Phytoalexin structures

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. 

Fig. 9.6 Chemical structures of phytoalexins from Thellungiella salsuginea Shandong ecotype 1-methoxybrassenin B (15), rapalexin A (16), wasalexins A (17) and B (18), biswasalexins A1 (19), and A2 (20)...

Pedras MSC, Zheng Q-A, Sarma-MamillapaUe VK (2007) The phytoalexins from Brassicaceae structure, biological activity, synthesis and biosynthesis. Nat Prod Commun 2 319-330... 

The functions of phenylpropanoid derivatives are as diverse as their structural variations. Phenylpropanoids serve as phytoalexins, UV protectants, insect repellents, flower pigments, and signal molecules for plant-microbe interactions. They also function as polymeric constituents of support and surface structures such as lignins and suberins [1]. Therefore, biosynthesis of phenylpropanoids has received much interest in relation to these functions. In addition, the biosynthesis of these compounds has been intensively studied because they are often chiral, and naturally occurring samples of these compounds are usually optically active. Elucidation of these enantioselective mechanisms may contribute to the development of novel biomimetic systems for enantioselective organic synthesis. 

Immune systems in plants are based on passive, structural immunity, such as a waxy surface or cuticle, and active immunity exists in the expression of some chemicals. The mechanism of this system is to prevent infectious agents from gaining access to plant cells. Plant immunity may also be protoplasmic. This means that the protoplast in cells is an unfavourable environment for pathogenic development. Plants do not, however, produce antibodies like animals do. The protoplasmic immunity is arranged generally by phytoalexins, non-specific... 

OS123 Kono, Y., S. Takeuchi, O. Kodama, and T. Akatsuka. Absolute configuration of Oryzalexin A and structures of its related phytoalexins isolated from rice blast leaves infected with Pyricularia oryzae. Agr Biol Chem 1984 48(1) 253-255. 

FIGURE 8.6 Structure of the phytoalexin isoflavonoid pterocarpans, maackianin, and pisatin from garden pea, and the isoflavones daidzein and genistein from soybean. 

Perrin, D.R., Bottomley, W. Studies on phytoalexins. V The structure of pisatin from Pisum sativum L. J Amer Chem Soc 1962 84 1919-1922. 

The pterocarpan pisatin was first isolated and characterized as a phytoalexin in Pi sum sativum in the early 1960s.234 235 Since then, structurally diverse phytoalexins have been reported from more than 30 families of higher plants. Much progress is also being made in studies on phytoalexin biosynthesis based on genomic information. 

Figure 29 Structures of some typical aromatic phytoalexins.

Lubimin, a phytoalexin found in several Solanaceae, has been assigned the spiro-structure (57) on n.m.r. and biosynthetic evidence,83 whilst the new sesquiterpenoid skeleton of taylorione (58) from the liverwort Mylia taylorii is thought84 to be biosynthesized via an aromadendrene-type precursor which may also generate the co-occurring myliol (59). 

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