Susceptibility of methicillin-resistant staphylococci to oregano essential oil, carvacrol and thymol

The aim of this study was to evaluate the susceptibility of methicillin-susceptible and methicillin-resistant staphylococci (MSS, MRS) to oregano essential oil, carvacrol and thymol. The commercial aerial parts of Origanum vulgare L. were hydrodistilled and the essential oil analysed by gas- chromatography/electron impact mass spectrometry. The inhibition efficacy of this essence and its major components was assayed against 26 MSS and 21 MRS, using an agar dilution method. The methicillin resistance was thoroughly typed by Epsilometer test (E-test), polymerase chain reaction for mecA gene detection and PBP2' latex agglutination test. The results clearly demonstrated that the comparison between the susceptibility of MSS and MRS to oregano oil, carvacrol and thymol showed no significant differences (Fisher's exact test, P > 0.05). The best minimum inhibitory concentration values were reported for carvacrol (0.015-0.03%, v/v) followed by thymol (0.03-0.06%, v/v) and oregano oil (0.06-0.125%, v/v).     

Polyamine derivatives from the bee pollen of Quercus mongolica with tyrosinase inhibitory activity

Eighteen constituents, including nine new compounds, were isolated from the bee pollen of Quercus mongolica. The structures of the new compounds were established on the basis of combined spectroscopic analysis. Structurally, the nine new compounds are polyamine derivatives with phenolic moieties which were assigned as one putrescine derivative, mogolicine A (2), seven spermidine derivatives, mongolidines A-G (3–5, 8, 12, 14, 17) and one spermine derivative, mogoline A (18). Evaluation of the biological activity of isolated compounds revealed that the polyamine derivatives with coumaroyl and caffeoyl moieties showed tyrosinase inhibition with IC₅₀ values of 19.5–85.8 μM; however, the addition of a methoxy group to phenolic derivatives reduced the inhibitory activity.     

Synthesis and tyrosinase inhibitory activity of novel N-hydroxybenzyl-N-nitrosohydroxylamines

Several novel N-substituted N-nitrosohydroxylamines were synthesized. They all inhibited mushroom tyrosinase, but the type of inhibition was different depending on the substituent. Some N-(mono- or dihydroxybenzyl)-N-nitrosohydroxylamines exhibited uncompetitive inhibition with respect to L-dopa. Among them, compound 6 was also a competitive inhibitor with respect to oxygen. This observation suggests that another interaction by the meta- or para-hydroxyl group might stabilize the binding of the inhibitor to the enzyme through the oxygen binding site.     

Biotransformation of thymol, carvacrol, and eugenol by cultured cells of Eucalyptus perriniana

The biotransformations of aroma compounds of spices, such as thymol (1), carvacrol (2), and eugenol (3), were investigated using cultured plant cells of Eucalyptus perriniana. Besides a beta-glucoside product (4, 3%), a biotransformation product, i.e., 5-methyl-2-(1-methylethyl)phenyl 6-O-(beta-d-glucopyranosyl)-beta-d-glucopyranoside (5, beta-gentiobioside, 87%), was isolated from the suspension cells after the five-day incubation of 1. On administration of 2, a beta-glucoside (6, 5%) and a beta-gentiobioside, i.e., 2-methyl-5-(1-methylethyl)phenyl 6-O-(beta-d-glucopyranosyl)-beta-d-glucopyranoside (7, 56%), were produced. Furthermore, E. perriniana cells also converted 3 into the corresponding beta-glucoside (8, 7%) and beta-gentiobioside (9, 58%). The cultured cells of E. perriniana are able to convert these aroma compounds of spices into glycosides which are accumulated in the cells.     

Synthesis,computational molecular docking analysis and effectiveness on tyrosinase inhibition of kojic acid derivatives

Tyrosinase inhibitors have become increasingly important as whitening agents and for the treatment of pigmentary disorders. In this study, the synthesis of kojic acid derivatives having 2-substituted-3-hydroxy-6-hyroxymethyl/chloromethyl/methyl/morpholinomethylpiperidinyl- methyl/pyrrolidinylmethyl-4H-pyran-4-one structure (compounds 1–30) with inhibitory effects on tyrosinase enzyme were described. One-pot Mannich reaction was carried out by using kojic acid/chlorokojic acid/allomaltol and substituted benzylpiperazine derivatives in presence of formaline. Subsequently, cyclic amine (morpholine, piperidine and pyrrolidine) derivatives of the 6th-position of chlorokojic acid were obtained with nucleophilic substitutions in basic medium. The structures of new compounds were identified by FT-IR, ¹H- and ¹³C NMR, ESI-MS and elemental analysis data. The potential mushroom tyrosinase inhibitory activity of the compounds were evaluated by the spectrophotometric method using l-DOPA as a substrate and kojic acid as the control agent. The potential inhibitory activity was also investigated in silico using molecular docking simulation method. Tyrosinase inhibitory action was significantly more efficacious for several compounds (IC₅₀: 86.2–362.1 µM) than kojic acid (IC₅₀: 418.2). Compound 3 bearing 3,4-dichlorobenzyl piperazine moiety was proven to have the highest inhibitory activity. The results of docking studies showed that according to the predicted conformation of compound 3 in the enzyme binding site, hydroxymethyl group provides a metal complex with copper ions and enzyme. Thus, this interaction explain the high inhibitory activities of the compounds 1, 3 and 4 possessing hydroxymethyl substituent supporting the mushroom assay results with docking studies. In accordance with the results, it is suggested that Mannich bases of kojic acid bearing substituted benzyl piperazine groups (compounds 1, 3, 4, 11, 13, 14, 23, 24, 28, and 29) could be promising antityrosinase agents. Additionally, considering the relationship between tyrosinase inhibitory activity results and molecular docking, a new tyrosinase inhibition mechanism can be proposed.     

Evaluation of the inhibition of mushroom tyrosinase and cellular tyrosinase activities of oxyresveratrol: comparison with mulberroside A

The inhibitory effects of oxyresveratrol, the aglycone of mulberroside A, on mushroom and cellular tyrosinase activities and melanin synthesis were evaluated. Mulberroside A and oxyresveratrol showed inhibitory activity against mushroom tyrosinase, with oxyresveratrol demonstrating a greater inhibitory effect than that of mulberroside A. Oxyresveratrol and mulberroside A strongly inhibited melanin production in Streptomyces bikiniensis and exhibited dose-dependent inhibition of tyrosinase activity and inhibition of melanin synthesis in B16F10 melanoma cells. However, the compounds exhibited nearly similar inhibitory effects on the activity of cellular tyrosinase and melanin synthesis in murine melanocytes. The inhibition of melanin synthesis by mulberroside A and oxyresveratrol was involved in suppressing the expression level of melanogenic enzymes, tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). These results indicate that the inhibition rate of mushroom tyrosinase might not provide an accurate estimate of the inhibition rate of melanin synthesis in melanocytes.     

Inhibitory effects of 4-vinylbenzaldehyde and 4-vinylbenzoic acid on the activity of mushroom tyrosinase

Tyrosinase (EC 1.14.18.1) catalyzes both the hydroxylation of tyrosine into o-diphenols and the oxidation of o-diphenols into o-quinones which form brown or black pigments. Here, the inhibitory effects of 4-vinylbenzaldehyde and 4-vinylbenzoic acid on the activity of mushroom tyrosinase have been investigated. The results showed that both 4-vinylbenzaldehyde and 4-vinylbenzoic acid could inhibit both monophenolase activity and diphenolase activity of the enzyme. For the monophenolase activity, 4-vinylbenzoic acid could lengthen the lag time, but 4-vinylbenzaldehyde could not. Both 4-vinylbenzaldehyde and 4-vinylbenzoic acid decreased the steady-state activity, and the IC₅₀ values were estimated as 93?μM and 3.0?mM for monophenolase activity, respectively. For the diphenolase activity, the inhibitory capacity of 4-vinylbenzaldehyde was stronger than that of 4-vinylbenzoic acid, and the IC₅₀ values were estimated as 23?μM and 0.33?mM, respectively. Kinetic analyses showed that inhibition by both compounds was reversible and their mechanisms were mixed-II type; their inhibition constants were also determined and compared.     

In vitro antibacterial and cytotoxic activities of carvacrol and terpinen-4-ol against biofilm formation on titanium implant surfaces

Abstract

This study evaluated the antibacterial properties of carvacrol and terpinen-4-ol against Porphyromonas gingivalis and Fusobacterium nucleatum and its cytotoxic effects on fibroblast cells. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were examined. The minimum biofilm inhibition concentration (MBIC) was evaluated by XTT assay. Biofilm decontamination on titanium surfaces was quantified (CFU ml^?1), evaluated by confocal laser scanning microscopy (CLSM) and cytotoxic activity by MTT. The MIC and MBC for carvacrol were 0.007% and 0.002% for P. gingivalis and F. nucleatum, and 0.06% for terpinen-4-ol for both microorganisms. The MBIC for carvacrol was 0.03% and 0.06% for P. gingivalis and F. nucleatum, and for terpinen-4-ol was 0.06% and 0.24%. The results indicated anti-biofilm activity using carvacrol (0.26%, 0.06%) and terpinen-4-ol (0.95%, 0.24%) and showed cytotoxic activity similar to chlorohexidine (CHX). However, terpinen-4-ol (0.24%) showed higher cell viability than other treatments. Carvacrol and terpinen-4-ol showed antibacterial activity in respect of reducing biofilms. Moreover, CHX-like cytotoxicity was observed.     

Synthesis and tyrosinase inhibition activity of trans-stilbene derivatives

Synthesis of a focussed library of trans-stilbene compounds through Wittig and other base catalysed condensation reactions is presented. The synthesized stilbenes were screened for their inhibitory potential against murine tyrosinase activity to explore the structure activity relationship (SAR). Presence of electron withdrawing group (–CN) at the double bond and hydroxyl group or halogen atom especially at para-position on the aromatic rings was found to significantly elevate the inhibitory activity. Among all the compounds screened, compounds 2, 6, 8, 10, 11, 15 and 21 were found to exhibit appreciable inhibitory activity. Compound 21 ((E)-2,3-bis(4-Hydroxyphenyl)acryonitrile) was found to be the most active with an IC₅₀ value of 5.06 μM which is less than half of the value 10.78 μM observed for resveratrol (common standard used in murine tyrosinase activity studies) under similar conditions. The results obtained from the present study reveal structural/functional group sensitivity for the tyrosinase inhibitory activity of stilbenoid moieties and are expected to be very helpful for the design and synthesis of novel, selective and effective tyrosinase inhibitors.     

Depigmenting activities of kojic acid derivatives without tyrosinase inhibitory activities

We synthesized benzoate ester derivatives of kojic acid with and without adamantane moiety. Benzoate derivatives 2a-e that did not contain an adamantane moiety showed potent tyrosinase inhibitory activities. However, depigmenting activity was not noted in a cell-based assay. Contrasting results were obtained for benzoate derivatives (3a-e) containing an adamantane moiety. Compounds 3a-e showed potent depigmenting activities without tyrosinase inhibitory activities. To the best of our knowledge, this is the first study showing the depigmenting activities of kojic acid derivatives without tyrosinase inhibitory activities.     

Synthesis of rotenoid derivatives with cytotoxic and topoisomerase II inhibitory activities

6-Deoxyclitoriacetal (1) and a series of 11 further derivatives of it (2-12) were synthesized and evaluated for their cytotoxic and topoisomerase IIα inhibitory activities. Compounds bearing epoxide (2), morpholine (6) and benzylamine (10) moieties showed promising in vitro cytotoxic activities against four cancer cell lines, with IC₅₀ values ranging from 0.38 to 0.73 μM. These three compounds also strongly inhibited topoisomerase II activity at 68.3-93.5% and showed a moderately high DNA intercalating property.     

Consequence of the antioxidant activities and tyrosinase inhibitory effects of various extracts from the fruiting bodies of Pleurotus ferulae

This study was initiated to screen the antioxidant activities, tyrosinase inhibitory effects on the fruiting bodies of Pleurotus ferulae extracted with acetone, methanol and hot water. The antioxidant activities were performed on β-carotene–linoleic acid, reducing power, DPPH, ferrous ions chelating abilities, and xanthine oxidase. In addition to this, phenolic compounds were also analyzed. The methanolic extract showed the strongest β-carotene–linoleic acid inhibition and high reducing power as compared to other extracts. The scavenging effects on DPPH radicals, the acetonic and methanolic extracts were more effective than hot water extracts. The strongest chelating effect was obtained from the methanolic extract as compared to the tested synthetic antioxidant. Gallic acid, protocatechuic acid, caffeic acid, vanillin, ferulic acid, naringin, resveratrol, naringenin, hesperetin, formononetin and biochanin-A were detected from acetonitrile and hydrochloric acid (5:1) solvent extract. Xanthine oxidase and tyrosinase inhibitory activities of acetonic, methanolic, and hot water extracts of P. ferulae increased with increasing concentration. The results suggested that consumption of P. ferulae might be beneficial to the antioxidant, xanthine oxidase, and tyrosinase protection system of the human body against oxidative damage and others complications.     

The inhibitory effect of some new synthesized xanthates on mushroom tyrosinase activities

Three iso-alkyldithiocarbonates (xanthates), as sodium salts, C₃H₇OCS₂Na (I), C₄H₉OCS₂Na (II) and C₅H₁₁OCS₂Na (III), were synthesized, by the reaction between CS₂ with the corresponding iso-alcohol in the presence of NaOH, and examined for inhibition of both cresolase and catecholase activities of mushroom tyrosinase (MT) from a commercial source of Agricus bisporus. 4-[(4-methylbenzo)azo]-1,2-benzendiol (MeBACat) and 4-[(4-methylphenyl)azo]-phenol (MePAPh) were used as synthetic substrates for the enzyme for the catecholase and cresolase reactions, respectively. Lineweaver-Burk plots showed different patterns of mixed and competitive inhibition for the three xanthates and also for cresolase and catecholase activities of MT. For cresolase activity, I and II showed a mixed inhibition pattern but III showed a competitive inhibition pattern. For catecholase activity, I showed mixed inhibition but II and III showed competitive inhibition. These new synthesized compounds are potent inhibitors of MT with K_i values of 9.8, 7.2 and 6.1 μM for cresolase inhibitory activity, and also 12.9, 21.8 and 42.2 μM for catecholase inhibitory activity for I, II and III, respectively. They showed a greater inhibitory potency towards the cresolase activity of MT. Both substrate and inhibitor can be bound to the enzyme with negative cooperativity between the binding sites (α>1) and this negative cooperativity increases with increasing length of the aliphatic tail in these compounds in both cresolase and catecholase activities. The cresolase inhibition is related to the chelating of the copper ions at the active site by a negative head group (S^? ) of the anion xanthate, which leads to similar values of K_i for all three xanthates. Different K_i values for catecholase inhibition are related to different interactions of the aliphatic chains of I, II and III with hydrophobic pockets in the active site of the enzyme.     

Thymol derivatives from Eupatorium fortunei and their inhibitory activities on LPS-induced NO production

In our survey on the chemical composition of Chinese folk medicines to further elucidate their chemical substances for the treatment of diseases, we investigated the chemical constituents of the plants Eupatorium fortunei. The investigation led to the isolation and identification of two new (1 and 2) and five known (3–7) thymol derivatives. Their structures were elucidated on the basis of extensive 1D and 2D NMR (COSY, HMQC, HMBC, and NOESY) and mass (ESIMS and HR-ESIMS) spectroscopic data analyses. The inhibitory activities on LPS-induced NO production of these compounds were also evaluated.     

Potent inhibitory effects of benzyl and p-xylidine-bis dithiocarbamate sodium salts on activities of mushroom tyrosinase

A novel monofunctional benzyldithiocarbamate, C₆H₅CH₂NHCSSNa (I), and a bifunctional p-xylidine-bis(dithiocarbamate), NaSSCNHCH₂C₆H₄CH₂NHCSSNa (II), as sodium salts, were synthesized by reaction between p-xylylenediamine or benzylamine with CS₂ in the presence of NaOH. They were characterized by spectroscopic techniques such as ¹H NMR, IR, and elemental analysis. These water-soluble compounds were examined for their inhibition of both activities of mushroom tyrosinase (MT) from a commercial source of Agricus bisporus. l-3,4- Dihydroxyphenylalanine (L-DOPA) and l-tyrosine were used as natural substrates for the catecholase and cresolase enzyme reactions, respectively. Kinetic studies showed noncompetitive inhibition of I and mixed type inhibition of II on both activities of MT. The inhibition constant (K_I) of II was smaller than that of I. Raising the temperature from 27 to 37°C caused a decrease in K_I values of I and an increase in values of II. The binding process for inhibition of I was only entropy driven, which means that the predominant interaction in the active site of the enzyme is hydrophobic; meanwhile, the electrostatic interaction can be important for the inhibition of II due to the enthalpy driven binding process. Fluorescence studies showed a decrease of emission intensity without a shift of emission maximum in the presence of different concentrations of compounds. An extrinsic fluorescence study did not show any considerable change of the tertiary structure of MT. Probably, the conformation of inhibitor-bound MT is stable and inflexible compared with uninhibited MT.     

Synthesis and DNase I inhibitory properties of some 4-thiazolidinone derivatives

Twelve new thiazolidinones were synthesized and, together with 41 previously synthesized thiazolidinones, evaluated for inhibitory activity against deoxyribonuclease I (DNase I) in vitro. Ten compounds inhibited commercial bovine pancreatic DNase I with an IC₅₀ below 200 μM and showed to be more potent DNase I inhibitors than crystal violet (IC₅₀ = 365.90 ± 47.33 μM), used as a positive control. Moreover, three compounds were active against DNase I in rat liver homogenate, having an IC₅₀ below 200 μM. (3-Methyl-1,4-dioxothiazolidin-2-ylidene)-N-(2-phenylethyl)ethanamide ( 41 ) exhibited the most potent DNase I inhibition against both commercial and rat liver DNase I with IC₅₀ values of 115.96 ± 11.70 and 151.36 ± 15.85 μM, respectively. Site Finder and molecular docking defined the thiazolidinones interactions with the most important catalytic residues of DNase I, including the H-acceptor interaction with residues His 134 and His 252 and/or H-donor interaction with residues Glu 39 and Asp 168. The three most active compounds against both commercial and rat liver DNase I ( 31 , 38 , and 41 ) exhibited favorable physico-chemical, pharmacokinetic, and toxicological properties. These observations could be utilized to guide the rational design and optimization of novel thiazolidinone inhibitors. Thiazolidinones as novel DNase I inhibitors could have potential therapeutic applications due to the significant involvement of DNase I in the pathophysiology of many disease conditions.     

Synthesis and anti-rheumatoid arthritis activities of 3-(4-aminophenyl)-coumarin derivatives

Rheumatoid arthritis is a chronic systemic disease characterised by an unknown aetiology of inflammatory synovitis. A large number of studies have shown that synoviocytes show tumour-like dysplasia in the pathological process of RA, and the changes in the expression of related cytokines are closely related to the pathogenesis of RA. In this thesis, a series of novel 3-(4-aminophenyl) coumarins containing different substituents were synthesised to find new coumarin anti-inflammatory drugs for the treatment of rheumatoid arthritis. The results of preliminary activity screening showed that compound 5e had the strongest inhibitory activity on the proliferation of fibroid synovial cells, and it also had inhibitory effect on RA-related cytokines IL-1, IL-6, and TNF-α. The preliminary mechanism study showed that compound 5e could inhibit the activation of NF-κB and MAPKs signal pathway. The anti-inflammatory activity of compound 5e in vivo was further determined in the rat joint inflammation model.     

The inhibitory effect of benzenethiol on the cresolase and catecholase activities of mushroom tyrosinase

The inhibitory effect of benzenethiol on the cresolase and catecholase activities of mushroom tyrosinase (MT) have been investigated at two temperatures of 20 and 30°C in 10 mM phosphate buffer solution, pHs 5.3 and 6.8. The results show that benzenethiol can inhibit both activities of mushroom tyrosinase competitively. The inhibitory effect of benzenethiol on the cresolase activity is more than the catecholase activity of MT. The inhibition constant (K_i) value at pH 5.3 is smaller than that at pH 6.8 for both enzyme activities. However, the K_i value increases in cresolase activity and decreases in catecholase activity due to the increase of temperature from 20 to 30°C at both pHs. Moreover, the effect of temperature on K_i value is more at pH 6.8 for both cresolase and catecholase activities. The type of binding process is different in the two types of MT activities. The binding process for catecholase inhibition is only entropy driven, which means that the predominant interaction in the active site of the enzyme is hydrophobic, meanwhile the electrostatic interaction can be important for cresolase inhibition due to the enthalpy driven binding process. Fluorescence and circular studies also show a minor change in the tertiary structure, without any change in the secondary structure, of the enzyme due to the electrostatic interaction in cresolase inhibition by benzenethiol at acidic pH.     

Synthesis,characterization and tyrosinase inhibitory properties of benzimidazole derivatives

1-Alkylbenzimidazole and 1,3-dialkyl benzimidazolium salts were synthesized and characterized by the data of IR, ¹H NMR, ¹³C NMR spectra and elemental analyses. These compounds were investigated as tyrosinase inhibitors. Tyrosinase has been purified from banana by affinity chromatography on a Sepharose 4B gel conjugated with L-tyrosine-p-aminobenzoic acid. All the synthesized compounds inhibited the tyrosinase activity. Among the compounds studied, 1,4-di(1H-benzo[d]imidazol-1-yl)butane was found to be the most active tyrosinase inhibitor (IC₅₀ 0.31 mM).     

Chemical synthesis and tyrosinase inhibitory activity of rhododendrol glycosides

The concise synthesis of rhododendrol glycosides 3–8, which are novel derivatives of (+)-epirhododendrin (1) and (−)-rhododendrin (2), has been achieved in six steps from benzaldehyde 9. The key reactions include aldol condensation and trichloroacetimidate glycosylation. From biological studies, it has been determined that synthetic derivatives of 1 and 2 possess potent tyrosinase inhibitory activity. Particularly, the inhibitory activity of cellobioside 8 (IC₅₀ = 1.51 μM) is six times higher than that of kojic acid. The R-epimers (4, 6, and 8) possessed more potent activity than the corresponding S-epimers (3, 5, and 7), indicating that tyrosinase inhibitory activity is significantly governed by stereochemistry of rhododendrol glycosides.