Benzoxazinoid acetal glucoside

Enzymatic and chemical degradation of the benzoxazinoid acetal glucoside DIBOA-GIc. 

Besides of Poaceae, benzoxazinoid acetal glucosides have been isolated from various species of the Acanthaceae, Ranunculaceae, and Scrophulariaceae as well. In most cases reported the discovery of benzoxazinoids was made by chance, i.e. a systematic search for them among other species of the families mentioned has not been undertaken nor has such a search been done within other plant families. Therefore, it seems most likely, that benzoxazinoids will be constituents of other wild plants, too, which are not at all as deeply investigated as agriculturally used ones. One reason for this assumption is the circumstance that the benzoxazinoids protecting effect especially for a young plant should be a favouring selection criterion in the evolution of any plant equipped with this system. 

Benzoxazinoid acetal glucosides are compounds of low toxicity which have been found to be stable imder neutral conditions. They can undergo a two step degradation, an enzymatic followed by a chemical one. In the non-injured plant cell, the acetal glucosides and the enzyme P-glucosidase... 

As a result of the chemical degradation accompanied by the loss of formic acid (substituted) benzoxazolin-2(3/i)-ones are formed in a ring contraction reaction. The half life of DIMBOA in the juice of injured maize cells is about one day [74]. In fact, it was from this end of the cascade that benzoxazinoid acetal glucosides were detected starting with the discovery of benzoxazolin-2(3/f)-one (BOA) from rye [87]. Meanwhile, several substituted benzoxazolin-2(3/7)-ones (Fig. (5)) have been found in plants. 

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,... 

Sicker, D., Hartenstein, H. and Kluge, M. 1997. Natural benzoxazinoids -Synthesis of acetal glucosides, aglucones, and analogues. In Pandalai, S. G. (Ed ), Recent Research Developments in Phytochemistry, Vol. 1. Research Signpost, Trivandrum, 203-223... 

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