Refinement of the pharmacophore of 3,4-dihydroquinazoline-2(1H)-thiones for their anti-melanogenesis activity

Newly Designed Quinazolinone Derivatives as Novel Tyrosinase Inhibitor: Synthesis, Inhibitory Activity, and Mechanism

We synthesized a series of quinazolinone derivates as tyrosinase inhibitors and evaluated their inhibition constants. We synthesized 2-(2,6-dimethylhepta-1,5-dien-1-yl)quinazolin-4(3H)-one (Q1) from the natural citral. The concentration, which led to 50% activity loss of Q1, was 103 ± 2 μM (IC₅₀ = 103 ± 2 μM). Furthermore, we considered Q1 to be a mixed-type and reversible tyrosinase inhibitor, and determined the K_I and K_IS inhibition constants to be 117.07 μM and 423.63 μM, respectively. Our fluorescence experiment revealed that Q1 could interact with the substrates of tyrosine and L-DOPA in addition to tyrosinase. Molecular docking studies showed that the binding of Q1 to tyrosinase was driven by hydrogen bonding and hydrophobicity. Briefly, the current study confirmed a new tyrosinase inhibitor, which is expected to be developed into a novel pigmentation drug.

Vegetable-derived indole enhances the melanoma-treating efficacy of chemotherapeutics

Food-drug interaction is an important but overlooked issue. For example, little is known concerning whether or not the chemotherapy of cancers is affected by the well-defined dietary chemicals such as 2-(indol-3-ylmethyl)-3,3'-diindolylmethane (LTr1) derived from daily consumed cruciferous vegetables. This work, inspired by the described melanogenesis reduction by certain indoles, presents that LTr1 mitigates the melanogenesis and thus potentiates the in vitro and in vivo anti-melanoma effectiveness of different chemotherapeutic agents including dacarbazine, vemurafenib, and sorafenib. In B16 melanoma cells, LTr1 was shown to inhibit the melanogenesis by acting towards the regulatory (R) subunit of protein kinase A (PRKAR1a) associated with the phosphorylation of cAMP-response element binding protein (CREB). This allows LTr1 to reduce the expression of melanogenesis-related enzymes such as tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), and tyrosinase-related protein 2 (TYRP2). Furthermore, LTr1 was addressed to bind to the aryl hydrocarbon receptor (AhR) and up-regulate the expression of CYP1A1 encoding cytochrome P450 1A1, leading to the escalation of reactive oxygen species (ROS) level. The increased ROS generation promotes the cysteine-to-cystine transformation to inhibit the pheomelanogenesis in melanomas. Collectively, the work identifies LTr1 as a new melanogenesis inhibitor that modulates the PKA/CREB/MITF and AhR/CYP1A1/ROS pathways, thereby providing a new option for (re)sensitizing melanomas to chemotherapeutics.

A bifunctional iminophosphorane squaramide catalyzed enantioselective synthesis of hydroquinazolines via intramolecular aza-Michael reaction to α,β-unsaturated esters

An efficient synthesis of enantioenriched hydroquinazoline cores via a novel bifunctional iminophosphorane squaramide catalyzed intramolecular aza-Michael reaction of urea-linked α,β-unsaturated esters is described. The methodology exhibits a high degree of functional group tolerance around the forming hydroquinazoline aryl core and wide structural variance on the nucleophilic N atom of the urea moiety. Excellent yields (up to 99%) and high enantioselectivities (up to 97 : 3 er) using both aromatic and less acidic aliphatic ureas were realized. The potential industrial applicability of the transformation was demonstrated in a 20 mmol scale-up experiment using an adjusted catalyst loading of 2 mol%. The origin of enantioselectivity and reactivity enhancement provided by the squaramide motif has been uncovered computationally using density functional theory (DFT) calculations, combined with the activation strain model (ASM) and energy decomposition analysis (EDA).

The activation of both aromatic and aliphatic ureas as N-centered nucleophiles in intramolecular Michael addition reactions to α,β-unsaturated esters was achieved under bifunctional iminophosphorane squaramide superbase catalysis.

Synthesis, antibacterial activities, and sustained perfume release properties of optically active5-hydroxy- and 5-acetoxyalkanethioamide analogues

5-Acetoxy- and 5-hydroxyalkanethioamide analogues showed high antibacterial activity against Staphylococcus aureus. Antibacterial thioamides were prepared from 5-alkyl-δ-lactones by amidation, thionation, and subsequent deacetylation. Optically active thioamides with 99% diastereomeric excesses were prepared by diastereomeric resolution using Cbz-L-proline as the resolving agent. Antibacterial thioamides were slowly lactonized by a lipase catalyst. Therefore, these thioamides are potential sustained-release perfume compounds having antibacterial properties.

A Simple Metal-Free Cyclization for the Synthesis of 4-Methylene-3-Substituted Quinazolinone and Quinazolinthione Derivatives: Experiment and Theory

A new series of 3-substituted 4-methylene-quinazolinthiones and 4-methylene-quinazolinones were synthesized in moderate to excellent yield through a simple reaction of 2-aminoacetophenones with isocyanates or isothiocyanates. The reaction shows good tolerance of many important functional groups in the presence of air and water under metal-free conditions. Only water is produced as a coproduct, rendering this “green” methodology a highly versatile and eco-friendly alternative to the existing methods for the construction of the quinazolinone/quinazolinthione framework. We have interpreted the reaction mechanism by use of quantum chemical calculations on the basis of state-of-the-art computational methods SMD-B3LYP-D3(BJ)/BS1//B3LYP/BS1.

Antityrosinase mechanism of ellagic acid in vitro and its effect on mouse melanoma cells

The activities of ellagic acid in inhibiting mushroom tyrosinase and cell proliferation were evaluated in this research. The results of enzyme kinetics indicated that ellagic acid could effectively inhibit tyrosinase activity. The value of the semi-inhibitory rate (IC₅₀ ) was 0.2 ± 0.05 mM. Ellagic acid inhibited tyrosinase activity in a reversible manner and was a mixed tyrosinase inhibitor. Furthermore, ellagic acid had a good inhibitory effect on the proliferation of mouse melanoma B₁₆ cells and could induce apoptosis. The results acquired from fluorescence spectroscopy revealed that the interaction of ellagic acid with tyrosinase depended on hydrogen bond and electrostatic force. In addition, computational docking showed that ellagic acid interacted with amino acid residues of tyrosinase (Asn19 and Lys372) by hydrogen bond and produced electrostatic interaction with amino residue Lys18. PRACTICAL APPLICATIONS: In the present research, the antityrosinase mechanism of ellagic acid and its effect on mouse melanoma cells were investigated. This study suggested that ellagic acid had a strong inhibitory activity against tyrosinase and cell proliferation,which laid an experimental foundation for the development of new drugs and whitening products. The combined multispectral methods used in this research can be applied to the screening of other antityrosinase inhibitors, further promoting the development and utilization of tyrosinase inhibitors.

Eco-friendly reactions in PEG-400: a highly efficient and green approach for stereoselective access to multisubstituted 3,4-dihydro-2(1H)-quinazolines using 2-aminobenzylamines

An efficient and stereoselective synthesis of novel 3,4-dihydro-2(1H)-quinazolines has been developed through cyclization reactions of 2-aminobenzylamines with α-oxoketene dithioacetals using PEG-400 as an inexpensive, easy to handle, non-toxic and recyclable reaction medium. The developed protocol is operationally simple and tolerates various substrates having different functionalities. This protocol features several attributes such as excellent yields, no work up, green reaction conditions, and being environmentally benign. The attractive feature of this new strategy is that all the reported final compounds have been isolated as single (E)-stereoisomeric forms, which was confirmed by 1HNMR and X-ray crystallographic studies.

Palladium-catalyzed selective synthesis of 3,4-dihydroquinazolines from electron-rich arylamines, electron-poor arylamines and glyoxalates

Palladium-catalyzed selective synthesis of various 3,4-dihydroquinazolines from electron-rich arylamines, electron-poor arylamines and glyoxalates was developed.

Rifampicin as a novel tyrosinase inhibitor: Inhibitory activity and mechanism

In this study, the inhibitory effect and mechanism of rifampicin on the activity of tyrosinase were investigated for developing a novel tyrosinase inhibitor. It was found to have a significant inhibition on the activity of tyrosinase (IC₅₀=90±0.6μM). From the kinetics analysis, it was proved to be a reversible and noncompetitive type inhibitor of the enzyme with the K_I value of 94±3.5μM. The results obtained from intrinsic fluorescence quenching indicated that rifampicin could interact with tyrosinase. In particular, the drastic decrease of fluorescence intensity was due to the formation of a rifampicin-enzyme complex in a static procedure which was mainly driven by hydrophobic forces and hydrogen bonding. Moreover, the ANS-binding fluorescence analysis suggested that rifampicin binding to tyrosinase changed the polarity of the hydrophobic regions. Molecular docking analysis further revealed that the hydrogen bonds were generated between rifampicin and amino residues Leu7, Ser52, and Glu107 in the B chain of the enzyme. And the hydrophobic forces produced through the interaction of rifampicin with B chain residues Pro9, Pro14, and Trp106. This work identified a novel tyrosinase inhibitor and potentially contributed to the usage of rifampicin as a potential hyperpigmentation drug.

2-(4-Fluorophenyl)-quinazolin-4(3H)-one as a novel tyrosinase inhibitor: Synthesis, inhibitory activity, and mechanism

2-(4-Fluorophenyl)-quinazolin-4(3H)-one (FQ) was synthesized, and its structure was identified with (1)H nuclear magnetic resonance ((1)H NMR), (13)C nuclear magnetic resonance ((13)C NMR), fourier transform infrared spectroscopy (FTIR), and high resolution mass spectrometry (HRMS). From the enzyme analysis, the results showed that it could inhibit the diphenolase activity of tyrosinase (IC50=120±2μM). Furthermore, the results of kinetic studies showed that the compound was a reversible mixed-type inhibitor, and that the inhibition constants were determined to be 703.2 (KI) and 222.1μM (KIS). The results of fluorescence quenching experiment showed that the compound could interact with tyrosinase and the substrates (tyrosine and l-DOPA). Molecular docking analysis revealed that the mass transfer rate was affected by FQ blocking the enzyme catalytic center. In brief, current study identified a novel tyrosinase inhibitor which deserved further study for hyperpigmentation drugs.

Analogues of ethionamide, a drug used for multidrug-resistant tuberculosis, exhibit potent inhibition of tyrosinase

Tyrosinase catalyzes two distinct sequential reactions in melanin biosynthesis: the hydroxylation of tyrosine to DOPA followed by the oxidation of DOPA to dopaquinone. The central roles of melanin in living species have motivated researchers to maintain constant efforts to discover new agents that modulate tyrosinase activity. In this study, we report on the inhibition of tyrosinase by ethionamide and its analogues. Ethionamide, 2-ethylpyridine-4-carbothioamide, is a second-line antituberculosis drug used for the treatment of multidrug-resistant tuberculosis. The chemical similarity of ethionamide to phenylthiourea, a well-known tyrosinase inhibitor, led us to investigate its inhibitory effects on mushroom tyrosinase and the IC50 was calculated as 4 μM. Five analogues of ethionamide, including another antituberculosis drug, prothionamide, were also inhibitory, with values for IC50 in the range of 3-43 μM. Fluorescence quenching experiments supported a mechanism of direct binding. In contrast, isoniazid, a structural analogue and first-line antituberculosis drug, was a poor inhibitor of tyrosinase. We also tested the effects of ethionamide and its analogues on melanin content in B16F10 cells. At a concentration of 50 μM, the molecules, pyridine-2-carbothioamide and thiobenzamide substantially decreased the melanin content by 44% and 37%, respectively. In addition to identifying other interactions, docking simulations showed that the carbothioamide groups of the molecules make essential contacts with the catalytic di-copper atoms. Our results suggest that carbothioamide can be a central moiety for the development of new and potent tyrosinase inhibitors.

Pd-catalyzed Heck-conjoined amidation and concomitant chemoselective Michael-addition: an efficient tandem approach to highly functionalized tetrahydroquinazolines from o-haloanilines

Efficient palladium-catalyzed tandem approach for the synthesis of highly functionalized tetrahydroquinazolines from o-haloanilines with acrylates and isothiocyanates/isocyanates via Heck-conjoined amidation/thioamidation and concomitant chemoselective Michael-addition is described.

On water: catalyst-free chemoselective synthesis of highly functionalized tetrahydroquinazolines from 2-aminophenylacrylate

A green and catalyst free atom-ecomonic straightforward tandem approach for the synthesis of highly functionalized tetrahydroquinazolines by the reaction of 2-aminophenylacrylate1with isothiocyanates2using water as an environmental friendly solvent is described.

Efficient Ionic Liquid-Catalysed Synthesis and Antimicrobial Studies of 4,6-diaryl- and 4,5-fused pyrimidine-2-thiones

One-pot three-component condensation of aromatic ketones (1-tetralones, acetophenones, indane-1,3-dione), substituted aromatic aldehydes and thiourea in the presence of N-methylpyridinium tosylate under solvent free conditions at 100–110 °C for 2–4 h afforded tetrahydrobenzo[ h]quinazoline-2-thiones, pyridimidine-2-thiones and indeno-pyrimidine-2-thiones in excellent yields. All synthesised thiones were screened for their antimicrobial activities.

Structural requirement of phenylthiourea analogs for their inhibitory activity of melanogenesis and tyrosinase

Effect of a series of 1-phenylthioureas 1a-k and 1,3-disubstituted thioureas 2a-k were evaluated against melanin formation in melanoma B16 cell line and mushroom tyrosinase. Inhibitory activity of tyrosinase of 1-phenylthioureas 1a-k is parallel to their melanogenic inhibition. Thus, the melanogenic inhibition in melanoma B16 cells of 1-phenylthioureas could be the result of inhibition of tyrosinase. However, 1,3-diaryl or 1-phenyl-3-alkylthioureas, 2a-k, appears as melanogenic inhibitor without inhibition of tyrosinase. The molecular docking study of 1e and 2b to binding pocket of tyrosinase provided convincing explanation regarding the necessity of direct connection of planar phenyl to thiourea unit without N'-substitution of phenylthioureas 1 as tyrosinase inhibitor and 2 as non-tyrosinase inhibitor.