The precursor for the biosynthesis of taraxasterol is squalene. In the first step of this formation squalene is cyclized with molecular oxygen, FAD, and NADPH via the enzyme squalene epoxidase a flavoprotein to yield (2S)-2,3-oxidosqualene. In the second step if the oxidosqualene is folded in the chair conformation in the enzyme a cascade of cyclizations will occur that results in the formation of the dammarenyl cation.[1]
The dammarenyl cation is then subjected to an alkyl shift to create a six-membered ring and relieving ring strain to form the baccharenyl cation. This allows the baccharenyl double bond to attack the secondary positive charge and forms a pentacyclic ring system to yield the tertiary lupanyl cation. A Wagner-Meerwein 1,2-alykl shift will occur to form the hexacyclic ring system and the secondary oleanyl cation. This is followed by a Wagner-Meerwein 1,2-methyl shift to create the tertiary taraxasteryl cation. This cation is the last intermediate in the taraxasterol pathway. An E2 reaction follows where deprotonation of a proton yields taraxasterol. The enzymes involved in this biosynthesis are oxidosesqualene: lupeopl cyclase and oxidosqualene: B-amyrin cyclase.[1]
Dammarenyl cation
Taraxasterol synthesis
References
^ abcDewick, Paul M. (2011). Medicinal Natural Products: A Biosynthetic Approach. Wiley. pp. 243–247. ISBN978-0-470-74168-9.
Dammarenyl cation
Taraxasterol synthesis
