Chemical Compounds and Biologic Activities: A Review of Cedrela Genus

The genus Cedrela P. Browne, which belongs to the Meliaceae family, has eighteen species. Trees of this genus are of economic interest due to wood quality, as well as being the focus of studies because of relevant biologic activities as in other Meliaceae species. These activities are mainly related to limonoids, a characteristic class of compounds in this family. Therefore, the aim of this review is to perform a survey of the citations in the literature on the Cedrela genus species. Articles were found on quantitative and qualitative phytochemical studies of the Cedrela species, revealing the chemical compounds identified, such as aliphatics acid and alcohol, flavonoids, tocopherol, monoterpenes, sesquiterpenes, triterpenes, cycloartanes, steroids, and limonoids. Although some activities were tested, the majority of studies focused on the insecticidal, antifeedant, or insect growth inhibitor activities of this genus. Nonetheless, the most promising activities were related to their antimalarial and antitripanocidal effects, although further investigations are still needed.


Introduction
The genus Cedrela P. Browne contains 18 species (Figure 1) and is one of 53 genera of trees and shrubs from the Meliaceae family. These species are distributed from northern Mexico to the northwest part of Argentina [1][2][3]. Table 1. Aliphatic acids and alcohol isolated from the genus Cedrela (1960-2020).

Compound Plant Species Plant Part References
stearic acid (1) Cedrela odorata L. bark and sapwood oil [21] oleic acid (2) linoleic acid (3) n-octacosanol (4) Molecules 2020, 25, x FOR PEER REVIEW 3 of 34 development of medicinal agents from this plant. Data were compiled from 1960 up to June 2020, focusing on all isolated compounds and also considering biological activities.

Chemical Compounds
Since 1960, more than 200 chemical constituents have been isolated from or identified in the genus Cedrela, including limonoids and triterpenes, but also several other compounds, such as monoterpenes, sesquiterpenes, steroids, and other metabolites. Their structures are shown below, and their names and corresponding plant and biological activity sources are compiled in the Tables.

Aliphatic Acid and Alcohol
Fatty acids are hydrocarbon chains with a carboxyl group at the end of the molecule and play a number of key roles in metabolism [18]. The main sources of fatty acids are vegetable oils, dairy products, meat products, grain, and fish oils [19], but they were identified in the bark and sapwood oil of C. odorata L. Oleic (2) and linoleic acids (3) are most common in plants, while stearic acid is more common in animals, and a minor component in plants [19]. Stearic (1), oleic, and linoleic fatty acids and n-octacosanol alcohol (4) were identified in the genus Cedrela (Table 1). Fatty alcohol is a class of aliphatic hydrocarbons containing one or more hydroxyl groups and are most prominent in terrestrial plants with C26 to C30 chain lengths [20]. Table 1. Aliphatic acids and alcohol isolated from the genus Cedrela (1960-2020).

Flavonoids
Flavonoids are a secondary metabolite class, also known as polyphenol antioxidants, found naturally in plants. Moreover, they are widely disbursed throughout plants and gives the flowers and fruits of many plants their vibrant colors [22]. However, De Paula et al. [23] and Da Silva et al. [24] reported the absence of proanthocyanidins-also known as tannins, whose building blocks can be catechin or epicatechin [25,26]-from C. odorata L. and their presence in Toona ciliata. Thus, "these constituents could have been translocated from the Toona stock to the Cedrela graft" [24] (p. 1085).
Considering that a review of the latest studies of the composition of Cedrela species found isolated flavonoids, further studies on the composition of Cedrela are important. Flavonoids such as catechin (5) and luteolin (6) identified in the genus Cedrela are shown in Table 2. Table 2. Flavonoids isolated from the genus Cedrela (1960-2020).

Flavonoids
Flavonoids are a secondary metabolite class, also known as polyphenol antioxidants, found naturally in plants. Moreover, they are widely disbursed throughout plants and gives the flowers and fruits of many plants their vibrant colors [22]. However, De Paula et al. [23] and Da Silva et al. [24] reported the absence of proanthocyanidins-also known as tannins, whose building blocks can be catechin or epicatechin [25,26]-from C. odorata L. and their presence in Toona ciliata. Thus, "these constituents could have been translocated from the Toona stock to the Cedrela graft" [24] (p. 1085).
Considering that a review of the latest studies of the composition of Cedrela species found isolated flavonoids, further studies on the composition of Cedrela are important. Flavonoids such as catechin (5) and luteolin (6) identified in the genus Cedrela are shown in Table 2. Table 2. Flavonoids isolated from the genus Cedrela (1960-2020).

Tocopherol
Tocopherols constitute members of the vitamin E group, essential dietary components in mammals, and are associated with a decreased risk of many diseases [29]. Their biosynthesis is potentially derivable from the oxidation of phenolic compounds to quinones, and isoprenoid sidechain added (four isoprene units) [18]. The terpenoid quinone (7) identified in the genus Cedrela is shown in Table 3. Table 3. Tocopherol isolated from the genus Cedrela (1960-2019)

Monoterpenes
Monoterpenes are a secondary metabolite class usually identified in the oils that can be obtained from different parts of many plants. Biosynthetically, these compounds can be steam from the condensation of two isoprene units [31]. The monoterpenes  identified in the genus Cedrela are shown in Table 4. Table 4. Monoterpenes identified from the genus Cedrela (1960-2020).

Tocopherol
Tocopherols constitute members of the vitamin E group, essential dietary components in mammals, and are associated with a decreased risk of many diseases [29]. Their biosynthesis is potentially derivable from the oxidation of phenolic compounds to quinones, and isoprenoid side-chain added (four isoprene units) [18]. The terpenoid quinone (7) identified in the genus Cedrela is shown in Table 3. Table 3. Tocopherol isolated from the genus Cedrela (1960-2019)

Tocopherol
Tocopherols constitute members of the vitamin E group, essential dietary components in mammals, and are associated with a decreased risk of many diseases [29]. Their biosynthesis is potentially derivable from the oxidation of phenolic compounds to quinones, and isoprenoid sidechain added (four isoprene units) [18]. The terpenoid quinone (7) identified in the genus Cedrela is shown in Table 3. Monoterpenes are a secondary metabolite class usually identified in the oils that can be obtained from different parts of many plants. Biosynthetically, these compounds can be steam from the condensation of two isoprene units [31]. The monoterpenes  identified in the genus Cedrela are shown in Table 4. C. odorata L.

Sesquiterpenes
Sesquiterpenes are a secondary metabolite class, whose chemical structures are formed from three isoprene units [18]. This class is mainly found in essential plant oil. The few studies about the essential oil composition of Cedrela species have shown that sesquiterpenes were found in abundance [21,[32][33][34].
Furthermore, according to Ogunwande et al. [33], there is a qualitative or quantitative expressive difference in essential oil composition from different botanic parts of Cedrela species. The authors affirmed that sesquiterpene hydrocarbons are present in the essential oil of leaves, while oxygenated derivates are predominant in steam bark essential oil. The sesquiterpenes  identified in the genus Cedrela are shown in Table 5.

Sesquiterpenes
Sesquiterpenes are a secondary metabolite class, whose chemical structures are formed from three isoprene units [18]. This class is mainly found in essential plant oil. The few studies about the essential oil composition of Cedrela species have shown that sesquiterpenes were found in abundance [21,[32][33][34].
Furthermore, according to Ogunwande et al. [33], there is a qualitative or quantitative expressive difference in essential oil composition from different botanic parts of Cedrela species. The authors affirmed that sesquiterpene hydrocarbons are present in the essential oil of leaves, while oxygenated derivates are predominant in steam bark essential oil. The sesquiterpenes  identified in the genus Cedrela are shown in Table 5.

Triterpenoids
Triterpenes Triterpenes, one of the largest classes of natural plant products, are initially formed from squalene, following complex enzymatic reactions [40]. However, in addition to the need for specific enzymes for cyclization, it also depends on the conformation of squalene, yielding mainly oleanane, ursane, lupane, and dammarane carbon skeletons [41]. Triterpenes have a range of biological effects and are used in the prevention and treatment of some diseases [42]. The triterpenes (119-151) identified in the genus Cedrela are shown in Table 6. Fruits and seeds [44] C. odorata L. Stems

Triterpenoids
Triterpenes Triterpenes, one of the largest classes of natural plant products, are initially formed from squalene, following complex enzymatic reactions [40]. However, in addition to the need for specific enzymes for cyclization, it also depends on the conformation of squalene, yielding mainly oleanane, ursane, lupane, and dammarane carbon skeletons [41]. Triterpenes have a range of biological effects and are used in the prevention and treatment of some diseases [42]. The triterpenes (119-151) identified in the genus Cedrela are shown in Table 6. Table 6. Triterpenes isolated from the genus Cedrela (1960-2020).

Cycloartanes
Cycloartanes are triterpenoids and key intermediates in the biosynthesis of phytosteroids, which contain a cyclopropane ring generated by the inclusion of carbon from the methyl at C-10 catalyzed by cycloartenol synthase enzymes [18,53]. The Cycloartanes (152-154) identified in the genus Cedrela are shown in Table 7.

Cycloartanes
Cycloartanes are triterpenoids and key intermediates in the biosynthesis of phytosteroids, which contain a cyclopropane ring generated by the inclusion of carbon from the methyl at C-10 catalyzed by cycloartenol synthase enzymes [18,53]. The Cycloartanes (152-154) identified in the genus Cedrela are shown in Table 7.

Steroids
Phytosterols are biosynthetically derived from cycloartenol and are characterized by the lack of methyl groups at C-4 and C-14 [54]. Plants have complex and diversified sterol compositions, which are structural components of biological membranes, and that should be a key element of many cellular processes [55]. The steroids (155-162) identified in the genus Cedrela are shown in Table 8. C. odorata L. Heartwood [21] β-sitosterol (158) C. odorata L.
Leaves [30] Steroids Phytosterols are biosynthetically derived from cycloartenol and are characterized by the lack of methyl groups at C-4 and C-14 [54]. Plants have complex and diversified sterol compositions, which are structural components of biological membranes, and that should be a key element of many cellular processes [55]. The steroids (155-162) identified in the genus Cedrela are shown in Table 8.
Heartwood [21] β-sitosterol (158) C. odorata L. Bark and sapwood essential oil [21] C. odorata L.  C. fissilis Vell. - - [27] Sitostenone (162) - Limonoids are a secondary metabolite class of highly oxygenated modified triterpenes. This compound is biosynthesized by the acetate-mevalonate pathway and is also known as a tetranorterpenoid because its biosynthesis occurs through oxidative processes of side-chain degradation, resulting in the loss of four carbon atoms and the formation of a furan ring [15,56,57].
The chemical structure formed after the previously mentioned oxidation processes is 4,4,8trimethyl-17-furanyl steroid, which is considered a precursor of limonoids [14,58]. All compounds of the limonoid class containing this basic structure are derived from different oxidation degrees and rearrangements that give rise to different skeletons [58]. The limonoids (163-215) identified in the genus Cedrela are shown in Table 9. Heartwood [62] Limonoids are a secondary metabolite class of highly oxygenated modified triterpenes. This compound is biosynthesized by the acetate-mevalonate pathway and is also known as a tetranorterpenoid because its biosynthesis occurs through oxidative processes of side-chain degradation, resulting in the loss of four carbon atoms and the formation of a furan ring [15,56,57].
The chemical structure formed after the previously mentioned oxidation processes is 4,4,8-trimethyl-17-furanyl steroid, which is considered a precursor of limonoids [14,58]. All compounds of the limonoid class containing this basic structure are derived from different oxidation degrees and rearrangements that give rise to different skeletons [58]. The limonoids (163-215) identified in the genus Cedrela are shown in Table 9.  Leaves [27] Kihadalactone A (168) C. odorata L. Leaves [45] 7α-11β-diacetoxydi hydronomilina (169) Leaves [63] 11β-acetoxyobacunil acetate (170) C. odorata L.    Limonoids are divided into ten classes, including fifteen types based on different seco-styles, carbon-chain styles, and ring types [16]. This classification was presented by Fang et al. [16], who sought to identify the class and type of limonoids isolated from the Cedrela species. Table 10 shows the analysis performed with 55 chemical structures of limonoids isolated from different Cedrela species found in this review, showing the different seco-styles and carbon frameworks of these limonoid types. As depicted in Table 10, mexicanolide (41.5%), gedunine (17.0%), and obacunol (13.2%) were the main limonoid types found. Thus, it was possible to identify that Cedrela limonoids are biosynthesized along only one route, giving rise to the ring-D lactone derivatives and then to the mexicanolide type, characteristic of Swietenioideae [10,23].
Da Silva et al. [10] report part of a biogenetic map for limonoids featuring all structural types found in Meliaceae. Route 1.1.2 shows the B,D-seco class, which is characteristic of Swietenioideae, as previously mentioned. This route is related to the most commonly found limonoid class in the genus Cedrela. As shown in Table 11, other classes were found; one can affirm that they are associated with the B,D-ring class as biosynthetic intermediaries. Since there is no mexicanolide type limonoid in the Toona genus, this may not be inserted in the Swietenioideae subfamily with Cedrela [10,12,13]. It must be emphasized that the chemical structure of Toona limonoids isolated until now present with all intact rings or ring-D intact and A,B-seco rings, which are characteristic of Melioideae subfamily and justify the insertion of Toona genus in this subfamily [10,23].

Antioxidant Activity
Solvent extracts of C. odorata stems were tested for free radical scavenging activity in a model reaction with stable 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) by Rashed [28], according to a standard protocol by Saha et al. [85]. The dichloromethane extract presented better activity than other solvent extracts tested (85.45% DPPH free radical scavenging effect).
Although some compounds (6, 120, and 121) were isolated from the most active extract, the oxidant potential was not tested for these compounds. Nevertheless, the authors carried out an investigation on the presence of phytochemicals in the solvent extracts of C. odorata stems as a reasoned justification for active extracts. Therefore, flavonoids, steroids, and triterpenes were detected, compounds with good antioxidant effects that could be due to the hydroxyl groups present in the compounds found and which were present in ample amounts in the extract.

Hsp90a Inhibitors and Anti-Cancer Activity
Compounds (155, 156, 125, 126, 168, 173, 176, 198, 204, 206, 211, 212, 213, and 215), isolated from C. odorata leaves, were assayed to evaluate the ability to inhibit Heat Shock Protein 90 (Hsp90) activity, adopting a multidisciplinary approach with Surface Plasmon Resonance (SPR) measurements and biochemical and cellular assays. Hsp90, considered a molecular chaperone, plays an essential role in many cellular processes, including the stabilization of a range of proteins necessary to the survival of many kinds of cancer [86]. As a result, the identification of an inhibitor of Hsp90 is the main target of the "development of more effective drugs for the treatment of various types of multidrug-resistant malignancies" [45].
In order to verify compounds with affinity for Hsp90, SPR was carried out which showed that some compounds (125, 168, 176 Comparing the thermodynamic (K D ) and kinetic constant (dissociation-k d and association-k a ) values for these three compounds, the authors suggest that they could interact with the protein from a different approach. Thus was suggested because compound 213 presented a low k d value, whereas compounds 211 and 215 presented better k a values and was confirmed when the limited proteolysis-mass spectrometry-based approach was performed, making it possible to lift and confirm the hypothesis that compounds 211 and 215 prevented the proteolytic digestion of Hsp90a at Lys564 and Lys614, which are two residues located in the protein C-terminal; C-terminal being the point of interaction of these compounds with Hsp90.
Possible biological effects for compounds 211 and 215 were evaluated and provided an understanding that the activity of the compounds was related to the Tetrahydrofuran ring at C-17, which is responsible for their more efficient pattern of hydrogen bonds and for some specific hydrophobic contacts with Glu477chainA.
Based on the possibility of compounds 211, 213, and 215 interacting with Hsp90, inhibiting its activity, the cytotoxic activity of these compounds was assessed against epithelial carcinoma cell lines (human HeLa) and breast carcinoma cell lines (MCF-7) by Microculture of Tetrazolium (MTT) proliferation assay. Results showed that for the two cell lines tested, compound 211 inhibited cell proliferation (IC 50 = 10.1 ± 0.2 µM in HeLa and 51.3 ± 0.3 µM in MCF-7 cells), in a concentration-dependent manner, whereas compounds 213 and 215 showed no significant results (IC 50 > 100 µM for two compounds in both cell lines).
Still considering the anti-cancer activity, in 2018, Wan et al. [49] investigated, through a number of bioassays, the action mechanism of the anti-cancer effect of compound 127, being known that this compound demonstrates oxidant potential, being able to interrupt the cell cycle of cancer cell lines MCF-7, NCI-H460, and A375-C5 [87]. Nonetheless, it is not known if compound 127, as well as other limonoids, could cause autophagy and other cellular responses in carcinoma cells.
Compound 127, isolated from C. odorata, inhibited cell growth in a time-dependent and concentration-dependent manner by induced cell death, which could have been due to apoptosis or autophagy. Flow cytometry results presented little or no apoptosis in the tested concentrations (8 µM, 16 µM, and 32 µM), showing that this is not the reason for the inhibition of cell proliferation.
Furthermore, it was noted that compound 127 induced the accumulation of excess reactive oxygen species (ROS), which can give rise to other molecular responses such as autophagy. This was observed as compound 127 increased autophagy marker levels early and provoked the conversion of Light Chain 3 (LC3) -I to LC3-II, which directly indicates autophagy. Adding these results to those observed in flow cytometry, the authors suggested that compound 127 induced autophagy.
With the purpose of evaluating the anti-cancer capacity of compound 127, Wan et al. [49] verified through western blot assay based on Lu et al. [88] the regulatory roles of compound 127 in ROS/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways and effects of these on the autophagy, migration, and invasion. N-acetyl-l-cysteine (NAC) was used as a ROS remover was able to suppress ROS production, and the role of compound 127 in MEK/ERK signaling. On the other hand, U0126 used as a MEK/ERK inhibitor did not inhibit ROS production, although a decrease in MEK/ERK activity was observed. Thus, it was possible to identify that compound 127 activated the MEK/ERK signaling, playing a crucial role.
The effect of compound 127 in vivo was also tested against MKN45 cell xenograft tumors and patient-derived xenograft (PDX) tumor models. This compound was able to inhibit tumor growth, where BALB/C nude mice did not present toxic syndromes, diminished activity, or death, and there were no dramatic changes in body weight with either tumor model. Moreover, and very importantly, the Ki67 expression was inhibited, which indicated that the tumor proliferation was inhibited.

Protein Tyrosine Phosphatase 1B Inhibition
The potential of compounds 136 and 137 isolated from C. odorata twigs and leaves [52] for the inhibition of protein tyrosine phosphatase 1B (PTP1B) was evaluated through a bioassay according to Zhang et al. [89]. These compounds (136 IC 50 = 13.09 µg/mL; 137 IC 50 = 3.93 µg/mL) presented significant PTP1B inhibition potential. PTP1B is an important therapeutic target of some metabolic disorders such as diabetes and obesity, and assays performed by Elchebly et al. [90] with PTP1B-deficient mice showed enhanced insulin sensitivity and resistance to diet-induced obesity.
Results of the bioassays with the extracts showed that dichloromethane root extracts were the most active, reducing the number of parasites in the infected mouse blood by 97.4%; 11 other extracts were significantly active at the higher concentration tested (lysis% ≥ 50), while nine others presented lysis in the 60% to 80% range. Assays were performed with extract concentrations of 4 mg/mL.
Triterpenes were the most active compounds. Tirucallane triterpenes (127-129), isolated from methanol stem extract, stood out for their high activity that could be justified by the presence of the hydroxyl group at C-3 and the cyclization of the side chain to a dihydroxy-tetrahydrofuran. Leite et al. [27] reported that compound 127 showed better activity than the positive control, demonstrating its potential to act as a substitute for gentian violet, which presents collateral effects; however, a toxicity assessment must be carried out. Moreover, C. fissilis proved to be efficient in the production of compounds that can be used to control Chagas disease.
Extracts of all parts tested of C. fissilis were inactive for both clones (IC 50 > 20 µg/mL), whereas C. odorata wood and C. salvadorensis leaf extracts were two of the most active against clones D6 and W2 (IC 50 < 20 µg/mL). However, compared to the other extracts tested, C. odorata showed higher activity. IC 50 values for these Cedrela species are presented in Table 11 [69].
An EtOH extract of C. odorata wood from Belize was more active than extracts of the same species from Costa Rica and Togo; Effective Concentrations (EC) of these extracts for W2 clone were, respectively, 1.10, 1.25, and 3.26 µg/mL.
Toluene extraction was also carried out, resulting in a cleaner extract and with a slightly higher content of compound 181 than EtOH extracts. In addition, these extracts were found to be active, with better efficacy against the W2 clone. EC values were: Togo, 2.77 µg/mL; Costa Rica, 0.70 µg/mL; and Belize, 0.65 µg/mL.
Previous phytochemical studies showed that limonoid contents in Meliaceae species present antimalarial activity, making it possible to suggest that the limonoid constituents in these extracts could be responsible for the activity. Thus, there was the recognition that compound 181 was present in C. odorata extract and was especially active, requiring further investigation.
Regarding compounds with antimalarial activity, none of the compounds showed better activity than compound 181. However, the study added knowledge to topics related to the structure-activity relationships for antimalarial activity of D-seco limonoids.
Based on assays with these structurally modified compounds, it proved possible to identify three systems in the chemical structure, which could be associated with the activity of compound 181: α,β-unsaturated ketone moiety in ring A, 7-acetate of ring B, and the furan ring.
Compounds 181d (IC 50 : D6 = 2610 ng/mL − W2 = 1280 ng/mL) and 181e (IC 50 : D6 = >10,000 ng/mL − W2 = >10,000 ng/mL) also showed some activity decrease in both cones. The authors affirmed that this was related to the group present at C-7 because when this group was a ketone group (compound 181e) it was observed to be inactive.
Finally, the majority of the compounds showed activity against chloroquine-resistant clones, with compound 181 having a lower IC 50 value of than chloroquine. Furthermore, the cytotoxicity of these compounds was evaluated using KB cells, as described previously by Likhitwitayawuid et al. [93], and an in vivo assay of compound 181. For the cytotoxicity assay, compounds 181 (2300 ng/mL), 181g (9400 ng/mL), and 181h (10,900 ng/mL) presented some cytotoxicity; however, less than drugs usually used to treat malaria, chloroquine (17,400 ng/mL), quinine (>20,000 ng/mL), mefloquine (3500 ng/mL), and artemisinin (>20,000 ng/mL), suggesting a possible new antimalarial. For the in vivo assay, where compound 181 was administered orally or subcutaneously to mice infected with Plasmodium berghei, during a four-day test, there was no inhibition of parasitemia. Nonetheless, according to the authors, the biological potential of compounds requires further study because of the focus on traditional remedies in Africa.
Considering the low in vivo activity present in the MacKinnon et al. [70] study, Omar et al. [71] mentioned possible reasons, for instance: "poor solubility and uptake of the drug due to its lipophilicity"; "first-pass metabolism of gedunin by cytochrome P450 enzymes of the small intestine, which reduce plasma levels of drugs; and hydrolysis of gedunin to the inactive and unstable metabolite, 7-deacetylgedunin" [71] (p. 135). Thus, Omar et al. [71] carried out compound co-precipitation with polyvinylpyrrolidone (PVP) for oral administration; compounds were tested alone and in binary treatment, where the compound was administered with dillapiol, a cytochrome P450 inhibitor. Another approach was that the semi-synthetic derivatives (compounds 181j, 181k, and 181l, Figure 3) had changes in the labile acetoxy group at the C-7 moiety because it was prone to hydrolysis and subsequent rearrangement. mentioned possible reasons, for instance: "poor solubility and uptake of the drug due to its lipophilicity"; "first-pass metabolism of gedunin by cytochrome P450 enzymes of the small intestine, which reduce plasma levels of drugs; and hydrolysis of gedunin to the inactive and unstable metabolite, 7-deacetylgedunin" [71] (p. 135). Thus, Omar et al. [71] carried out compound coprecipitation with polyvinylpyrrolidone (PVP) for oral administration; compounds were tested alone and in binary treatment, where the compound was administered with dillapiol, a cytochrome P450 inhibitor. Another approach was that the semi-synthetic derivatives (compounds 181j, 181k, and 181l, Figure 3) had changes in the labile acetoxy group at the C-7 moiety because it was prone to hydrolysis and subsequent rearrangement.
The mean blood concentration of compound 181, after 3 and 6 h, was found to be 6.2 µg/mL. A preliminary pharmacokinetic study was performed with Sprague-Dawley rats to identify the concentrations of compound 181. Poor absorption and rapid clearance from the blood were clearly observed; thus, a binary treatment was conducted, combining dillapiol with semi-synthetic derivatives.
Oral administration of compound 181 and dillapiol in CD-1 mice infected with P. berghei showed better parasite clearance (79.0% ± 5.3%), in which the increase was dose-dependent with compound 181 doses up to 50 mg·kg −1 ·day −1 , with dillapiol held constant at 25 mg·kg −1 ·day −1 . In addition, the mean blood concentration of compound 181 increased to 13.1 µg·mL −1 , which could be related to cytochrome P450 inhibition in the small intestine, although the dillapiol penetrant properties may play a role. Regarding the toxicity of the binary treatment, preliminary studies show that there were no significant differences in total body or organ weight, gross anatomy, or three liver enzyme levels relative to the control group; nevertheless, chronic toxicity studies need to be carried out.
Among the semi-synthetic derivatives, only compounds 181j and 181l showed antiplasmodial activity, although it was lower than the activity of compound 181. The in vivo bioassay was accomplished with compound 181j, due to lower molecular weight, and was relatively active. This compound showed better activity than compound 181 when given alone and in binary treatment, with a clearance of 67.5% ± 1.3% (50 mg·kg −1 ·day −1 ) and 80.7% ± 5.1% (50 mg·kg −1 ·day −1 of compound 181j and 25 mg·kg −1 ·day −1 of dillapiol), respectively. When compared to a conventional drug used in antimalarial therapy (quinine = 60 ± 10%-10 mg·kg −1 ·day −1 ), these compounds showed promising results, which could contribute to the development of effective phytomedicines based on traditionally used antimalarial plants.
This activity was also tested by Omar et al. [72] for compound 181, isolated from C. odorata wood, against the rice weevil, Sitophilus oryzae (L.) using a method developed by Xie et al. [95]. Four concentrations (0%, 0.05%, 0.25%, and 0.50% w/w) were tested, however the authors reported that the compound was active at 0.50% (w/w), with a consumption of diet value of 31.2% ± 6.3% control ± SEM.

Insecticidal Activity
Triterpenes (121 and 122) and a limonoid (207) were isolated from C. fissilis roots. Insecticidal activity was tested against Atta sexdens rubropilosa by Leite et al. [42], and this survey was a continuation of the tests of Bueno et al. [96] where C. fissilis root extracts showed activity on leaf-cutting workers, A. sexdens rubropilosa.
Compounds (100 µg/mL) tested were administered in an artificial diet (0.4-0.5 g per dish), according to Bueno et al. [97] and offered daily. A control diet was used with the addition of compounds or without. The ants were followed for 25 days, and the number of dead ants was registered daily.
Among the compounds tested, triterpenes and limonoid of C. fissilis showed significant activity when compared to the other compounds and control. The authors reported that activity could be related to triterpenes and these compounds tested are promising in controlling leaf-cutting ants.
Limonoids (178, 180, 181, 182, 184, and 185) from C. fissilis roots and leaves showed insecticidal activity against A. sexdensrubropilosa ants and was also tested by Ambrozin et al. [67] using the same previously mentioned methodology. The limonoids tested and the control showed the same survival medium time; however, compound 184 presented a significant difference to the control according to the log-rank test (p < 0.05). All these limonoids are of the gedunin type, and the authors affirmed that this type does not seem to be highly active against these ants. The authors further suggest that the toxicity of C. fissilis extract could be associated with the synergism between limonoids and other compounds in the extracts.
The insecticidal activity was also tested by Jimenez et al. [59]; compound 164 present in C. salvadorensis had an effect against Ostrinianubilalis (the European corn borer). This compound was administered in an artificial diet with a concentration of 5 or 50 ppm for neonate larvae, after which thirty of them were transferred to separate vials with corresponding diet cubes. On the 20th day, the following were observed: weight gains, mortality, time to pupation and adulthood, the weight of pupae and adults, the mortality of larvae, and adult deformities.
Compound 164 inhibited growth at the larval stage; on day 20, this compound clearly showed a reduction in larval growth, moderate larval mortalities (<37%), and delays in time to pupation were observed in 5 ppm cedrelanolide-treated males, 50 ppm treated females when compared to the humilinolides from Swietenia humilis. Regarding survival to the adult stage, as compared to the pupal stage, compound 164 presented no further reductions. The authors affirmed that, similar to other limonoids, the reduction in insect growth from compound 164 and other limonoids evaluated can be associated with a combination of antifeedant action and post-digestive toxicity.
The insect growth regulatory activity of an epimeric mixture of compounds 164, 177, and 178, and 181 from C. dugessi and C. salvadorensis heartwood was evaluated against Spodoptera frugiperda by Céspedes et al. [62].
Previously mentioned compounds and an anomeric acetate mixture (compounds 177a and 178a [75], Figure 4 shows these derivatives' chemical structure) were dissolved in ethanol and administered at different concentrations (ranging from 5 to 50 ppm) in an artificial diet prepared according to Mihm [98]. Only one neonate first instar larvae was placed in contact with the diet, for seven days, with different concentrations and compounds, inclusively with a positive control (toosendanin). After seven days, surviving larvae were transferred to separate vials containing a fresh stock diet for 21 days, and weight gains, mortality, and other lifecycle measurements were evaluated. administered at different concentrations (ranging from 5 to 50 ppm) in an artificial diet prepared according to Mihm [98]. Only one neonate first instar larvae was placed in contact with the diet, for seven days, with different concentrations and compounds, inclusively with a positive control (toosendanin). After seven days, surviving larvae were transferred to separate vials containing a fresh stock diet for 21 days, and weight gains, mortality, and other lifecycle measurements were evaluated. At the larval stage, all tested compounds at 52 ppm, except cedrelanolide, inhibited growth. At lower concentrations, only compounds 177a and 178a showed higher insecticidal activity, with 83.3% larval mortality at 10 ppm. After 21 days, it was observed that compound 181 showed better results than the positive control, toosendanin, at 5 ppm.
All compounds reduced the percentage of larvae that reached the pupation stage, compared to the control. On the other hand, none of them significantly reduced pupation time. Nonetheless, compounds 177a and 178a showed a drastic reduction in adult emergence percentages at all concentrations tested. At the larval stage, all tested compounds at 52 ppm, except cedrelanolide, inhibited growth. At lower concentrations, only compounds 177a and 178a showed higher insecticidal activity, with 83.3% larval mortality at 10 ppm. After 21 days, it was observed that compound 181 showed better results than the positive control, toosendanin, at 5 ppm.
All compounds reduced the percentage of larvae that reached the pupation stage, compared to the control. On the other hand, none of them significantly reduced pupation time. Nonetheless, compounds 177a and 178a showed a drastic reduction in adult emergence percentages at all concentrations tested.
The action mechanism of limonoids is not clear; however, it could be related to physiological effects, with the oxygenated function at C-23 being necessary for the activity of compounds 177, 178, 177a, 178a, and 181; the authors suggest, based on Champagne et al. [99] and Isman et al. [100], that there could be a combination between antifeedant action and/or post-digestive toxicity, as found for other limonoids. Moreover, although the compounds tested showed activity compared to the positive control, except 164, suggesting additional production, none of them demonstrated the outstanding activity of azadirachtin [59].

Plant Growth Inhibitory Activity
Céspedes et al. [60,66] carried out assays to investigate the phytotoxic properties of compounds from different Cedrela species, on germination, root, and shoot development, and the respiration of seeds of two monocots (Lolium multiflorum and Triticum vulgare) and two dicots (Physalis ixocarpa and Trifolium alexandrinum). With similar methodologies, these studies differed mainly in the compound tested, bioactivity-guided isolation [66], and verification of possible effects on the photosynthesis system presented by Céspedes et al. [60].
Céspedes et al. [66] accomplished bioactivity-guided isolation, in which heartwood parts of C. ugesii were extracted with CH 2 Cl 2 against two monocots seeds. The authors were able to verify the most active fraction (F3-L. multiflorum = IC 50 24.0 µg/mL; T. vulgare = IC 50 23.0 µg/mL) and to arrive at the compound responsible for the activity, which was an epimeric mixture of compounds 177 and 178.
The epimeric mixture of compounds 177 and 178 and semi-synthetic acetylated derivatives were reported in Céspedes et al. [75] (compounds 177a and 178a, Figure 4), and were assessed for phytotoxic effects on monocot and dicot seed germination. Both compounds and mixtures showed similar inhibition profiles; however, monocot seeds (T. vulgare and L. mutlifloreum) were most sensitive at 50 µM and 500 µM, respectively, for photogedunin epimeric acetates, presenting with an almost 100% inhibition. Comparing concentrations that inhibit 50% of seed germination (GI 50 ), the low values for photogedunin acetate mixtures showed that they were better inhibitors. Moreover, this comparison allowed speculation that the low activity of the mixture of compounds 177 and 178 could be related to the hydrophilicity of the free C-23, where the hydroxyl group makes it difficult for photogedunin to reach the target.
As for growth inhibition, a dose-dependent pattern was shown, which stimulated or inhibited germination for both seeds. In the case of monocot seeds, there were inhibitory effects of the photogedunin mixture on root and coleoptile development, whereas, in dicot seeds, the promotion of root and hypocotyl development was observed. Nonetheless, according to the authors, the root developed to a greater extent than coleoptile or hypocotyl development (the lowest median infective dose (ID 50 ) values). Higher ID 50 values showed that dicot seed growth was more sensitive to photogedunin acetate mixture.
With respect to dry weight and respiration, these decrease with increases in photogedunin mixture concentration; however, the L. multiflorum respiration rate was one exception, as it was more sensitive to inhibition while T. alexandrinum showed higher resistance. This suggests that the photogedunin mixture acted as an uncoupler to phosphorylation at low concentrations, but at higher concentrations it either inhibited energy transduction or the respiration redox enzymes. It was shown that the photogedunin epimeric mixture was more selective and potent towards monocots than dicots.
The authors presented graphics comparing the inhibition of the mixtures tested, showing that the acetylated derivative was ten times larger than the photogedunin mixture, which could be active in vivo, and also suggests that compounds and mixtures can have more than one target of interference because germination inhibition occurs at lower concentrations than respiration.
On the other hand, as a complement to the investigations of Lotina-Hennsen et al. [101] on biologically active limonoids with potential herbicidal properties, Céspedes et al. [60] carried out assays to evaluate phytotoxic properties of compound 164 from the heartwood of C. salvadorensis against the same species of monocot and dicot seeds presented in Céspedes et al. [66].
In general, if compared to the Céspedes et al. [66] assays with 177 and 178, 164 showed a better inhibition profile. Concentration-dependent, 164 inhibited respiration, germination, shoot and root elongation, and dry weight of the tested species, especially monocot species. It is worth pointing out that L. multiflorum was shown to be the most susceptible to this compound, with GI 50 120.6 µM, and causing 100% germination inhibition at 300 µM.
In the case of growth inhibition, no significant influence on T. vulgare growth (100% inhibited at 500 µM) was observed and a lower inhibition effect on L. multiflorum (300 µM), indicating that the mechanism of action of compound 164 could be different for germination and respiration. The authors affirmed that, based on a pre-emergency assay, oxygenated functions of the molecule played an inhibition role in germination due to lipophilicity or the hydrophilicity of the oxygenated function of compound 164 (at physiological pH), making it difficult for compound 164 to reach the target site.
Regarding interference in photosynthesis, the authors evaluated the effects of compounds on different photosynthetic reactions. Based on the obtained results and compared to other group studies, Céspedes et al. [60] assert that compound 164 inhibits the proton chain (IC 50 = 34.9 µM) and further suggests that it can inhibit all the electron transport chain of water to methyl viologen at the phosphorylation of photosynthesis of water to methyl viologen (inhibited totally at 60 µM; IC 50 = 29.5 µM). The authors associated electron transport inhibition to the oxygenated functions of compound 164, which significantly increased the inhibition potency that was similar to that of the Hill's reaction inhibiting effect of some commercial herbicides.

Conclusions
This article presents 215 chemical compounds, including chemical structures, found in quali or quantitative phytochemical studies on Cedrela species from early 1960 to 2020. It was possible to observe that of 18 species, the most commonly studied species was C. odorata L.; however, other species such as C. fissilis Vell., C. salvadorensis Standl., C. dugesii S. Watson, C. montana Moritz ex Turcz., C. angustifolia DC. and C. oaxacensis C.DC. and Rose were also studied. It can also be noted that there are few studies about it; thus, these species and species that still remain unresearched should be considered in further phytochemical and pharmacological studies, which may be a promising direction in the search for new compounds with pharmacological properties.
To date, as shown below in Scheme 1, four aliphatic hydrocarbons, three phenolic compounds, and 208 terpenes have been identified or isolated. For the Terpene class, which is the biggest class, 25 monoterpenes, 86 sesquiterpenes, and 97 triterpenoids have been found.
that there are few studies about it; thus, these species and species that still remain unresearched should be considered in further phytochemical and pharmacological studies, which may be a promising direction in the search for new compounds with pharmacological properties.
To date, as shown below in Scheme 1, four aliphatic hydrocarbons, three phenolic compounds, and 208 terpenes have been identified or isolated. For the Terpene class, which is the biggest class, 25 monoterpenes, 86 sesquiterpenes, and 97 triterpenoids have been found.

Scheme 1. Compound classes isolated or indentified from Cedrela species.
With respect to triterpenoids identified in the genus Cedrela, these belong to triterpenes, cycloartanes, steroids, and limonoids, and 33, three, eight, and 53 of these classes were found, respectively, as pictured in Scheme 2, below. With respect to triterpenoids identified in the genus Cedrela, these belong to triterpenes, cycloartanes, steroids, and limonoids, and 33, three, eight, and 53 of these classes were found, respectively, as pictured in Scheme 2, below. As limonoids are a characteristic class of the Meliaceae family, these compounds found in Cedrela species were classified based on Fang et al. [16]. Scheme 3 shows the classes and types of limonoids found in the genus Cedrela. As depicted, B,D-seco was the main class found, with 25 limonoids, most of them mexicanolide type (22). Other limonoid types were also found but in much smaller quantities, such as gedunine (9), obacul (7), neotecleanin (5), evodulone (1), delevoyin (1), havenensin (4), and andirobin (3). One degraded limonoid was also found; nonetheless, Fang et al. [16] did not relate this limonoid type to any class. These authors suggest that this type could be the origin of degradation of intact limonoids since it possesses a furan ring and the C and D ring portions of the original limonoids.
The presence of mexicanolide, obacunol, and gedunin types indicates that Cedrela limonoids are ring-D lactone derivatives and of the mexicanolide type, which is characteristic of the Swietenioideae subfamily [10,23]. As limonoids are a characteristic class of the Meliaceae family, these compounds found in Cedrela species were classified based on Fang et al. [16]. Scheme 3 shows the classes and types of limonoids found in the genus Cedrela. As depicted, B,D-seco was the main class found, with 25 limonoids, most of them mexicanolide type (22). Other limonoid types were also found but in much smaller quantities, such as gedunine (9), obacul (7), neotecleanin (5), evodulone (1), delevoyin (1), havenensin (4), and andirobin (3). One degraded limonoid was also found; nonetheless, Fang et al. [16] did not relate this limonoid type to any class. These authors suggest that this type could be the origin of degradation of intact limonoids since it possesses a furan ring and the C and D ring portions of the original limonoids.
The presence of mexicanolide, obacunol, and gedunin types indicates that Cedrela limonoids are ring-D lactone derivatives and of the mexicanolide type, which is characteristic of the Swietenioideae subfamily [10,23].
Biological activities were also compiled in this article. As expected, due to the known insecticidal activity of limonoids, more articles were found reporting this activity, antifeedant, and growth inhibition of insects. However, of the limonoids tested, none demonstrated better activity than or compared to azadirachtin.
In the case of activities related to human health, promising results were achieved in the antitripanocidal activity of compound 127 and in the antimalarial activity of compound 181. Although these results are interesting, more studies must be conducted in order to describe the real efficacy, besides continuing the pharmacological studies. These can be interpreted because of the concentration of these compounds in the botanical parts or in the species, therefore phytochemical studies that use validated analytical methods, or in vitro culturing, aimed at obtaining these secondary metabolites in a sustainable way are required.
of them mexicanolide type (22). Other limonoid types were also found but in much smaller quantities, such as gedunine (9), obacul (7), neotecleanin (5), evodulone (1), delevoyin (1), havenensin (4), and andirobin (3). One degraded limonoid was also found; nonetheless, Fang et al. [16] did not relate this limonoid type to any class. These authors suggest that this type could be the origin of degradation of intact limonoids since it possesses a furan ring and the C and D ring portions of the original limonoids.
The presence of mexicanolide, obacunol, and gedunin types indicates that Cedrela limonoids are ring-D lactone derivatives and of the mexicanolide type, which is characteristic of the Swietenioideae subfamily [10,23].

Scheme 3. Class and types of limonoids found in the genus Cedrela.
Biological activities were also compiled in this article. As expected, due to the known insecticidal activity of limonoids, more articles were found reporting this activity, antifeedant, and growth inhibition of insects. However, of the limonoids tested, none demonstrated better activity than or compared to azadirachtin.
In the case of activities related to human health, promising results were achieved in the antitripanocidal activity of compound 127 and in the antimalarial activity of compound 181. Although these results are interesting, more studies must be conducted in order to describe the real efficacy, besides continuing the pharmacological studies. These can be interpreted because of the concentration of these compounds in the botanical parts or in the species, therefore phytochemical Scheme 3. Class and types of limonoids found in the genus Cedrela.
Studies using analytical methods could also help to understand if Cedrela species are sources of substances that have or have not had their activities reported by the articles mentioned here, or that have already been isolated from other species and have been subject to pharmacological and toxicological studies.