# Secondary Metabolites and Their Applications
## 2 Contributions  
This Special Issue brings together seven research articles and four review articles presenting the latest advances in the study of secondary metabolites from different natural sources and their potential applications. The scientific results are presented that led to the identification of secondary metabolites in samples of terrestrial and marine origin, obtained by classic and innovative extractive methodologies, as well as studies to evaluate their effect in different areas such as health, biopesticides, etc. Invasive alien species are recognized for triggering various impacts, such as habitat modification, alteration of community structure, and affecting ecosystem processes. The characterization of secondary metabolites in invasive species could be a way of valuing and increasing the search for available biomass promoting its harvest and contribute to the conservation of biodiversity and sustainability of the ecosystem. This is one of the objectives of the studies carried out by [PERSON] et al. [8] and [PERSON] et al. [9], in which the secondary metabolite composition of two invasive species, one terrestrial (_Acacia lealbuta_ L) and one marine (seaweed _Asparagopsis armata_ [PERSON]), respectively, are presented. The results show that the hydroethanolic extract of non-mature flowers of _Acacia lealbuta_ exhibits the greatest potential as an antioxidant and acetylcholinesterase inhibitor, these activities being correlated with the higher content of chalcones present [8]. These authors suggest the extract as a source of compounds capable of improving brain functions, while collecting the flower at an early stage of flowering contributes to interrupting the plant's reproduction, which will help to control its invasive potential. [PERSON] et al. [9] address new perspectives for the valuation of _Asparagopsis armata_, an invasive alga in Europe, and have determined the profile of the secondary metabolites of this species using GC-MS and UHPLC-MS techniques. The authors established the species as a source of halogenated compounds and fatty acids, with 1,4-dibromobuten-1-ol and palmitic acid being the two most abundant compounds identified in the lipophilic fraction, while in the polar fraction, brominated phenolic compounds derived from cinnamic acid are predominant. This work also shows that changing the extraction method modifies the metabolomic profile of the obtained extract. The use of ethanol under microwave energy extracted almost exclusively one compound, the 2,3-diphenylpropanoic acid derivative with one hydroxyl group and two bromine atoms in each aromatic ring [9]. The [PERSON] group [10] also uses samples of marine origin, in this case the cyanobacterium _Arthospira platensis_ [PERSON], and optimizes the extraction with pulsed electric fields to propose a more selective, sustainable, and efficient methodology to extract chlorophylls, carotenoids, and phenolic compounds, which have applications as nutritional and antioxidants agents. In recent years, natural phytotoxic compounds derived from plants have been extensively investigated for herbicidal properties and have been shown to suppress weeds. These compounds can then be used as promising models for standard biohebicides. In this sense, [PERSON] et al. [11] have demonstrated in their manuscript for the first time the presence of methyl chlorateate in _Garcinia xanthochymus_ Hook.f. ex T.Anderson, as well as its phytotoxic properties. Vanillic acid was also identified. Both compounds have significant growth inhibitory activities in watercress and timothy, demonstrating as such the potential of the leaves of _Garcinia xanthochymus_ in weed management. The leaves of _Afzelia xylocarpa_ ([PERSON] were investigated as a natural source of herbicides. [PERSON] et al. [12] have identified vanillic acid and _trans_ ferulic acid as the major bioactive compounds, both being responsible for the phytotoxic activity of _Afzelia xylocarpa_.