Benzoxazinoid hydroxamic acids

Figure 10.12 Biosynthesis and transformation of benzoxazinoid hydroxamic acids.

Benzoxazolin-2(3H)-one is a phytotoxic allelochemical resulting from a two step degradation and root exudation process based upon an acetal glucoside of the 2,4-dihydroxy-2H-1,4-benz-oxazin-3(4H)-one skeleton. Such benzoxazinoids or cyclic hydroxamic acids occur in Acanthaceae, Poaceae, Ranunculaceae, and Scrophulariaceae. Their aglucones and resulting benzoxazolinones act as a plant s... 

These early findings, together with the ability to act as plant resistance factors towards pests, led to a cascade of some hundred papers dealing in an interdisciplinary manner with all aspects of benzoxazinoids. This name seems to be more correct than the name cyclic hydroxamic acids, which has often been used to name this class of compounds. However, it is not exact from the structural point of view, because it omits the fact that also a variety of acetal glucosides with lactam units was found in plants. They also may be split enzymatically to form lactam aglucones, but cannot undergo chemical decay into benzoxazolin-2(3H)-ones. Benzoxazinoids occur in Acanthaceae, Ranunculaceae, Scrophulariaceae,... 

The entire subject has been reviewed in detail several times.32,56,57,65 Recently, a new adsorptive method for the isolation of DIMBOA has been reported.49 The impact of benzoxazinoids on the western corn rootworm (Diabrotica virgifera LeConte) development has been studied.17 The allocation of a hydroxamic acid and biomass during vegetative development of rye has been investigated.27 Effects of benzoxazinoids from maize on survival and fecundity of aphids have been explored.13 DIMBOA concentrations have been measured in various isolines of wheat and corresponding plant introduction lines.55 The variation of the content of several benzoxazinoids in relation to the age and plant organ has been determined in maize plants.12... 

Baumeler, A., Hesse, M., and Werner, C. 2000. Benzoxazinoids - cyclic hydroxamic acids, lactams and their corresponding glucosides in the genus Aphelandra (Acanthaceae). Phytochemistry 53, 213-222... 

Plants release allelochemicals as volatiles, leaf leachates, and root exudates. In addition, all the constituents of plant residues are eventually released into the environment through microbial decomposition. During this process, most allelochemicals lose their activity but some compounds, for example, benzoxazinoids (cyclic hydroxamic acids), can be activated after hydrolysis.1-3... 

It was the ability to act as a plant own source for the resistance of cereals towzirds pests, which immediately caused a really interdisciplinary research directed on the understanding of all aspects of this imique class of natural products, which is often named hydroxamic acids or cyclic hydroxamic acids. We will rather shortly call them benzoxazinoids or benzoxazinones for the following reasons. Though most of them contain a cyclic hydroxamic acid and some the related lactam, it is only by the direct combination with the cyclic hemiacetal unit that these compounds receive their unique bioactive properties. As mentioned below, the bioactivity is clearly enhanced by a donor substituent in position 7. Hence, to avoid misinterpretations of the features responsible for biological effects, the neutral terms benzoxazinones or benzoxazinoids, are better suitable to name the class. 

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