Benzoxazinoids: Reactivity and Modes of Action of a Versatile Class of Plant Chemical Defenses

Abstract

In order to protect themselves from biotic stresses, including enemies and competitors, many plants recruit defensive secondary metabolites. Compounds containing a 2-hydroxy-2H-1,4benzoxazin-3(4H)-one skeleton and their derivatives, collectively known as benzoxazinoids, are common secondary metabolites in many grasses, including important cereal crops such as maize, wheat, and rye, as well as several dicot species. This diverse class of compounds is known for its broad range of antifeedant, insecticidal, antimicrobial, and allelopathic activities. However, the mechanisms underlying such biological activities are not yet completely understood. The present review aims to summarize the current knowledge on the chemical reactivity of benzoxazinoids in biological systems and associate it to their proposed modes of action. Structure-activity relationships for a wide spectrum of biological effects are critically discussed and directions for future research are addressed.

Plant defense and herbivore counter-defense: benzoxazinoids and insect herbivores

“…The degradation rates depend on conditions such as pH, temperature and solvent, and structural features such as the nature of the N -substituent group and other substituents on the aromatic ring (Atkinson et al 1991). Several mechanisms have been proposed to explain this degradation (Bredenberg et al 1962; Grambow et al 1986; Maresh et al 2006; Niemeyer et al 1982a; Smissman et al 1972; Wouters et al 2016). …”

“…Due to the economic and ecological importance of BXDs, many aspects of these compounds have been reviewed, including their biological activities (Macías et al 2009; Niemeyer 2009), organic synthesis (Macías et al 2006; Sicker and Schulz 2002), chemical reactivities (Hashimoto and Shudo 1996; Wouters et al 2016), and biosynthetic evolution and genetics (Frey et al 2009; Makowska et al 2015). The present review aims to categorize the spectrum of biological activities observed for BXDs towards insect herbivores with different feeding behaviors: chewing, piercing-sucking, and root herbivores.…”

Conversions of Benzoxazinoids and Downstream Metabolites by Soil Microorganisms

“…Microorganisms differed markedly in their compound-modifying and degradation abilities, with P. polymyxa (51) and A. aminovorans (49) being the most active representatives. Generation of APO from DIBOA is most likely attributed to the degradation of α-oxoaldehyde, the intermediate formed upon ring opening of DIBOA (Sicker and Schulz, 2002;Zikmundová et al, 2002;Niemeyer, 2009;Wouters et al, 2016). On root surfaces, consortia of microorganisms may act in concert to achieve more rapid compound elimination, for instance for HBOA degradation via AAP and nitro-AAP.…”

Toxicity and Anti-promastigote Activity of Benzoxazinoid Analogs Against Leishmania (Viannia) braziliensis and Leishmania (Leishmania) infantum

“…22 The Bex-derived stand out for their importance as allelochemicals, used for plant-plant, plant-insect, or plant-microorganisms communication (or interaction), and display a wide range of anti-infective, insecticidal and antimicrobial activities. 12,13,23 In addition to the defensive effect against phytopathogens, Bex-derived compounds have also shown activity against microorganisms of medical interest. [14][15][16][17] Bravo et al 15 reported that the Bexs benzoxazolin-2-one (BOA), 2-hydroxy-1,4-benzoxazin-3-one (HBOA) and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) exhibit antibacterial effects against Staphylococcus aureus and Streptococcus mutans at concentrations of 500 μg/mL, and against Escherichia coli at a concentration of 1,000 μg/mL according to microdilution broth assays.…”

“…12 Bexs are characterized by the presence of a 2-hydroxy-2H-1,4benzoxazin-3(4H)-one skeleton and are known to show anti-inflammatory, antinociceptive, reproductive and immune stimulatory, antitumor and appetite suppressor activities. 12,13 Moreover, recent work has uncovered a critical antimicrobial activity for the compounds, covering bacteria, yeast, molds, and retroviruses of great medical importance. [14][15][16][17] Our group has previously developed and synthesized a series of new Bex analogs that have shown antimicrobial activity against microorganisms of high medical relevance such as Enterococcus faecalis, Staphylococcus aureus, Acinetobacter baumannii, Candida albicans, C. tropicalis and C. glabrata.…”