Sesquiterpene phytoalexins

In the Andes, nearly all of the about 160 varieties of wild potatoes, and two of the eight cultivated species are toxic. Some frost-resistant species that grow above 3600 m have high levels of alkaloids, which are bitter and potentially toxic. These are hybrids between Solanum stenotonum and wild potatoes such as Solanum megistacrolohum and Solanum acaulc. Other secondary plant compounds in potatoes are saponins, phytohemagglutinin, proteinase inhibitors, sesquiterpene phytoalexins, and phenols. 

Direct-defense compounds can be either constitutively present in (specific parts of) the plant or be produced after induction by pathogens or herbivores. The latter compound will be less costly for the plant. For example, elicitor-induced accumulation of the antimicrobial sesquiterpenoid capsidiol correlated with the induction of 5-ept-aristolochene synthase, which is a branch-point sesquiterpene cyclase involved in the synthesis of sesquiterpene phytoalexins (8). In rice Oryza saliva L.), 14 diterpenoid phytoalexins have been identified. All these compounds are accumulated in rice leaves after inoculation with the... 

A new HPLC technique has been developed for the rapid analysis of sesquiterpene phytoalexins such as capsidiol, rishitin, luminin, and phytuberol. This method employs a cyanopropyl-bonded phase column with an isocratic mixture of hexane and isopropanol. Flame ionization and UV detection were used for the analysis of capsidiol, rishitin, lubimin, phytuberol, and debneyol. Although both detectors proved to be useful, the signal response with the flame ionization detector was proportional to the mass of each of the phytoalexins, while the signal with the UV detector was proportional to the number of carbon—carbon bonds in each of the compounds. 

R. S. Burden and M. S. Kemp, "Sesquiterpene Phytoalexins from Ulmus glabra". Phytochemistry. 23, 383-385 (1984). 

A sesquiterpene phytoalexin, C17H26O4, Mr 294.39, oil, [ain -35.9° (CHCI3) formed, together with rish-itin and many other components (including vetispi-ranes), by potatoes Solarium tuberosum) after infection by the putrefactive bacterium Erwinia carotovora. Deacetylation furnishes phytuberol, C,5H240j, Mr 252.35, oil. P. can also be isolated from the culture medium of potato cell cultures after elicitation with Phy-tophthora infestans. Some sorts of tobacco Nicotiana tabacum) produce P. after infection with various Pseudomonas spp. or the tobacco mosaic virus pretreatment with a cellulase shows the same effect. 

A number of sesquiterpene phytoalexins accumulate in potato (Solanum tuberosum) in response to attack by Monol-inia fruticola, Phytophthora infestans, mdAlternaria solani. Among these are rishitin (32), lubimin (33), phytotuberin (34), and several other sesquiterpenes (Brooks and Watson, 1985 Kuc, 1992). Cell walls of P. infestans contain an elici-tor of ph) oalexin accumulation in potato (Kuc, 1982). Similar phytoalexins are synthesized by a number of other solana-... 

Fig. 2. Biosynthesis of some sesquiterpene phytoalexins. Phytub rin, solavetivone, lubimin, hydroxylu-bimin and rishitin are produced by Phytophthora-iniected potatoes (Soianum tuberosum) and by potato tuber disks treated with Elicitor (see). Capsidiol is a phytoalexin from Capsicum, [P.A.Brindle D.R.Threlfall Biochem. Society Transactions ft (1983) 516-522]...

Nicotiana tabacum 71D20 5-epiaristoloehene 1,3-dihydroxylase Sesquiterpene Phytoalexins Capsidiol [218] [121]... 

Figure 10.5 Plant cell cultures have proven to be very useful for studying plant-pathogen interactions and isoprenoid metabolism. Tobacco cell cultures respond rapidly to the addition of fungal elicitors (0.5 pg cellulase/ml of culture) by browning (A) (analogous to a hypersensitive response) and the production of phytoalexins (B). Media was collected from elicited cell cultures at the indicated times, partitioned against an organic solvent, and concentrated aliquots run on a silica TLC plate. The plates were then sprayed with a suspension of Cladosporium cucumerinum spores and incubated in a humid environment for 5 days before viewing (B). The compound released from the elicitor-treated tobacco cells that inhibits spore germination is capsidiol, a sesquiterpene.

In Gossypium spp. (Malvaceae), sesquiterpenoid phytoalexins identified so far are cadinene derivatives that are biosynthesized from -cadinene.241 CAD1-A and CAD1-C were functionally identified as sesquiterpene cyclases that catalyze the conversion of farnesyl diphosphate into -cadinene (Figure 23). GaWRKY 1 is a... 

Bicyclic sesquiterpenes include a variety of bioactive compounds including the Solanaceae phytoalexins capsidiol (G61G6) from Capsicum frutescms (pepper) and the Solanum tuberosum (potato) antifungals rishitin (G61C6) and solavetivone (G6-G5) the Ipomoea batatus... 

Yet another family producing polyacetylenes is the Composltae two acetylenics safynol and dehydrosafynol are formed in the diseased safflower (24). Our own experiments at Reading Indicate that acetylenes are formed In other members. This is however a very large family and other responses have been detected as well. TVo sesquiterpene lactones have been encountered as phytoalexins In Lac-tuca (25) while coumarins are reported as such In the sunflower Hellanthus annuus (26) ... 

Abstract- The isolation and biological activity of several sesquiterpenes classified as phytoalexin are described. The synthesis of these sesquiterpenes, are described. Several routes have been developed to synthesize a particular sesquiterpenes. 

Katsui et al.,76 isolated two phytoalexins sesquiterpenes lubimin (144) and oxylubimin (145) from white potato tubers (Rishri) infected by an incompatible race of Phytophthora infestans. It has already been mentioned that from white potato tubers also have been isolated sesquiterpene rishitin (40). In the year 1971 Metliskii and coworkers77 isolated lubimin (144) along with rishitin (40) from white potato tubers (S.tuberlosum Lubimets ) stressed with various pathogens. 

We have described the chemistry of some selected sesquiterpenes which have been classified as phytoallexins. We would to apologize for unintentional omission of any important information in this review, which we tried to make as comprehensive as possible. A variety of synthetic reactions has been used to achieve the total synthesis of these phytoalexin sesquiterpenes. The isolation and biological activity of these sesquiterpenes have been discussed. It is necessary to mention that Takasugi et al.81 have reported for the first time costunolide is an antifungal sesquiterpene which inhibited spore germination of Ceratocystis fimbriata at concentration of 32 pg/ml. Many diterpenes and flavonoides have been also listed as phytoallexins. It is hoped that the research workers would find some useful information in this article. It is safe to predict from discussions in this article that many organic chemists would try to isolate antifungal sesquiterpenes. 

From Table XII it is obvious that the alkaloid levels found in the cell and tissue cultures of Nicotiana species vriry widely. The cultures do produce a variety of other secondary metabolites as well sterols and triterpenes 245,246), ubiquinone 247), cinnamoyl putrescines 248-251), and the phytoalexin capsidiol and related sesquiterpenes 252-254). 

Ipomeamarone. Formula see ipomeanin. C,5H220], Mr 250.34, [aJi> +27 (C2H5OH), a phytoalexin of the class of furan sesquiterpenes. I. was first isolated from sweet potatoes (Ipomoea batatas) afflicted by black rot. liie amount of I. reaches ca. 2 weight-% of the plant after a short time, it then acts as a highly active fungicide. ... 

The latter are formed as stress metabolites after infection by fungi or bacteria such as Erwinia carotovora and Phytophthora infestans together with other compounds such as phytuberin. Compounds (3), (4), (5), and (6) in the given order are precursors in the biosynthesis of the phytoalexin rishitin. The V. are formed biosynthetically from eudesmane type sesquiterpenes. Lit. J. Am. Chem. Soc. 120, 1747 (1998) (synthesis) Tetrahedron Lett. 37, 8703 (1996). 

Several sesquiterpenes are phytoalexins (Brooks and Watson, 1985 Gross, 1977 Kuc, 1992). These compounds... 

Several sesquiterpenes play well-defined and essential roles in higher and lower plants, including the hormone abscisic acid, furanoid phytoalexins, lactone antifeedants, and numerous fungal antibiotics (Herout, 1971 Rucker, 1972). No specific function has been demonstrated for most sesquiterpenes however, an allelopathic or allelochemic role is commonly ascribed to these compounds, as for monoterpenes. Like monoterpenes, sesquiterpenes are not metabolically inert, but are rapidly synthesized and catabolized (Croteau and Loomis, 1972 Francis, 1972) and thus may also play a dynamic role in metabolism. Virtually nothing is known about the catabolism of sesquiterpenes. 

Ipomoeamarone a Phytoalexin (see) with a sesquiterpene structure. I. is formed when sweet potatoes are infected by phytopathogenk microorganisms. For synthesis, see Rg. 

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