Abietadiene Abietic acid

Figure 6 Pathway of conifer diterpene resin acid biosynthesis. Bifunctional di-TPS convert geranylgeranyl diphosphate to various diterpenes, which are oxidized stepwise by multisubstrate and multifunctional cytochromes P450 to the corresponding diterpene acid. The oxidation of (-)-abietadiene to (-)-abietic acid is shown as an example.

R-(1 a,4ap,4ba,10aa)]-1,2,3,4,4a,4b,5,6,10,1 Oa-Deca-hydro-1,4a-dimethyi-7-(1-methylethyl)-1-phenanthrene-carboxyllcacid, 7,13-Abietadien-18-olc acid Abietate Abietic acid l-Abietic acid AI3-17273 CCRIS 3183 EINECS 208-178-3 13-... 

Abietic acid, a common component of conifer rosin, is formed from (-)-abieta-7(8),13(14)-diene ((-)-abietadiene) (Scheme 18 A) [144]. The cyclization of GGPP to abietadiene requires several discrete steps and enzyme-bound intermediates, yet is catalyzed by a single protein, abietadiene synthase. The mechanism of this enzyme involves protonation-induced cyclization of GGPP to enzyme-bound (-i-)-CPP, followed by typical ionization of (-i-)-CPP and cyclization to the transient olefin intermediate, pimaradiene, which undergoes reprotonation at the vinyl substituent, methyl migration and deprotonation to (-)-abietadiene [145]. Similarly, the route to (-)-kaurene involves protonation-initiated cyclization of GGPP to yield (-)-CPP, followed by ionization-initiated cyclization of (-)-CPP to a pimarenyl cation, methyl migration and deprotonation to (-)-kaurene (Scheme 18 B) [20]. 

Stevia rebaudiana, Asteraceae), known as sweet leaf. Abietadiene is a precursor of abietic acid (see 3-156) in resins in coniferous trees. 

The lOO.OOOg supernatant obtained from the extract showed a diterpene cyciase activity. The resulting olefinic product was identified by radio-GLC and argentation liquid chromatography. This compound has the same retention time on GC, as weli as on silice-sllver nitrate column, as 7,13-abietadiene (standard marker synthesized by reduction of abietic acid). 

The photochemistry of the abietadienes continues to attract attention. In methanol solution, methyl abietate affords the adducts (80) and (81). On irradiation in ethanol, 8,13-cyclopropanes are also formed. However, methyl neoabietate undergoes a curious photochemical dehydrogenation to give (82). 18-Norabieta-8,ll,13-triene is obtained from the irradiation of the resin acids in acetone solution. 

More than 200 diterpenes with an abietane skeleton are reported to exist naturally Numerous representatives oeeur in conifers. Selected examples include palustra-diene, also referred to as (-)-8,13-abietadiene, from the pine tree Pintds palustris, from the so-called berries of the sade tree Juniperus sabina (Cupressaceae) and other species of juniper trees, (-)-abietenol from the pine Pinus silvestris and the fir Abies sibirica, (-)-abietic aeid belonging to the resin acids of turpentine and wide-spread in conifers such as various pines Pinus), larch trees Larix) and firs Abies), as well as (+)-palustric acid from the balm and the roots of Pinus palustris, isolated from gum rosin. 

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