The use of natural products as therapeutic agents has become increasingly popular. The World Health Organization estimates that 80% of the world’s developing countries used locally the medicinal plants in primary healthcare, because they are easily accessible and less expensive [1] . The genus Uvaria, family Annonaceae, comprises over 100 species distributed in the tropical regions of Asia, New Guinea, New Caledonia, Oceania, Africa and Madagascar. It is mainly composed of shrubs, lianas or sarmentose bushes, most often with unduly stellate hairs [2] . Several species have been reputed to possess medicinal properties and are reported to be used in the treatment of urinary disorders, fevers, jaundice, rheumatic affections, skin diseases, malaria, stomach disorders, dysentery, infections, especially those related to sexually transmitted diseases, tumours and mental illness [3] [4] . From a chemical viewpoint, studies carried out on this genus mainly reported the presence of alkaloids, flavonoids, chalcones, polyoxygenated cyclohexenes, xanthenes and terpenoids [3] [4] [5] . This chemodiversity is endowed with varied and significant pharmacological traits, including antimalarial, cytotoxic, antifungal, α-glucosidase inhibitory, antitubercular, antitrypanosomal and antileishmanial compounds [3] [4] . In our ingoing to search new bioactive metabolites from Ivorian medicinal plants [6] [7] [8] , we investigated Uvaria tortilis, a lianescent species with alternate simple leaves endemic to the Côte d’Ivoire. This species grows only in the undergrowth of the tropical forests and savannahs where it is used to treat amenorrhea and as uterotonic [9] [10] . Previous phytochemical studies realized on the essential oils of its stem barks revealed the presence of γ-terpinene, β-caryophyllene and germacrene D as major components [2] . The present study reports the results of a phytochemical investigation of the stem barks of U. tortilis which resulted in the isolation and identification of one new C-benzyl (1) together with six (2 - 7) known compounds.

The crude MeOH extract of the stem barks of U. tortilis was sequentially partitioned using hexane and ethyl acetate to provide the corresponding sub-extracts. These sub-extracts individually fractioned using various chromatographic techniques resulted in the isolation of the new C-benzyl derivative, uvriatortilisin (1), together with the six known compounds: dichamanetin (2) [11] , chamanetin (5) [12] , uvaretin (6) [13] , (-)-epicatechin (7) [14] , β-sitosterol (3) and stigmasterol (4) [15] (Figure 1). The structures of the isolated compounds were elucidated by spectroscopic techniques including UV, IR, NMR and MS analysis. These compounds were isolated four thirst time from U. tortilis.

Compound 1 was obtained as an amorphous solid. The HRESIMS exhibited an ion peak at m/z 501.1917 [M + H]⁺ (calcd for C₃₀H₂₉O₇, 501.1913), indicating the molecular formula of C₃₀H₂₈O₇ that corresponding to seventeen degrees of hydrogen deficient. The UV spectrum showed an absorption maximum at 267 and 262 nm, and the IR spectrum displayed bands for hydroxy and carbonyl functional groups at 3340 and 1721 cm⁻¹, respectively. The ¹H NMR spectrum (Table 1) demonstrated resonances for eight aromatic protons of two 1,2-disubstitued benzenes [δ_H 7.61 (1H, dd, J = 7.6 and 1.9 Hz), 7.44 (1H, dd, J = 7.6 and 1.8 Hz), 7.10 (2H, ddd, J = 8.6, 8.0 and 1.8 Hz), 6.90 (2H, m) and 6.84 (2H, dd, J = 8.0 and 1.1 Hz)], five aromatic protons of a mono-substituted benzene [δ_H 7.29 (2H, m), 7.24 (2H, m) and 7.21 (1H, m)], a methoxy group [δ_H 3.74 (3H, s)], two coupled methylene groups [δ_H 3.42 and 3.01 (each, 2H, t, J = 7.8 Hz], and two isolated methylene groups [δ_H 3.95 and 3.88 (each, 2H, s)], together with signal for a chelated hydroxy group [δ_H 13.57 (1H, s)]. The ¹³C NMR and Dept 135 spectra (Table 1) showed resonances for 30 carbons including an ester carbonyl

carbon (δ_C 179.0), eleven quaternary aromatic carbons (δ_C 161.3, 159.1, 158.7, 152.6 (2C), 141.2, 126.3, 126.2, 113.6, 111.9 and 109.0), thirteen aromatic methine carbons (δ_C 132.2, 131.6, 128.4 (4C), 128.0, 127.8, 126.1, 121.2, 121.1, 115.7 and 115.6), four methylene carbons (δ_C 43.9, 31.1, 23.6 and 23.0), and a methoxy carbon (δ_C 63.7). These NMR data were similar with those of diuvaretin [16] except for the replacement of the signal of α, β-unsatured carbonyl (δ_C near 205) with signal for ester carbon unit (δ_C 179.0). Thus, the aromatic protons of the 1,2-disubstitued benzenes at δ_H 7.61, 7.44, 7.10, 6.90 and 6.84 were assigned to H-6''', H-6'', H-4''/H-4''', H-5''/H-5''' and H-3''/H-3''', respectively, due to their multiplicities and the HMBC correlations of H-6''' to C-2''' (δ_C 152.6), C-4''' (δ_C 127.8), C-8' (δ_C 23.0) and C-1' (δ_C 133.5); of H-6'' to C-2'' (δ_C 152.6), C-4'' (δ_C 128.0) and C-7' (δ_C 23.6); of H-4''/H-4''' to C-2''/C-2''' and C-6'' (δ_C 132.1)/C-6''' (δ_C 131.6); of H-5''/H-5''' to C-1'' (δ_C 126.2)/C-1''' (δ_C 126.3) and C-3'' (δ_C 115.7)/C-3''' (δ_C 115.6); and H-3''/H-3''' to C-1''/C-1''' and C-5'' (δ_C 121.1)/C-5''' (δ_C 121.2). The mono-substituted benzene was further identified to be the aromatic ring of a phenyl propanoic ester group that was confirmed by interpretation of the 1D- and 2D-NMR spectroscopic data of 1, including COSY, HSQC and HMBC spectroscopy experiments (Figure 2). The methoxy group was assigned to C-6' (δ_C 159.1) according to the HMBC correlation observed between the signal at δ_H 3.74 and C-6' as well as C-6' with the methylene protons of one of the two C-benzyl groups at δ_H 3.88 (H-7') that also presented HMBC cross peaks with C-5' (δ_C 113.6) and C-4' (δ_C 158.7). The other C-benzyl group was located at C-3' because the signal of its methylene protons at δ_H 3.95 (H-8') showed HMBC correlations with C-2' (δ_C 161.3), C-3' (δ_C 111.9) and C-4' (δ_C 158.7). The HMBC correlations of the signal of proton of the chelated OH (δ_H 13.57) with those of C-1', C-2' (δ_C 161.3) and C-3' (δ_C 111.9) allowed to locate this OH group at C-2'.

Further, NOE effects observed between protons of the methylene at δ_H 3.01 (H-7) and 3.94 (H-8) with protons of the methoxy and the chelated OH suggested that the ester group is located at C-1' (Figure 2). Compound 1 was thus elucidated as 2,4-dihydroxy-3,5-bis(2-hydroxybenzyl)-6-methoxyphenyl 3-phenylpropanoate that we called uvariatortilisin. Compounds, such as 1, 2, 5 and 6, containing one or two hydroxylated C-benzyl groups, have been mainly isolated from Annonaceae species, precisely in the genera Cleistochlamys [11] , Melodorum [17] , Sphaerocoryne [18] , Uvaria [5] [13] and Xylopia [19] . All these genera belong to Annonoideae sub-family [20] . Thus, the natural occurrence limited of these compounds can be considered as characteristic chemotaxonomical value of Annonoideae sub-family that supporting phylogenetic relationships between its genera.

Phytochemical investigation of the MeOH extract of stem barks of Uvaria tortilis resulted in the isolation of uvariatortilisin (1), a novel phenolic 3-phenylpropanoic acid ester derivative containing two C-benzyl hydroxylated groups, together with dichamanetin (2), chamanetin (5), uvaretin (6), (-)-epicatechin (7), β-sitosterol (3) and stigmasterol (4). All these compounds were isolated for the first time from Uvaria tortilis. Certain of them, with C-benzyl hydroxylated groups in their structure, could be have a chemotaxonomic importance that would support phylogenetic relationships between genera Cleistochlamys, Melodorum, Sphaerocoryne, Uvaria and Xylopia, all from Annonoideae sub-family.

The authors wish to thank Professor Pierre CHAMPY in the Pharmacognosy Laboratory of the UFR of Pharmacy of Paris-Saclay University (France), for the recording of NMR spectra and HR-ESIMS of the isolated compounds. They are grateful to the CNF (Centre National de Floristique) of the Félix Houphouët-Boigny University, Abidjan-Cocody, Côte d’Ivoire, for the plant authentication.

The authors declare no conflicts of interest regarding the publication of this paper.

Okpekon, A.T., Seri, S.C., Dade, M.E.J., Agnes, A.S., San, Y. and Kouakou, Y.L. (2023) Phytochemical Constituents of the Stem Barks of Uvaria tortilis, an Endemic Annonaceae from Côte d’Ivoire. Open Journal of Applied Sciences, 13, 888-895. https://doi.org/10.4236/ojapps.2023.136071