## 2 The Phytochemistry of _Artemisia annua_ L. (Qinghao)
### Phenylpropanoids  
The phenylpropanoids, all of which contain a C\({}_{3}\) substituent fused to a benzene ring (C\({}_{6}\)), are produced by the shikimate pathway, which is unique to plants. Most of the simple phenylpropanoids reported in Table 15 were described from GC-MS studies. Compounds **166-182** (Table 16), which are esters formed by various combinations of ferulic and cinnamic acid with the four hydroxyl groups of quinic acid, were isolated from a single HPLC-MS study [71]. Some of the coumarins reported in Table 17 have also been obtained from undifferentiated tissue cultures (callus and suspension) of _A. annua_ (see Section 4.2). The structures of both of the 2,2-dihydroxychromene natural products **190** and **191**, which appear in Table 17, are questionable on thermodynamic grounds - one might expect both to lose a molecule of water thereby forming a more highly conjugated coumarin. \begin{table}
\begin{tabular}{|l|l|l|} \hline
**Name** & **Alternative Name(s)** & **CAS Number** & **Refs** \\ \hline Methyl cinnamate (**164**) & 3-phenyl-2-propenoic acid methyl ester & [103-26-4] & [24] \\ Benzyl cinnamate (**165**) & 3-phenyl-2-propenoic acid benzyl ester & [103-41-3] & [24] \\ Chlorogenic acid (**166**) & 3-3-d-Dihydroxy-5-[3-(4-hydroxy-3-methoxyphenyl)-1-oxo-2-propenyl]oxy-, (**167**) & [327-97-9] & [71] \\ cyclohexanecarboxyloxide acid, 3-[3-(3,4-dihydroxyoxyphenyl)-1-oxo-2-propenyl]oxy-, (**168**) & [342811-68-1] & [71] \\ cyclohexanecarboxyloxide acid 3-[3-(3,4-dihydroxyoxyphenyl)-1-oxo-2-propenyl]oxy-, (**168**) & 3-d-Di-\(O\)-caffeoylquinic acid & [4534-61-3] & [71] \\ Isochloroogenic acid B (**169**) & 4-O-Fernoloyl-5-\(O\)-caffeoylquinic acid & [125132-81-2] & [71] \\
3,4-Diferanoylquinic acid (**171**) & 3,5-_bis_(3,4-Dihydroxycimamoyl)quinic acid) & [2450-53-5] & [71] \\
3-Caffeoyl-5-ferlovlovquinic acid (**173**) & & [478156-24-0] & [71] \\
3-Feruloyl-5-caffeoylquinic acid (**174**) & & [1039007-73-2] & [71] \\
3,5-Diferanoylquinic acid (**175**) & & [333753-65-4] & [71] \\ Isochloroogenic acid C (**176**) & & [57378-72-0] & [71] \\
4-Calroy-5-fentivolquinic acid (**177**) & & [478156-25-1] & [71] \\
4-Feruloyl-5-caffeoylquinic acid (**178**) & & [882535-14-0] & [71] \\
4,5-Diferanoylquinic acid (**179**) & & [342811-69-2] & [71] \\ cyclohexanecarboxyloxide acid, 3-[3-(3,4-dihydroxyoxyphenyl)-1-oxo-2-propenyl]oxy-, (**180**) & & [865095-58-5] & [71] \\
1-Caffeoyl-5-ferlovquinic acid (**181**) & & [865095-57-4] & [71] \\ Cyclohexaneacyloxide acid, 3-[3-(3,4-dihydroxyoxy)-1-[3-(4-dihydroxy)-2-propenyl]oxy-]oxy-, (**182**) & & [437611-66-0] & [71] \\
1-Caffeoyl-5-ferlovquinic acid (**183**) & & [342811-69-2] & [71] \\
1-Caffeoyl-5-ferlovquinic acid (**184**) & & [865095-57-4] & [71] \\ Cyclohexaneacyloxide acid, 3-[3-(3,4-dihydroxyoxy)-1-oxo-2-propenyl]oxy-, (**182**) & & [437611-66-0] & [71] \\ \hline \end{tabular}
\end{table} 
Table 16: Cinnamyl, Caffeoyl and Ferruloyl esters. \begin{table}
\begin{tabular}{|l|l|l|} \hline
**Name** & **Alternative Name(s)** & **CAS Number** & **References** \\ \hline _p_-Allylanisole (**157**) & 1-Methoxy-4-(2-propenyl)benzene & [140-67-0] & [29; 72; 73] \\ Antehole (**158**) & 1-Methoxy-4-(1-propenyl)benzene & [4180-23-8] & [32; 43; 50] \\
3-Allyl-6-methoxyphenol (**159**) & 4-Allyl-2-hydroxy-1-methoxybenzene & [501-19-9] & [48] \\ Eugenol (**166**) & 2-Methoxy-4-(2-propenyl)phenol & [97-53-0] & [19; 32; 41; 43; 74] \\ Methyl eugenol (**161**) & 1,2-Dimethoxy-4-(2-propenyl)benzene & [93-15-2] & [43; 48] \\ Eugenyl isovalerate (**162**) & 2-Methoxy-4-(2-propenyl)phenol 3-methylbutanoylI & [61114-24-7] & [34] \\
2-Methoxy-3-(2-propenyl)phenol (**163**) & & [1941-12-4] & [23] \\ \hline \end{tabular}
\end{table} 
Table 15: Simple phenylpropanoids.