Introduction

Over 100 trillion microbes are estimated as spending most of their lifetime on and within human beings including some of them involved in either human health or in diseases affecting humans through numerous mechanisms (Gill et al., 2006; Ley, Turnbaugh, Klein, & Gordon, 2006; Wang, Yao, Lv, Ling, & Li, 2017). Infectious diseases commonly spread among humans are caused by the production of toxins by microbes in the human host also called dysbiosis of the human microbiota which will have a significant incidence on the immune system, leading to antibiotic resistance or causing the new emerging infectious or microbial diseases like HIV, hepatitis and many others (Brenchley & Douek, 2012; Cohen, 2016; Hand et al., 2012; Hu et al., 2016). Moreover, the resistance of infectious pathogens to existing drugs has been the major cause of the increasing rate of microbial diseases and the emergence of new ones around the world (Kemayou et al., 2021; Tabekoueng et al., 2020). The medicinal plants including those of the genus Ficus have been long used as the first line of treatment in folk medicine to manage several microbial illnesses and might represent a good source of new antimicrobial lead compounds to address the need for new potent drugs to face that resistance (Happi et al., 2021; Mbobda et al., 2021; Mbougnia et al., 2021). Ficus sycomorus (Moraceae) is one of the 840 species of Ficus genus which grows as a semi-deciduous tree with green or yellow to orange bark and is widely distributed in tropical regions of Africa (Hossain, 2019). The tree can reach up to 20 m in height and 6 m wide. Its leaves are deep green and heart-shaped; the fruit is large (2 to 3 cm in diameter), maturing from buff-green to yellow or red; the flowers are spherical, greenish and unisexual (Hossam, Heba, Abdelrahman, Reem, & Gehan, 2019). Different parts of F. sycomorus are introduced in the preparations of traditional medicines for the cure of microbial infections like diarrhoea, dysentery, urinary tract infections, cough, skin rashes, ulcers and tuberculosis (Abubakar et al., 2015; Fowler, 2007). Previous studies undertaken on the aerial parts of Ficus species revealed the presence of different classes of compounds including triterpenoids, coumarins and flavonoids (Chiang & Kuo, 2002; Chiang, Chang, Kuo, Chang, & Kuo, 2005; Popwo et al., 2019). Those reported compounds exhibited a large range of activities including antimicrobial, antiviral, antioxidant, and anti-proliferative activities (Dzubak et al., 2006; Yan et al., 2014). As a way forward in our search for antimicrobial and cytotoxic leads from Cameroonian medicinal plants (Tegasne et al., 2020; Wouamba et al., 2020), we have investigated the stem bark and roots of F. sycomorus for its chemical constituents and their antibacterial, antifungal and cytotoxicity activity against a panel of microbial strains and VERO cell line. The methodology for isolation and analyses of the compounds, the discussion on results obtained and the chemophenetic significance of this study are all herein presented.

Materials and Methods

General instrumentation

Instruments used during this study for isolation and analyses of the isolated compounds can be found in the supplementary information (Appendix A ).

Plant material

The stem bark and the roots of F. sycomorus were collected at Malentouen (GPS coordinates: 5°30′20″N, 10°00′00″E, Elevation 1100 m), a locality of Foumban, West region, Cameroon, in January 2017. Mr Victor Nana, a botanist of the National Herbarium of Cameroon, Yaounde, made the identification of the plant and a specimen has been kept under the voucher number 13750/HNC.

Extraction and isolation

The air-dried and powdered stem bark (2.10 kg) and roots (2.00 kg) of F. sycomorus were separately macerated twice in methanol for 48 h and 24 h, respectively. The crude extracts of stem bark (200.55 g) and roots (34.55 g) were obtained after removing the solvent. The purification processes of the two extracts were separately conducted and led to the isolation of 24 distinct compounds as summarized in Figure 1 and Figure 2.

Figure 1

Summarized protocol for isolation of compounds from F. sycomorus bark

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Figure 2

Summarized protocol for isolation of compounds from F. sycomorus root

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Briefly, part of the stem bark extract (195.00 g) was submitted to flash chromatography using EtOAc, EtOAc/MeOH (70:30, v/v) and MeOH as solvents, to afford EtOAc fraction (25.15g); EtOAc/MeOH fraction (80.05 g) and MeOH fraction (85.10 g). A part of the EtOAc fraction (22.15 g) was chromatographed on silica gel column chromatography with an increasing amount of EtOAc in n-Hexane (Hex) from 5% to 100% (v/v). A total of 232 fractions (100 ml each) have been collected and combined on the basis of TLC analyses into seven sub-fractions (F1‒F7). Sub-fraction F1 [225.55 mg, 5% of EtOAc in Hex (v/v)] was purified on silica gel column chromatography, with a gradient solvent system starting by 2.5 % of EtOAc in Hex (v/v) and gave compounds 14 (8.5 mg), the mixture of 2 and 4 (20.1 mg) and 8 (12.8 mg), then, with the solvent system 5% of EtOAc in Hex (95:5, v/v) to give compound 9 (13.5 mg). The mixture of 12 and 15 (20.0 mg) precipitated from F2 [135.10 mg, Hex–EtOAc (90:10, v/v)] purified following elution with an isocratic solvent system of Hex–EtOAc (92.5:7.5, v/v). Following the same process, the sub-fraction F3 [134.50 mg, Hex–EtOAc (85:15, v/v)] gave compounds 1 (8.2 mg) and 10 (10.5 mg). The mixture of compounds 3 and 5 precipitated from sub-fraction F4 [76.55 mg, Hex–EtOAc (80:20, v/v)] while compounds 11 (9.1 mg), 21 (11.5 mg) and the mixture of 23 and 24 (21.5 mg). Were obtained from the sub-fraction F5 [126.50 mg, Hex–EtOAc (75:25, v/v)]. Furthermore, compound 22 (5.8 mg) was obtained from sub-fraction F6 [90.50 mg, Hex–EtOAc (70:30, v/v)] and compound 16 (80.7 mg) precipitated from F7 [95.55 mg, Hex– EtOAc (25:75, v/v)].

Likewise, part of the methanol crude extract of roots (30.00 g) was fractionated following the same procedure as performed with the stem bark extract. Therefore, the EtOAc fraction from the root gave six fractions (F1'‒F6'). From purification using silica gel column chromatography as described earlier, Fraction F1' [105.50 mg, Hex–EtOAc (90:10, v/v)] afforded compound 12 (7.2 mg), 13 (7.6 mg), 9 (10.1 mg) and 7 (13.8 mg). Fraction F2' [200.50 mg, Hex–EtOAc (85:15, v/v)] led to the obtention of compounds 17 (14.6 mg), 18 (8.56 mg), 19 (13.4 mg) and 20 (25.20 mg), while fraction F3' [155.50 mg, Hex–EtOAc (80:20, v/v)] led to compounds 3 (9.2 mg) and 5 (12.3 mg). Compounds 23 (15.5 mg) and 24 (25.3 mg) were obtained after elution of the fraction F4' [99.50 mg, Hex–EtOAc (75:25, v/v)] and compounds 6 and 16 were obtained from Fraction F5' [90.50 mg, Hex–EtOAc (70:30, v/v)] and the recrystallization of F6' [75.50 mg, Hex–EtOAc (40:60, v/v)], respectively.

Spectral data of isolated compounds

The 1H and 13C NMR spectra (Figures 1S‒45S, Appendix A) as well as the full assignations (Tables 1S‒24S, Appendix A) of all the carbon and hydrogen atoms of the isolated compounds 124 are provided in the supplementary information attached to this paper (Appendix A ).

Antimicrobial and cytotoxicity evaluations

Some compounds obtained in sufficient amounts for biological tests have been evaluated for their antibacterial, antifungal and cytotoxicity potencies. The full protocol for each test can be consulted in the supplementary material (Appendix A ). For instance, eight bacterial strains namely Salmonella typhimurium cpc, S. enteritidis cpc, S. typhi cpc, Staphylococcus aureus MR, S. aureus (ATCC25922), Klebssiella pneumonae (ATCC13883), Escherishia coli (ATCC35218), Pseudomonas aeruginosa ; seven fungal strains including Candida albicans, C. krusei, C. parasilosis, Cryptococcus neoformans, Trichophyton mentagrophytes, Microsporium audouinii, Epidermophyton flocosum as well as the VERO cell line ATCC CRT-1586 have been used during the three biological evaluations.

The antibacterial assay has been done using the broth microdilution method was used for susceptibility testing of bacteria species in 96 well-microtiter sterile plates as described by (Newton, 2002). The lowest concentration at which no visible colour change was observed was considered the Minimum Inhibitory Concentration (MIC) while the smallest concentration at which no colour change was observed was considered the Minimum Bactericidal Concentration (MBC). The tests were performed in duplicates. The ratio MBC/MIC was calculated to determine the bactericidal (MBC/MIC ≤ 4) and bacteriostatic (MBC/MIC > 4) effects (Mativandlela, Lall, & Meyer, 2006).

In antifungal activity evaluation, the MIC of each sample was determined by using broth microdilution techniques according to the guidelines of the Clinical and Laboratory Standards Institute (CLSI, formerly National Committee for Clinical and Laboratory Standards, NCCLS) for yeasts (M27-A2). MIC values were assessed visually after the corresponding incubation period and were taken as the lowest product concentration at which there was no growth or virtually no growth, while the lowest concentration that yielded no growth after the subculturing was taken as the Minimum Fungicidal Concentration (MFC). The assay was repeated three times.

Finally, cytotoxicity activity was investigated on VERO cell line ATCC CRT-1586 using a rezasurin-based assay as previously described by Mosmann (1983). The results were expressed as a percentage of viability of the control cells and CC50 values were calculated as a sigmoidal dose-response curve using GraphPad Prism 4.03 software using the nonlinear regression log (inhibitor) vs. response algorithm.

Results and Discussion

Phytochemical study

The chemical investigations of the stem bark and roots of the medicinal plant Ficus sycomorus led to the isolation and identification of twenty-four distinct compounds (Figure 3) including ten triterpenoids belonging to five different classes including one taraxastane-type triterpenoid named epi-ψ-taraxastanonol or 3-oxo-20R-hydroxytaraxastane (1) (Anjaneyulu et al., 1999), two ursane-type triterpenoids α-amyrin acetate (2) and ursolic acid (3) (Tabekoueng et al., 2020; Wouamba et al., 2020), three oleanane-type triterpenoids β-amyrin acetate (4), oleanolic acid (5) and 2-O-trans-p-coumaroyl maslinic acid (6) (Yan et al., 2014), one friedelane-type triterpenoid named canophyllol (7) (Ngouamegne et al., 2008), as well as three lupane-type triterpenoids lupeol (8), betulinic acid (9) and lupeol acetate (10) (Javed et al., 2021; Mbougnia et al., 2021). Additionally to the ten triterpenoids, we isolated one diterpenoid called ent-kauran-2β,3α,16α-triol (11) (Dongmo et al., 2019); five steroids including stigmasterol (12), stigmast-22-ene-3,6-dione (13) (Lima, Diaz, & Diaz, 2013), stigmast-7-en-3-one (14) (Wu et al., 1990), β-sitosterol (15) and β-sitosterol-3-O-β-D-glucopyranoside (16) (Mbougnia et al., 2021); four flavonoids among which three isoflavones namely alpinumisoflavone (17) (Kuete et al., 2008), derrone (18) (Chibber & Sharma, 1980) and 3'-(3-methylbut-2enyl)-biochanin A (19) (Abiy, Jacob, Mathias, & Martin, 1998), as well as one flavone named atalantoflavone (20) (Nsangou et al., 2021). Further compounds have been characterized as one benzoquinone identified as 2,6-dimethoxybenzoquinone (21) (Dongmo et al., 2019); one phenylethanol derivative named 2-(4-hydroxyphenyl)-ethyldocyoctadecanoate (22) (Acevedo et al., 2000) and two peptide derivatives viz. asperphenamate (23) and asperglaucide (24) (Popwo et al., 2019).

Figure 3

Structures of compounds 124 from stem bark and roots of F. sycomorus.

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The results showed that the plant produces chemical constituents with a high structural diversity from terpenoid derivatives (triterpenoids and steroids) identified as the major classes of compounds to flavonoids and other phenolic compounds. The significant change observed in the core structures from one compound to another is mainly oxidation of some functional groups and it might play an important role in their potencies and the understanding of their action mechanisms (Dzouemo, Happi, Happi, Tsopgni, & Wansi, 2022; Happi et al., 2020).

Antimicrobial and cytotoxicity activities of the isolated compounds

Eleven compounds (14, 10, 13, 14, 1719 and 22), the crude methanolic extracts of stem bark and roots as well as the EtOAc fraction from stem bark have been tested for their potency against eight bacterial strains and seven fungal strains as well as for their cytotoxicity against the VERO cell line ATCC CRT-1586.

The antibacterial assays have been carried out against bacterial strains listed in section 2.4 and ciprofloxacin was the standard drug. The results (Table 1) indicated that compound 18 showed good activity against Escherichia coli (MIC = 31.25 µg/ml) and moderate potency against Salmonella typhimurium cpc and Pseudomonas aeruginosa (MIC = 125 µg/ml, each). Compounds 10, 13 and 14 showed moderate activities on almost all the tested strains and compound 13 was the most potent against E. coli (MIC = 125 µg/ml). All the two crude extracts demonstrated moderate activities against almost all the tested strains (MIC = 250 µg/ml, MBC/MIC = 2) on S. enteritidis and E. coli. These results showed that the other compounds in the extracts might play an antagonistic effect on compound 18 (MIC = 31.25 µg/ml) which is the most active we found so far in this study.

Furthermore, the results of the antifungal activity (Table 2) showed that the methanol extract of the stem bark exhibited good activity against Candida albicans with a MIC value of 31.5 µg/ml and a fungicidal effect with an MFC/MIC ratio of 4. Almost all the isolated compounds showed weak activity against some yeast and dermatophytes with MIC values from 125 µg/ml to 500 µg/ml and fungicidal with an MFC/MIC ratio of either 2 or 4. The good activity of the methanol extract from the stem bark may justify its use in folk medicine for the treatment of infectious illnesses.

Finally, the samples were evaluated for their cytotoxic activity on VERO cell line ATCC CRT-1586. Their potencies are reported in Table 3. According to the results, all the tested extracts showed cell viability greater than 100 μg/ml, indicating that they have no risk for living cells. Compounds 18 and 19 showed the higher inhibition of cell lines with CC50 values of 52.60 μg/ml and 69.10 μg/ml, respectively, indicating that they have a risk for living cells.

Table 1

Minimum Inhibitory Concentrations (MIC) and Minimum Bactericidal Concentrations (MBC) of root extract, stem bark extract and isolated compounds

Samples

Parameters

STM

SEcpc

STcpc

SAMR

SA

KP

EC

PA

Methanolic Root extract

MIC (µg/mL)

500

250

500

500

500

500

250

500

MBC (µg/mL)

>500

500

>500

>500

>500

>500

500

>500

MBC/MIC

ND

2

ND

ND

ND

ND

2

ND

Methanolic Stem bark extract

MIC (µg/mL)

>250

>250

>250

>250

>250

>250

>250

>250

MBC (µg/mL)

ND

ND

ND

ND

ND

ND

ND

ND

MBC/MIC

ND

ND

ND

ND

ND

ND

ND

ND

EtOAc fraction of the stem bark

MIC (µg/mL)

>250

>250

>250

>250

>250

>250

>250

>250

MBC (µg/mL)

ND

ND

ND

ND

ND

ND

ND

ND

MBC/MIC

ND

ND

ND

ND

ND

ND

ND

ND

1

MIC (µg/mL)

>125

>125

>125

>125

>125

>125

>125

>125

MBC (µg/mL)

ND

ND

ND

ND

ND

ND

ND

ND

MBC/MIC

ND

ND

ND

ND

ND

ND

ND

ND

2 + 4

MIC (µg/mL)

500

500

500

250

500

500

500

250

MBC (µg/mL)

>500

>500

>500

500

>500

>500

>500

500

MBC/MIC

ND

ND

ND

2

ND

ND

ND

2

3

MIC (µg/mL)

>125

>125

125

>125

>125

>125

>125

>125

MBC (µg/mL)

ND

ND

250

ND

ND

ND

ND

ND

MBC/MIC

ND

ND

2

ND

ND

ND

ND

ND

10

MIC (µg/mL)

250

500

500

250

500

500

500

250

MBC (µg/mL)

500

>500

>500

500

>500

>500

>500

500

MBC/MIC

2

ND

ND

2

ND

ND

ND

2

13

MIC (µg/mL)

500

250

250

500

500

500

125

250

MBC (µg/mL)

>500

500

500

>500

>500

>500

250

500

MBC/MIC

ND

2

2

ND

ND

ND

2

2

14

MIC (µg/mL)

500

500

500

500

˃500

500

˃500

500

MBC (µg/mL)

>500

>500

>500

>500

ND

>500

ND

>500

MBC/MIC

ND

ND

ND

ND

ND

ND

ND

ND

17

MIC (µg/mL)

500

500

500

500

˃500

500

˃500

˃500

MBC (µg/mL)

>500

>500

>500

>500

ND

>500

ND

ND

MBC/MIC

ND

ND

ND

ND

ND

ND

ND

ND

18

MIC (µg/mL)

>125

>125

125

>125

>125

>125

31.25

125

MBC (µg/mL)

ND

ND

250

ND

ND

ND

125

250

MBC/MIC

ND

ND

2

ND

ND

ND

4

2

19

MIC (µg/mL)

500

500

500

250

500

500

500

500

MBC (µg/mL)

>500

>500

>500

500

>500

>500

>500

>500

MBC/MIC

ND

ND

ND

2

ND

ND

ND

ND

22

MIC (µg/mL)

250

500

>500

250

>500

500

500

500

MBC (µg/mL)

500

>500

ND

500

ND

>500

>500

>500

MBC/MIC

2

ND

ND

2

ND

ND

ND

ND

Ciprofloxacin

MIC (µg/mL)

2

1

0.5

1

1

0.5

0.5

0.5

MBC (µg/mL)

4

2

1

2

2

1

2

2

MBC/MIC

2

2

2

2

1

2

4

4

[i] STM: Salmonella typhimurium cpc ; SE: Salmonella enteritidis cpc ; ST: Salomonella typhi cpc ; SAMR: Staphylococcus aureus MR ; SA: Staphylococcus aureus (ATCC25922); KP: Klessiella pneumonae (ATCC13883) ; EC: Escherishia coli (ATCC35218); PA: Pseudomonas aeruginosa. ND: not determined. MIC = Minimum inhibitory concentration; MBC = Minimum bactericidal concentration; MBC/MIC; The ratio MBC/MIC determine the bactericidal (MBC/MIC ≤ 4) or bacteriostatic (MBC/MIC > 4) effects of extracts. The antibacterial activity of a sample of plant-isolated compounds is strong, moderate, or weak if their MIC was ≤10, 10−100, or >100 μg/mL, respectively. However, the activity of plant extracts will be classified as significant (MIC < 100 μg/mL), moderate (100−625 μg/mL), or weak (MIC > 625 μg/mL). (Kuete et al., 2010).

Table 2

Minimum Inhibitory Concentrations (MIC) and Minimum Fungicidal Concentrations (MFC) of root extract, stem bark extract and isolated compounds.

Samples

Parameters

CA

CK

CP

CN

TM

MA

EF

Methanolic root crude extract

MIC (µg/mL)

500

500

500

500

500

500

500

MFC (µg/mL)

>500

>500

>500

>500

>500

>500

>500

MFC/MIC

ND

ND

ND

ND

ND

ND

ND

Methanolic stem bark crude extract

MIC (µg/mL)

31.25

>250

>250

>250

>500

>500

>500

MFC (µg/mL)

125

ND

ND

ND

ND

ND

ND

MFC/MIC

4

ND

ND

ND

ND

ND

ND

Ethyl acetate fraction of stem bark

MIC (µg/mL)

250

500

500

250

˃500

˃500

˃500

MFC (µg/mL)

500

>500

>500

500

ND

ND

ND

MFC/MIC

2

ND

ND

2

ND

ND

ND

1

MIC (µg/mL)

>125

>125

125

>125

>500

>500

>500

MFC (µg/mL)

ND

ND

>500

ND

ND

ND

ND

MFC/MIC

ND

ND

ND

ND

ND

ND

ND

2 + 4

MIC (µg/mL)

500

500

500

500

500

500

250

MFC (µg/mL)

>500

>500

>500

>500

>500

>500

500

MFC/MIC

ND

ND

ND

ND

ND

ND

2

3

MIC (µg/mL)

>125

>125

>125

>125

>500

>500

>500

MFC (µg/mL)

ND

ND

ND

ND

ND

ND

ND

MFC/MIC

ND

ND

ND

ND

ND

ND

ND

10

MIC (µg/mL)

500

500

500

250

500

500

500

MFC (µg/mL)

>500

>500

>500

500

>500

>500

>500

MFC/MIC

ND

ND

ND

2

ND

ND

ND

13

MIC (µg/mL)

500

>500

500

500

>500

500

>500

MFC (µg/mL)

>500

ND

>500

>500

ND

>500

ND

MFC/MIC

ND

ND

ND

ND

ND

ND

ND

14

MIC (µg/mL)

˃500

˃500

250

500

500

500

500

MFC (µg/mL)

ND

ND

500

>500

>500

>500

>500

MFC/MIC

ND

ND

2

ND

ND

ND

ND

17

MIC (µg/mL)

250

˃500

500

250

˃500

500

500

MFC (µg/mL)

500

ND

>500

500

ND

>500

>500

MFC/MIC

2

ND

ND

2

ND

ND

ND

18

MIC (µg/mL)

125

125

>125

>125

>500

>500

>500

MFC (µg/mL)

>500

>500

ND

ND

ND

ND

ND

MFC/MIC

ND

ND

ND

ND

ND

ND

ND

19

MIC (µg/mL)

500

125

500

125

500

250

500

MFC (µg/mL)

>500

250

>500

250

>500

500

>500

MFC/MIC

ND

2

ND

2

ND

2

ND

21

MIC (µg/mL)

500

500

>500

>500

>500

>500

>500

MFC (µg/mL)

>500

>500

ND

ND

ND

ND

ND

MFC/MIC

ND

ND

ND

ND

ND

ND

ND

22

MIC (µg/mL)

>500

250

500

250

500

250

>500

MFC (µg/mL)

ND

500

>500

500

>500

500

ND

MFC/MIC

ND

2

ND

2

ND

2

ND

Nystatin

MIC (µg/mL)

0.5

0.25

1

0.25

MFC (µg/mL)

2

1

2

1

MFC/MIC

4

0.25

2

0.25

Griseofulvin

MIC (µg/mL)

0.25

1

0.5

MFC (µg/mL)

1

2

2

MFC/MIC

0.25

2

4

[i] MIC : Minimum Inhibitory Concentrations, MFC : Minimum Fungicidal Concentrations, ND : Not determined, CA : Candida albicans, CK : Candida krusei, CP : Candida parasilosis, CN : Cryptococcus neoformans, TM : Trichophyton mentagrophytes, MA : Microsporium audouinii, EF : Epidermophyton flocosum.

Table 3

Cytotoxicity assay against vero cell line ATCC CRT-1586

Samples

CC50 (µg/mL)

1

>100

2

>100

3

>100

13

>100

14

>100

17

>100

18

52.60

19

69.10

Methanol crude extract of stem bark

>100

EtOAc fraction of the stem bark

>100

EtOAc/MeOH fraction the stem bark

>100

Methanol crude extract of root

>100

Podophyllotoxin

1.77

[i] Values are expressed as means ± SEM. Each test was performed in triplicate

Chemophenetic significance of the study

In the present work, we have reported the identification of twenty-four known extractives from F. sycomorus, including ten pentacyclic triterpenoids (1‒10), one diterpenoid (11), five sterols (1216), four flavonoids (17‒20), one benzoquinone (21), one phenyl ethanol derivative (22) and two peptide derivatives (2324). Based on an extensive literature survey, and to the best of our knowledge, compounds 6, 11 and 22 are reported herein for the first time from Moraceae family and compound 20 from Ficus genus. However, the four compounds have been already isolated from other plants species including Hippophae rhamnoides L. (Elaeagnaceae) (Yang et al., 2007), Psiadia punctulata (DC.) (Asteraceae) (Piaz et al., 2018) and Buddleja cordata (Scrophulariaceae) (Acevedo et al., 2000), respectively.

Pentacyclic triterpenes (29) constituted the main class of secondary metabolites herein reported, which were already obtained from several Ficus species. Thus, compounds 25 and 7 were reported from F. aripuanensis (Nascimento, Arruda, Arruda, Muler, & Yoshiok, 1999), compound 8 from F. natalensis (Mbougnia et al., 2021), F. benjamina (Simo et al., 2008), F. pseudopalma (Santiago & Mayor, 2014), F. polita (Kamga et al., 2010) and F. auriculata (El-Fishawy, Rawia, & Sherif, 2011). Moreover, compound 9 was reported from F. natalensis (Mbougnia et al., 2021), F. benjamina (Simo et al., 2008), F. polita (Kamga et al., 2010), F. auriculata Lour (El-Fishawy et al., 2011) and F. conraui (Kengap et al., 2011), while compound 10 was reported from F. racemosa (Kosankar & Aher, 2018), F. sansibarica (Awolola et., 2014), F. thonningii  (Ango et al., 2015) and F. mucuso (Bankeu et al., 2010). From this evidence, we can partially conclude that the genus Ficus is a rich source of different classes of triterpenoids including ursane-, lupane- and oleanane-type triterpenoids as the most prominent in the genus.

Steroids 12 and 1416 are the main constituents of many species and were reported from many Ficus species (Awolola, Chenia, Baijnath, & Koorbanally, 2018). They were also reported from another family including Cola rostrata (Malvaceae) (Dongmo et al., 2019). Flavonoids are also highly represented in Ficus genus. Compounds 17 and 18 were reported from many Ficus species e.g., F. nymphaefolia (Darbour et al., 2007) and F. auriculata (Qi et al., 2018) and compound 19 was reported from F. tikoua (Liao et al., 2015) and (Darbour et al., 2007). These isoflavones were also reported from Erythrina species (Fabaceae) e.g., E. senegalensis (Lee et al., 2009; Nkengfack et al., 2001) and E. lysistemon (Mvondo, Njamen, Fomum, Wandji, & Vollmer, 2011). Compound 20 was newly discovered from Ficus genus, it could be used to distinguish F. sycomorus from the other species. Compounds 23 and 25 were previously reported from Ficus exasperata (Popwo et al., 2019).

Concluding remarks

In our search for antimicrobial and cytotoxic compounds from Cameroonian medicinal plants, we have isolated and characterized twenty-four compounds from the stem bark and roots of F. sycomorus, a medicinal plant used in folk medicine for the treatment of microbial illnesses. The results of the biological evaluations performed indicated that some compounds including lupeol acetate (10), stigmast-22-ene-3,6-dione (13), stigmast-7-en-3-one (14) and derrone (18) exhibited good to moderate activity ranging from MIC values 31.25 µg/ml to 125 µg/ml, while only derrone (18) and 3'-(3-methylbut-2enyl)-biochanin A (19) showed important inhibition of the VERO cell line ATCC CRT-1586 with CC50 values of 52.60 µg/ml and 69.10 µg/ml, respectively. From this evidence, derrone (18) was the most active compound from the extract and the other compounds in extract might play an antagonistic effect on its effectiveness. Additionnaly, although compound 18 display promising antimicrobial activity, it might have a risk for living cells due to its higher inhibition of VERO cells. These insights indicate that derrone (18) might be a lead compound that deserves further pharmaceutical investigations and chemical derivatization to reduce its toxicity and further increase its potency as much as possible. Moreover, it seemed obvious to the best of our knowledge that 2-O-trans-p-coumaroyl maslinic acid (6), ent-kauran-2β,3α,16α-triol (11) and 2-(4-hydroxyphenyl)-ethyldocyoctadecanoate (22) are reported for the first time from Moraceae family whereas atalantoflavone (20) is isolated herein for the first time from the genus Ficus. The results of this study extend the number of the chemical constituents of F. sycomorus and support its use in traditional medicine for the treatment of some microbial infections.

Conflicts of interest

The authors declare no conflict of interest.

Author contributions

Research concept and design : VSMM, ENH; Collection of data : WDTT; Data analysis and interpretation: MFN, GMH, AFKW, ENH; Writing the article : VSMM, MFN, GMH; Supervision, critical revision : GMH, AFKW ; Final approval of the article : ENH.