## 3 Biosynthetic Routes to Nitrogen-Containing and Phenolic Metabolites in Cannabis
### Stilbenes of Cannabis  
As it relates to _Camnabis_, stilbenes are a group of phenolic compounds that can be distinguished into three different classes, based on their chemical structure: phenanthrenes, dihydroistilbenes, and spiroindans [60] (Figure 13). To date, a total of thirty-eight stilbenes have been identified: seven phenanthrenes, fifteen dihydroistilbenes, and sixteen spiroindans [5; 12; 19]. Like flavonoids, stilbenes are found in the flowers, leaves, and stems of the _Camabis_ plant, and they share the same biosynthetic origin. No mention of stilbenes in the roots of _Camnabis_ has been reported. Stilbene synthase (STS) is thought to have evolved independently from chalcone synthase several times during natural history (75-90% sequence homology), explaining the disparate distribution of stilbenes in the plant kingdom, while flavonoids are ubiquitous [35; 61]. Some researchers have hypothesized that stilbene production could compete with flavonoid production in vivo in _Camnabis_[60]. Indeed, there appears to be an inverse relationship between stilbene and flavonoid concentrations in _Camnabis_ cultivars, suggesting competition at the level of their precursors, cinnamic acids [57]. One study investigated a _Camnabis_ type II 4-coumarate ligase (Cs4 CL4) and a biphenyl synthase (CsBBS2), suspected to be involved in stilbene production, which have a higher affinity for \(p\)-coumaric and caffeic acids among other cinnamic acids, corroborated by the chemical structures of stilbenes reported in _Camnabis_[57; 62]. Figure 12: Biosynthesis of cannflavirus. FNSI/II, flavone synthase I and II. F3\({}^{\prime}\)H, flavonoid 3\({}^{\prime}\)-hydroxylase. Arrow represents one biochemical reaction. SAM-MT, S-adenosyly-L-methionine methyltransferase. GT, geranyltransferase. PT, prenyltransferase. SAH, S-adenosylyI-L-homocysteine. Lute-olin can be obtained from naringinin by the consecutive action of a flavone synthase (I or II) (E.C. 1.14.20.5) (E.C. 1.14.19.76), which will produce a double bond at C2 and C3, and a NADPH-dependent flavonoid 3\({}^{\prime}\)-hydroxylase (E.C. 1.14.18.2). A SAM-methyltransferase transferase will methylate the hydroxyl group just added in 3\({}^{\prime}\) of the B ring by the F3\({}^{\prime}\)H to form chrysoeriol and produce SAH. A geranyltransferase and a prenyltransferase will add their respective group on the C7 of the A ring of chrysoeriol, to obtain cannflavirus A and B, respectively. To produce cannflavin C, a geranyltransferase adds its geranyl group to C-9 of the A ring of chrysoeriol. Biosynthesis of Cannabis Stilbenes  
In a general sense, stilbenes can be biosynthesized via one of two pathways: either following the catalytic activity of STS or of BBS (Figure 14). These two enzymes essentially accommodate the same precursors, namely cinnamic acid thioesters, particularly \(p\)-coumaric and caffeic acids for STS and their dihydrated equivalents for BBS [62]. _Cannabis_ most probably uses BBS rather than STS. A structural study of the _Cannabis_ biphenyl synthase 2 enzyme (CsBBS2) indicates that it has undergone a narrowing at the level of the hydrophobic pocket of the active site, when compared to STS, explaining the greater affinity for the dihydrated form of cinnamic acid thioesters [62]. It is useful to note that ferulic acid and cinnamic acid (and their dihydrated homologues) can be accommodated by these enzymes, but significantly less well than their preferred substrates, while sinapic acid is not viable at all as a precursor for these enzymes [62]. This would mean that stillenes presenting methoxy groups in their structure are likely to have had them added following the production of the stilbene/bibenyl skeleton by methyltransferases, as is the case for flavonoids, rather than obtaining these groups from precursors such as ferulic or sinapic acid. [PERSON] et al. identified nine _C. sativa_ double bond reductase homologues (CsDBR1-9) in _Cannabis_, and all are classified as NAD(P)H-dependent alkenal/one reductases.