Indoles phytoalexins

Fig. 9.9 Transformation of the phytoalexin brassinin (28) by (i) L. maculans virulent on canola to indole-3-carboxaldehyde (30) and (ii) L. maculans virulent on brown mustard to indolyl-3-methanamine (31)...

Pedras MSC Okinyo DPO (2008) Remarkable incorporation of the first sulfur containing indole derivative another piece in the puzzle of crucifer phytoalexins. Org Biomol Chem 6 51-54... 

Indole-3-acetaldoxime (30) and 4-hydroxyphenylacetaldoxime were shown to be metabolized by plant and pest fungi to 32 and to other related indole- and 4-hydroxyphenyl carboxylic acids, however, the biochemical transformation differed between the two fungi. These biochemical transformations may be relevant to the ability of certain fungi to cause plant diseases . Compound 30 has been shown to be a key intermediate in the biosynthesis of camalexin, 3-thiazolyl-2 -yl-indole, a member of the family of phytoalexins that are produced in response to pathogen attack. It was demonstrated that CYP71A13 catalyzes the conversion of 30 to indole-3-acetonitrile, which is essential for the biosynthesis of camalexin. Thus, the literature supplies a large body of evidence for the existence of a set of enzymes dedicated to the production of the auxin, 32, from tryptophan via indole-3-acetaldoxime (30). 

Chart 12.2 Phytoalexins (reEtoHarbome 1999b, unless otherwise stated) (5max=39, av=14 5 ///max=0.77, av=0.4). Alkal. benzoxazins D/a f/j s phytoalexin (Dianthtds caryophyllus, Caryophyllaceae phytoalexin) and open form, avenalumin I (Gramineae, Ang.), see also Frey 1997 sulflirated indole brassicanol A, camalexin, brassilexin (Cruciferae, Ang.). 

Furstner and coworkers have continued to explore the titanium-mediated formation of indoles from o-V-diacylanilines. The use of a sodium-aluminum oxide mixture prepared from alumina and molten sodium was developed. This material has the advantage over potassium-graphite of being non-pyrophoric. <95S63> Additional specific applications of the reaction were also reported, for example the synthesis of the phytoalexin camalexin, 21b. <95T773>... 

When plants undergo various stresses, certain secondary metabolites, including defense compounds, accumulate. Several secondary metabolites such as terpenoid indole alkaloids, indole glucosinolate, nicotine alkaloids, and polyamines are known to accumulate through the induction of biosynthetic genes by jasmonates.898-900 MeJA also induces genes involved in the formation of tryptophan derivatives, terpenoid indole alkaloids.901 These compounds are known to be involved in defense response to pathogen attack as phytoalexins. 

Several naturally occurring indoles possessing sulfur at C-2 have been isolated, such as the phytoalexin sinalexin (11), which was identified as a product formed in white mustard Sinapis alba) under elicitation by e.g. the blackspot fungal pathogen Allemaria brassicae <97P(46)833>. A recent synthetic study provided the first route to 11, also including an... 

Camalexin, 3-thiazol-2 -yl-indole, is an indole alkaloid belonging to the family of phytoalexins which is constituted by more than 300 compounds identified in diverse plant species and are involved in defense against a wide range of pathogens [195, 196]. Camalexin was first identified in 1991 [197], specially found in cruciferous... 

A series of antifungal sulfur-containing indole derivatives (27-31), which appear to be related to glucobrassicin (3), are produced as phytoalexins in Raphanus sativus and Brassica campestris in response to the fungus Leptosphaeria macu-lans (Devys et al., 1990 Harbome, 1989) (Fig. 17.8). 

Lion and colleagues prepared 5,6,7-trimethoxyindole for a molecular mimic of combretastatin [30], and indole 21 became the indole unit in rapalexin B in a synthesis of this cruciferous phytoalexin by Pedras and colleagues [31], Indole 22 was needed for a biosynthetic study of the paraherquamide natural products [32], and Corey s team employed 6,7-dimethoxyindole (16) (71%) in their synthesis of aspidophytine [33]. 

Nevertheless, there are several other oxidation (dehydrogenation) routes to indoles from indolines. In a series of papers, Somei and colleagues used sodium tungstate to synthesize A-hydroxyindole derivatives from the corresponding indolines (Scheme 11, equations 1 and 2) [64, 103-107]. The simple l-hydroxy-6-nitroindole [106] and 4-, 6-, and 7-ethoxy-l-methoxyindoles were synthesized in similar fashion [107]. Pedras and coworkers employed the Somei method to prepare the natural phytoalexin methyl l-methoxyindole-3-carboxylate [108], and McNab and... 

Bottcher C, Westphal L, Schmotz C, Prade E, Scheel D, Glawischnig E (2009) The multifunctional enzyme CYP71B15 Phytoalexin Deficients) converts cysteine-indole-3-acetonitrile to camalexin in the indole-3-acetonitrile metabolic network of Arabidopsis thaliana. Plant Cell 21 1830-1845... 

Mono- and sesquiterpenes are the main constituents of the essential oils, while the other terpenes are constituents of balsams, resins, waxes, and rubber. Oleoresin is a roughly equal mixture of turpentine (85 % Cio-monoterpenes and 15 % C15- sesquiterpenes) and rosin (C2o-diterpene) that acts in many conifer species as a toxic material to invading insects and their pathogenic fungi [12]. A number of angiosperm species have inducible terpenoid defensive compounds (phytoalexins) [13]. These include both sesquiterpenoid and diterpenoid t)pes. Isoprenoid units are also found within the framework of other natural molecules. Thus, indole alkaloids, several quinones (vitamin K), alcohols (vitamin E, vitamin A formed from p-carotene), phenols, and isoprenoid alcohols (also known as terpenols or polyprenols) also contain terpenoid fragments. The biogenesis. 

Whitehead IM, ThrelfaU DR, Ewing DF (1989) 5-epi-Aristolochene is a common precursor of the sesquiterpenoid phytoalexins capsidiol and debneyol. Phytochemistry 28 775-779 Wijayanti L, Kobayashi M, Eujioka S, Yoshizawa K, Sakuiai A (1995) Identification and quantification of abscisic acid, indole-3-acetic acid and gibberellins in phloem exudates of Pharbitis nil. 

---