Essential Oils of Duguetia Species A. St. Hill (Annonaceae): Chemical Diversity and Pharmacological Potential

Duguetia A. St. Hill (Annonaceae) is recognized as one of the major genera with approximately 100 species, 67 of which are found in Brazil (29 of those are endemic). They are arboreal species with edible fruits known as “pindaíba”, “pindaíva” “pinha”, and “envira” in Brazil. Many Duguetia species, in particular, have been used in traditional medicine to treat renal colic, stomachache, rheumatism, cough, toothache, muscle pain, fever, gastrointestinal pain, and breathing difficulties. In this study, we reviewed the chemical constituents and pharmacological properties of essential oils (EOs) from Duguetia species. A total of 12 species were found, along with their EO chemical constituents and bioactivities. Bicyclogermacrene, humulene epoxide II, spathulenol, germacrene D, caryophyllene oxide, viridiflorene, α-pinene, β-caryophyllene, and β-pinene were the main chemical constituents reported. The pharmacological effects of Duguetia species EOs included anti-inflammatory, antinociceptive, antibacterial, antifungal, antioxidant, anti-trypanosoma, cytotoxic and antitumor properties. This information adds to our understanding of the potential of the EOs of Duguetia species.

Duguetia A. St. Hill., along with Guatteria and Annona, is one of the largest genera in the Annonaceae family. This genus is found throughout the neotropics, including South America (from Nicaragua to Brazil) and the African Atlantic coast. Its trees or shrubs have flowers in the upper part of the trunk or long branches close to the ground from the trunk's base. Leaves are adistichous with a midrib impressed on the upper side; flowers range from white to yellow. Fruits are pseudosyncarpous (carpels strongly coherent, but not or only partly connate), composed of 5 to over 500 carpels, with seeds (dark brown, obovoid, smooth, not arillate) embedded in a fleshy pulp [4,5].
Many species in the Duguetia genus are widely used to treat diseases such as renal colic, stomachache, rheumatism, cough, toothache, muscle pain, fever, gastrointestinal pain, and breathing difficulties [6,[10][11][12][13][14][15][16][17]. The species used in traditional medicine are summarized in Table 1. On the other hand, while many ethnopharmacological uses for Duguetia species have been reported, only a few studies involving the chemical and therapeutic properties of this genus' plants have been found.  [14] According to Perez and Cassels [6], the chemical composition of this genus includes secondary metabolites, particularly alkaloids, found in various parts of Duguetia species. Furthermore, numerous studies have revealed the presence of steroids, flavonoids, aromatic compounds and terpenes. However, knowledge of the chemical composition and biological activities of this genus' essential oils (EOs) is limited.
To guide future research, we discuss the chemical constituents and pharmacological properties of EOs of Duguetia species in this review. Google Scholar, PubMed, Science Direct, SciFinder, Scopus and Web of Science were used for searches. The following keywords were used: "Annonaceae"; Duguetia"; "essential oil"; "volatile constituents"; "volatile compounds"; and "biological activity". A total of 82 articles were identified and reviewed, with those that included chemical constituents and biological activities of EOs being chosen and discussed.
Valter et al. [29] identified bicyclogermacrene as the major constituent in the EOs from the leaves of D. furfuracea, whereas it was only a minor component in EOs from the stem of D. furfuracea [17,26,28], D. pycnastera and D. trunciflora [24], and in EOs from the leaves of D. furfuracea [27,29], D. pycnastera and D. trunciflora [24].
Germacrene D has been identified as a major component in EOs extracted from the leaves of D. gardneriana and D. moricandiana [30], as well as the bark and stem of D. flagellaris [24,25]. However, it was discovered as a minor constituent in the EOs from the leaves of D. furfuracea [29], D. gardneriana [31] and D. pycnastera [24], as well as the EOs from the stem of D. pycnastera [24] and aerial parts of D. quitarensis [36].
In D. trunciflora, α-pinene was found to be the most abundant constituent in stem and leaf EO samples [24]. On the other hand, it was not considered the major compound in EOs from the leaves of D. gardneriana [30], D. moricandiana [30] and D. riparia [24]. Although α-pinene was found in the EOs extracted from the flowers of D. asterotricha [23] and the stem of D. riparia [24], it was in a lower proportion. The 2,4,5-trimethoxystyrene identified in D. furfuracea [26] was described as the main component in the EO from the stem; however, it was present in lower concentrations in the EOs from the leaves of D. lanceolata [34] and the stem of D. furfuracea [17,27,28].
Allo-aromadendrene is the main constituent in the EO from the leaves of D. gabriuscula, as reported by Siqueira et al. [32]; however, it was found as a minor constituent in the EO samples from the stem and leaves of D. pycnastera [24]. Sabinene is the component with the highest percentage in EO extracted from D. furfuracea leaves [29]. β-Elemene is the most prevalent constituent in EO samples from bark and branches of D. lanceolata [33,35], but it is considered a minor constituent in the EO from the bark of D. flagellaris [24].
β-Phellandrene was found in high concentrations in the EOs extracted from the leaves of D. furfuracea [29] and the bark of D. trunciflora [24]. Similarly, α-gurjunene was identified as a major constituent in EO extracted from the stem of D. furfuracea [27]. This component has been found in lower concentrations in other studies of EO samples from the same species' stem [17,28].
α-Asarone was found as a major constituent in EO from the stem of D. furfuracea [17], whereas no similar results were found in other studies of stem EO samples from the same species [26,27]. According to Maia et al. [24], α-eudesmol was the main component in EO samples from the leaves and stem of D. eximia, whereas β-bisabolene was the main compound identified in the EOs from the leaves of D. gardneriana [31] and D. lanceolata [34]. Terpinen-4-ol, limonene, 4-heptanol and (E)-asarone were found in the highest concentrations in the EOs extracted from D. furfuracea leaves [29], D. asterotricha flowers [23], D. quitarensis aerial parts [36] and D. furfuracea stem [28], respectively.
Caryophyllene oxide was found in the EOs of D. flagellaris bark [24], D. furfuracea leaves [29], D. lanceolata bark and branches [33,35], and D. riparia leaves and stem [24]. Humulene epoxide II was found in the leaves and stem EOs of D. flagellaris and D. trunciflora [24]. This component can also be found in EOs derived from the bark of D. flagellaris [24] and D. lanceolata [33].
Cyperene was identified as a chemical component in EOs extracted from the stem of D. flagellaris [25] and D. furfuracea [17,27,28], and D. flagellaris bark [24]. Whereas Almeida et al. [30] discovered β-pinene in the EOs extracted from the leaves of D. gardneriana and D. moricandiana. This last constituent can also be found in EOs derived of D. trunciflora leaves and stem [24].
β-Selinene was detected in EOs extracted from the bark and branches of D. lanceolata [33,35]. Elemol was identified in EOs extracted from the leaves and stem of D. pycnastera [24]. Globulol was discovered in EOs extracted from the leaves and stem of D. trunciflora [24]. Viridiflorol was found in EOs extracted from the leaves of D. furfuracea [27] and D. gabriuscula [29].

Pharmacological Properties of Duguetia Species EO
Natural products' medicinal capabilities have historically been recognized in the most diverse cultures, allowing for widespread use in traditional folk medicine [41]. These findings have piqued the interest of the scientific community, which has been looking for novel drugs in medicinal plants for decades. As a result, new molecules with biological activities are being discovered, investigated, and converted for clinical use at an increasing rate [42].
In this study, we discovered that the most commonly reported actions of Duguetia species EOs are anti-inflammatory, antinociceptive, antimicrobial, antioxidant and cytotoxic activities. The pharmacological properties of Duguetia species EOs are summarizes in Table 3.

Anti-Inflammatory Activity
In the carrageenan-induced edema assay in the paws of Wistar rats, the anti-inflammatory activity of D. lanceolata bark EO was demonstrated [43]. The edema volume was significantly reduced when tested at doses of 50, 100 and 200 mg/kg, corresponding to reductions of 20.83%, 36.46% and 48.96%, respectively. Following that, D. lanceolata branch EO was tested in carrageenan-induced paw edema and pleurisy in rats as well as in mouse models of acute ear inflammation caused by croton oil and arachidonic acid [35]. In this case, EO (200 mg/kg), which contains the sesquiterpenes β-elemene (8.3%), caryophyllene oxide (7.7%) and β-eudesmol (7.2%) as main components, reduced paw edema by 44.1% while also significantly reducing carrageenan-induced exudate volume (50%) and the number of leukocytes (32.2%) in the pleurisy of the animals. In a dose-dependent manner, EO also significantly reduced the ear edema induced by arachidonic acid and croton oil.

Antinociceptive Activity
The antinociceptive properties of EO derived from D. lanceolate and D. furfuracea have been studied. Sousa et al. [44] demonstrated that D. lanceolata bark EO was effective in the acetic-acid-induced abdominal-contraction assay and in the reduction in time of paw licking induced by formalin, attributing the positive results to the probable action of the EO components on the central and peripheral nervous systems. In the acetic-acid-induced writhing test, an effective dose of 50% (ED 50 ) of 21.79 mg/kg was found, with a significant antinociceptive effect ranging from the dose of 10 mg/kg to total inhibition of writhing at 200 mg/kg. Paw-licking time was also reduced in a dose-dependent manner, with an ED 50 of 5.27 mg/kg in the first phase (neurogenic phase) and 1.43 mg/kg in the second phase (inflammatory phase) [43].
D. lanceolata branch EO was also evaluated. After administration of EO at 100 and 200 mg/kg, there was a significant inhibition of acetic-acid-induced abdominal contractions. EO reduced paw-licking time in the neurogenic and inflammatory phases at doses of 50, 100 and 200 mg/kg. After 60 and 90 min of treatment with D. lanceolata EO, the animals' response time in the hot-plate assay significantly increased, with the antinociceptive capacity partially maintained even in the presence of an opioid antagonist. Finally, in the tail-immersion assay, treatment allowed for a significant increase in the duration of pain latency [35].
The antinociceptive effects of EO extracted from the stem of D. furfuracea were also studied at doses of 10 and 30 mg/kg [28]. Paw-licking time was significantly reduced in the neurogenic and inflammatory phases after treatment with both doses, with the highest dose inhibiting formalin-induced nociception by 45.62% and 34.17%, respectively. The opioid antagonist naloxone (5 mg/kg) quickly reversed this effect in both the primary and secondary phases. In the LPS-induced thermal-hyperalgesia model, EO administration increased reaction time, allowing for a longer-lasting antinociceptive response (greater than 6 h after LPS-induced nociception) than morphine administration (7.5 mg/kg). Its antinociceptive activity may be mediated by adenosinergic and opioidergic pathways, but the rota-rod test revealed no changes in mouse motor coordination after treatments with 3, 10 and 30 mg/kg of the EO [28].
Similarly, Saldanha et al. [17] demonstrated the antinociceptive capacity of the phenylpropanoid-enriched fraction of D. furfuracea EO. For doses of 30 mg/kg, formalininduced nociception was inhibited in both phases, with inhibition indices of 44.06% in paw-licking time in the first phase and 39.84% in the second. The reaction time to the LPS-induced thermal-hyperalgesia model increased. These effects were mediated by adenosinergic-and opioidergic-receptor activation, but without causing losses in the coordinative motor capacity of the tested animals [17].

Antibacterial and Antifungal Activities
The antimicrobial properties of EO extracted from the leaves of D. gardneriana and D. moricandiana were tested using the standard gel-diffusion method against a panel of fungal and bacterial strains. The results showed that the EO had a low inhibitory capacity against the tested microorganisms. Total EO of D. gardneriana (100% concentration), with the main components germacrene D (28.1%), viridiflorene (24.0%) and β-pinene (12.6%), demonstrated action against Staphylococcus aureus and Candida guilliermondii. The total EO of D. moricandiana, which contained the main constituents germacrene D (44.3%), αpinene (13.0%), and viridiflorene (9.3%), was only effective against Staphylococcus aureus and Candida albicans. The average diameter of the halos was 12 mm in all cases [30].
The chemical composition and biological activities of EO extracted from the bark of D. lanceolata were found to be dependent on the extraction time [33]. Its main constituents were β-elemene (12.7 and 14.9%), caryophyllene oxide (12.4 and 10.7%) and β-selinene (8.4 and 10.4%). The use of EO in concentrations of 5, 10 and 25 mg inhibited the growth zone of Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli and Candida albicans. The measurement of minimum inhibitory concentrations (MIC), which ranged from 20 to 125 µg/mL among microorganisms, confirmed this finding.

Trypanocidal Activity
The trypanocidal activity of EO derived from the aerial parts of D. quitarensis Benth against T. cruzi trypomastigote and amastigote forms has been reported. The inhibitory concentration of 50% (IC 50 ) for the EO was calculated to be 0.26 ± 0.06 µg/mL, which is approximately four times lower than the IC 50 for benznidazole. However, when compared to the IC 50 of EO in L929 cells, the selectivity index was found to be low (2.1 fold) [36].

Antioxidant Activity
Oxidative damage has been linked to the development and maintenance of inflammation, as well as the progression of many diseases. As a result, the antioxidant capacity of plants is being extensively researched. Sousa et al. [35] discovered antioxidant activity in D. lanceolata branch EO. The EO concentration required to scavenge 50% (effective concentration of 50%: EC 50 ) of DPPH (2,2-diphenyl-1-picrylhydrazyl) free radicals was 159.4 ± 1.2 µg/mL, which was lower than the Fe 3+ reducing power (187.8 ± 0.6 µg/ mL). The β-carotene/linoleic-acid bleaching assay also demonstrated this EO's ability to inhibit lipid peroxidation by 41.5 ± 2.4%.

Cytotoxic and Antitumor Activity
Cytotoxicity studies are an important part of the drug-development process because they quickly provide vital information that serves as the initial platform in the search for new therapies for diseases such as cancer [45,46]. Despite being common among Annonaceae species, few studies have looked into the cytotoxic capacity of Duguetia species EO or their main components [47].
Finally, Sousa et al. [35] evaluated the acute toxicity of D. lanceolata branch EO in Swiss albino mice. After oral administration of up to 3 g/kg of EO, the 50% lethal dose was calculated and determined to be 2.9 g/kg for 48 h. This assessment enabled the safe estimation of pharmacological doses for future experiments.

Other Activities
Ribeiro et al. [34] demonstrated the antiaflatoxigenic and insecticidal properties of EO extracted of D. lanceolata leaves. The EO, which is primarily composed of βbisabolene (56.2%) and 2,4,5-trimethoxystyrene (19.1%), inhibited radial growth of Aspergillus flavus CCT7638 (Ascomycota) and the production of aflatoxin B1 from this isolate in a concentration-dependent manner.
Finally, the insecticidal activity was demonstrated using a residual-contact bioassay, which revealed a promising lethal effect on the adult forms of Sitophilus zeamais and Zabrotes subfasciatus (LC 50 = 457 mg/kg and 442 mg/kg, respectively). The EO also significantly reduced the number of individuals emerging from the treated samples (EC 50 = 480 mg/kg in adult S. zeamais; EC 50 = 119 mg/kg in F1 progeny Z. subfasciatus), as well as the number of Z. subfasciatus eggs per treated sample (EC 50 = 118 mg/kg) [34].

Conclusions
In recent years, studies on the genus Duguetia have focused on alkaloid constituents, resulting in few studies on EOs. As a result, this study discussed the chemical composition and pharmacological activities of the EOs of Duguetia species, demonstrating that this genus is a promising source of biologically active compounds. In this study, we discovered 56 chemical constituents found in 37 EOs of Duguetia species. The majority of the reported components are terpenes, specifically, monoterpenes, hydrocarbon and oxygenated sesquiterpenes. Bicyclogermacrene, humulene epoxide II, spathulenol, germacrene D, caryophyllene oxide, viridiflorene, α-pinene, β-caryophyllene and β-pinene are among these. The EOs of Duguetia species have been shown to have anti-inflammatory, antinociceptive, antibacterial, antifungal, antioxidant, anti-trypanosoma, cytotoxic, antitumor, antiaflatoxigenic and insecticidal properties. Figure 2 summarizes these findings. Further research into the chemical composition and pharmacological properties of the EOs of Duguetia species should be carried out in other species in order to assess their promising potential. In terms of future perspectives, mechanisms of action and toxicology studies should also be carried out in order to conduct clinical trials with these EOs.
quiterpenes. Bicyclogermacrene, humulene epoxide II, spathulenol, germacrene D, caryophyllene oxide, viridiflorene, α-pinene, β-caryophyllene and β-pinene are among these. The EOs of Duguetia species have been shown to have anti-inflammatory, antinociceptive, antibacterial, antifungal, antioxidant, anti-trypanosoma, cytotoxic, antitumor, antiaflatoxigenic and insecticidal properties. Figure 2 summarizes these findings. Further research into the chemical composition and pharmacological properties of the EOs of Duguetia species should be carried out in other species in order to assess their promising potential. In terms of future perspectives, mechanisms of action and toxicology studies should also be carried out in order to conduct clinical trials with these EOs.