Natural-derived acetophenones: chemistry and pharmacological activities

1 Introduction

Acetophenones, as a group of phenolic compounds, produced by many plants of various families for some reasons such as repelling insects [1]. The proven ability of acetophenone-rich plants to fend off pests and insects has shed light on the perspective of using acetophenone derivatives as pesticides. With the crops suffering catastrophic losses due to pest attacks and diseases, and the public opinion bending towards mitigating the use of chemical pesticides, acetophenone rises as a candidate for an eco-friendly alternative for synthetic pesticides [2]. Plant-derived acetophenones, also, are important precursors for drug production. For example, acetophenone derivatives such as apocynin (207) and paeonol (217) show anti-inflammatory traits without any negative side effects, which make them perfect option for synthesizing drugs. The use of plants containing paeonol in folk medicine for their therapeutic properties dates back to a millennia ago [3]. Acetophenones can also contribute more to therapeutic applications due to their other biological activities such as anticancer, analgesic, antioxidant, cardioprotective, neuroprotective, and antidiabetic [4]. In addition to their biological applications, acetophenone derivatives are used in the food and fragrance industries, primarily for their orange blossom flavor [5]. They are also used as fragrance ingredients in detergents, soaps, and perfumes. In addition, acetophenones and their derivatives also have a variety of applications in the cosmetics production, especially in the making of odorless and colorless cosmetics with good antiseptic effects [6]. They are also used in the production of sunscreen products to protect against UV radiation [7]. Additionally, acetophenone compounds are employed in the production of alcohol, aldehydes, resins, esters, fragrances, and pharmaceuticals. They are important intermediates for the synthesis of natural products and marketed drugs, and they find wide use in fields such as biology, pesticides, polymers, and materials science. Moreover, they are ideal synthons for multicomponent reactions, including three- and four-component reactions, due to their commercial availability and accessibility [8]. Furthermore, highly functionalized acetophenone derivatives have interesting biological properties and are valuable compounds for supramolecular or medicinal chemistry [9]. This article provides a review study over the various natural acetophenone compounds that have been extracted and analyzed plants and microbial populations until January 2024.

2 Search strategy

An extensive survey of the “acetophenone”, “acetophenone derivatives”, and “biological activities” was conducted in scientific databases, including Scopus, Web of Science, PubMed, Google Scholar and Reaxys. The articles which included reports of novel isolated acetophenone were taken into account; however, the synthetic ones were excluded. Also, the reference lists of the included studies were manually investigated. Figure 1 illustrates the number of papers that have reported the isolation of novel acetophenone derivatives from natural resources. The number of isolated novel acetophenone compounds from different families of plants and fungi is also depicted in Fig. 2.

Open image in new window

Open image in new window

3 Acetophenone derivatives produced by plants

3.1 Rutaceae

Containing well over 2040 species categorized within around 170 genera, Rutaceae family, many members of which are aromatic plants [10] is well-known for its rich chemical profile that makes it the most chemically versatile plant family [11]. Species of Rutaceae have been used in the industries of gastronomy and perfumery and also in traditional medicine [10]. Regarding biological activities, the species of this family have displayed to possess antimicrobial, anticholinesterase, antidiarrheal, antileishmanial, larvicidal, antiprotozoal, fungicidal, and antioxidant activities [10].

3.1.1 The genus Melicope

Consisting of around 250 species, Melicope plants are scattered through the tropical regions of southern hemisphere [12]. Like genus Acronychia, the species of genus Melicope have been utilized for their therapeutic and healing properties during centuries [13]. The chemical diversity of Melicope species is owed to the presence of compounds such as flavonoids, benzopyrans, alkaloids, and acetophenones [14]. Prenylated acetophenone compounds, however, are the key compounds that constitute the chemotaxonomic traits of the genus [15]. Li et al. reported the isolation of meliviticine A (1) and meliviticine B (2) from M. viticina (16). The former (1) was identified to be a non-aromatic prenylated isopropylated acetophenone derivative; furthermore, the zero value of the specific optical rotation of 1 hinted to it being a racemic mixture. 2 was also figured to be an isopropylated rearranged prenylated acetophenone [16]. The application of subsequent chiral HPLC resolution led to the isolation of the two pairs of enantiomers (1a and 1b) and (2a and 2b) for 1 and 2, respectively [16]. 1 and 2 were moderately effective against six strains of bacteria and fungi [16]. Adsersen et al. isolated and characterized two novel prenylated acetophenones, namely 2,6-dihydroxy-4-geranyloxyacetophenone (3) and 4-geranyloxy-2,6,b-trihydroxyacetophenone (4) from M. obscura and two acetophenones from M. obtusifolia var. arborea, namely 2,6-dihydroxy-4-geranyloxy-3-prenylacetophenone (5) and 4-geranyloxy-3-prenyl-2,6,b-trihydroxyacetophenone (6) [15]. Xu et al. extracted five acetophenone derivatives, three of which were with inseparable interconverting mixtures of tautomers from M. pteleifolia, specified as melicoptelin A (7), melicoptelin B1 (8a) and B2 (8b), melicoptelin C1 (9a) and C2 (9b), melicoptelin D1 (10a) and D2 (10b), and melicoptelin E (11) [17]. Prenylated acetophenone epimers, melicolone A (12) and melicolone B (13) were isolated from M. pteleifolia, followed by performing further chiral HPLC which yielded the entiomers (+)- and (-)- of both compounds [18]. Nine more acetophenone derivatives, namely melicolones C-K (14–22) were also isolated from M. pteleifolia and examined for their drug resistance reduction characteristics [19]. 14–17 were identified to be as racemic mixtures and 18–22 were pure optically upon extraction. 18–22 boosted the cytotoxicity of doxorubicin with a reversal fold variating between 6.2 and 13.3 in a mixture with doxorubicin at the concentration of 5 µg/mL [19]. Xu et al. furthered isolated four new stereoisomer acetophenone compounds, evodialones A − D (23–26) from M. pteleifolia whose chiral-phase HPLC resolution resulted in the retrieval of eight enantiomers [20]. Shaari et al. investigated the core components of the extract of M. pteleifolia champ ex benth and identified 2,4,6-trihydroxy-3-geranylacetophenone (tHGA) (27) as the compound responsible for its attributed anti-inflammatory characteristics [21]. Upon the application on PBML 5-LOX human enzyme, 27 exerted an inhibitory activity with the IC₅₀ value of 0.42 µM. It also dose-dependently inhibited the LTC₄ production with the IC₅₀ value of 1.8 µM with no inflicted cell toxicity [21]. Nakashima et al. succeeded in isolating four acetophenone derivatives assigned to as di-C-glycosides, pteleifolols A–D (28–31) from M. pteleifolia [22]. Studying on the same plant (M. pteleifolia), Nguyen et al. also isolated six more acetophenone derivatives, including five compounds with spiroketal-hexofuranoside rings, denoted melicospiroketal A-E (32–36) and one di-C-glycosidic phloroacetophenone, elucidated as 5-C-β-D-glucopyranosyl-3-C-(6-O-trans-p-coumaroyl)-β-Dglucopyranoside phloroacetophenone (37). The analysis of the extracted compounds indicated little to zero inhibitory effect against H1N1 influenza virus below the concentration of 400 µM [23]. Parsons et al. introduced three new acetophenone derivatives extracted from the stem bark of M. stipitata, named furostipitol (38), 3β- hydroxydihydropyranostipitol-4⍺-ethyl ether (39), and 3,4-dihydroxydihydropyranostipitol (85–40) [24]. The screening of the extract of M. borbonica resulted in the isolation of xanthoxylin (41) and methylxanthoxylin (42), neither 41, nor 42 possessed anti-inflammatory features against HeLa cells; regarding antifungal activities, however, both compounds proved effective. 41 and 42, inhibited Candida albicans and Penicillium expansum with the MIA (minimum inhibitory amount) of 25 and 15 µg, and > 50 and 20 µg, sequentially [25]. Xanthoxylin (41) has been proven to possess various pharmacological traits and potential applications. It has demonstrated anticancer properties, inhibiting the proliferation of oral squamous carcinoma cells, inducing apoptosis, autophagy, and cell cycle arrest [26]. Furthermore, xanthoxylin has shown promise as an agent targeting doxorubicin-resistant breast cancer cells, reducing their stemness and sensitizing them to doxorubicin [27]. Heterodimer compounds bearing acetophenone derivatives, namely meliquercifolin A (43) and meliquercifolin B (44) were found in the leaves of M. quercifolia [28]. 43 revealed to have strong cytotoxic activity against HeLa cancer cells with the IC₅₀ value of 2.6 µM, while 44 maintained ineffective in this regard. Neither 43 nor 44 exhibited any inhibitory effects against P-388 and MCF-7 cancer cells [28]. Chen et al. reported the extraction of three acetophenone compounds from the fruits of M. semecarpifolia (45–47) [14]. The anti-inflammatory qualities of isolated compounds were evaluated by assessing both the suppressing of fMLP/CB-induced superoxide anion and the release of elastase by human neutrophils. With respect to the first test, 45–47 exerted the IC₅₀ values of 21.37, 23.24, and 30.61 µg/mL, respectively. Regarding the latter evaluation, the IC₅₀ values of 27.35, 26.62, and 28.73 µg/mL were documented in the same order [14]. M. lunu-ankenda afforded three prenylated acetophenone derivatives, listed as 8-Acetyl-3,4-dihydroxy-5,7-dimethoxy-2,2-dimethylchroman (48), Isoevodionol (49), and Isoevodionol methyl ether (50) [29]. Phenylethanones acetophenones (51–52) were also extracted from Euodia lunu-ankenda [30]. Le et al. detected the presence of two newly-discovered acetophenone compounds, namely melibarbinon A (53), and melibarbinon B (54) from M. barbigera. The cytotoxic availability of 54 was assessed against A2780 cell lines, which were suppressed at the IC₅₀ value of 30 µM [31]. Vu et al. isolated three acetophenone derivatives, namely patulinones E − G (55–57) from M. patulinervia. The experiment regarding the inhibitory activity of the isolated compounds against α-glucosidase indicated the IC₅₀ values of 41.68, 6.02, and 67.44 μM, attributed to 55–57, respectively [32]. Simonsen isolated four non-aromatic acetophenone compounds, named coodeanone A (58), coodeanones E-B (59), coodeanones Z-B (60) and coodeanone C (61) from M. coodeana [12]. Coodeanone B could be detected in the configuration of either E or Z; hence, being counted as two acetophenone derivatives [12]. The extract of M. erromangensis revealed to contain six novel acetophenone derivatives (62–67) [33]. Acetophenone compounds, refered to by the trivial names of melicopol (68) and methylmelicopo (69) were isolated from the bark of M. broadbentiana [34]. Isolated Acetophenones (1–69) from the genus Melicope are depicted in Fig. 3.

Open image in new window

3.1.2 The genus Acronychia

The genus Acronychia is comprised of 44 species, distributed mainly along Asia and Australia [35]. The various parts of these plants including roots, leaves, stems, and the fruits have a wide range of medical applications such as mitigating diarrhea, asthma, itchy skin, cough, scales, hemorrhage, fever, etc. [36]. Acronychia species are also utilized for the treatment of fungal infection, spasm, pyrexia, stomachache, and rheumatism [35]. The species of the genus Acronychia have been a rich source of bioactive compounds including flavonoids, quinoline, lignans, steroids, coumarins, triterpenes, acridone alkaloids, and acetophenones [35]. Apart from owning therapeutic characteristics, different part of Acronychia plants have had other usages as their essential oil (EO) is used in cosmetics and their aerial parts are used as food and condiments [35].

The chemical compounds of Acronychia oligophlebia were studied by Chen et al. and seven new acetophenone-derived compounds were identified. These compounds, named acrolione A-G (70–76) were all discerned to be responsible for the antioxidant activities of their host plant as they were elucidated to possess the pertaining effects, using DPPH radical-scavenging capacity and FRAP assays. As regards the anti-inflammatory characteristics, 70, 72, 73, and 74 proved to be effective at the IC₅₀ values of 26.4, 46.0, 79.4, and 57.3 µM against RAW 264.7 cells, respectively [37]. Three prenylated acetophenone derivatives, called acronyculatin (P-R) (77–79), were also extracted from A. oligophlebia by Niu et al. [16]. The cytotoxic activity of 77–79 against MCF-7 cancer cells was tested, which resulted in the inhibitory effect at the IC₅₀ values of 56.8, 40.4, and 69.1 µM, respectively [16]. Yang et al. did conducted another investigation on A. oligophlebia which resulted in the isolation of six new acetophenone derivatives from the leaves of the plant (80–85). The cytotoxic activity of 81–85 were evaluated against MCF-7 cancer cells. 81 and 85 exhibited moderate inhibitory activities with the IC₅₀ values of 33.5 and 25.6 µM, respectively; whereas 82–84 exerted weak effects with the IC₅₀ values of 80.2, 71.1 and 46.3 μM, in the same order [38].

Acrovestone (86) was extracted and structurally elucidated from A. pedunculata by Wu et al. [39]. This compound displayed potent cytotoxic activity by exerting total inhibition at the concentration of 0.5 µg/mL in human KB tissue culture. It also demonstrated strong cytotoxicity against A-549, L-1210, and P-388 cancer cells at the ED₅₀ values of 0.98, 2.95, and 3.28 µg/mL, respectively [39]. The continuation of examination on A. pedunculata led to the extraction of an undescribed arylketone acetophenone (87) [40]. Ito et al. discovered three novel acetophenone compounds, namely acrophenones A-C (88–90), in A. pedunculata, all of which failed to inhibit the growth of five leukemia cell lines (NALM6, Jurkat, HPB-ALL, K562, and PBMNC [41]. In pursuit of exploiting the chemical components of A. pedunculata for cancer prevention application, three more acetophenone derivatives were extracted from A. pedunculata by Ito et al., denoted acrophenones D-F (91–93) [42]. Kouloura et al. isolated three more acetophenone dimers from A. pedunculata and elucidated them as: acropyrone (94), acropyranol A (95), and acropyranol B (96). It is noteworthy that prenylated acetophenone dimers are found exclusively in the genus Acronychia [43]. The continuation of research on A. pedunculata, led to the isolation of five more acetophenone compounds by Su et al. acronyculatins A-E (97–101) [44]. 77 was also discovered to be in the chemical profile of A. pedunculata [45]. Upon the application on murine leukemia P-388 cells, 77 displayed an inhibitory effect with the IC₅₀ value of 15.42 µM [45]. Acetophenone compounds, assigned as acroquinolones A-B (102 and 103), belonging to a class of acetophenone-alkaloid hybrids were extracted from A. pedunculata (L.) Miq. These compounds were tested against a group of cancer cell lines and proved to exhibit minor inhibitory effects against A549 and HCT116 and moderate cytotoxicity against HT29 and HeLa with the IC₅₀ values of 21.8 and 14.2 µg/mL, respectively [46]. Nathabumroong et al. isolated an isoprenylated acetophenone, named 5’-prenylacrovestone (104) from A. pedunculata [47]. Seven acetophenone monomers, named acronyculatins I − O (105–111) were detected and extracted from A. trifoliolata by Miyake et al. The isolated compounds were evaluated for their antiproliferative properties against five lines of human cancer cells specified as A549, KB, KB-VIN, MDA-MB 231, and MCF-7. While 105 and 106 caused their corresponding inhibitory effects at the IC₅₀ values of 26.6, 25.6, 19.2, > 40, and 30.8 µM (105), and 19.9, 20.4, 16.2, 22.6, and 19.4 µM (106), respectively, the remainder of isolated compounds exhibited IC₅₀ values excessing 40 µM for the collective cell lines [48]. A. crassipetala was elucidated to host two prenylated acetophenones, namely crassipetalonol A (112) and crassipetalone A (113). The latter (113) had been previously detected in Euodia lunu-ankenda, along with the report of its fungicide activity [30], and Urtica dioica L.. 112 also showed to possess high levels of toxicity and little to none antibacterial traits when tested at the high concentration of 156 µM against ESKAPE pathogenes [49]; Comparatively, 113 elucidated to have strong antibacterial activity as it inhibited Entercoccus faecium and Gram-positive bacteria, S. aureus at the MIC₇₅ values of 2.6 and 20.6 µM, respectively [49]. The derived acetophenone compounds from the genus Acronychia are illustrated in Fig. 4.

Open image in new window

3.2 Other Rutaceae species

Several actephonones were isolated from other species of Rutaceae (Fig. 5). Goh et al. introduced two phloroacetophenone derivatives, namely melifolione 1a (114) and melifolione 1b (115) from Euodia latifolia [50]. The leaves of Bosistoa euodifoumis afforded the prenylated acetophenone derivative, called franklinone (116) [51]. Chou et al. extracted acetophenone derivatives, identified as 4-(1'-geranyloxy)-2,6-dihydroxy-3-isopentenylacetophenone (117), 2-(1'-geranyloxy)-4,6-dihydroxyacetophenone (118), 4-(1'-geranyloxy)-2,6-dihydroxyacetophenone (119), and 4-(1'-geranyloxy)-P,2,6-trihydroxyacetophenone (120) from E. merrillii [52]. Hartmann and Nienhaus discovered an acetophenone compound, xanthoxylin (41), that was extracted from the bark of Citrus limon, infected two strains of fungi, Hendersonula toruloidea and Phytophthora citrophthora. Having been absent in the healthy barks of Citrus lemon, the lesion-tissue-extracted 41 was found trice the concentration it had when inhibiting the growth of the pertaining fungi in vitro at the ED₅₀ value of 0.8 mM. The concentration of 41, also, peaked in the dead tissue [53]. Four novel prenylated acetophenone compounds were isolated from Bosistoa selwynii identified as selwynone (121), pyranoselwynone (122), furanoselwynone (123), and isofuranoselwynone (124) [54]. Quader et alextracted and characterized acetophenones 41 from Acradenia frankliniae [55].

Open image in new window

3.3 Asteraceae

Titled the biggest family of flowering plants, Asteraceae is comprised of more than 1600 genera and 25,000 species scattered around the world [56]. Most species, however, are present more densely in the arid and semi-arid regions of subtropical areas [57]. Members of Asteraceae have been long used for their medicinal traits such as antipyretic, hepatoprotective, smooth muscle relaxant, laxatives and their ability to heal flatulence, lumbago, hemorrhoids, etc. Furthermore, the anti-oxidant and anti-inflammatory activities of the members of this family are well-acknowledged [57]. Therefore it can be deduced that the majority of Asteraceae members are categorized as medicinal plants, owing to their rich chemical profile, including flavonoids, mucilage, tannins, glycosides, and carbohydrate [57]. The presence of more phytochemical components, namely lignans, polyphenolic compounds, sterols, phenolic acids, diterpenoids, polyphenols and saponins has also been reported to contribute to their therapeutic effects [58]. Acetophenones discovered in some genera of Asteraceae have proven to contribute to the pertaining properties of the family species. Embarking on the attempt to explore the cytotoxic constituents of Eupatorium fortune, Chang et al. isolated an acetophenone derivative, known as eupatofortunone (125) that was elucidated to contribute to the therapeutic values of the host plant [59]. 2-Hydroxy-4-methylacetophenone (126) [60] was also extracted during the process. Compounds 125 and 126 were assayed as to their ability to suppress the proliferation of MCF-7 and A549 cells. Regarding 125, the inhibition was observed at the IC₅₀ value of 82.15 and 86.63 µM, respectively. In another study, 126 showed no the antiproliferation effect (IC₅₀ values of > 100 µM) for both cell lines [59]. Trang et al. also extracted 126 from the aerial parts of E. stoechadosmum [60]. Mendes do Nascimento et al. obtained two p-hydroxyacetophenone (127) derivatives from Calea uniflora and denoted them 2-senecioyl-4-(methoxyethyl)-phenol (128), and 2-senecioyl-4(pentadecanoyloxyethyl)-phenol (129). p-Hydroxyacetophenone (127) has shown various pharmacological activities and potential applications. It has been found to possess hepatoprotective, antioxidative, and anti-inflammatory properties, making it a potential treatment for alcoholic liver disease. It has also demonstrated antioxidative, antinociceptive, and anti-inflammatory effects, suggesting its therapeutic potential in inflammation-associated diseases [61]. Both 128 and 129 exhibited trypanocidal activities against Trypanosoma cruzi parasite. At the administration doses of 100, 250, and 500 µg/mL, 128 and 129 inflicted lysis on Trypanosoma cruzi at the percentage-wise records at three different concentrations of 27.5 (10 µg/mL), 28.9 (250 µg/mL), 42.0 (500 µg/mL), and 8.8 (10 µg/mL), 24.7 (250 µg/mL), and 70.9 (500 µg/mL), respectively [62]; furthermore, 128 and 129 both displayed antifungal traits against four strains of Candida spp, namely C. albicans, C. krusei, C. parapsilosis, C. glabrata, and four dermatophytes including two strains of Trichophyton rubrum (Tr-5 and Tr-19), and two strains of Trichophyton mentagrophyte (Tm-9 and Tm-17). Both 128 and 129 exerted fungitoxicity against all the strains of dermatophytes with the MIC value of 1000 µg/mL. While both compounds were ineffective against inhibiting C. krusei and C. parapsilosis, both 128 and 129 suppressed C. albicans at the same MIC value of 500 µg/mL, and 128 deterred the proliferation of C. glabrata with the MIC value of 500 µg/mL [62]. The aerial parts of Ophryosporus macrodon yielded eight novel diprenylated p-hydroxyacetophenone derivatives (130–137). 136 and 137 were elucidated to be threo and erythro isomers, respectively [63]. 4'-Hydroxy-3'-(3-methylbutanoyl)acetophenone (138) was isolated from Flourensia cernua by Bohlmann and Grenz [64] and from Polymnia sonchifolia by Takasugi and Masuda [65]. 5-Acetyl-2-(1-hydroxy-lmethylethyl)benzofuran (139) was also isolated in this assay. Thomas-Barberan et al. identified 4-hydroxy3(isopentent-2-yl) acetophenone (140) from Helichrvsum italicum, and revealed its antibacterial activity against gram positive bacteria (Bacillus sp. and Staphylococcus epidermidis) and E. coli gram negative bacteria at the MIC values of > 100 and 25 ug/mL, respectively [66]. 140, also, exhibited antifungal quality by inhibiting 5 strains of fungi (Cladosporium herbarum, Phyrhophthora capsica, Neurospora crassa, Penicillium italicurn, and P. digitalum) at the MIC values of 10, 50, 100, 100, and 50 µg/mL, respectively [66]. Takasugi and Masuda also extracted 140 from Polymnia sonchifolia [65]. The examination of H. italicum with respect to its constituting compounds led to the identification of a new acetophenone derivative, named gnaphaliol 9-O-propanoate (141) [67]. Rigano et al. [67] isolated acetoxytremetone (142), 10-hydroxytremetone (143), and 1-[2-[1-[(acetyloxy)methyl]ethenyl]-2,3-dihydro-3-hydroxy-5-benzofuranyl]-ethanone (144) from this plant. Rigano et al. [67], also identified 13-(2methylpropanoyloxy)toxol (145), and gnaphaliol (146) in H. italicum that had been previously isolated from Diplostephium cinereum [68], in addition to being extracted from Gnaphalium polycaulon [67, 69]. Compounds 141, 142, and 144 were tested for evaluation of their biological effects, namely anti-inflammatory and antioxidant properties. Regarding the former, none of the aforementioned compounds proved to have such an effect; and only 142, which was previously denoted for its spasmolytic activity [70], showed to possess antioxidant activities [67]. Sala et al., also, isolated three previously-unidentified acetophenone glucosides, (147–149) [71] from H. italicum and reported the anti-inflammatory effects of them on TPA-induced mouse ear edema, where 147, 148, and 149 managed to reduce the ear thickness by values approximating roughly 200 µm [71]. Senecio graveolens is another member of Asteraceae whose biochemical profile was shown to host two novel 127 derivatives, namely 5-acetylsalicylaldehyde (150) and 4-hydroxy-3-(3′’-hydroxyisopentyl)acetophenone (151) [72]. The last novel acetophenone compounds from the family Asteraceae were extracted from Helianthus annuus L., elucidated as 4-hydroxy-3-(2′-hydroxy-3′-methyl-1′-butenyl) acetophenone-1′-O-β-dglucopyranoside (152), 4-hydroxy-3-((Z)-3′-hydroxy-3′-methyl-1′-butenyl) acetophenone-8-O-β-D-glucopyranoside (153), 4,6-hydroxy-3-((Z)-3′-hydroxy-3′-methyl-1′-butenyl) acetophenone-8-O-β-D-glucopyranoside (154), and 4-hydroxy-3-((Z)-3′-hydroxy-3′-methyl-1′-butenyl) acetophenone-6-O-β-D-glucopyranoside (155) [73]. None of these compounds showed to possess any significant cytotoxicity upon their application on MH-S cells. Furthermore, these compounds displayed no noticeable anti-inflammatory activities with regard to the inhibition of NO secretion at either 12.5 or 25 µM concentrations. Acetophenone compounds, extracted from the family Asteraceae are elucidated in Fig. 6.

Open image in new window

3.4 Asclepiadaceae

The biggest genus of the family is Cynanchum L., the species of which have been used in traditional medicine for the treatment of various diseases and disorders [74]. The phytochemical components of those species account for their immune regulation, anti-tumor, and anti-oxidation properties [75]. Hwang et al. extracted two acetophenone derivatives, cynandione A (156) and cynanchone A (157), from the roots of Cynanchum wilfordii, neither of which showed any multidrug-resistance [76]. In another study on the components of the root bark of C. wilfordii, three acetophenone derivatives, namely cynwilforones A-C (158–160) were discovered by Jiang et al. [77]. 158 reportedly exhibited hypoglycemic effects in the primary hepatocytes of mice by inhibiting hepatic gluconeogenesis through down-regulating the expression of G6P and PEPCK enzymes, which are responsible for the control of gluconeogenesis [77]. The application of two doses of 158 at 20 µM and 40 µM yielded the suppression of hepatic gluconeogenesis by 12.5% and 29.4%, respectively; hence, positing the potential healing traits of the root barks of C. wilfordii, along with their current use for mitigating neurasthenia, abscesses, impotency, and lumbago [77]. Cynandione A (156) and its dimers, cynandiones B & C (161 and 162) were isolated from C. taiwanianum [78]. In continuation of this study, one more acetophenone derivative was identified and extracted from C. taiwanianum, named cynanchone D (163) [78]. Cynanchone A (157) was also isolated in this assay [78]. A cytotoxic acetophenone, called cynantetrone (164) was isolated from C. taiwanianum by Huang et al. [79]. The assessment for its bioactivity revealed a cytotoxic trait against PLC/PRF/5, and T-24 cancer cell lines with the ED₅₀ values of 6.6 and 3.5 µg/mL. The inhibitory effect of 164 on KB cell lines was proven to be insignificant [79]. Having investigated C. bungei, Li et al. isolated four acetophenone glucoside compounds which were regarded to as bungeisides A-D (165–168) [80]. This species later exhibited to possess four more novel acetophenone compounds identified as 4-hydroxyacetophenone (169), 2,5-dihydroxyacetophenone (170), baishouwubenzophenone (171), and 2,4-dihydroxyacetophenone (172) [81]. 169 was also later discovered in C. auriculatum and C. wilfordii [82–84]. Figure 7 shows the structures of extracted acetophenones from Asclepiadaceae.

Open image in new window

3.5 Euphorbiaceae

Euphorbiaceae contains 299 genera and 8000 species, grouped into seven subfamilies, listed as Euphorbioideae, Crotonoideae, Acalyphoideae, Cheilosoideae, Peroideae, Oldfieldioideae, and Phyllanthoideae, which are found in the forms of trees, shrubs, and annual plants [85]. The species belonging to Euphorbiacea family are best grown in tropical and subtropical regions and rarely grow in cold temperate climates [86]. Euphorbia is the vastest genus, containing over 200 species. The members of this family are defined among the most phytochemically diverse species [87]. Alkaloids, tannins, diterpenes, cyanogenic glycosides, triterpenes, and glucosinolated lipids are some of the significant secondary metabolites, reported from the species of Euphorbiaceae [86]. Du et al. extracted the previously-unknown acetophenone glycoside, 2-hydroxy-6-methoxyacetophenone-4-O-(6′-acetate)-β-D-glucopyranoside (173) from E. fischeriana [88]. 173 elucidated to possess antiproliferative activity against AGS (IC₅₀ = 39.85 µM) and Hep-G2 (IC₅₀ = 35.06 µM) cancer cell lines [88]. Three acetophenone glycosides, (174–176) were also isolated from E. fischeriana by Huang et al. [89]. The iosolated compounds were ineffective against a group of human cancer cell lines (MCF-7, LoVo, SH-SY5Y, U87, U118, and U251) with the IC₅₀ values of more than 100 µM [89]. Wang et al. obtained an acetophenone glycoside denoted (177) from E. ebracteolate (91). By exploiting the DPPH scavenging assay, 177 was discovered to possess antioxidant activity at the IC₅₀ value of 34.62 µg/mL [90]. Yin et al. isolated two acetophenone derivatives (178 and 179) from E. ebracteolate [91]. Acetophenone compounds, (180 and 181) were extracted from E. ebracteolata Hayata [92]. The cytotoxicity activity of 180 and 181 were assessed against four lines of human cancer cells, namely Hela-60, MCF-7, A-549, and SMMC-7541, which elucidated the following results: 180 hindered the cell lines with the IC₅₀ values of 0.095, 6.85, 8.71, and 16.52 μg/mL in the same order, whereas 181 left its cytotoxic effects at the IC₅₀ values of 2.69, 0.346, 0.879, and 12.86 μg/mL, respectively [92]. Acetophenone glycosides: langduphenone A (182), langduphenone B (183), and langduphenone C (184) were extracted from E. fischeriana [93]. Compounds 182–184 were elucidated to possess inhibitory qualities against cancer cells and bacteria. Regarding the former, the isolated compounds were applied to five lines of cancer cells including Hep-G2, Hep-3B, A549, NCI–H460, and AGS; 182 indicated the cytotoxic effects with the IC₅₀ values of 33.9, 30.2, 39.4, 27.3, and 44.8 µM, respectively. 183 and 184, too, displayed the same trait at the sequential values of 27.8, 25.4, 37.2, 31.6, 38.2 µM and 45.4, > 50, 37.2, 36.4, > 50 µM. As for the antibacterial activity, two Gram-negative bacteria, E. coli P. aeruginosa, and two strains of Gram-positive bacteria, i.e., S. aureus and B. subtilis were used for the measurement; compounds 182–184 inhibited the proliferation of the four aforementioned bacteria with the ternary MIC values listed as: (12.5, 6.25, 6.25), (6.25, 12.5, 3.12), (6.25, 3.12, 1.56), and (6.25, 3.12, 3.12) µg/mL, respectively [93]. Sun and Liu elucidated the structure of 2,4-dihydroxy-6-methoxy-1-acetophenone (185) and 2,4-Dihydroxy-6-methoxy-3-methylacetophenone (186) [94] which were originally isolated from E. fischeriana by che et al. [95] and liu et al. [96]. Research into the phloroglucinol derivatives of Mallotus japonicus gave rise to the identification of a new acetophenone compound, called mallophenone (187), and three of its derivatives, namely isomallotochromene (188), mallotochroman (189), and isomallotochroman (190). The cytotoxicity of 187–190 against HeLa cancer cells were measured and their ID₅₀ values were registered respectively as follows: 14.80, 0.28, 49.10, and 8.80 µg/mL. 198–201, also, had the Anti HSV-1 activities with the in-turn ED₅₀ values of 6.18, 0.11, 48.00, and 0.97 µg/mL, respectively [97]. From the fruits of Mallotus japonicus, Ariswa et al. identified another acetophenone derivative, called mallotophenone (191) [98]. Having been tested against Leukemia L-5178Y cells of mice in vitro, compound 191 performed inhibitory activity with the ED50 value of 6.10 µg/mL [98]. Regarding the toxicity in the KB system, 191, also, showed potent with the ED50 value of 2.40 µg/mL [98]. The acetone extract of the roots of E. kansui provided two acetophenone derivatives (192 and 193) [99]. Geng et al. identified an acetophenone trimer from E. ebracteolate and assigned it as ebracteolatain C (194) [100]. Euphorbiaceae’s derived acetophenone derivatives are illustrated in Fig. 8.

Open image in new window

3.6 Myrtaceae

Family Myrtaceae consists of about 142 genera and 5500 species. Myrtaceae is well-defined for its glandular leaves that contain aromatic polyphenolic and terpenoid substances [101, 102]. The majority of Myrtaceae species are trees that mainly distributed in tropical to temperate regions [102]. The EO of Mytraceae plants is primarily consisted of monoterpenes and sesquiterpenes, and often the mixture of both. Complex terpenes, such as triterpenes are also found in less values. Other compounds, like alkyl derivatives, β-triketones and aromatic compounds, such as acetophenone compounds also occur in the species, however, less commonly [102]. Eucalyptus gomphocephala is one of the most widely used plants with versatile uses across the globe and it has been used for therapeutic purposes since ancient times for its antiseptics and respiratory tract infection inhibitory features, etc. [103]. An experiment, designed for identifying the phenolic compounds from the E. gomphocephala, afforded two novel acetophenone derivatives, namely 2,4,6-trihydroxy-5-methyl-acetophenone 2-O-β-D-glucopyranoside (195) and Benzyl alcohol 7-O-(3',4',6'-tri-O-galloyl)-β-D glucopyranoside (196) [103]. 195 exhibited no cytotoxic activity on HeLa cells, the trait which 196 possessed at extremely low levels with an IC₅₀ value of 367.1 µM [103]. Ha et al. isolated two acetophenone compounds from the foliage of Cleistocalyx operculatus (197 and 198) [104]. Both compounds revealed to be moderately effective against neuraminidase of various strains of swine influenza virus including H9N2, H1N1, H1N1 (WT), and H274Y. 197 expressed inhibitory effects at the IC₅₀ values of 38.00, 45.57, 43.84, and 36.72 µM, respectively, as did 198 at the IC₅₀ values of 40.33, 48.25, 44.13, and 48.07 µM in the same order [104]. The screening of the extract from the cloves of Syzygium aromaticum revealed two previously-unknown acetophenones (199 and 200) [105]. Both compounds were subjected for their inhibitory abilities of prolyl endopeptidase, the result of which demonstrated the IC₅₀ values of 218.9 and 17.2 µM attributed to 199 and 200, respectively. This assay shed light on the potent applicability of 199 for preventing memory loss [105]. Ryu et al. also isolated phloroacetophenone-O-glycoside compounds, 2,4,6-trihydroxy-3-methylacetophenone-2-O-β-D-glucoside (201) and 2,4,6-trihydroxyacetophenone-3-C-β-D-glucoside (202) from S. aromaticum; 201 was obtained from the flower buds of the plant [106], and 202 from both flower buds and its leaves [106, 107]. The cytotoxic activities of 201 and 202 were assessed against A2780 human cancer cells which disproved the pertaining abilities of both compounds as they both showed the inhibitory effect with the IC₅₀ of > 100 µM [106]. These novel acetophenone compounds are shown in Fig. 9.

Open image in new window

3.7 Other Families

Four acetophenone derivatives (203–206) were extracted from Iris japonica (Iridaceae) by Shi et al. [108]. Hoang et al., also, identified apocynin acetophenone (207) from Iris spp [109]. Apocynin (207) is an important naturally occurring acetophenone with various pharmacological activities. It has been studied for its potential in treating a variety of disorders, including diabetic complications, neurodegeneration, cardiovascular disorders, lung cancer, hepatocellular cancer, pancreatic cancer, and pheochromocytoma [110–113]. It has been formulated into various nanoparticles to enhance its absorption and duration of action [114]. Additionally, apocynin has shown promise in the treatment of various disorders, including diabetic complications, neurodegeneration, cardiovascular disorders, lung cancer, hepatocellular cancer, pancreatic cancer, and pheochromocytoma [112]. Its primary reported mechanism of action is as an NADPH oxidase (NOX) inhibitor, but recent studies have also highlighted its off-target effects, such as scavenging non-radical oxidant species [115]. Zulfiqar et al. isolated three acetophenone C-glycosides (208–210) from the stem of Upuna borneensis (Dipterocarpaceae) using acetone solvent [116]. Lendl et al. screened the extract of Chione venosa (sw) (Rubicaceae) and identified three acetophenone derivatives as: ortho-hydroxy-acetophenone-azine (211), acetophenone-2-O-[β-D-apiofuranosyl-(1″ → 6’)-O-β-D-glucopyranoside] (212), and acetophenone-2-O-β-D-glucopyranoside (213) [117]. A polyoxygenated acetophenone, denoted as 2,6-dimethoxy-4-hydroxyacetophenone (214) was identified in the bulbs of Pancratium maritimum (Amaryllidaceae) [118]. Analyzing the constituents of P. biflorum led to the identification of two previously-undiscovered acetophenone glycosides, named 4,6-Dimethoxyacetophenone-2-O-β-D-glucoside (215) and 2,6-Dimethoxyacetophenone-4- O-β -D-glucoside (216) [119]. Miyazawa and Kawata detected the presence of two acetophenone compounds, namely paeonol (217) and acetanisole (218), in the essential oil of Cimicifuga simplex (Ranunculaceae) [120]. Paeonol (217), a significant bioactive acetophenone, shows a range of pharmacological and biological activities. It has been shown to possess substantial anticancer effects, including the induction of apoptosis, inhibition of cell proliferation, and modulation of multiple signaling pathways [121]. Paeonol also shows potential as a therapeutic agent for atherosclerosis, with anti-atherosclerotic effects and protective effects on important cell types involved in the disease [122]. In osteoarthritis, paeonol has been found to mitigate inflammation, prevent extracellular matrix degradation, and inhibit chondrocyte apoptosis through the activation of the SIRT1 pathway [123]. Paeonol has proven to be effective in treating chronic dermatitis, reducing scratching behavior and skin inflammation [124]; It also has therapeutic effects in ulcerative colitis (UC) [125]. It has also shown promise in treating dry skin diseases by reducing inflammation and itching behavior through the CXCR3 pathway [124]. Furthermore, paeonol has various applications in different industries. It has been found to effectively inhibit the growth of Aspergillus flavus, a fungus that can damage agricultural products [126]. Paeonol treatment can also promote reendothelialization, the process of regrowing the endothelial layer of blood vessels, which is important for the treatment of vascular diseases [127].

Sancin (1971) identified acetophenone derivative, named acetovanillone (219) in the roots of Apocynum venetum (Apocynaceae) [128]. It also yielded p-hydroxyacetophenone (126) that was hitherto unidentified in the plant [128]. Research into Polygonum multiflorum from Polygonaceae family afforded a novel acetophenone compound, called polygoacetophenoside (220) [129]. Screening the chemical composition of Rumex aquatica extract, Yoon et al. extracted a new acetophenone compound, named rumexin (221) [130].

The roots of Sanguisorba minor from Rosaceae family produced 2′,6′-dihydroxy-4′-methoxyacetophenone (222) [131]. 222 exerted its phytoalexin characteristics by inhibiting the germination of two strains of fungi, namely Botrytis cinerea and Phomopsis perniciosa with the ED₅₀ values of 45 and 410 µM, respectively [131]. Prasad (1998), exploring the therapeutic constituents of Prunus armeniaca, extrcated the aromatic glycoside acetophenone, named 4-O-glycosyloxy-2-hydroxy-6-methoxyacetophenone (223) [132]. Acetophenone derivatives, knema pachycarpa A (224), and knema pachycarpa B (225) were isolated from the stems of Knema pachycarpa (Myristicaceae) [133]. Both compounds were evaluated for their cytotoxic activities against three cancer cell lines, including Hela, MCF7, and Hep3B; while both 224 and 225 reflected moderate activities against Hela cells with the IC₅₀ values of 26.92 and 30.20 µM, neither of them performed noticeable inhibitory activities against MCF7 and Hep3B cell lines (52.88 and 46.22 µM against the former, and > 100 and 70.80 against the latter, respectively) [133].

Kanchanapoom et al. detected two acetophenone compounds from Erythroxylum cambodianum (Erythroxylaceae) (226 and 227) [134]. Acetophenone glycoside (228) was isolated from Cassia sophera (Fabaceae) [135]. Edayadulla and Ramesh pinpointed the occurrence of a novel prenylated acetophenone compound, 1-[2,4-dihydroxy-5-(3-methylbut-2-enyl)phenyl]ethenone (229) a derivative of 2,4-dihydroxyacetophenone, from Derris indica (Leguminosae) [136]. Kuang et al. extracted 3,5-dimethyl-6-hydroxy-2-methoxy-4-O-D-glucopyranosyl-oxy-acetophenone (230) from Dryopteris fragrans (Asplenaceae) [137]. Aladesanmi et al. isolated p-hydroxyacetophenone (127) for the first time from the leaves of Dysoxylum lenticellare (Meliaceae) [138]. In addition, Wei-sheng et al. isolated the same compound from Saxifraga stolonifera (Saxifragaceae) that was previously unknown in the genus [139]. The research into the identification of acetophenone components from different species edged into sampling herbal products, as Quispe et al. extracted also 127 and its glucoside derivatives from an infusion made of the aerial parts of Fabiana imbricata (Solanaceae) [140]. An acetophenone glycoside was isolated from Exacum affine (Gentianaceae) by Kuwajima et al. who defined it as affinoside (231) [141]. 2,3,4-Trihydroxy-5-methylacetophenone (232) was extracted from the sap of Borassus flabellifer Linn (Arecaceae) [142]. The antibacterial activity of 232 was put to test and it inhibited the growth of seven strains of bacteria, namely B. cereus, E. coli, K. pneumoniae, M. smegmatis, S. aureus, S. epidermidis, and S. simulans, with the MIC values of 62.5, 62.5, 125, 125, 62.5, 250, and 250 μg/mL, respectively. Regarding the anti-oxidant activity, compound 232 displayed an IC₅₀ value of 20.02 µM for the DPPH radical scavenging activity [142]. Cortex Moutan, the root bark of Paeonia suffruticosa (Paeoniaceae), was revealed to contain paeonol acetophenone (217) [143]. In vitro examination identified this compound as the anticoagulative agent of the plant, a quality which was posited to stem from the compounds involvement in the formation of A2 from arachidonic acid [143]. Three decades later, another member of Paeoniaceae family, Paeonia ostia, was found to host two novel acetophenones, namely 2-hydroxy-4-methoxy-acetophenone-3-O-[β-D-apiofuranosyl (1 → 6)-β-Dglucoside (233), and 4-hydroxy-2-O-β-rutinosyl acetophenone (234) [144]. Neither of these compounds possessed any significant anti-inflammatory activity as they failed to inhibit nitric oxide production in vito.

There are reports of the presence of acetophenone compounds in Gymnosperms. Osswald et al. reported the extraction of p-hydroxyacetophenone (127) in Picea abies (spruce needles) (Pinaceae) and explored the fungitoxic activity of that compound towards Cladosporium cucumerinum and Ospbaera kalkhoffii [145]. Attempts to screen the compounds from the members of gymnosperms perpetuated as Inatomi et al. identified seven acetophenone derivatives from Juniperus occidentalis (Cupressaceae). These compounds were elucidated as Juniperoside Ⅲ – Ⅸ (235–241) [146]. Figure 10 illustrates the aforementioned acetophenone compounds.

Open image in new window

4 Acetophenone derivatives produced by fungi

Fungi are a diverse group of organisms, with over 5 million estimated species [147], However, only a small fraction of these species have been cultivated, described, and studied for their chemical properties [148]. They have recently garnered significant attention from the scientific community due to their ability to produce bioactive secondary metabolites with novel structures and there have been attempts to isolate acetophenone compounds from various strains of fungi [149]. A novel acetophenone derivative, identified as 4-prenyloxyclavatol (242) was identified in and extracted from Nigrospora sphaerica fungus [150]. Eremophylane acetophenone conjugates, colletotricholides A (243) and colletotricholides B (244) were extracted from Colletotrichum gloeosporioides XL1200, an endophytic fungus collected from Salvia miltiorrhiza [151]. Compounds 243 and 244 showed no inhibitory effects towards any strains of pathogenic microorganism tested i.e., bacteria and fungi [151]. Another strain of fungi, referred to as Mycosphaerella sp. L3A1, was recently discovered to contain a previously undetected acetophenone, namely acetophenone-4-O-methyl-β-D-glucopyranoside (245). This compound proved ineffective against a group of cancer cells (MDA-MB-231, MDA-MB-435, HCT116, SNB19, PC-3, and A549) [152]. Lindgomyces madisonensis (G416) represents another fungal strain that yielded seven novel acetophenone compounds upon being isolated from submerged wood. These compounds were extracted and elucidated as madisone (246), 4′-demethoxydimadisone (247), dehydromadisone (248), 2″-methoxymadisone (249), dihydroallovisnaginone (250), dimadisone (251), and 4′-methoxydimadisone (252). Fungi-derived acetophenone compounds are elucidated in Fig. 11.

Open image in new window

A summary of the biological activities of acetophenones are listed in Table 1.

5 Conclusion

Natural products (NPs) are a diverse and abundant source of biologically active compounds with enormous potential for new drug discovery and other applications. In today's clinical landscape, more than half of all drugs in use are either natural products or their derivatives, with plants contributing no less than a quarter of this total [153]. NPs have been used for centuries to treat a wide range of diseases, and modern research has shown that they possess a wide range of biological activities, including cytotoxicity, antibacterial, antifungal, antiviral, and antiparasitic activity. NPs are produced by a variety of organisms, including microbes and plants [154]. However, only a small fraction of the world's biodiversity has been studied for its pharmaceutical potential, suggesting that the vast majority of NPs remain to be discovered. Acetophenone compounds which are present in a relatively wide variety of plant species and some strains of fungi are garnering increasing focus by natural products researches as they have proven to possess diverse biological activities. The exploration of various plant and fungal species has yielded 266 natural acetophenone compounds and derivatives, many of which exhibit a wide range of biological activities. This illustrates the depth of possibilities that the study of acetophenones can offer in the realms of medicine and science.

Notes

Acknowledgements

The authors are also grateful to Mashhad University of Medical Sciences, School of Pharmacy, Mashhad, Iran, for financial support.

Author contributions

VS, JA, and Ash designed the study and edited of the manuscript. HA and HA wrote the manuscript. AFT analyzed the data, edited of the figures and tables. All authors approved the final version of the manuscript.

Data availability

Not applicable.

Declarations

Competing interests

The authors declare no conflict of interest.