Potential antioxidants and tyrosinase inhibitors from synthetic polyphenolic deoxybenzoins

Structural elucidation, binding sites exploration and biological activities of bound phenolics from Radix Puerariae Thomsonii

Radix puerariae thomsonii (RPT) contains many phenolics and exhibits various health benefits. Although the free phenolics in RPT have been identified, the composition and content of bound phenolics, which account for approximately 20% of the total phenolic content, remain unknown. In this study, 12 compounds were isolated and identified from RPT-bound phenolic extracts, of which 2 were novel and 6 were reported first in RPT. ORAC and PSC antioxidant activities of 12 compounds, as well as their effects on alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), α-glucosidase, and α-amylase were evaluated. Genistein exhibited the highest ORAC activity, while daidzin demonstrated superior PSC activity. Five compounds, including two new compounds, exhibited the ability to activate both ADH and ALDH. All the compounds except 4-hydroxyphenylacetic acid methyl ester and 2,4,4'-trihydroxydeoxybenzoin demonstrated inhibitory effects on α-glucosidase and α-amylase. Alkaline hydrolysis and stepwise enzymatic hydrolysis revealed that bound phenolics in RPT mainly exist within starch.

Na2S-Mediated One-Pot Selective Deoxygenation of α-Hydroxyl Carbonyl Compounds including Natural Products

A practical method for the deoxygenation of α-hydroxyl carbonyl compounds under mild reaction conditions is reported here. The use of cheap and easy-to-handle Na₂S·9H₂O as the reductant in the presence of PPh₃ and N-chlorosuccinimide (NCS) enables the selective dehydroxylation of α-hydroxyl carbonyl compounds, including ketones, esters, amides, imides and nitrile groups. The synthetic utility is demonstrated by the late-stage deoxygenation of bioactive molecule and complex natural products.

Structure–antioxidant activity relationships of dendrocandin analogues determined using density functional theory

Quantum-chemical calculations based on the density functional theory (DFT) at the B3LYP/6–311 + + G(2d,2p)//B3LYP/6–31G(d,p) level were employed to study the relationship between the antioxidant properties and chemical structures of six dendrocandin (DDCD) analogues in the gas phase and two solvents (methanol and water). The hydrogen atom transfer (HAT), electron-transfer-proton-transfer (ET-PT), and sequential proton-loss-electron-transfer (SPLET) mechanisms are explored. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), reactivity indices (η, μ, ω, ω⁺, and ω^–), and molecular electrostatic potentials (MEPs) were also evaluated. The results suggest that the D ring plays an important role in mediating the antioxidant activity of DDCDs. For all the studied compounds, indicating that HAT was identified as the most favorable mechanism, whereas the SPLET mechanism was the most thermodynamically favorable pathway in polar solvents. The results of our study should aid in the development of new or modified antioxidant compounds.

Benzylic Aroylation of Toluenes Mediated by a LiN(SiMe3)2/Cs+ System

Chemoselective deprotonative functionalization of benzylic C-H bonds is challenging, because the arene ring contains multiple aromatic C(sp²)-H bonds, which can be competitively deprotonated and lead to selectivity issues. Recently it was found that bimetallic [MN(SiMe₃)₂ M = Li, Na]/Cs⁺ combinations exhibit excellent benzylic selectivity. Herein, is reported the first deprotonative addition of toluenes to Weinreb amides mediated by LiN(SiMe₃)₂/CsF for the synthesis of a diverse array of 2-arylacetophenones. Surprisingly, simple methyl benzoates also react with toluenes under similar conditions to form 2-arylacetophenones without double addition to give tertiary alcohol products. This finding greatly increases the practicality and impact of this chemistry. Some challenging substrates with respect to benzylic deprotonations, such as fluoro and methoxy substituted toluenes, are selectively transformed to 2-aryl acetophenones. The value of benzylic deprotonation of 3-fluorotoluene is demonstrated by the synthesis of a key intermediate in the preparation of Polmacoxib.

The effect of IL-2 stimulation and treatment of TRPM3 on channel co-localisation with PIP2 and NK cell function in myalgic encephalomyelitis/chronic fatigue syndrome patients

BACKGROUND

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a serious multifactorial disorder. The origin remains ambiguous, however reduced natural killer (NK) cell cytotoxicity is a consistent immunological feature of ME/CFS. Impaired transient receptor potential melastatin 3 (TRPM3), a phosphatidylinositol dependent channel, and impaired calcium mobilisation have been implicated in ME/CFS pathology. This investigation aimed to examine the localisation of TRPM3 at the NK cell plasma membrane and co-localisation with phosphatidylinositol 4,5-bisphosphate (PIP₂). The effect of IL-2 priming and treatment using pregnenolone sulfate (PregS) and ononetin on TRPM3 co-localisation and NK cell cytotoxicity in ME/CFS patients and healthy controls (HC) was also investigated.

METHODS

NK cells were isolated from 15 ME/CFS patients and 15 age- and sex-matched HC. Immunofluorescent technique was used to determine co-localisation of TRPM3 with the NK cell membrane and with PIP₂ of ME/CFS patients and HC. Flow cytometry was used to determine NK cell cytotoxicity. Following IL-2 stimulation and treatment with PregS and ononetin changes in co-localisation and NK cell cytotoxicity were measured.

RESULTS

Overnight treatment of NK cells with PregS and ononetin resulted in reduced co-localisation of TRPM3 with PIP₂ and actin in HC. Co-localisation of TRPM3 with PIP₂ in NK cells was significantly reduced in ME/CFS patients compared with HC following priming with IL-2. A significant increase in co-localisation of TRPM3 with PIP₂ was reported following overnight treatment with ononetin within ME/CFS patients and between groups. Baseline NK cell cytotoxicity was significantly reduced in ME/CFS patients; however, no changes were observed following overnight incubation with IL-2, PregS and ononetin between HC and ME/CFS patients. IL-2 stimulation significantly enhanced NK cell cytotoxicity in HC and ME/CFS patients.

CONCLUSION

Significant changes in co-localisation suggest PIP₂-dependent TRPM3 function may be impaired in ME/CFS patients. Stimulation of NK cells with IL-2 significantly enhanced cytotoxic function in ME/CFS patients demonstrating normal function compared with HC. A crosstalk exists between IL-2 and TRPM3 intracellular signalling pathways which are dependent on Ca²⁺ influx and PIP₂. While IL-2R responds to IL-2 binding in vitro, Ca²⁺ dysregulation and impaired intracellular signalling pathways impede NK cell function in ME/CFS patients.

A comprehensive review on tyrosinase inhibitors

Tyrosinase is a multi-copper enzyme which is widely distributed in different organisms and plays an important role in the melanogenesis and enzymatic browning. Therefore, its inhibitors can be attractive in cosmetics and medicinal industries as depigmentation agents and also in food and agriculture industries as antibrowning compounds. For this purpose, many natural, semi-synthetic and synthetic inhibitors have been developed by different screening methods to date. This review has focused on the tyrosinase inhibitors discovered from all sources and biochemically characterised in the last four decades.

New antibacterial and 5-lipoxygenase activities of synthetic benzyl phenyl ketones: Biological and docking studies

We investigated twelve benzyl phenyl ketone derivatives which are synthetic precursors of isoflavonoids that are shown be good 5-hLOX inhibitors, especially those that have the catechol group, but these precursors never have been assayed as 5-hLOX inhibitors being a novelty as inhibitors of the enzyme, due to sharing important structural characteristics. Screening assays, half maximal inhibitory concentration (IC₅₀) and kinetic assays of all the studied molecules (5 µg/ml in media assay) showed that 1-(2,4-dihydroxy-3-methylphenyl)-2-(3-chlorophenyl)-ethanone (K205; IC₅₀ = 3.5 µM; K_i = 4.8 µM) and 1-(2,4-dihydroxy-3-methylphenyl)-2-(2-nitrophenyl)-ethanone (K206; IC₅₀ = 2.3 µM; K_i = 0.7 µM) were potent, selective, competitive and nonredox inhibitors of 5-hLOX. Antioxidant behavior was also assayed by DPPH, FRAP, and assessing ROS production, and those with antibacterial and antiproliferative properties relating to 1-(2,4-dihydroxy-3-methylphenyl)-2-(2-chlorophenyl)-ethanone (K208) established it as the most interesting and relevant compound studied, as it showed nearly 100% inhibition of bacterial growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Finally, docking studies were done that helped to characterize how the inhibitor structures correlated to decreased 5-hLOX activity.

Design and Biological Evaluation of Antifouling Dihydrostilbene Oxime Hybrids

By combining the recently reported repelling natural dihydrostilbene scaffold with an oxime moiety found in many marine antifoulants, a library of nine antifouling hybrid compounds was developed and biologically evaluated. The prepared compounds were shown to display a low antifouling effect against marine bacteria but a high potency against the attachment and growth of microalgae down to MIC values of 0.01 μg/mL for the most potent hybrid. The mode of action can be characterized as repelling via a reversible non-toxic biostatic mechanism. Barnacle cyprid larval settlement was also inhibited at low μg/mL concentrations with low levels or no toxicity observed. Several of the prepared compounds performed better than many reported antifouling marine natural products. While several of the prepared compounds are highly active as antifoulants, no apparent synergy is observed by incorporating the oxime functionality into the dihydrostilbene scaffold. This observation is discussed in light of recently reported literature data on related marine natural antifoulants and antifouling hybrids as a potentially general strategy for generation of improved antifoulants.

Free-Radical-Scavenging, Antityrosinase, and Cellular Melanogenesis Inhibitory Activities of Synthetic Isoflavones

In this study, we examined the potential of synthetic isoflavones for application in cosmeceuticals. Twenty-five isoflavones were synthesized and their capacities of free-radical-scavenging and mushroom tyrosinase inhibition, as well as their impact on cell viability of B16F10 murine melanoma cells and HaCaT human keratinocytes were evaluated. Isoflavones that showed significant mushroom tyrosinase inhibitory activities were further studied on reduction of cellular melanin formation and antityrosinase activities in B16F10 melanocytes in vitro. Among the isoflavones tested, 6-hydroxydaidzein (2) was the strongest scavenger of both ABTS(.+) and DPPH(.) radicals with SC50 values of 11.3 ± 0.3 and 9.4 ± 0.1 μM, respectively. Texasin (20) exhibited the most potent inhibition of mushroom tyrosinase (IC50 14.9 ± 4.5 μM), whereas retusin (17) showed the most efficient inhibition both of cellular melanin formation and antityrosinase activity in B16F10 melanocytes, respectively. In summary, both retusin (17) and texasin (20) exhibited potent free-radical-scavenging capacities as well as efficient inhibition of cellular melanogenesis, suggesting that they are valuable hit compounds with potential for advanced cosmeceutical development.

Citrus fruit and fabacea secondary metabolites potently and selectively block TRPM3

BACKGROUND AND PURPOSE

The melastatin-related transient receptor potential TRPM3 is a calcium-permeable nonselective cation channel that can be activated by the neurosteroid pregnenolone sulphate (PregS) and heat. TRPM3-deficient mice show an impaired perception of noxious heat. Hence, drugs inhibiting TRPM3 possibly get in focus of analgesic therapy.

EXPERIMENTAL APPROACH

Fluorometric methods were used to identify novel TRPM3-blocking compounds and to characterize their potency and selectivity to block TRPM3 but not other sensory TRP channels. Biophysical properties of the block were assessed using electrophysiological methods. Single cell calcium measurements confirmed the block of endogenously expressed TRPM3 channels in rat and mouse dorsal root ganglion (DRG) neurones.

KEY RESULTS

By screening a compound library, we identified three natural compounds as potent blockers of TRPM3. Naringenin and hesperetin belong to the citrus fruit flavanones, and ononetin is a deoxybenzoin. Eriodictyol, a metabolite of naringenin and hesperetin, was still biologically active as a TRPM3 blocker. The compounds exhibited a marked specificity for recombinant TRPM3 and blocked PregS-induced [Ca(2+)]i signals in freshly isolated DRG neurones.

CONCLUSION AND IMPLICATIONS

The data indicate that citrus fruit flavonoids are potent and selective blockers of TRPM3. Their potencies ranged from upper nanomolar to lower micromolar concentrations. Since physiological functions of TRPM3 channels are still poorly defined, the development and validation of potent and selective blockers is expected to contribute to clarifying the role of TRPM3 in vivo. Considering the involvement of TRPM3 in nociception, TRPM3 blockers may represent a novel concept for analgesic treatment.

Synthesis and antioxidant activity of polyhydroxylated trans-restricted 2-arylcinnamic acids

A series of sixteen polyhydroxylated trans-restricted 2-arylcinnamic acid analogues 3a–p were synthesized through a one-pot reaction between homophthalic anhydrides and various aromatic aldehydes, followed by treatment with BBr₃. The structure of the newly synthesized compounds was confirmed by spectroscopic methods and the configuration around the double bond was unequivocally estimated by means of gated decoupling ¹³C-NMR spectra. It was shown that the trans-cinnamic acid fragment incorporated into the target compounds’ structure ensures the cis-configuration of the stilbene backbone and prevents further isomerization along the carbon–carbon double bond. The antioxidant activity of compounds 3a–p was measured against 1,1-diphenyl-2-picrylhydrazyl (DPPH^●), hydroxyl (OH^●) and superoxide (O₂^●▬) radicals. The results obtained showed that the tested compounds possess higher activities than natural antioxidants such as protocatechuic acid, caffeic acid and gallic acid. Moreover, it was shown that a combination of two different and independently acting fragments of well-known pharmacological profiles into one covalently bonded hybrid molecule evoke a synergistic effect resulting in higher than expected activity. To rationalize the apparent antioxidant activity and to establish the mechanism of action, a SAR analysis and DFT quantum chemical computations were also performed.

Alleviation effect of arbutin on oxidative stress generated through tyrosinase reaction with L-tyrosine and L-DOPA

BACKGROUND

Hydroxyl radical that has the highest reactivity among reactive oxygen species (ROS) is generated through L-tyrosine-tyrosinase reaction. Thus, the melanogenesis might induce oxidative stress in the skin. Arbutin (p-hydroxyphenyl-β-D-glucopyranoside), a well-known tyrosinase inhibitor has been widely used for the purpose of skin whitening. The aim of the present study was to examine if arbutin could suppress the hydroxyl radical generation via tyrosinase reaction with its substrates, L-tyrosine and L-DOPA.

RESULTS

The hydroxyl radical, which was determined by an electron spin resonance-spin trapping technique, was generated by the addition of not only L-tyrosine but L-DOPA to tyrosinase in a concentration dependent manner. Arbutin could inhibit the hydroxyl radical generation in the both reactions.

CONCLUSION

It is presumed that arbutin could alleviate oxidative stress derived from the melanogenic pathway in the skin in addition to its function as a whitening agent in cosmetics.

A new natural nucleotide and other antibacterial metabolites from an endophytic Nocardia sp

Nine compounds were isolated from Nocardia sp. YIM 64630, and their structures were elucidated as 5'-O-acetyl-2'-deoxyuridine (1), 22E,24R-5α,6α-epoxyergosta-8(14),22-diene-3β,7α-diol (2), 22E,24R-5α,6α-epoxyergosta-8,22-diene-3β,7α-diol (3), 22E,24R-ergosta-7,22-diene-3β,5α,6β-triol (4), 5α,8α-epidioxyergosta-6,22-dien-3β-ol (5), 4',5,6-trihydroxy-7-methoxyisoflavone (6), 2,4,4'-trihydroxy-deoxybenzoin (7), methyl [4-hydroxyphenyl]acetate (8) and daidzein by extensive spectroscopic analyses. Compound 1 was isolated from natural resources for the first time. The antimicrobial and antioxidant activities of compounds 1-8 were investigated.

Density functional theory study of the structure-antioxidant activity of polyphenolic deoxybenzoins

Quantum chemical calculations based on the density functional theory (DFT) have been employed to study the relationship between the structure and the antioxidant activity of four polyphenolic deoxybenzoins (DOBs) in solvents and the gas phase. The three main working mechanisms, H-atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) have been investigated. The calculated results closely matched experimental values. The results obtained prove that for the HAT mechanism, the most efficient system possessed ortho-dihydroxy functionality. The results suggested that HAT would be the most favourable mechanism for explaining the radical-scavenging activity of polyphenolic DOBs in the gas phase, whereas the SPLET mechanism is the thermodynamically favourable pathway in polar solvents.

Some monohydroxy tetradecanoic acid isomers as novel urease and elastase inhibitors and as new antioxidants

A series of some 3-,6-,7-,9-,12- monohydroxy tetradecanoic acids were evaluated for their antiurease, antielastase and antioxidant activities for the first time in this study. All the test compounds exhibited antioxidant, antielastase and antiurease activities. The relationship between the position of the hydroxy group and the enzyme inhibition effect is studied in this work. The mentioned biological activities are depending on the position of hydroxy group of tetradecanoic acid isomers. The results obtained in this work are indicating that 3-,6-,7-,9-,12-monohydroxy tetradecanoic acid isomers can be used in agriculture, pharmacy and cosmetic industries due to their excellent antielastase, antiurease and antioxidant activities.

Anti-proliferative, anti-inflammatory and antioxidant effects of curcumin analogue A₂

In the present study, we determined the anti-proliferative, anti-inflammatory and antioxidant effects of a curcumin analogue, 2,6-bis(3,4-dihydroxybenzylidene) cyclohexanone (designated as A2). In vitro studies showed that A2 had a stronger inhibitory effect on the growth of mouse macrophage RAW 264.7 cells than curcumin. A2 also showed a stronger inhibitory effect than curcumin on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced increases in NF-κB activation and IL-1β expression as well as in aldose reductase activity. A2 was a stronger antioxidant than curcumin as determined by inhibition of lipid peroxidation, inhibition of 1,1-diphenyl-2-picryl-hydrazyl free radical formation, and inhibition of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radical formation. In vivo studies indicated that A2 was more potent than curcumin for inhibiting TPA-induced ear edema and TPA-induced increases in IL-1β. In addition, oral administration of A2 at a dose of 2,000 mg/kg body weight did not cause acute toxicity in mice. Taken together, the results of our study indicate that the curcumin analogue A2 has stronger anti-proliferative, anti-inflammatory and antioxidant activities than curcumin.

Estrogenic effect of three substituted deoxybenzoins

Deoxybenzoins (1-(2,4-dihydroxyphenyl)-2-(4-hydroxyphenyl)ethanone) are possible precursors or metabolites of isoflavanones which may have xenoestrogenic potential on estrogen receptor (ER). In this study we evaluated three 2'-substituted deoxybenzoin derivatives for their estrogenic effect based upon their ability to affect the proliferation of ERα(+) MCF7 cells, ERβ(+) PC3 cells and Hep2 cells stably transfected and expressing either ERα or ERβ. These compounds designated as CMPD3, CMPD6 and CMPD9 had -COOH, -(CH(2))(4)-CH(3) and -CH(3) substitutions, respectively on the 2'-position of the 2,4-dihydroxyphenyl ring of deoxybenzoin. We found that all three compounds increased the proliferation of ERα(+) MCF7 cells (EC(50)~1-12 μM) and ERα(+) Hep2 cells, while causing apoptosis in ERβ(+) PC3 cells (IC(50)~1-5 μM) and ERβ(+) Hep2 cells. The compounds also up-regulated the expression of estrogen sensitive genes, trefoil factor 1 (TFF1, previously known as pS2) and cathepsin-D (CTSD), in these cells. We performed in vitro ER transcription activation assays using Hep2 cells transiently co-transfected with estrogen response element driven luciferase and either ERα or ERβ vectors to ascertain the mechanism of action of these compounds through the 'classical' genomic pathway of estrogenic activity and to determine their ER subtype selectivity. Molecular docking of the compounds with the Ligand Binding Domain of ERα and ERβ showed similar docking scores (Glidescores of -6.5 to -8.5 kcal/mol) indicating that these compounds were ligands of both ERα and ERβ with similar affinity.

Evaluation of in vitro and in vivo anti-melanogenic activity of a newly synthesized strong tyrosinase inhibitor (E)-3-(2,4 dihydroxybenzylidene)pyrrolidine-2,5-dione (3-DBP)

BACKGROUND

Tyrosinase inhibitors have become increasingly important because of their ability to inhibit the synthesis of the pigment melanin. A search for new agents with strong tyrosinase activity led to the synthesis of the tyrosinase inhibitor (E)-3-(2,4-dihydroxybenzylidene)pyrrolidine-2,5-dione (3-DBP).

METHODS

The inhibitory effect of 3-DBP on tyrosinase activity and melanin production was examined in murine melanoma B16F10 cells. Additional experiments were performed using HRM2 hairless mice to demonstrate the effects of 3-DBP in vivo.

RESULTS

The novel compound, 3-DBP, showed an inhibitory effect against mushroom tyrosinase (IC50=0.53 μM), which indicated that it was more potent than the well-known tyrosinase inhibitor kojic acid (IC50=8.2 μM). When tested in B16F10 melanoma cells treated with α-melanocyte stimulating hormone (α-MSH), 3-DBP also inhibited murine tyrosinase activity, which in turn induced a decrease in melanin production in these cells. The anti-melanogenic effect of 3-DBP was further verified in HRM2 hairless mice. The skin-whitening index (L value) of HRM2 hairless mice treated with 3-DBP before irradiation with UVB was greater than that of UVB-irradiated mice that were not treated with 3-DBP.

GENERAL SIGNIFICANCE

The newly synthesized 3-DBP has a potent inhibitory effect on tyrosinase. In addition to an in vitro investigation of the effects of 3-DBP on tyrosinase, in vivo studies using an HRM2 hairless mouse model demonstrated the anti-melanogenic potency of 3-DBP. Our newly synthesized 3-DBP showed efficient tyrosinase inhibitory effect in vivo and in vitro. Our finding suggests that 3-DBP can be an effective skin-whitening agent.

(E)-1-(Thio-phen-2-yl)-3-(2,4,6-tri-meth-oxy-phen-yl)prop-2-en-1-one

There are two crystallograpically independent mol-ecules in the asymmetric unit of the title heteroaryl chalcone derivative, C(16)H(16)O(4)S, with slightly different conformations. The thienyl ring of one mol-ecule is disordered over two positions, with a refined site-occupancy ratio of 0.713 (5):0.287 (5). The mol-ecules are twisted: the dihedral angle between the thienyl and benzene rings is 9.72 (19)° in the ordered mol-ecule, and 3.8 (4) and 2.1 (8)° for the major and minor components, respectively, in the disordered mol-ecule. In both mol-ecules, all three substituted meth-oxy groups are coplanar with the benzene ring to which they are attached. In each mol-ecule, a weak intra-molecular C-H⋯O inter-action generates an S(6) ring motif. In the crystal structure, adjacent mol-ecules are linked into a three-dimensional network by weak C-H⋯O inter-actions.

Antioxidant xanthone derivatives induce cell cycle arrest and apoptosis and enhance cell death induced by cisplatin in NTUB1 cells associated with ROS

In an effort to develop novel antioxidant as anticancer agents, a series of xanthones were prepared. In vitro screening, the synthetic xanthones revealed significant inhibitory effects on xanthine oxidase and ABTS radical-cation scavenging activity. The selective compounds 2 and 8 induced an accumulation of NTUB1 cells in the G(1) phase arrest and cellular apoptosis by the increase of ROS level. The combination of cisplatin and 2 significantly enhanced the cell death in NTUB1 cells. Compounds 2 and 8 did not show cytotoxic activity in selected concentrations against SV-HUC1 cells. The present results suggested that antioxidants 2 and 8 may be used as anticancer agent for enhancing the therapeutic efficacy of anticancer agents and to reduce their side effect.

Synthesis and structure-activity relationship study of deoxybenzoins on relaxing effects of porcine coronary artery

Deoxybenzoins are potent antioxidants and tyrosinase inhibitors with potential to be developed as food preservatives and cosmetic ingredients. To explore the potential in cardiovascular protection, 25 polyphenolic deoxybenzoins were synthesized and evaluated for inhibitory effects on KCl-induced porcine coronary arterial contraction. The results revealed deoxybenzoins are significant inhibitors of KCl-induced arterial contraction. Among those synthesized, two-thirds of the deoxybenzoins exhibited moderate to good efficacy on relaxing contracted artery including 2,4-dihydroxydeoxybenzoin with EC50=3.30 μM (Emax=100%, n=7) and 2,4-dihydroxy-4'-methoxydeoxybenzoin EC50=3.70 μM (Emax=100%, n=5). Deoxybenzoins displayed an endothelium-dependent relaxing manner on the contracted artery; the contractile responses of neither endothelium denuded nor L-NAME deactivated rings were inhibited. The structure-activity relationships of deoxybenzoin on arterial relaxing effects concluded that the 2,4-dihydroxylated deoxybenzoins presented a potential vascular relaxing pharmacophore, with favoring substitution on ring B in the order of H≥p-OMe>p-OH>o-OMe>m,p-diOMe≥m-OMe.

(E)-1-(2-Fur-yl)-3-(2,4,6-trimeth-oxy-phen-yl)prop-2-en-1-one

In the title heteroaryl chalcone derivative, C₁₆H₁₆O₅, the dihedral angle between the furan and benzene rings is 14.45 (6)°. The three meth­oxy groups are almost coplanar with their attached benzene ring [C—C—O—C torsion angles = 2.07 (17), −5.04 (17) and 2.85 (16)°]. An intra­molecular C—H⋯O hydrogen bond occurs. In the crystal, adjacent mol­ecules are linked into X-shaped chains along the c axis by weak C—H⋯O(enone) inter­actions. These chains are stacked along the b axis. C⋯O [3.3308 (13)–3.4123 (14) Å] short contacts are also observed.

Generation mechanism of radical species by tyrosine-tyrosinase reaction

Alleviated melanin formation in the skin through inhibition of tyrosine-tyrosinase reaction is one of the major targets of cosmetics for whitening ability. Since melanin has a pivotal role for photoprotection, there are pros and cons of inhibition of melanin formation. This study applying electron spin resonance (ESR)-spin trapping method revealed that ^•H and ^•OH are generated through tyrosine-tyrosinase reaction. When deuterium water was used instead of H₂O, the signal of 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-H (a spin adduct of DMPO and ^•H) greatly decreased, whilst DMPO-OH (a spin adduct of DMPO and ^•OH) did not. Thus, it is suggested that ^•H was derived from H₂O, and ^•OH through oxidative catalytic process of tyrosine to dopaquinone. Our study suggests that tyrosinase inhibitors might contribute to alleviate the oxidative damage of the skin by inhibiting ^•OH generation via the enzyme reaction.