## 2 Discussion
Furuncoumarins such as marmesin are derived from prenylated coumarins and these originate from the ortho-hydroxylation of cinnamic acid, which is rare. Psoralens have been considered to be the phytoalexins that give celery resistance against pathogens, it has also been shown that marmesin (a precursor of psoralens) has antifungal activity in vitro 100 times greater than psoralens. Furthermore, as celery became more susceptible to the pathogen during storage, psoralen levels increased, while marmesin levels decreased. From this, it follows that marmesin is the compound that gives celery resistance against pathogens [130]. Psoralen acts as a skin photosensitizer, causing erythema and darkening of the skin. On the other hand, naphthodianthrones are compounds that derive from the polyketide biosynthetic pathway to produce a compound with two anthrone structures fused to a naphthalene skeleton (Figure 9). One of the most relevant compounds of this group is hypericin, which is responsible for the antidepressant, anticancer and antiviral activities of different species of the genus _Hypericum_[131]. Table 1 shows the biological activity, sources, and methods of identification for a furanocoumarin and a naphthodianthrone. Figure 8: The chemical structure for some bioactive group of alkaloids. Figure 9: The chemical structures for hypericin (a naphthodianthrone) and furanocoumarin. Proteins are polymers of amino acids linked by amide bonds called peptide bonds (Figure 10). Proteins can weigh several tens of thousands of daltons and have very varied functions, many of them are specific in an organism, such as the case of enzymes. On the other hand, short chains of amino acids are called peptides or polypeptides. Some organisms can use nonprotein amino acids, known as \"rare amino acids\" to produce small polypeptides that are toxins such as phalloidin or amantiins, which inhibit RNA polymerase. Amanitins, from _Amanitins phalloides_, are toxins from this fungus that inhibit protein synthesis in mammals; within 6-15 h of ingestion, they cause violent gastroenteritis, fever, tachycardia, hyperglycemia, alteration in electrolyte balance, and liver and kidney dysfunction. They can be lethal. Some of these \"rare amino acids\" are octopine and napaline derived from arginine and found in plasmids of _Agrobacteriumum tumefaciens_, a tumor-causing pathogen (crown galls) in legumes. Other examples of these amino acids are canavanine, 3,4-dihydroxyphenylalanine, 5-hydroxy tryptophan, azetidine-2-carboxylic acid. A characteristic of these \"rare amino acids\" is that they are very similar to the amino acids used for the biosynthesis of proteins--for example, canavanine with arginine; azetidine-2-carboxylic acid with proline. This means that, in some cases, the toxicity is due to an error in the incorporation of nonprotein amino acid, being mistaken for a protein one, which originates from a nonfunctional protein either because its tertiary structure was modified or because it produced some other change that affects its catalytic property. As extra data, the isoelectric point of canavanine is 8.2, which makes this amino acid much less basic than arginine, whose isoelectric point is 10.8, which could affect the ability of the enzyme to bind to the substrate or catalyze chemical reactions. Table 1 exemplifies a bioactive peptide isolated and characterized recently. The obtaining of raw material from plants to evaluate the presence of active principles with beneficial effects on human health is a critical task for researchers. Diverse techniques have been used to obtain biologically active molecules from plants. These applications involve the use of solvents capable of interacting due to their chemical properties. This is the case of the use of critical supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE) methodologies, which, in recent years, have gained notoriety for their ample yields in the extraction of bioactive compounds without causing degradation [132].