Structure−Activity Relationships (SAR) Studies of Benzoxazinones, Their Degradation Products and Analogues. Phytotoxicity on Standard Target Species (STS)

Abstract

Benzoxazinones 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA) and 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA) have been considered key compounds for understanding allelopathic phenomena in Gramineae crop plants such as corn (Zea mays L.), wheat (Triticum aestivum L.), and rye (Secale cereale L.). The degradation processes in the environment observed for these compounds, in which soil microbes are directly involved, could affect potential allelopathic activity of these plants. We present in this work a complete structure-activity relationships study based on the phytotoxic effects observed for DIMBOA, DIBOA, and their main degradation products, in addition to several synthetic analogues of them. Their effects were evaluated on standard target species (STS), which include Triticum aestivum L. . They showed high inhibitory activity over almost all species growth. The fact that APO is a degradation product from DIBOA with high phytotoxicity and stability makes it possible to assign an important ecological role regarding plant defense mechanisms. 2-Deoxy derivatives of natural benzoxazinones display a wide range of activities that allow proposing them as new leads for natural herbicide models with a 1,4-benzoxazine skeleton.

Optimization of Benzoxazinones as Natural Herbicide Models by Lipophilicity Enhancement

“…The phytotoxic effect of the more lipophilic compounds could be due to their accumulation in the seed surface during the experiment, avoiding the seed water uptake (as could happen with Mir-D-DIBOA), rather than a "true" phytotoxic effect in which the active chemical reaches the corresponding molecular target site. Thus, 6-methoxy-D-DIBOA derivatives modulate the transport phenomena for this compound, enhancing the phytotoxic effect in the case of A. fatua shoot length, but in the context of the intrinsic activity of this chemical, in which the methylation of the aromatic ring makes it less active, as in the case of the previously reported 7-methoxy derivative (20,22).…”

“…Soon after their discovery, they were found in a wide variety of plants mainly belonging to Gramineae, Ranunculaceae, and Scrophulariceae families (15). Their antifungal (16), antimicrobial (17), and phytotoxic effects (18)(19)(20)(21)(22), in addition to their interesting ecological role (23), raised interest in their isolation and synthesis in the search for an accurate explanation of the defense mechanisms of benzoxazinone producer plants. Moreover, the discovery of microbial degradation phenomena (24,25), which led to the detection of new chemicals with different structures, effects, ecological roles, and potential utilities, increased the interest in the development of analytical methods (26) and the design of experiments in which all of the chemicals present in the plant-plant interaction involving benzoxazinones could be present (23).…”

Challenges, achievements and opportunities in allelopathy research

“…This suggests that a large multidisciplinary approach may be needed to make significant progress in this area. One successful example of this type of approach in Europe involved chemists, physiologists and ecologists; they successfully investigated the ability of a winter rye cover crop (Secale cereale ) to produce a variety of allelochemicals over time, which formed biologically active metabolites in various soil settings (Macias et al 2005a(Macias et al , 2005b. This work was performed to determine the role of potential allelochemicals as phytotoxins or toxins in a managed agroecosystem.…”

Proving Allelopathy in Crop–Weed Interactions

“…Furthermore, soil microbes can convert less-phytotoxic root exudates to more phytotoxic compounds, making the discovery of the true ''allelochemical'' even more difficult. An example of this is the formation of the highly phytotoxic 2-aminophenoxazin-3-one from 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(H)-one released from some Gramineae crop species such as barley (Macías et al 2005). …”