Eugenol and its synthetic analogues inhibit cell growth of human cancer cells (Part I)

Therapeutic Effects of Essential Oils and Their Bioactive Compounds on Prostate Cancer Treatment

Since prostate cancer (PCa) relies on limited therapies, more effective alternatives are required. Essential oils (EOs) and their bioactive compounds are natural products that have many properties including anticancer activity. This review covers studies published between 2000 and 2023 and discusses the anti-prostate cancer mechanisms of the EOs from several plant species and their main bioactive compounds. It also provides a critical perspective regarding the challenges to be overcome until they reach the market. EOs from chamomile, cinnamon, Citrus species, turmeric, Cymbopogon species, ginger, lavender, Mentha species, rosemary, Salvia species, thyme and other species have been tested in different PCa cell lines and have shown excellent results, including the inhibition of cell growth and migration, the induction of apoptosis, modulation in the expression of apoptotic and anti-apoptotic genes and the suppression of angiogenesis. The most challenging aspects of EOs, which limit their clinical uses, are their highly lipophilic nature, physicochemical instability, photosensitivity, high volatility and composition variability. The processing of EO-based products in the pharmaceutical field may be an interesting alternative to circumvent EOs' limitations, resulting in several benefits in their further clinical use. Identifying their bioactive compounds, therapeutic effects and chemical structures could open new perspectives for innovative developments in the field. Moreover, this could be helpful in obtaining versatile chemical synthesis routes and/or biotechnological drug production strategies, providing an accurate, safe and sustainable source of these bioactive compounds, while looking at their use as gold-standard therapy in the close future.

Regioselectivity in the Nitration of Eugenol Is Independent of Inorganic Reagents: An Experimental and Theoretical Investigation with Synthetic and Mechanistic Implications

In this study, we reinvestigated the straightforward nitration of eugenol using traditional reagents and bismuth nitrate. NMR analysis of the obtained products revealed that the regioselectivity of eugenol nitration was independent of the inorganic nitrating reagent used, consistently resulting in the formation of 6-nitroeugenol. This contradicts previous literature reports because the elusive synthesis of 5-nitroeugenol using Bi(NO3)3·5H2O was not achievable through straightforward methods; instead, this isomer could only be prepared via the well-established three-step synthesis. Theoretical investigations using DFT calculations, considering both the dielectric constant of the medium and explicit water molecules, substantiated this regioselectivity. It was found that hydration water played a critical role in the formation of a Zundel cation, shifting the thermodynamic equilibrium toward the exclusive production of 6-nitroeugenol. These results imply that all biological studies involving eugenol derivatives synthesized via direct nitration with Bi(NO3)3·5H2O should be reviewed, as they dealt with 6-substituted eugenol derivatives rather than the previously assumed 5-substituted eugenol.

Antifungal Activity of 2-Allylphenol Derivatives on the Botrytis cinerea Strain: Assessment of Possible Action Mechanism

Botrytis cinerea is a phytopathogenic fungus that causes serious damage to the agricultural industry by infecting various important crops. 2-allylphenol has been used in China as a fungicide for more than a decade, and it has been shown that is a respiration inhibitor. A series of derivatives of 2-allylphenol were synthesized and their activity against B. cinerea was evaluated by measuring mycelial growth inhibition. Results indicate that small changes in the chemical structure or the addition of substituent groups in the aromatic ring induce important variations in activity. For example, changing the hydroxyl group by methoxy or acetyl groups produces dramatic increases in mycelial growth inhibition, i.e., the IC50 value of 2-allylphenol decreases from 68 to 2 and 1 μg mL−1. In addition, it was found that the most active derivatives induce the inhibition of Bcaox expression in the early stages of B. cinerea conidia germination. This gene is associated with the activation of the alternative oxidase enzyme (AOX), which allows fungus respiration to continue in the presence of respiratory inhibitors. Thus, it seems that 2-allylphenol derivatives can inhibit the normal and alternative respiratory pathway of B. cinerea. Therefore, we believe that these compounds are a very attractive platform for the development of antifungal agents against B. cinerea.

A comprehensive and systematic review on potential anticancer activities of eugenol: From pre-clinical evidence to molecular mechanisms of action

BACKGROUND

Eugenol (1-allyl-4-hydroxy-3-methoxybenzene) is an important simple phenolic compound mainly derived from Syzygium aromaticum and many other plants. It is traditionally used in ayurveda and aromatherapy for the healing of many health problems. It also has significant applications in dentistry, agriculture, and flavour industry. This simple phenol has an eclectic range of pharmacological properties, such as antioxidant, anti-inflammatory, and anticancer activities. It is regarded as safe by the Food and Agricultural Organization of the United Nations due to its non-carcinogenic and non-mutagenic properties.

PURPOSE

The aim of this comprehensive review is to present a critical and systematic assessment of the antitumor ability of eugenol and its associated molecular targets in various cancers.

METHODS

It was carried out following the preferred reporting items for systematic reviews and meta-analysis guidelines. Risk of bias assessment was performed using the SYstematic review centre for laboratory animal experimentation guidelines. The literature search was performed in standard databases such as Science Direct, PubMed, Google Scholar, Scopus, and Web of Science using the keywords 'eugenol' or 'eugenol essential oil' and 'anti-cancer properties of eugenol'.

RESULTS

The scientific information from fifty-three studies was encompassed in the present review work. Eugenol exhibits significant anticancer effects in a variety of biological pathways, namely apoptosis, autophagy, cell cycle progression, inflammation, invasion, and metastasis. Eugenol-induced apoptosis has been noticed in osteosarcoma, skin tumors, melanoma, leukemia, gastric and mast cells. It decreases the expression of cyclin D1, cyclin B, proliferating cell nuclear antigen, nuclear factor-ƙB, inhibitor of nuclear factor ƙB, and B-cell lymphoma-2. Eugenol increases the expression of B-cell lymphoma-2 (BCL-2) associated X, BH3-interacting domain death agonist, BCL-2 associated agonist of cell death, apoptotic protease activating factor 1, cytochrome c, p21, and p53.

CONCLUSION

The anticancer potential exhibited by eugenol is mainly attributed to its anti-metastatic, anti-proliferative, anti-angiogenic, anti-inflammatory, cell cycle arrest, apoptotic, and autophagic effects. Hence, the use of eugenol alone or along with other chemotherapeutic anticancer agents is found to be very effective in cancer therapy.

Study on Cytotoxic and Genotoxic Potential of Bulgarian Rosa damascena Mill. and Rosa alba L. Hydrosols—In Vivo and In Vitro

The Rosa alba L. and Rosa damascena Mill. growing in Bulgaria are known for their extremely fine essential oil and valuable hydrosols. Irrespectively of its wide use in human life, little research exists on the cytotoxic and genotoxic activity of the hydrosols. This set our goal to conduct cytogenetic analyses to study these effects. A complex of classical cytogenetic methods was applied in three types of experimental test systems—higher plant in vivo, ICR mice in vivo, and human lymphocytes in vitro. Mitotic index, PCE/(PCE + NCE) ratio, and nuclear division index were used as endpoints for cytotoxicity and for genotoxicity—induction of chromosome aberrations and micronuclei. Rose hydrosol treatments range in concentrations from 6% to 20%. It was obtained that both hydrosols did not show considerable cytotoxic and genotoxic effects. These effects depend on the type of the tested rose hydrosols, the concentrations applied in the experiments, and the sensitivity and specificity of the test systems used. Human lymphocytes in vitro were the most sensitive to hydrosols, followed by higher plant and animal cells. Chromosomal aberrations and micronucleus assays suggested that R. damascena and R. alba hydrosols at applied concentrations possess low genotoxic risk. Due to the overall low values in terms of cytotoxic and/or genotoxic effects in all test systems, hydrosols are promising for further use in various areas of human life.

Eugenol β-Amino/β-Alkoxy Alcohols with Selective Anticancer Activity

Eugenol, 4-allyl-2-methoxyphenol, is the main constituent of clove essential oil and has demonstrated relevant biological activity, namely anticancer activity. Aiming to increase this activity, we synthesized a series of eugenol β-amino alcohol and β-alkoxy alcohol derivatives, which were then tested against two human cancer cell lines, namely gastric adenocarcinoma cells (AGS) and lung adenocarcinoma cells (A549). An initial screening was performed to identify the most cytotoxic compounds. The results demonstrated that three β-amino alcohol derivatives had anticancer activity that justified subsequent studies, having been shown to trigger apoptosis. Importantly, the most potent molecules displayed no appreciable toxicity towards human noncancer cells. Structure-activity relationships show that changes in eugenol structure led to enhanced cytotoxic activity and can contribute to the future design of more potent and selective drugs.

Control of ER-positive breast cancer by ERα expression inhibition, apoptosis induction, cell cycle arrest using semisynthetic isoeugenol derivatives

New semi-synthetic effective and safe anticancer agents isoeugenol derivatives were synthesized, characterized, and screened for their cytotoxic activity against MCF-7. Moreover, their selective cytotoxicity was assessed against MCF-10A. Three derivatives, 2, 8 and 10 were significantly more active than the reference drug 5-FU with IC₅₀ values of 6.59, 8.07 and 9.63 and 30.93 μM, respectively. Also interestingly, these derivatives demonstrated some degree of selectivity to cancer cells over normal cells. Furthermore, derivative 2 was subjected to other in vitro experiments against MCF-7 where it inhibited colony formation by 87.5% and lowered ERα concentration to 395.7 pg/mL compared to 1129 pg/mL in untreated control cells. In continuation of the investigation, the apoptotic activity of compound 2, was assessed where it significantly enhanced total apoptotic cell death by 9.16-fold (18.70% compared to 1.64% for the untreated MCF-7 control cells) and arrested the cell cycle at the G2/M phase. Furthermore, the molecular mechanism of apoptotic activity was investigated at both the gene (RT-PCR) and protein (western plotting) levels where upregulation of pro-apoptotic and down regulation of anti-apoptotic genes was detected. Additionally, compound 2 treatment enhanced the antioxidant (GSH, CAT, SOD) activities. Finally, in vivo experiments verified the effective anticancer activity of compound 2 through inhibition of tumor proliferation by 47.6% compared to 22.9% for 5-FU and amelioration of the hematological, biochemical, and histopathological examinations near normal. In effect, compound 2 can be viewed as a promising semi-synthetic derivative of isoeugenol with some degree of selectivity for management of breast cancer through apoptotic induction and ERα downregulation.

In silico molecular docking and dynamic simulation of eugenol compounds against breast cancer

Breast cancer is one of the most severe problems, and it is the primary cause of cancer-related death in females worldwide. The adverse effects and therapeutic resistance development are among the most potent clinical issues for potent medications for breast cancer treatment. The eugenol molecules have a significant affinity for breast cancer receptors. The aim of the study has been on the eugenol compounds, which has potent actions on Erα, PR, EGFR, CDK2, mTOR, ERBB2, c-Src, HSP90, and chemokines receptors inhibition. Initially, the drug-likeness property was examined to evaluate the anti-breast cancer activity by applying Lipinski's rule of five on 120 eugenol molecules. Further, structure-based virtual screening was performed via molecular docking, as protein-like interactions play a vital role in drug development. The 3D structure of the receptors has been acquired from the protein data bank and is docked with 87 3D PubChem and ZINC structures of eugenol compounds, and five FDA-approved anti-cancer drugs using AutoDock Vina. Then, the compounds were subjected to three replica molecular dynamic simulations run of 100 ns per system. The results were evaluated using root mean square deviation (RMSD), root mean square fluctuation (RMSF), and protein-ligand interactions to indicate protein-ligand complex stability. The results confirm that Eugenol cinnamaldehyde has the best docking score for breast cancer, followed by Aspirin eugenol ester and 4-Allyl-2-methoxyphenyl cinnamate. From the results obtained from in silico studies, we propose that the selected eugenols can be further investigated and evaluated for further lead optimization and drug development.

Enzymatic Synthesis of Eugenyl Acetate from Essential Oil of Clove Using Lipases in Liquid Formulation as Biocatalyst

In this research, eugenyl acetate, a compound with flavoring, antioxidant, and antimicrobial properties, was obtained from essential oil of clove (Syzygium aromaticum) via liquid lipase-mediated acetylation. Clove essential oil was extracted by drag water vapor from dry flower buds and its physic-chemical characteristics were analyzed. For the enzymatic synthesis, an extensive evaluation of reaction parameters was accomplished through employment of distinct reaction temperatures, acetic anhydride to eugenol molar ratios, enzyme loads, and three different lipases (a lyophilized enzyme produced by solid-state fermentation of sunflower seed with Penicillium sumatrense microorganism and other two commercial lipases - Lipozyme TL 100L and CALB L). The product eugenyl acetate was confirmed by 1H-NMR, 13C-NMR Distortionless Enhancement by Polarization Transfer (DEPT 135), and Heteronuclear Multiple Bond Correlation (HMBC). Through optimized conditions (55 °C, acetic anhydride to eugenol molar ratio of 1:1, 10 wt% of Lipozyme TL 100L), 91.80% of conversion after 2 h was achieved to the eugenyl acetate production. With the results obtained, it was possible to conclude that the use of lipases in liquid formulation is a promising alternative for the synthesis of essential esters largely applied on food, cosmetic, and pharmaceutical industries.

Pleiotropic Effects of Eugenol: The Good, the Bad, and the Unknown

Phytocompounds and medicinal herbs were used in traditional ancient medicine and are nowadays increasingly screened in both experimental and clinical settings due to their beneficial effects in several major pathologies. Similar to the drug industry, phytotherapy is interested in using nanobased delivery systems to view the identification and characterization of the cellular and molecular therapeutic targets of plant components. Eugenol, the major phenolic constituent of clove essential oil, is a particularly versatile phytochemical with a vast range of therapeutic properties, among which the anti-inflammatory, antioxidant, and anticarcinogenic effects have been systematically addressed. In the past decade, with the emerging understanding of the role of mitochondria as critical organelles in the pathophysiology of noncommunicable diseases, research regarding the role of phytochemicals as modulators of bioenergetics and metabolism is on a rise. Here, we present a brief overview of the major pharmacological properties of eugenol, with special emphasis on its applications in dental medicine, and provide preliminary data regarding its effects, alone, and included in polyurethane nanostructures, on mitochondrial bioenergetics, and glycolysis in human HaCaT keratinocytes.

Exploring the Potential of Aromatherapy as an Adjuvant Therapy in Cancer and its Complications: A Comprehensive Update

BACKGROUND

Aromatherapy is a traditional practice of employing essential oils for the therapeutic purposes, currently headed under the category of complementary and adjuvant medicine.

OBJECTIVE

The aim of this review article is to summarize the potential health benefits of aromatic essential oil from traditional times till the present. It also proposed some mechanisms which can be utilized as basis for using aromatherapy in cancer and cancer linked complications.

METHODS

To find out the relevant and authentic data, several search engines like Science direct, Pubmed, research gate, etc. were thoroughly checked by inserting key words like aromatherapy, complementary, adjuvant therapy etc. to collect the relevant material in context of article. Also, the chemical components of essential oil were classified based on the presence of functional groups, which are further explored for their cytotoxic potential.

RESULTS

The result depicted the anti-cancer potential of chemical constituents of essential oil against different types of cancer. Moreover, the essential oils show promising anti-inflammatory, anti-microbial, anti-oxidant and anti-mutagenic potential in several studies, which collectively can form the basis for initiation of its anti-cancer utility.

CONCLUSION

Aromatherapy can serve as adjuvant economic therapy in cancer after the standardization of protocol.

Acetyleugenol from Acacia nilotica (L.) Exhibits a Strong Antibacterial Activity and Its Phenyl and Indole Analogues Show a Promising Anti-TB Potential Targeting PknE/B Protein Kinases

Acetyleugenol is a phytochemical compound with broad effects against infectious diseases and tumors. Here, we extracted, characterized, and elucidated the structure of acetyeugenol, for the first time, from the leaves of Acacia nilotica (L.)—a well-known medicinal plant. The broad antibacterial potential of acetyleugenol was first confirmed against seven bacterial clinical isolates, which reveal a strong activity against Proteus sp., Salmonella typhi, Staphylococcus aureus, and Streptococcus pneumonia with similar or better zone of inhibition comparing to that of the control amoxicillin. To further investigate its effect against Mycobacterium tuberculosis, acetyleugenol and its indole and phenyl analogues were subjected to molecular docking experiments against two potential tuberculosis drug targets—MtPknE and MtPknB Ser/Thr protein kinases. The results reveal that all of the analogs have improved docking scores compared to the acetyleugenol. The indole analogues EUG-1 and EUG-3 were more effective with better docking scores for MtPknE with −11.08 and −10.05 kcal/mol, respectively. Similar results were obtained for the MtPknB. In contrast, only the EUG-2 phenyl analogue has given rise to similar docking scores for both targets. This opens the door for further comprehensive studies on these acetyleugenol analogues with in vitro and in vivo experiments to validate and get more insights into their mechanisms of action.

A novel series of substituted 1,2,3-triazoles as cancer stem cell inhibitors: Synthesis and biological evaluation

An alarming increase in global death toll resulting from cancer incidents, particularly due to multidrug resistance and reduced efficacy as a consequence of target mutations, has compelled us to look for novel anticancer agents. Cancer stem cells (CSCs), contributing majorly to the chemoresistance and tumor relapse, seem to the main culprits. In the present investigation, new chemical entities (NCEs) belonging to four novel chemical series (A: 4'-allyl-2'-methoxyphenoxymethyl-1,2,3-triazoles; B: 4'-acetamidophenoxymethyl-1,2,3-triazoles; C: naphthalene-1'-yloxymethyl-1,2,3-triazoles, and D: naphthalene-2'-yloxymethyl-1,2,3-triazoles) were synthesized via Copper (I)-catalyzed alkyne-azide cycloaddition reaction and evaluated for in vitro anticancer activity. A total of 30 NCEs (39-68) were screened at 10 μM concentration in cell viability assay against cancer cell lines such as breast (MDA-MB-231), prostate (PC-3), glioma (U87 MG), along with cervical (SiHa) and lung (A549). The NCEs from Series C (56-60) and D (61-68) were more potent than those in Series A (39-45) and Series B (46-55) at the tested concentration. Furthermore, NCEs with >80% inhibition at 10 μM were evaluated for dose response. A total of five NCEs, 48, 56, 61, 65 and 66, were further assessed in soft-agar assay and found to be relatively potent (IC₅₀  < 10 μM). Finally, the hits were screened in sphere assay to identify potential CSC inhibitors against mammospheres (MDA-MB-231) and prostatospheres (PC-3). More so, the hits were also evaluated to understand in vitro cytotoxicity against normal cells using mouse embryonic fibroblast cell line (NIH/3T3) and human peripheral blood mononuclear cells (hPBMCs). Overall, hits 56 and 61 exhibited potent anticancer as well as CSC inhibitory activities with notably less toxicity toward NIH/3T3 and hPBMCs. On the whole, our arduous study led to the identification of potential hits with anticancer and CSC inhibitory activities, with minimal or no toxicity to normal cells.

Crystal structure and Hirshfeld surface analysis of 4-allyl-2-meth-oxy-6-nitro-phenol

The asymmetric unit of the title compound, C10H11NO4, which was synthesized via nitration reaction of eugenol (4-allyl-2-meth-oxy-phenol) with a mixture of nitric acid and sulfuric acid, consists of three independent mol-ecules of similar geometry. Each mol-ecule displays an intra-molecular hydrogen bond involving the hydroxide and the nitro group forming an S(6) motif. The crystal cohesion is ensured by inter-molecular C-H⋯O hydrogen bonds in addition to π-π stacking inter-actions between the aromatic rings [centroid-centroid distances = 3.6583 (17)-4.0624 (16) Å]. The Hirshfeld surface analysis and the two-dimensional fingerprint plots show that H⋯H (39.6%), O⋯H/H⋯O (37.7%), C⋯H/H⋯C (12.5%) and C⋯C (4%) are the most important contributors towards the crystal packing.

Natural Products and Synthetic Analogs as a Source of Antitumor Drugs

Cancer is a heterogeneous disease and one of the major issues of health concern, especially for the public health system globally. Nature is a source of anticancer drugs with abundant pool of diverse chemicals and pharmacologically active compounds. In recent decade, some natural products and synthetic analogs have been investigated for the cancer treatment. This article presents the utilization of natural products as a source of antitumor drugs.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

Co-Delivery of Eugenol and Dacarbazine by Hyaluronic Acid-Coated Liposomes for Targeted Inhibition of Survivin in Treatment of Resistant Metastatic Melanoma

While melanoma remains a challenge for oncologists, possibilities are being continuously explored to fight resistant metastatic melanoma more effectively. Eugenol is reported to inhibit survivin protein in breast cancer cells. Survivin is also overexpressed by melanoma cells, and is known to impart resistance to them against chemotherapy-induced apoptosis. To be able to fight resistant melanoma, we formulated hyaluronic acid (HA)-coated liposomes loaded with an effective combination of anti-melanoma agents (Dacarbazine and Eugenol), using a solvent injection method. Quality-by-Design (QbD) was applied to optimize and obtain a final formulation with the desired quality attributes, and within an acceptable size range. The optimized formulation was then subjected to performance analysis in cell lines. Coated-Dacarbazine Eugenol Liposomes were found to possess 95.08% cytotoxicity at a dacarbazine concentration of 0.5 µg/mL, while Dacarbazine Solution showed only 10.20% cytotoxicity at the same concentration. The number of late apoptotic cells was also found to be much higher (45.16% vs. 8.43%). Furthermore, migration assay and proliferation study also revealed significantly higher inhibition of cell migration and proliferation by Coated-Dacarbazine Eugenol Liposomes, signifying its potential against metastasis. Thus, surface-functionalized dacarbazine- and eugenol-loaded liposomes hold great promise against resistant and aggressive metastatic melanoma, with much less unwanted cytotoxicity and reduced doses of the chemotherapeutic agent.

Assessment of Polysaccharides from Mycelia of genus Ganoderma by Mid-Infrared and Near-Infrared Spectroscopy

Ganoderma lingzhi (G. lingzhi), G. sinense, G. applanatum, etc. belongs to the Ganoderma genus of polypore mushrooms which contain rich polysaccharides valuable for nutrition and positive medicinal effects. In order to evaluate polysaccharide content in Ganoderma mycelia obtained in the fermentation process quickly and accurately, in this work we employed infrared spectroscopy to examine different Ganoderma stains of samples from diversified sources. Through mid-infrared (mid-IR) spectroscopy, we could identify the most relevant spectral bands required for polysaccharide evaluation, and through near-infrared (NIR) spectroscopy, we could establish the quantification model for making satisfactory prediction of polysaccharide ingredient content. As such, we have achieved an effective and convenient approach to quantitative assessment of the total polysaccharides in Ganoderma mycelia but also demonstrated that infrared spectroscopy can be a powerful tool for quality control of Ganoderma polysaccharides obtained from industrial production.

The Dual Antioxidant/Prooxidant Effect of Eugenol and Its Action in Cancer Development and Treatment

The formation of reactive oxygen species (ROS) during metabolism is a normal process usually compensated for by the antioxidant defense system of an organism. However, ROS can cause oxidative damage and have been proposed to be the main cause of age-related clinical complications and diseases such as cancer. In recent decades, the relationship between diet and cancer has been more studied, especially with foods containing antioxidant compounds. Eugenol is a natural compound widely found in many aromatic plant species, spices and foods and is used in cosmetics and pharmaceutical products. Eugenol has a dual effect on oxidative stress, which can action as an antioxidant or prooxidant agent. In addition, it has anti-carcinogenic, cytotoxic and antitumor properties. Considering the importance of eugenol in the area of food and human health, in this review, we discuss the role of eugenol on redox status and its potential use in the treatment and prevention of cancer.

Perspectives on medicinal properties of natural phenolic monoterpenoids and their hybrids

Carvacrol, thymol and eugenol belong to a class of naturally presenting phenols with a ten-carbon unit, which are present in essential oils of many plants. These versatile molecules are incorporated as useful ingredients in many food products and find applications in agricultural, pharmaceutical, fragrance, cosmetic, flavor and other industries. They are wide ranging of biological and pharmaceutical activities: anti-inflammatory, antimicrobial, analgesic, anticancer and antioxidant. This review summarizes pharmacological and medicinal activities of these phytochemicals and their synthetic hybrids.

Toxicity of clove essential oil and its ester eugenyl acetate against Artemia salina

Abstract The production of compounds via enzymatic esterification has great scientific and technological interest due to the several inconveniences related to acid catalysis, mainly by these systems do not fit to the concept of “green chemistry”. Besides, natural products as clove oil present compounds with excellent biological potential. Bioactives compounds are often toxic at high doses. The evaluation of lethality in a less complex animal organism can be used to a monitoring simple and rapid, helping the identification of compounds with potential insecticide activity against larvae of insect vector of diseases. In this sense, the toxicity against Artemia salina of clove essential oil and its derivative eugenyl acetate obtained by enzymatic esterification using Novozym 435 as biocatalyst was evaluated. The conversion of eugenyl acetate synthesis was 95.6%. The results about the evaluation of toxicity against the microcrustacean Artemia salina demonstrated that both oil (LC50= 0.5993 µg.mL–1) and ester (LC50= 0.1178 µg.mL–1) presented high toxic potential, being the eugenyl acetate almost 5 times more toxic than clove essential oil. The results reported here shows the potential of employing clove oil and eugenyl acetate in insecticide formulations.

Essential oil eugenol: sources, extraction techniques and nutraceutical perspectives

Graphical representation regarding sources, extraction techniques and nutraceutical perspectives of eugenol.

Encapsulation of eugenyl acetate in PHBV using SEDS technique and in vitro release evaluation

Eugenyl acetate obtained via enzymatic esterification using Lipozyme TL IM enzyme was encapsulated in biopolymer poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) through solution-enhanced dispersion by supercritical fluids (SEDS). Produced particles were characterized by SEM and confocal microscopy techniques and in addition in vitro release assays were performed in isopropanol and ethyl acetate. Experimental micronization conditions comprised 8 and 10 MPa, 308 and 313 K and eugenyl acetate concentration ranging from 5 to 20 mg mL^-1, keeping PHBV concentration constant (20 mg mL^-1 in dichloromethane). The maximum encapsulation efficiency was 58.0 % for 5 mg mL^-1of eugenyl acetate at 8 MPa and 308 K. The morphology of the encapsulated particles for most of the trials was spherical, with particle size ranging from 0.061 to 0.276 μm. Regarding the release in ethyl acetate and isopropanol solvents the higher the affinity of the encapsulated ester of these solvents, the faster the release was observed. These results demonstrate the importance of essential clove oil esterification reaction and encapsulation of the ester by SEDS method so that this encapsulated ester can be used in different industrial applications.

Antitumor phenylpropanoids found in essential oils

The search for new bioactive substances with anticancer activity and the understanding of their mechanisms of action are high-priorities in the research effort toward more effective treatments for cancer. The phenylpropanoids are natural products found in many aromatic and medicinal plants, food, and essential oils. They exhibit various pharmacological activities and have applications in the pharmaceutical industry. In this review, the anticancer potential of 17 phenylpropanoids and derivatives from essential oils is discussed. Chemical structures, experimental report, and mechanisms of action of bioactive substances are presented.

Essential oils and their constituents as anticancer agents: a mechanistic view

Exploring natural plant products as an option to find new chemical entities as anticancer agents is one of the fastest growing areas of research. Recently, in the last decade, essential oils (EOs) have been under study for their use in cancer therapy and the present review is an attempt to collect and document the available studies indicating EOs and their constituents as anticancer agents. This review enlists nearly 130 studies of EOs from various plant species and their constituents that have been studied so far for their anticancer potential and these studies have been classified as in vitro and in vivo studies for EOs and their constituents. This review also highlights in-depth various mechanisms of action of different EOs and their constituents reported in the treatment strategies for different types of cancer. The current review indicates that EOs and their constituents act by multiple pathways and mechanisms involving apoptosis, cell cycle arrest, antimetastatic and antiangiogenic, increased levels of reactive oxygen and nitrogen species (ROS/RNS), DNA repair modulation, and others to demonstrate their antiproliferative activity in the cancer cell. The effect of EOs and their constituents on tumour suppressor proteins (p53 and Akt), transcription factors (NF- κB and AP-1), MAPK-pathway, and detoxification enzymes like SOD, catalase, glutathione peroxidase, and glutathione reductase has also been discussed.

Eugenol derivatives as potential anti-oxidants: is phenolic hydroxyl necessary to obtain an effect?

OBJECTIVES

Eugenol, obtained from clove oil (Eugenia caryophyllata), possess several biological activities. It is anti-inflammatory, analgesic, anaesthesic, antipyretic, antiplatelet, anti-anaphylactic, anticonvulsant, anti-oxidant, antibacterial, antidepressant, antifungal and antiviral. The anti-oxidant activity of eugenol have already been proven. From this perspective testing, a series of planned structural derivatives of eugenol were screened to perform structural optimization and consequent increase of the potency of these biological activities.

METHODS

In an attempt to increase structural variability, 16 compounds were synthesized by acylation and alkylation of the phenolic hydroxyl group. Anti-oxidant activity capacity was based on the capture of DPPH radical (2,2-diphenyl-1-picryl-hydrazyl), ABTS radical 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), measure of TBARS (thiobarbituric acid-reactive species), total sulfhydryl and carbonyl content (eugenol derivatives final concentrations range from 50 to 200 μm).

KEY FINDINGS

Four derivatives presented an efficient concentration to decrease 50% of the DPPH radical (EC50 ) < 100 μm, which has a good potential as a free-radical scavenger. Three of these compounds also showed reduction of ABTS radical. Eugenol derivatives presenting alkyl or aryl (alkylic or arylic) groups substituting hydroxyl 1 of eugenol were effective in reducing lipid peroxidation, protein oxidative damage by carbonyl formation and increase total thiol content in cerebral cortex homogenates. In liver, the eugenol derivatives evaluated had no effect.

CONCLUSIONS

Our results suggest that these molecules are promising anti-oxidants agents.

Eugenol--from the remote Maluku Islands to the international market place: a review of a remarkable and versatile molecule

Eugenol is a major volatile constituent of clove essential oil obtained through hydrodistillation of mainly Eugenia caryophyllata (=Syzygium aromaticum) buds and leaves. It is a remarkably versatile molecule incorporated as a functional ingredient in numerous products and has found application in the pharmaceutical, agricultural, fragrance, flavour, cosmetic and various other industries. Its vast range of pharmacological activities has been well-researched and includes antimicrobial, anti-inflammatory, analgesic, anti-oxidant and anticancer activities, amongst others. In addition, it is widely used in agricultural applications to protect foods from micro-organisms during storage, which might have an effect on human health, and as a pesticide and fumigant. As a functional ingredient, it is included in many dental preparations and it has also been shown to enhance skin permeation of various drugs. Eugenol is considered safe as a food additive but due to the wide range of different applications, extensive use and availability of clove oil, it is pertinent to discuss the general toxicity with special reference to contact dermatitis. This review summarises the pharmacological, agricultural and other applications of eugenol with specific emphasis on mechanism of action as well as toxicity data.

Antifungal activity of eugenol analogues. Influence of different substituents and studies on mechanism of action

Twenty one phenylpropanoids (including eugenol and safrole) and synthetic analogues, thirteen of them new compounds, were evaluated for antifungal properties, first with non-targeted assays against a panel of human opportunistic pathogenic fungi. Some structure-activity relationships could be observed, mainly related to the influence of an allyl substituent at C-4, an OH group at C-1 and an OCH₃ at C-2 or the presence of one or two NO₂ groups in different positions of the benzene ring. All active compounds were tested in a second panel of clinical isolates of C. albicans and non-albicans Candida spp., Cryptococcus neoformans and dermatophytes. The eugenol derivative 4-allyl-2-methoxy-5-nitrophenol (2) was the most active structure against all strains tested, and therefore it was submitted to targeted assays. These studies showed that the antifungal activity of 2 was not reversed in the presence of an osmotic support such as sorbitol, suggesting that it does not act by inhibiting the fungal cell wall synthesis or assembly. On the other hand, the Ergosterol Assay showed that 2 did not bind to the main sterol of the fungal membrane up to 250 µg mL⁻¹. In contrast, a 22% of fungal membrane damage was observed at concentrations = 1 × MIC and 71% at 4× MIC, when 2 was tested in the Cellular Leakage assay. The comparison of log P and MICs for all compounds revealed that the antifungal activity of the eugenol analogues would not to be related to lipophilicity.

Bismuth nitrate pentahydrate-induced novel nitration of eugenol

Background

Eugenol, the main constituent of clove oil possesses a number of medicinal activities. To enhance the medicinal property, structural modification is required. On the other hand, bismuth nitrate pentahydrate has been established as an excellent eco-friendly nitrating agent for several classes of organic compounds.

Results

Bismuth nitrate pentahydrate-induced nitration of eugenol has been investigated very thoroughly. Twenty five different conditions have been studied. The microwave-induced solvent-free reaction has been identified as the best condition.

Conclusions

Spectral analyses confirm that 5-nitroeugenol is the sole product in all the cases. No oxidized or isomerized product could be detected.