Elucidating the Transformation Pattern of the Cereal Allelochemical 6-Methoxy-2-benzoxazolinone (MBOA) and the Trideuteriomethoxy Analogue [D₃]-MBOA in Soil

Abstract

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.

Transformation kinetics of 6-methoxybenzoxazolin-2-one in soil

“…[18] Limits of detection (LOD) were determined according to Miller and Miller [31] using six replicates for each compound. LOD were 21.19 pmol g -1 soil for MBOA, 21.88 pmol g -1 soil for AMPO, and 7.74 pmol g -1 soil for AAMPO.…”

Allelochemicals: sources, toxicity and microbial transformation in soil —a review

“…Soil sterilisation stabilised the arbutin, hydroquinone and gallic acid effectively, but benzoquinone was degraded rapidly under this nonmicrobial oxidative condition. Degradation of MBOA and its isotopomer 6-trideuteriomethoxybenzoxazolin-2-one ([D3]-MBOA) in soil yielded AMPO and AAMPO, and several novel compounds were also detected (Etzerodt et al, 2006).…”

Biologically active secondary metabolites in white clover (Trifolium repens L.) – a review focusing on contents in the plant, plant–pest interactions and transformation

“…The soil environment is mainly aerobic, and the microbial environment is very complex, but anaerobic micro-sites exist in soil, and anaerobic and aerobic pathways can produce the same compounds. There have been degradation studies of these compounds using isolated fungi, but these have proved to be useful for soil degradation studies on other groups of natural defense compounds (Etzerodt et al, 2006;Fomsgaard, 2006;Fomsgaard et al, 2004Fomsgaard et al, , 2006Gents et al, 2005;Understrup et al, 2005). Information about possible degradation products obtained from these studies is a useful basis to understand soil degradation of white clover natural defense compounds.…”