**5. Phytochemistry**

Several categories of phytochemicals have been identified in the leaves, bark, and wood of *T. impetiginosa.* From *T. impetiginosa* bark, 19 glycosides comprised of four iridoid glycosides, two lignan glycosides, two isocoumarin glycosides, three phenylethanoid glycosides, and eight phenolic glycosides were methanol-extracted [35]. Major constituents of *T. impetiginosa* are furanonaphthoquinones, naphthoquinones, anthraquinones (e.g., anthraquinone-2-carboxylic acid (Compound **1** in Figure 2)), quinones, benzoic acid, flavonoids, cyclopentene dialdehydes, coumarins, iridoids, and phenolic glycosides [4,8,36]. The presence of naphthoquinones attracted scientific attention, with lapachol (**2**) and β-lapachone (**3**) especially piquing the interest of professionals in the medical field. Lapachol inhibits proliferation of tumor cells, while β-lapachone exhibits strong toxicity in murine and human cells. Lapachol has been shown to reduce the number of tumors caused by doxorubicin in *Drosophila melanogaster* heterozygous for the tumor suppressor gene. Lapachol can also decrease the invasion of HeLa cells, which could represent an interesting scaffold for the development of novel antimetastatic compounds [4].

Fatty acids, especially oleic acid (**4**), palmitic acid (**5**), and linoleic acid (**6**), are found in the bark of *T. impetiginosa*. Free sugars also were identified in the bark, with glucose being the most abundant, followed by fructose and sucrose. Organic acids, especially oxalic acid (**7**), are present, as well as the fat-soluble alcohols α-tocopherol (**8**) and γ-tocopherol (**9**). α-Tocopherol can reduce cardiovascular disease risk and neurodegenerative disorders [4]. In addition, *T. impetiginosa* has some volatile constituents that exhibit antioxidant activity. The major volatile constituents in *T. impetiginosa* include 4-methoxybenzaldehyde (**10**), 4-methoxyphenol (**11**), 5-allyl-1,2,3-trimethoxybenzene (**12**), 1-methoxy-4-(1*E*)-1-propenylbenzene (**13**), and 4-methoxybenzyl alcohol (**14**) [37].

Cyclopentene derivatives are secondary metabolites of plants, and this constituent from *T. impetiginosa* contained six known cyclopentenyl esters (avallaneine A–F (**15–20**)), two new cyclopentyl esters (avallaneine G (**21**) and H (**22**)), and two known cyclopentenyl esters. These cyclopentene derivatives may provide a significant anti-inflammatory effect on the lipopolysaccharide (LPS)-mediated inflammatory response by blocking the production of NO and PGE2; therefore, it is important to determine the molecular mechanism whereby cyclopentenyl esters from *T. impetiginosa* inhibit inflammatory responses [16]. Moreover, Koyama et al. [38] isolated two cyclopentene dialdehydes, 2-formyl-5-(4--methoxybenzoyloxy)-3-methyl-2-cyclopentene-1-acetaldehyde (**23**) and 2-formyl-5-(3-,4--dimethoxybenzoyloxy)-3-methyl-2-cyclopentene-1-acetaldehyde (**24**), that exert anti-inflammatory activity in human leukocytes. Thus, it is necessary to further investigate their activities.

**Figure 2.** Chemical structures of *Tabebuia impetiginosa*-derived components.
