Benzoxazinone glucosides

Two reviews cover the whole synthetic literature in the field until 1997.1,67 Suitable syntheses for the main aglucones DIBOA68 and DIMBOA64 74 have been reported, as well as a general diastereoselective glucosidation method to form DIBOA-GIc, DIMBOA-GIc and other benzoxazinone glucosides.46... 

Hence, the plant own defensive system is able to liberate a toxic, bioactive weapon from a non-toxic precursor very rapidly and in appreciable amounts, because of the benzoxazinone glucoside content in seedlings can reach concentrations between 1-10 mmoles per kg of fresh weight [85,86]. E.g., 530 mg of DIMBOA have been isolated from 1 kg of frozen maize shoots [79]. 

On principle, the benzoxazinone glucoside synthesis has the same challenge, but there is no asymmetric induction from the aglucone unit. 

Blepharin (see Fig. (1)) was the first benzoxazinone glucoside synthesised using the brominated aglucone as acceptor for tetraacetylglucose in the presence of mercury(II) cyanide [130] (Fig. (17)). 

Hydrolytic Dehalogenation Simazine was shown by Roth (1957) to degrade in the presence of com extracts, but was stable in the presence of extracts from a susceptible wheat crop. Castelfranco et al. (1961) described a similar nonenzyme constituent of expressed com sap that hydrolyzed simazine to hydroxysimazine [2,4-bis(ethylamino)-6-hydroxy-y-triazine]. Wahlroos and Virtanen (1959) and Hamilton (1964) have established that the catalytic conversion of simazine to hydroxysimazine in roots and shoots of resistant species is caused by 2,4-dihydroxy-7-methoxy-l,4-benzoxazin-3-one (benzoxazinone) or its 2-glucoside as follows ... 

Natural benzoxazinone acetal glucosides with cyclic hydroxamic acid unit. 

It is clear that BOA detoxification, mainly via glucoside carbamate production of the species tested, is not a feature of certain plant families but is rather combined with their occurrence in defined plant communities where benzoxazinone containing character species exist with high density covers. Plantago major is regarded as an exception. 

Kluge, M. and Sicker, D. 1996. Double diastereoselective glucosidation of cyclic hemiacetals synthesis of the 1,4-benzoxazinone acetal glucosides GDIBOA and GDIMBOA from Gramineae. Tetrahedron 52, 10389-10398... 

The discovery of natural benzoxazinones was based on the finding that rye plants showed an increased resistance towards pathogenic fungi. Hence, the first aglucone and the first glucoside were reported from rye in two successive papers [1,2]. Acetal glycosides of the 2-hydroxy-2/f-l,4-... 

It is the aim of this review to present a detailed overview on natural sources of benzoxazinones and their enzymatic and chemical degradation, on the synthetic access both to aglycones and acetal glucosides, on medical effects and on the molecular allelopathy of these bioactive natural products. 

Benzoxazinone Acetal Glucosides and their Position among the Natural Products... 

All natural benzoxazinone glycosides reported are D-glucosides of the (substituted) 2-hydroxy-2//-l,4-benzoxazin-3(4i7)-one skeleton as shown in Fig. (1). Usually, several acronyms derived from the rational names are used to name the compounds in papers, as it will be done here. E.g. the... 

Aglucones are released by p-glucosidase on a pest attack from their preinfectional glucosidic precursors deposited in the plant cell vacuole, as will be shown below. Furthermore, aglucones can be passively set free into the environment by rotting plant material [62] or actively by root exudation [63]. An overview on benzoxazinone aglucones is given in Fig. (3). 

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