bisabolol and farnesyl-pyrophosphate

The production of artemisinin, the most effective antimalarial compound, is limited to Artemisia annua. Enzymes involved in artemisinin biosynthesis include amorpha-4,11-diene synthase (ADS), amorpha-4,11-diene 12-monooxygenase (CYP71AV1) and artemisinic aldehyde Δ(11)13 reductase (DBR2). Although artemisinin and its specific intermediates are not detected in other Artemisia species, we reported previously that CYP71AV1 and DBR2 homologs were expressed in some non-artemisinin-producing Artemisia plants. These homologous enzymes showed similar functions to their counterparts in A. annua and can convert fed intermediates into the following products along the artemisinin biosynthesis in planta These findings suggested a partial artemisinin-producing ability in those species. In this study, we examined genes highly homologous to ADS, the first committed gene in the pathway, in 13 Artemisia species. We detected ADS homologs in A. absinthium, A. kurramensis and A. maritima. We analyzed the enzymatic functions of all of the ADS homologs after obtaining their cDNA. We found that the ADS homolog from A. absinthium exhibited novel activity in the cyclization of farnesyl pyrophosphate (FPP) to koidzumiol, a rare natural sesquiterpenoid. Those from A. kurramensis and A. maritima showed similar, but novel, activities in the cyclization of FPP to (+)-α-bisabolol. The unique functions of the novel sesquiterpene synthases highly homologous to ADS found in this study could provide insight into the molecular basis of the exceptional artemisinin-producing ability in A. annua.

Topics: Alkyl and Aryl Transferases; Amino Acid Sequence; Antimalarials; Artemisia; Artemisia annua; Artemisinins; Biosynthetic Pathways; Fabaceae; Gene Expression Regulation, Plant; Lactones; Mixed Function Oxygenases; Monocyclic Sesquiterpenes; Oxidoreductases; Phylogeny; Plant Proteins; Polycyclic Sesquiterpenes; Polyisoprenyl Phosphates; Sequence Alignment; Sesquiterpenes

We report the structures and stereochemistry of seven bisabolyl-derived sesquiterpenes arising from an unprecedented 1,6-cyclization (cisoid pathway) efficiently catalyzed by tobacco 5-epi-aristolochene synthase (TEAS). The use of (2Z,6E)-farnesyl diphosphate as an alternate substrate for recombinant TEAS resulted in a robust enzymatic cyclization to an array of products derived exclusively (>/=99.5%) from the cisoid pathway, whereas these same products account for ca. 2.5% of the total hydrocarbons obtained using (2E,6E)-farnesyl diphosphate. Chromatographic fractionations of extracts from preparative incubations with the 2Z,6E substrate afforded, in addition to the acyclic allylic alcohols (2Z,6E)-farnesol (6.7%) and nerolidol (3.6%), five cyclic sesquiterpene hydrocarbons and two cyclic sesquiterpene alcohols: (+)-2-epi-prezizaene (44%), (-)-alpha-cedrene (21.5%), (R)-(-)-beta-curcumene (15.5%), alpha-acoradiene (3.9%), 4-epi-alpha-acoradiene (1.3%), and equal amounts of alpha-bisabolol (1.8%) and epi-alpha-bisalolol (1.8%). The structures, stereochemistry, and enantiopurities were established by comprehensive spectroscopic analyses, optical rotations, chemical correlations with known sesquiterpenes, comparisons with literature data, and GC analyses. The major product, (+)-2-epi-prezizaene, is structurally related to the naturally occurring tricyclic alcohol, jinkohol (2-epi-prezizaan-7beta-ol). Cisoid cyclization pathways are proposed by which all five sesquiterpene hydrocarbons are derived from a common (7R)-beta-bisabolyl(+)/pyrophosphate(-) ion pair intermediate. The implications of the "cisoid" catalytic activity of TEAS are discussed.

Topics: Catalysis; Cyclization; Molecular Structure; Monocyclic Sesquiterpenes; Nicotiana; Polyisoprenyl Phosphates; Recombinant Proteins; Sesquiterpenes