Novel biphenyl ester derivatives as tyrosinase inhibitors: Synthesis, crystallographic, spectral analysis and molecular docking studies

Biphenyls in Clusiaceae: Isolation, structure diversity, synthesis and bioactivity

Clusiaceae plants contain a wide range of biologically active metabolites that have gotten a lot of interest in recent decades. The chemical compositions of these plants have been demonstrated to have positive effects on a variety of ailments. The species has been studied for over 70 years, and many bioactive compounds with antioxidant, anti-proliferative, and anti-inflammatory properties have been identified, including xanthones, polycyclic polyprenylated acylphloroglucinols (PPAPs), benzophenones, and biphenyls. Prenylated side chains have been discovered in many of these bioactive substances. To date, there have been numerous studies on PPAPs and xanthones, while no comprehensive review article on biphenyls from Clusiaceae has been published. The unique chemical architectures and growing biological importance of biphenyl compounds have triggered a flurry of research and interest in their isolation, biological evaluation, and mechanistic studies. In particular, the FDA-approved drugs such as sonidegib, tazemetostat, daclatasvir, sacubitril and trifarotene are closely related to their biphenyl-containing moiety. In this review, we summarize the progress and development in the chemistry and biological activity of biphenyls in Clusiaceae, providing an in-depth discussion of their structural diversity and medicinal potential. We also present a preliminary discussion of the biological effects with or without prenyl groups on the biphenyls.

Druggability modification strategies of the diarylpyrimidine-type non-nucleoside reverse transcriptase inhibitors

Drug discovery of human immunodeficiency virus (HIV) is a hot field in medicinal chemistry community for many years. The diarylpyrimidines (DAPYs) are the second-generation non-nucleoside reverse transcriptase inhibitors (NNRTIs) targeting reverse transcriptase, playing a great irreplaceable role in HIV transcriptional therapy. However, fast-growing drug-resistant mutations as nonnegligible challenge are still unpredictably appeared in the clinical practice, leading to deactivate or reduce the existing drugs. In the last 20 years, more and more novel DAPY derivatives have developed with the purpose to counter the mutants. Nevertheless, most of them have dissatisfactory pharmacokinetics (PK) or poor antiviral activity toward resistant mutant strains. In this article, we will analyze the NNRTI derivatives with promising druggability, and summarize a series of druggability modification strategies to improve the antiviral activity, reduce toxicity and improve the PK properties in recent years. The prospects of DAPYs and the directions for future efforts will be discussed.

Inhibitory effects and molecular mechanism on mushroom tyrosinase by condensed tannins isolation from the fruit of Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chow

The structure of extracted condensed tannin (CT) from the fruit of Sour jujube (Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chow) and the molecular mechanisms by which CT inhibits the activity of mushroom tyrosinase were investigated. The structure of CT was characterized by high performance liquid chromatography electrospray ionization mass spectrometry, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The kinetic assays were used to detect inhibition effect, type and mechanism. UV scanning, fluorescence quenching, copper interacting, o-quinone interaction and molecular docking assays were also used to reveal the molecular mechanisms by which CT inhibit tyrosinase. The results showed the structural units of CT containing afzelechin/epiafzelechin, catechin/epicatechin, and gallocatechin/epigallocatechin. Kinetic analysis showed that CT inhibits both the monophenolase and diphenolase activities of tyrosinase and exhibits reversible, mixed type mechanism. The fruit CT interacts primarily with the copper ions and specific amino acid residue (Asn191, Thr203, Ala202, Ser206, Met201, His194, His54, Glu182 and Ile42) in the active site of tyrosinase to disturb oxidation of substrates by tyrosinase. These results suggested the sour jujube fruit is a potential natural source of tyrosinase inhibitors, and has a potential to be used in food preservation, whitening cosmetics.

Evaluation of in vitro inhibitory effects of some natural compounds on tyrosinase activity and molecular docking study: Antimelanogenesis potential

Tyrosinase enzyme is a functional oxidase that is extensively divided in nature. It is the main enzyme in melanin synthesis and is also involved in designating the color of mammalian hair and skin. Additionally, it is accountable for the unfavorable enzymatic browning that happens in plant-derived foods, limiting the shelf-life of new-cut crops with the resultant economic harm. Recently, there has been a remarkable concern to study the inhibitory activity of the tyrosinase enzyme and some inhibitory molecules isolated from natural sources. For tyrosinase enzyme, afzelin, narcissoside, justiciresinol, thalassiolin B, carpachromene, neobavaisoflavone, and kojic acid (as standard) as natural phenols have IC₅₀ values in the range of 2.37-7.90 µM. Theoretical methods, such as gaussian software program and molecular modeling, were used to compare the biological and chemical activity values of molecules. To compare the biochemical and chemical activity values of molecules, chemical activities with quantum chemical parameters, and biological activities against tyrosinase with the ID of 5M8L molecules were investigated.

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.

Lipase-Catalyzed Chemoselective Ester Hydrolysis of Biomimetically Coupled Aryls for the Synthesis of Unsymmetric Biphenyl Esters

Lipases are among the most frequently used biocatalysts in organic synthesis, allowing numerous environmentally friendly and inexpensive chemical transformations. Here, we present a biomimetic strategy based on iron(III)-catalyzed oxidative coupling and selective ester monohydrolysis using lipases for the synthesis of unsymmetric biphenyl-based esters under mild conditions. The diverse class of biphenyl esters is of pharmaceutical and technical relevance. We explored the potency of a series of nine different lipases of bacterial, fungal, and mammalian origin on their catalytic activities to cleave biphenyl esters, and optimized the reaction conditions, in terms of reaction time, temperature, pH, organic solvent, and water–organic solvent ratios, to improve the chemoselectivity, and hence control the ratio of unsymmetric versus symmetric products. Elevated temperature and increased DMSO content led to an almost exclusive monohydrolysis by the four lipases Candida rugosa lipase (CRL), Mucor miehei lipase (MML), Rhizopus niveus lipase (RNL), and Pseudomonas fluorescens lipase (PFL). The study was complemented by in silico binding predictions to rationalize the observed differences in efficacies of the lipases to convert biphenyl esters. The optimized reaction conditions were transferred to the preparative scale with high yields, underlining the potential of the presented biomimetic approach as an alternative strategy to the commonly used transition metal-based strategies for the synthesis of diverse biphenyl esters.

Crystal structure and Hirshfeld surface analysis of 2-(4-nitro-phen-yl)-2-oxoethyl benzoate

The title com-pound, C15H11NO5, is relatively planar, with the planes of the two aromatic rings being inclined to each other by 3.09 (5)°. In the crystal, mol-ecules are linked by a pair of C-H⋯O hydrogen bonds, forming inversion dimers, which enclose an R 2 2(16) ring motif. The dimers are linked by a further pair of C-H⋯O hydrogen-bonds forming ribbons enclosing R 4 4(26) ring motifs. The ribbons are linked by offset π-π inter-actions [centroid-centroid distances = 3.6754 (6)-3.7519 (6) Å] to form layers parallel to the ac plane. Through Hirshfeld surface analyses, the d norm surfaces, electrostatic potential and two-dimensional fingerprint (FP) plots were examined to verify the contributions of the different inter-molecular contacts within the supra-molecular structure. The shape-index surface shows that two sides of the mol-ecule are involved with the same contacts in neighbouring mol-ecules, and the curvedness plot shows flat surface patches that are characteristic of planar stacking.

Crystal structure and Hirshfeld surface analysis of 2-(4-nitro-phen-yl)-2-oxoethyl 2-chloro-benzoate

The title compound, C15H10ClNO5, is relatively planar with the two aromatic rings being inclined to each other by 3.56 (11)°. The central -C(=O)-C-O-C(=O)- bridge is slightly twisted, with a C-C-O-C torsion angle of 164.95 (16)°. In the crystal, mol-ecules are linked by C-H⋯O and C-H⋯Cl hydrogen bonds, forming layers parallel to the (101) plane. The layers are linked by a further C-H⋯O hydrogen bond, forming a three-dimensional supra-molecular structure. There are a number of offset π-π inter-actions present between the layers [inter-centroid distances vary from 3.8264 (15) to 3.9775 (14) Å]. Hirshfeld surface analyses, the d norm surfaces, electrostatic potential and two-dimensional fingerprint plots were examined to verify the contributions of the different inter-molecular contacts within the supra-molecular structure. The shape-index surface shows that two sides of the mol-ecule are involved in the same contacts with neighbouring mol-ecules, and the curvedness plot shows flat surface patches that are characteristic of planar stacking.

Crystal Correlation Of Heterocyclic Imidazo[1,2-a]pyridine Analogues and Their Anticholinesterase Potential Evaluation

Imidazo[1,2-a]pyridine-based compounds are clinically important to the treatments of heart and circulatory failures, while many are under development for pharmaceutical uses. In this study, a series of imidazo[1,2-a]pyridine-based derivatives 2(a-o) were synthesized by reacting a-haloketones with 2-aminopyridines in a basic media at ambient temperature. Single crystal X-ray diffraction studies suggest that with low degree-of-freedom, the introduction of bulky adamantyl or electron-rich biphenyl moiety into the imidazopyridine derivatives will not affect its structural occupancy. Imidazo[1,2-a]pyridine-based derivatives with biphenyl side chain are potential AChE inhibitors. Compound 2h which bears a biphenyl side chain and methyl substituent at the position R4 of the imidazo[1,2-a]pyridine ring showed the strongest AChE inhibition with an IC50 value of 79 µM. However, imidazo[1,2-a]pyridine derivatives with phenyl side chain exhibit better BChE inhibition effect among the series. Compound 2j with 3,4-dichlorophenyl side chain and unsubstituted imidazo[1,2-a]pyridine ring appears to be the strongest BChE inhibitor with an IC50 value of 65 µM and good selectivity. The inhibitory effects of active compounds were further confirmed by computational molecular docking studies. The results unveiled that peripheral anionic sites of AChE and acyl pocket of BChE were the predominated binding sites for the subjected inhibitors.

Tyrosinase inhibition potency of phthalimide derivatives: crystal structure, Hirshfeld surface analysis and molecular docking studies

A new series of seven 2-((pyridinylamino)methyl)isoindoline-1,3-dione derivatives were synthesized under mild condition and characterized by spectroscopy analysis. The crystal structures of these derivatives were further determined using single crystal X-ray diffraction technique. All derivatives adopt a V-shape conformation. The dihedral angle between phthalimide and pyridine rings increases as the torsion angle C1–N1–C9–N2 between phthalimide ring and methylene group increases. The torsion angles and molecular conformations are comparable to those related structures from the Cambridge Structural Database (CSD). Furthermore, the intermolecular interactions of all studied crystal structures were quantified and analyzed using Hirshfeld surface (HS) analysis. The quantitative data on the percentage contributions of overall interactions in all compounds are calculated by the two-dimensional (2D) fingerprint plots from the HS analysis. These compounds were evaluated for their antioxidant and antityrosinase properties. Noteworthy, 2-(((6-methoxypyridin-3-yl)amino)methyl)isoindoline-1,3-dione (compound g) exhibited higher tyrosinase inhibitory activity (EC50=753 μg/mL) than the positive control ‘arbutin’ (EC50=403 μg/mL). The inhibitory effect of compound g was further confirmed by computational molecular docking studies and the result revealed the 6-methoxypyridin-3-yl substituent has a better binding affinity toward tyrosinase.

Inhibitors of Melanogenesis: An Updated Review

Melanins are pigment molecules that determine the skin, eye, and hair color of the human subject to its amount, quality, and distribution. Melanocytes synthesize melanin and provide epidermal protection from various stimuli, such as harmful ultraviolet radiation, through the complex process called melanogenesis. However, serious dermatological problems occur when there is excessive production of melanin in different parts of the human body. These include freckles, melasma, senile lentigo, pigmented acne scars, and cancer. Therefore, controlling the production of melanin is an important approach for the treatment of pigmentation related disorderes. In this Perspective, we focus on the inhibitors of melanogenesis that directly/indirectly target a key enzyme tyrosinase as well as its associated signaling pathways.