Synthesis of benzoxazinoid acetal glucosides naturally occurring in Gramineae

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Synthesis of benzoxazinoid acetal glucosides naturally occurring in <em>Gramineae </em>

461-475Benzoxazinoid acetal glucosides, a unique class of natural hemiacetal ethers from Gramineae and other species, are of interest as precursors of aglucones which exhibit high bioactivity as plant resistance factors against microbial diseases and insects, allelo chemicals and endogeneous ligands. This review gives a survey on synthetic methods which give rise to the hemiacetalic aglucones of the 2-hydroxy-2H-1 ,4-benzoxazin- 3(4H)-one skeleton, efficiently. As a result of investigations in the area of acetal glucosidation a double diastereoselective glucosidation method of racemic cyclic hemiacetals has been developed that affords an access to the acetal glucosides of natural configuration as well as to their enantiomers

Evaluation of DIMBOA analogs as antifeedants and antibiotics towards the aphid Sitobion avenae in artificial diets

A total of 25 compounds including benzoxazinones, benzoxazolinones, and N-glyoxylamide derivatives were tested as antifeedants and antibiotics towards the aphid Sitobion avenae in diet bioassays. The antifeedant and mortality indexes increased with the presence of electron-donating groups in the 7 position of the benzoxazinone moiety, the replacement of the oxygen atom by sulfur in the heterocyclic ring, the presence of a hemiacetal instead of an acetal at C-2 of the benzoxazine moiety (and hence the possibility of ring opening), and the presence of a hydroxyl group at C-4 of the benzoxazine moiety (hydroxamic acid) instead of a hydrogen atom (lactam). The results support earlier hypotheses on the chemical bases for the mode of action of these compounds

Conversions of Benzoxazinoids and Downstream Metabolites by Soil Microorganisms

Benzoxazinoids, secondary metabolites of several Poaceae, and some benzoxazinoid downstream metabolites are bioactive compounds that act as allelochemicals and natural pesticides. Since a short lifetime of the substances is crucial to avoid long-term environmental effects, total degradation by microorganisms is of exceptional importance. We performed a screening with cultivable microorganisms (Species names and strain numbers: Mycobacterium fortuitum, 7; Bacillus aryabhattai, 34; Bacillus cereus, 59; Bacillus megaterium, 21, 48; Bacillus methylotrophicus, 58; Lysinibacillus xylanilyticus, 56; Paenibacillus polymyxa, 51; Aminobacter aminovorans, 49; the fungi Papulaspora sepedonioides, 12 and Trichoderma viride, 47) isolated from soil previously used for wheat and Persian clover mixed-culture systems to assess their behavior in the presence of the compounds. The microorganisms were exposed to glucosylated benzoxazinones, the benzoxazinones HBOA, DIBOA, and DIMBOA, the benzoxazolinones BOA, BOA-6-OH, and MBOA, and to several downstream products (AP, AAP, oHPMA, glucoside carbamate) in liquid culture to avoid interferences with soil minerals and other organisms. The microorganisms differed strongly in their metabolic activities in terms of growth, compound modification, and degradation. We observed degradation with DIBOA and GDIMBOA but rarely with DIMBOA, whereas BOA and MBOA showed almost no degradation when directly applied. Hydroxylation of BOA and demethylation of MBOA by the plant, resulting in BOA-6-OH, activated the benzoxazolinones for bacterial nitration. The resulting NBOA-6-OH was short-lived but could function temporarily as an allelochemical by inhibiting photosynthesis, e.g., in young seedlings of cress and kohlrabi. The BOA downstream products AP and oHPMA were converted to AAP, which can be nitrated to N-(2-OH-5-nitrophenyl)-acetamide and then degraded by A. aminovorans (49) and P. polymyxa (51). Only P. sepedonioides (12) and P. polymyxa (51) failed in the conversion of HBOA into AAP. While DIBOA, DIMBOA, MBOA, NBOA-6-OH, AP, AAP, and oHPMA reduced the growth of most microorganisms, glucoside carbamate promoted their growth. GDIMBOA had a stimulatory effect toward the fungi and three bacterial species. These findings lead to the hypothesis that in a natural habitat, such as the root surface, microorganisms may cooperate, perhaps by involving the plant, for the successful elimination of benzoxazinoids and their downstream metabolites