Geranyl acetate (**245**) & (E)-3,7-Dimethyl-2,6-octation-1-ol acetate & [105-87-3] & [23, 51] \\
3,7-Dimethyl-2,6-octationj, isobutyric acid, (E)-Isobutyric acid, 3,7-dimethyl-2,6-ocatadienyl & [1188-06-3] & [50] \\ acid, ester (**246**) & ester & \\
2,6-Ocatdenen-1-ol, 2,6-dimethyl-8- & & [80444-67-3] & [23] \\ \([\)(tetralabydro-2H-pyran-2-y)oxyl\(]\)- (**247**) & & & \\ Nerol (**248**) & (Z)-3,7-Dimethyl-2,6-ocatadien-1-ol & [106-25-2] & [23, 58] \\ Neryl acetate (**249**) & (Z)-3,7-Dimethyl-2,6-ocatadien-1-ol acetate & [141-12-8] & [45] \\ Linalool (**250**) & 3,7-Dimethyl-1,6-ocatadien-3-ol & [78-70-6] & [19, 28, 31, 32, 45, 51, 74, 111] \\ \hline Linalyl acetate (**251**) & 3,7-Dimethyl-1,6-ocatadien-3-ol acetate & [115-95-7] & [32, 43] \\
3,7-Ocatdeni-2-ol, 2,6-dimethyl- (**252**) & & [62911-76-6] & [23] \\ Myrcenol (**253**) & 2-Methyl-6-methylene-7-octen-2-ol & [543-39-5] & [30] \\ Myrcene (**254**) & 7-Methyl-3-methylene-1,6-ocatadiene & [123-35-3] & [19, 23, 29, 32, 33, 43, 45, 50, 51, 73, 112, 113] \\ Ipsdienol (**255**) & 2-Methyl-6-methylene-2,7-ocatadien-4-ol & [35628-00-3] & [28] \\ _allo_-Ocimene (**256**) & 2,6-Dimethyl-2,4,6-ocatriene & [673-84-7] & [22] \\ _trans_-\(\alpha\)-Ocimene (**257**) & 3,7-Dimethyl-1,3,7-Ocatriene & [27400-72-2] & [22, 32, 111] \\ \((E)\)-3,7-Dimethyl-1,3,6-octatriene (**258**) & & [3779-61-1] & [43] \\ \((Z)\)-3,7-Dimethyl-1,3,6-octatriene (**259**) & & [3338-55-4] & [32, 43] \\
2,6-Dimethyl-3,5,7-ocatrien-2-ol (**260**) & & [103272-78-2] & [23] \\
3,7-Dimethyl-1,5,7-ocatrien-3-ol (**261**) & & [29957-43-5] & [48] \\
2,6-Dimethyl-1,5,7-ocatrien-3-ol (**262**) & & [29414-56-0] & [23] \\
3,7-Ocatdeni-2-ol, 2-methyl-6-methylene & & [22459-09-2] & [31] \\
**(263)** & & & \\ \(\beta\)-myrcene hydroperoxide (**264**) & 2-Methyl-6-methylene-3,7-ocatadiene-2-ol (\(E\)), 2- & [9, 114] \\ hydroperoxide & & & [9, 114] \\ \(\alpha\)- myrcene hydroperoxide (**265**) & 2-Methyl-6-methylene-1,7-ocatadiene, 3-hydrox- & [9, 114] \\ peroxide & & peroxide & [1079223-79- [43] \\ methylene- (**266**) & & [1079223-79- [43] \\
1,7-Ocatdeni-3-one, 2-methyl-6- & 2-Methyl-6-methylene-1,7-ocatadien-3-one & [41702-60-7] & [20] \\ methylene- (**267**) & & & \\ \(cis\)-Epoxyocimene (**268**) & 3,7-Dimethyl-1,3,6-Ocatriene 6R,7-epoxide & [255832-06-5] & \\
2,6-Dimethyl-1,3,5,7-ocatetraene (**269**) & & [90973-78-7] & [50] \\ Perline (**270**) & 3-(4-Methyl-3-pentenyl)furan & [539-52-6] & [23, 43] \\
1,10-Oxy-\(\alpha\)-myrcene hydroxide (**271**) & & & [9] \\
1,10-Oxy-\(\beta\)-myrcene hydroxide (**272**) & & & \\ \hline \end{tabular}
\end{table} 
Table 23: Regular Acyclic Monoterpenoids (2,6-Dimethyllocatene, 9 CI, 8 CI). Myrcene (**254**) is the most abundant regular acyclic monoterpene from _A. annua_, and can account for up to 5% of the essential oil [22,33,43]. The secondary and tertiary allylic hydroperoxides, \(\alpha\)- and \(\beta\)-myrcene hydroperoxide (**265** and **264**), have been isolated from _A.