Structure−Activity Relationship (SAR) Studies of Benzoxazinones, Their Degradation Products, and Analogues. Phytotoxicity on Problematic Weeds Avena fatua L. and Lolium rigidum Gaud.

Abstract

Avena fatua L. (wild oat) and Lolium rigidum Gaud. (rigid ryegrass) are highly problematic weeds affecting a wide variety of cereal crops worldwide. The fact that both of these weeds have developed resistance to several herbicide groups made them optimal candidates as target organisms for ongoing research about the potential application of allelochemicals and analogue compounds as natural herbicide models. Benzoxazinones, a family of natural allelochemicals present in corn, wheat, and rye, including 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one, together with some degradation products, found in crop soils as well as in other systems, and some synthetic analogues of them were tested on wild oat and rigid ryegrass seeds; the results were statistically treated, and some structure-activity relationships, useful in further development of natural herbicide models, were elucidated. The most active compounds were the synthetic benzoxazinone 2-acetoxy-(2H)-1,4-benzoxazin-3(4H)-one and the degradation product 2-aminophenoxazin-3-one, with highly significant inhibition on the development of both weeds. The ecological role of these compounds is discussed by considering both degradability and phytotoxicity. The bioactivity of aminophenoxazines has been correlated by their aqueous solubility-lipophilicity predicted by means of computational methods.

Plants Release Precursors of Histone Deacetylase Inhibitors to Suppress Growth of Competitors

“…DIBOA and DIMBOA typically undergo rapid degradation in natural environments. The resulting product APO is a highly potent phytotoxin, which is also the case, although to a lesser extent, for AMPO (Macías et al, 2006(Macías et al, , 2009. The allelochemicals APO and AMPO as well as their precursors have been detected in plants in proximity to DI(M)BOA donor plants (Macías et al, 2014).…”

“…We focused our analysis on APO, due to its superior allelopathic activity, its higher solubility in aqueous medium, and its lower lipophilicity compared with AMPO (Macías et al, 2006); mock-and TSA-treated seedlings served as controls. We validated successful enrichment for H3ac by quantitative real-time PCR (Supplemental Figure 10 and Supplemental Table 2).…”

“…Grasses in particular have the ability to interfere with and to outcompete neighboring plants via the biosynthesis of phytotoxic root exudates. Cyclic hydroxamic acids (e.g., benzoxazinoids or benzoxazinones), with their main representatives DIBOA [4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one] and its methoxylated analog DIMBOA [2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one], were among the first active allelochemicals identified and are present in root exudates of several major cereal crops (Belz and Hurle, 2005;Macías et al, 2006;Belz, 2007). In nature, these substances typically undergo rapid degradation via the intermediates benzoxazolin-2(3H)-one (BOA) and 6-methoxybenzoxazolin-2(3H)-one (MBOA).…”

“…In nature, these substances typically undergo rapid degradation via the intermediates benzoxazolin-2(3H)-one (BOA) and 6-methoxybenzoxazolin-2(3H)-one (MBOA). The resulting benzoxazolinone metabolites are much more stable, and in particular, the aminophenoxazinone compounds 2-amino-3H-phenoxazin-3-one (APO) and 2-amino-7-methoxy-3H-phenoxazin-3-one (AMPO) are highly potent phytotoxins (Macías et al, 2006(Macías et al, , 2009. The precursors DIBOA and DIMBOA as well as their degradation products APO and AMPO have been detected in target plants (Macías et al, 2014).…”

“…As they exert physiological effects on a variety of plant species, it has been surmised that these allelochemicals act on highly conserved central cellular pathways or structures (Duke, 2007;Dayan et al, 2009). In vivo bioassays confirmed growth inhibitory activity for hydroxamic-acid-derived allelochemicals, such as APO and AMPO, that is comparable to that of commercial herbicides (Macías et al, 2006). However, the modes of action and molecular targets affected by this type of allelopathic interaction between plants have remained mostly unresolved (Duke, 2010).…”