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Growing cereals (especially rye), which are incorporated into the soil to increase soil fertility or organic matter content, is a common practice in crop rotation. The additional sanitizing effect of this incorporation has often been appreciated and is said to be due to leaching of benzoxazinones and subsequent formation of benzoxazolinones. In this study wheat (Stakado) and rye (Hacada) sprouts were incorporated into soil in amounts that simulated agricultural practice. By extraction and subsequent LC-MS analysis the disappearance and appearance of benzoxazinones, benzoxazolinones, and phenoxazinones in soil were followed. In the wheat experiments 6-methoxybenzoxazolin-2-one (MBOA) was detected as the main compound. 2-Hydroxy-7-methoxy-1,4-benzoxazin-3-one (HMBOA) and 2-hydroxy-1,4-benzoxazin-3-one (HBOA) were detected as well. No phenoxazinones were detected. For the rye experiment the picture was more complex. In the first 2 days of incubation MBOA and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) were detected as the main allelochemicals along with HBOA, HMBOA, and benzoxazolin-2-one (BOA), in decreasing order. Later in the incubation period some 2-amino-3H-phenoxazin-3-one (APO) was detected and the amount of HBOA increased considerably and decreased again. The profiling of the benzoxazinone metabolites and their derivates in soil was dynamic and time-dependent. The highest concentrations of most of the compounds were seen at day 1 after incorporation. A maximum concentration was reached at day 4 for a few of the compounds. This study is the first of its kind that shows the dynamic pattern of biologically active benzoxazinone derivates in soil after incorporation of wheat and rye sprouts. Methods for organic synthesis of HBOA and HMBOA were developed as part of the study.

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To deduce the structure of the large array of compounds arising from the transformation pathway of 6-methoxybenzoxazolin-2-one (MBOA), the combination of isotopic substitution and liquid chromatography analysis with mass spectrometry detection was used as a powerful tool. MBOA is formed in soil when the cereal allelochemical 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) is exuded from plant material to soil. Degradation experiments were performed in concentrations of 400 microg of benzoxazolinone/g of soil for MBOA and its isotopomer 6-trideuteriomethoxybenzoxazolin-2-one ([D3]-MBOA). Previously identified metabolites 2-amino-7-methoxyphenoxazin-3-one (AMPO) and 2-acetylamino-7-methoxyphenoxazin-3-one (AAMPO) were detected. Furthermore, several novel compounds were detected and provisionally characterized. The environmental impact of these compounds and their long-range effects are yet to be discovered. This is imperative due to the enhanced interest in exploiting the allelopathic properties of cereals as a means of reducing the use of synthetic pesticides.