Epi Aristolochene

F. Ewing. 5-Epi-aristolochene is a common precursor of the sesquiterpenoid phytoalexins capsidiol and debneyol. Phytochemistry 1989 28(3) 775-779. Borys, D. J., S. C. Setzer, L. J. Ling. CNS depression in an infant after the ingestion of tobacco A case report. Vet Hum Toxicol 1988 30(1) 20-22. Deutsch, H. M., K. Green, and L. H. Zalkow. Water soluble high molecular weight components from plants with potent intraocular pressure lowering activity. Curr Eye Res 1987 6(7) 949-950. 

The formation of the sesquiterpene (+)-5-epi-aristolochene (2) represents, from a biosynthetic point of view, the transformation requiring the fewest steps among those discussed in this review. A single enzyme, tobacco 5-epi-aristolochene synthase (TEAS), converts the biosynthetic precursor, farnesyl diphosphate (6), to... 

Fig. 3 Proposed mechanisms for the formation of (+)-5-epi-aristolochene (2) and (-)-premnaspir-odiene (3) from famesyl-diphosphate (6) by the action of TEAS and HPS, respectively...

Unlike the biosynthetic route to 2 and 3, the synthetic approaches to these molecules are characterized, instead, by deconstruction of terpene natural products further along the biosynthetic pathway. Preparation of (+)-5-epi-aristolochene (2) has so far only been carried out using a semisynthetic strategy from the natural product 12 [27], which is available from pepper (Capsicum annum) fruits in high quantities [28]. The synthetic route started with O-acetylation of 12 to give... 

Figure 10.11 A proposed pathway for the biosynthesis of capsidiol in elicitor-treated tobacco cell cultures. Earlier work had not resolved how 5-epi-aristolochene, synthesized from FPP by the action of 5-epi-aristolochene synthase, was converted to capsidiol.

Figure 10.12 Gas chromatograms of the reaction products formed upon incubation of microsomes isolated from yeast over-expressing a tobacco terpene hydroxylase gene (panels A C) (CYP71D20) or harboring only the expression vector DNA (control) (B D). Microsomes were incubated with 5-epi-aristolochene (A B) or 1-deoxycapsidiol (C D) in the presence (blue line) or absence (red line) of NADPH. 5-epi-aristolochene, 1-deoxycapsidiol and capsidiol were all verified by MS.58...

STARKS, C. M., BACK, K. W., CHAPPELL, J., NOEL, J. P, Structural basis for cyclic terpene biosynthesis by tobacco 5- epi-aristolochene synthase, Science, 1997, 111, 1815-1820. 

Whitehead, I.M., Threlfall, D.R., Ewing, D.F., 5-epi-aristolochene is a common precursor of the sesquiterpenoid phytoalexins capsidiol and debneyol, Phytochemistry, 1989,28,775-779. 

RALSTON, L., KWON, S. T., SCHOENBECK, M., RALSTON, J., SCHENK, D. J., COATES, R. M., CHAPPELL, J., Cloning, heterologous expression, and functional characterization of 5-epi-aristolochene-l,3-dihydroxylase from tobacco (Nicotiana tabacum., Arch. Biochem. Biophys., 2001, 393,222-235. 

The three-dimensional structures of three non-plant sesquiterpene synthases reveals a single domain composed entirely of a-hehces and loops despite the low homology on amino acid sequence level [14,16,17]. The secondary elements of 5-epi-aristolochene synthase, a plant sesquiterpene synthase, conform to this pattern with the exception of two domains solely composed of a-helices and loops. It is reasonable, but still a matter of debate, to extrapolate these data to the case of amorpha-4,11-diene synthase, which will probably only display a-hehces and loops once the crystal structme has been solved. 

Nt-EAS Nicotiana tabacum 5-epi-aristolochene synthase tps terpene synthase... 

Because of the striking similarities in properties, mechanisms and primary structures between the plant monoterpene, sesquiterpene, and diterpene synthases [21], the recent crystallization and X-ray diffraction analysis of 5-epi-aristolochene synthase (Nt-EAS) [62] is of central importance in providing the first three-dimensional model with which fundamental and common structural themes may be proposed. This model provides a convenient starting point for discussing general structure/function relationships of all terpene cyclases. 

Neither capsidiol nor glutinosone could be detected in healthy tissues. According to Bohlmann et al. (2002) . it is conceivable that capsidiol contributes not only to an inducible defense against pathogens, but also to a constitutive defense in an organ-specific manner in some species of Nicotiana Constitutive expression of 5-epi-aristolochene synthase (EAS) and capsidiol accumulation could not be observed in shoots of N. attenuata, but enzyme transcripts were induced by feeding of Manduca sexta, the tobacco homworm. However, EAS was expressed constitutively in roots of this N. species and N. sylvestris Spec. Comes. 

In recent years, a range of cytochrome P450 enzymes involved in cyclic terpene hydroxyla-tion has been characterized at the molecular level. These include monoterpene hydroxylases involved in the biosynthesis of essential oils in commercial mint [52], a sesquiterpene hydroxylase performing successive hydroxylations of 5-epi-aristolochene in the biosynthesis of the tobacco phytoalexin capsidiol [53], diterpene hydroxylases involved in the formation of taxol [54, 55], and triterpene hydroxylases involved in the biosynthesis of saponins [56] and brassi-nosteroids [57]. 

O Maille, RE. et al. (2006) Biosynthetic potential of sesquiterpene synthases alternative products of tobacco 5-epi-aristolochene synthase. Arch. Biochem. Biophys. 448, 73-82... 

Protonation-induced cychzation of germacrene A generates the cis-decalin skeleton of the eudesmyl cation, an intermediate in the biosynthesis of the phytoalexin capsidiol (79). The eudesmane skeleton is converted to the 5-epi-aristolochene (80) skeleton by Wagner-Meerwein rearrangements of a hydride and a methyl group (Cane 1990). Hydroxylation of 80 then produces capsidiol. The entire process of formation of epi-aristolochene from FPP is mediated by a single synthase which has been purified from tobacco (Starks et al. 1997). The intermediacy of germacrene A in the biosynthesis was demonstrated by mutation of... 

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