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The neotropical bracken fern Pteridium arachnoideum (Kaulf.) Maxon. (Dennstaedtiaceae) is described as an aggressive pioneer plant species. It invades abandoned or newly burned areas and represents a management challenge at these invaded sites. Native to the Atlantic Forest and Cerrado (Tropical Savanna) Brazilian biomes, P. arachnoideum has nevertheless become very problematic in these conservation hotspots. Despite some reports suggesting a possible role of allelopathy in this plant's dominance, until now there has been little evidence of isolated and individually identified compounds with phytotoxic activities present in its tissues or in the surrounding environment. Thus, the aim of this study was to investigate the allelopathic potential of P. arachnoideum by isolating and identifying any secondary metabolites with phytotoxic activity in its tissues, litter, and soil. Bioguided phytochemical investigation led to the isolation and identification of the proanthocyanidin selligueain A as the major secondary compound in the green fronds and litter of this fern. It is produced by P. arachnoideum in its green fronds, remains unaltered during the senescence process, and is the major secondary compound present in litter. Selligueain A showed phytotoxic activity against the selected target species sesame (Sesamum indicum) early development. In particular, the compound inhibited root and stem growth, and root metaxylem cell size but did not affect chlorophyll content. This compound can be considered as an allelochemical because it is present in the soil under P. arachnoideum patches as one of the major compounds in the soil solution. This is the first report of the presence of selligueain A in any member of the Dennstaedtiaceae family and the first time an isolated and identified allelochemical produced by members of the Pteridium species complex has been described. This evidence of selligueain A as a putative allelochemical of P. arachnoideum reinforces the role of allelopathy in the dominance processes of this plant in the areas where it occurs.

Broomrapes attack important crops, cause severe yield losses and are difficult to eliminate because their seed bank is virtually indestructible. In the absence of a host, the induction of seed germination leads to inevitable death due to nutrient starvation. Synthetic analogues ofgermination-inducing factorsmay constitute a cheap and feasible strategy to control the seed bank. These compounds should be easy and cheap to synthesise, as this will allow their mass production. The aim of this work is to obtain new synthethic germinating agents. Nineteen N-substituted phthalimides containing a butenolide ring and different substituents in the aromatic ringwere synthesised. The synthesis started with commercially available phthalimides. The complete collection was assayed against the parasitic weeds Orobanche minor, O. cumana, Phelipanche ramosa and P. aegyptiaca, with the synthetic strigolactone analogue GR24 used as a positive control. These compounds offered low EC50 values: O. cumana 38.3 𝝁M, O. minor 3.77 𝝁M, P. aegyptiaca 1.35 𝝁Mand P. ramosa 1.49 𝝁M. The synthesiswas carried out in a fewsteps and provided the target compounds in good yields. The compounds tested showed great selectivity, and low EC50 values were obtained for structures that were simpler than GR24.

Guaianolides constitute a large and diverse group of biologically active sesquiterpenes. Guaianolide and seco-guaianolides can also be used as, for example, scaffolds for the development of new active molecules that are readily accessible by synthetic methods. Nevertheless, these lactones often have complex structures that make their synthesis difficult. The aim of this microreview is to provide an overview of the developments in guaianolide synthesis by the two major synthetic strategies: semi-synthesis and total synthesis. Partial and total syntheses of guaianolides are described, with particular emphasis placed on the methods reported in the last decade. The methods discussed include rearrangements, cycloadditions, ring-closing metathesis, the use of transitionmetal catalysts, photochemical reactions, and other recently developed techniques as key steps.