Phytoalexins

Phytoalexins are low molecular weight compounds produced in plants as a defense mechanism against microorganisms. They do, however, exhibit toxicity to humans and other animals in addition to microbes (30). Coumarins, glycoalkaloids, isocoumarins, isoflavonoids, linear furanocoumarins, stilbenes, and terpenes aU. fall into the category of phytoalexins (31). Because phytoalexins are natural components of plants, and because their concentration may increase as a response to production and management stimuli, it is useful to recogni2e the possible effects of phytoalexins in the human diet. 

Other common phytoalexins in food materials are pisatin, cinnamylphenols, glyceolin, phaseolin [13401 -40-6] (14), and 5-deoxykieritol in peas, beans, soybeans, and lima beans viniferin in grapes momilactones and ory2alexins in rice a-tomatine in tomato lubimen in eggplant and capsidiol in green peppers. 

In fact, iodination of methyl l-methoxyindole-3-carboxylate (109), a wasabi phytoalexin (98P1959), with KI and NaI04 (60LA84, 911OC5903) in TFA-HjO provides methyl 5-iodo-l-methoxyindole-3-carboxylate (110,72%) predominantly... 

In the previous review (91YGK205, 99H1157), we reported that l-hydroxy-4-nitroindole forms active ester derivatives by reaction with carboxylic acids, which can be applied to acylation of various nucleophiles. To expand the scope of the reaction and obtain novel fungicidal compounds, an attempt has been made to prepare derivatives of wasabi phytoalexin 109 (98P1959). 

In the presence of DCC, 140 is allowed to react with both l-hydroxy-5-nitroindole (36) and 1-hydroxy-1,2,3-benzotriazole (141). Interestingly, their corresponding active esters, 142 and 143, are obtained in excellent yields as stable crystalline compounds. Both compounds are found to react with variety of nucleophiles, such as alcohols and amines, to produce 144 and 145 in good to excellent yields, as can be seen from the typical examples shown in Scheme 22 (2001H2361). As aresult, it becomes possible to produce various kinds of derivatives of wasabi phytoalexin utilizing 142 and 143. 

The reaction of wasabi phytoalexin (109) with excess 15% aqueous NaSMe gives methyl 2-methylthioindole-3-carboxylate (184,70%) and 140 (20%). In this reaction, formation of 2-methylthioindole-3-carboxylic acid (185) is not observed under various reaction conditions. The fact indicates that once 140 is formed, it does not undergo nucleophilic substitution reaction. In addition, hydrolysis of the... 

Comparison of these reactivities and antifungal activities of phytoalexin derivatives is an interesting future subject. 

Pedras and co-workers (98P1959) isolated a phytoalexin from Wasabi (Wasabia japonica, syn. Eutrema wasabi) and determined its structure to be methyl l-methoxyindole-3-carboxylate (109) (Scheme 38). Compound 109 had already been synthesized by Acheson and co-workers [78JCS(P1)1117] in ten steps from o-nitroaniline. Pedras and co-workers (98P1959) combined our tungstate method and Acheson s work, and synthesized 109 in 9% overall yield but in an impure state. 

Daikon and wasabi phytoalexins are weak fungicidal alkaloids having a stabilized 1-methoxyindole structure. Relying on the expectation that more potent substances can be found among their derivatives, synthetic studies are in progress according to the method developed in Scheme 22 in Section IV.G. 

Lo, S.-C. et al., Phytoalexin accumulation in sorghum identification of a methyl ether of luteolinidin, Physiol Mol. Plant Pathol, 49, 21, 1996. 

Wharton, P.S. and Nicholson, R.L., Temporal synthesis and radiolabelling of the sorghum 3-deoxyanthocyanidin phytoalexins and the anthocyanin, cyanidin 3-dima-lonyl glucoside, New Phytol, 145, 457, 2000. 

Darvill AG, Albersheim P (1984) Phytoalexins and their elicitors - a defence against microbial infection in plants. Ann Rev Plant Physiol 35 243-275... 

Studies on the antibacterial activities of mulberry phytoalexin in vitro it was 101... 

Protection against pathogens Defensive response to invasion (e.g.. phytoalexins)... 

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