Synthesis, anti-browning effect and mechanism research of kojic acid-coumarin derivatives as anti-tyrosinase inhibitors.

Thirteen kojic acid-coumarin derivatives were synthesized using the principle of molecular hybridization, and their structures were characterized by 1H NMR, 13C NMR, and HRMS. In vitro enzyme inhibition experiments showed that all newly synthesized derivatives have excellent inhibition of tyrosinase (TYR) activity. As a mixed inhibitor, compound 6f has the strongest activity, with an IC50 value of 0.88 ± 0.10 µM. Multispectral experiments have confirmed that the mode of action of compound 6f on TYR was static quenching. In addition, compound 6f formed a new complex with TYR, which increased the hydrophobicity of the enzyme microenvironment, reduced the content of the α-helix in the enzyme, and changed the secondary structure. The experimental results showed that compound 6f effectively inhibited the browning of lotus root slices and had low cytotoxicity. Therefore, compound 6f is believed to have great development potential as a TYR inhibitor in the food industry.

Synthesis, biological evaluation and action mechanism of 7H-[1,2,4] triazolo [3,4-b] [1,3,4] thiadiazine-phenylhydrazone derivatives as α-glucosidase inhibitors.

In our work, several 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine-phenylhydrazone derivatives as α-glucosidase inhibitors (α-GIs) were synthesized and characterized by 1H NMR, 13C NMR, and HRMS spectrum. Then, their bio-activity against the α-glucosidase (α-Glu) was further evaluated. Among them, almost all compounds displayed better bio-activity with IC50 from 31.23 ± 0.89 to 213.50 ± 4.19 µM than acarbose (IC50 = 700.20 ± 10.55 µM). In particular, compound 5o showed the best potency to inhibit α-Glu in a mixed manner. Moreover, the action mechanisms of 5o were further clarified including fluorescence quenching, circular dichroism spectra, three-dimensional fluorescence spectra, molecular docking, etc. All mechanism studies revealed that 5o could arouse the changed secondary structure of α-Glu to hinder enzyme catalytic activity. It was observed from an in vivo study that 5o of 20 mg/kg could significantly decrease by 24.45 % postprandial blood glucose in mice vs. the control. Meanwhile, 5o had low drug-drug interaction potential and was likely to be an orally active compound. Moreover, 5o was observed to be no obvious cytotoxicity to HEK-293 cells. In summary, compound 5o exhibited one potential to be further applied as an antidiabetic drug.

Design, synthesis, biological evaluation, and docking study of new triazole-phenylacetamide derivatives as α-glucosidase inhibitors.

To discover potent α-glucosidase inhibitors, a class of novel triazole-phenylacetamide derivatives (5a-5p) were designed, prepared, and tested for their α-glucosidase inhibitory effects. All tested compounds (5a-5p) displayed a strong α-glucosidase inhibitory activity (IC50 = 6.69 ± 0.18-113.65 ± 2.94 µM) in comparison with the positive control acarbose (IC50 = 723.06 ± 11.26 µM). Thereinto, 5g (IC50 = 6.69 ± 0.18 µM) showed the best anti-α-glucosidase activity and behaved as a mixed-type inhibitor with the value of Ki and Kis to be 1.65 µM and 4.54 µM, respectively. Besides, fluorescence quenching experiment, three-dimensional fluorescence spectra assay, circular dichroism analysis, and molecular docking studies indicated that 5g may inhibit α-glucosidase activity by binding with its active site as well as changing the secondary structure of α-glucosidase. Combined with the inhibition effect on the rise of postprandial blood glucose level and low cytotoxicity of 5g, it could be concluded that these title compounds may play a role as lead compounds to develop novel α-glucosidase inhibitors.

Utilizing bio-affinity ultrafiltration combined with UHPLC Q-Exactive Plus Orbitrap HRMS to detect potential α-glucosidase inhibitors in Oxalis corniculate L.

Oxalis corniculate L. (O. corniculate) was used to treat diabetes in Chinese folk as a popular tea drink. In this work, 31 compounds from O. corniculate were screened and identified as potential α-Glucosidase inhibitors (α-GIs). Among them, 6 compounds displayed stronger inhibitory activity than acarbose (IC50 = 212.9 ± 5.98 µg/mL). Especially, the most effective compounds quercetin (Qu, IC50 = 4.70 ± 0.40 µg/mL) and luteolin (Lu, IC50 = 15.72 ± 0.75 µg/mL) inhibited α-Glu in competitive and mixed manners, respectively. Moreover, fluorescence quenching, circular dichroism (CD), and molecular docking study revealed that they can arouse the changes in the secondary structure and hydrophobic micro-environment of the enzyme mainly through a hydrophobic binding. Furthermore, it was observed that oral administration of Qu (20 mg/kg) can significantly reduce postprandial blood glucose (PBG) levels in mice vs. the control group. To sum up, the above research confirmed that O. corniculate could prevent and treat postprandial hyperglycemia as a good tea drink, and the plant was an excellent source to obtain natural α-GIs.

Novel kojic acid-1,2,4-triazine hybrids as anti-tyrosinase agents: Synthesis, biological evaluation, mode of action, and anti-browning studies.

A class of new kojic acid hybrids (7a-7o) bearing a 1,2,4-triazine moiety were prepared, and their inhibitory activities and mechanism on tyrosinase were investigated. All derivatives showed good to excellent anti-tyrosinase activity with IC50 values ranging from 0.34 ± 0.06 µM to 8.44 ± 0.73 µM. In kinetic study, compound 7m was a mixed-type inhibitor with Ki and Kis of 0.73 and 1.27 µM, respectively. The interaction mechanism toward tyrosinase of compound 7m was further elaborated in combination with molecular docking and various spectral techniques. The results showed that compound 7m could change the secondary structure of tyrosinase to reduce its catalytic activity. Anti-browning assays demonstrated that 7m inhibited the browning of bananas effectively during storage. What's more, 7m was found to have low cytotoxicity in vitro. In conclusion, compound 7m has the potential to be applied as an anti-browning agent.

Anti-browning and antibacterial dual functions of novel hydroxypyranone-thiosemicarbazone derivatives as shrimp preservative agents: Synthesis, bio-evaluation, mechanism, and application.

To develop new shrimp preservative agents with dual functions of anti-browning and antibacterial, thirteen hydroxypyranone-thiosemicarbazone derivatives were prepared according to molecular hybridization. Thereinto, compound 7j (IC50 = 1.99 ± 0.19 µM) shown the strongest anti-tyrosinase activity and was about twenty-three folds stronger than kojic acid (45.73 ± 4.03 µM). The anti-tyrosinase mechanism of 7j was illustrated through enzyme kinetic, copper ion chelating ability, fluorescence quenching, ultraviolet spectrum, AFM analysis, and molecular docking study. On the other hand, antibacterial assay and time-kill kinetics analysis confirmed that 7j also had good antibacterial activity against V. parahaemolyticus (MIC = 0.13 mM). PI uptake test, SDS-PAGE, and fluorescence spectrometry analysis proved that 7j can affect the bacterial cell membrane. Finally, the shrimp preservation and safety study indicated that 7j has dual effects of inhibiting bacterial growth and preventing enzyme browning, and can be applied to the preservation of fresh shrimp.

Diagnostic, clustering, and immune cell infiltration analysis of m6A regulators in patients with sepsis.

RNA N6-methladenosine (m6A) regulators are required for a variety of biological processes, including immune responses, and increasing evidence indicates that their dysregulation is closely associated with many diseases. However, the potential roles of m6A regulators in sepsis remain unknown. We comprehensively analyzed the transcriptional variations in and interactions of 26 m6A regulators in sepsis based on the Gene Expression Omnibus (GEO) database. A random forest (RF) model and nomogram were established to predict the occurrence and risk of sepsis in patients. Then, two different m6A subtypes were defined by consensus clustering analysis, and we explored the correlation between the subtypes and immune cells. We found that 17 of the 26 m6A regulators were significantly differentially expressed between patients with and without sepsis, and strong correlations among these 17 m6A regulators were revealed. Compared with the support vector machine (SVM) model, the RF model had better predictive ability, and therefore was used to construct a reliable nomogram containing 10 candidate m6A regulators to predict the risk of sepsis in patients. In addition, a consensus clustering algorithm was used to identify two different subtypes of m6A, which helped us distinguish different levels of immune cell infiltration and inflammation in patients with sepsis. Comprehensive analysis of m6A regulators in sepsis revealed their potential roles in sepsis occurrence, immune cell infiltration and inflammation in patients with sepsis. This study may contribute to the development of follow-up treatment strategies for sepsis.

Tyrosinase inhibitory mechanism and anti-browning properties of novel kojic acid derivatives bearing aromatic aldehyde moiety.

Kojic acid-aromatic aldehydes 6a-6m were synthesized and screened for their anti-tyrosinase activities. These compounds showed potently anti-tyrosinase activity with IC50 values in the range of 5.32 ± 0.23 to 77.89 ± 3.36 µM compared with kojic acid (IC50 = 48.05 ± 3.28 µM). Thereinto, compound 6j with 3-fluorine and 4-aldehyde substitutions showed the most potent anti-tyrosinase activity (IC50 = 5.32 ± 0.23 µM). Enzyme kinetic study revealed that 6j is a noncompetitive tyrosinase inhibitor (Ki = 2.73 µM). The action mechanism of 6j was evaluated by fluorescence spectrum quenching, molecular docking, 1H NMR titration, etc. The anti-browning assay showed that 6j could delay the enzymatic browning of fresh-cut apples. Besides, the cell viability assay proved that 6j had a good safety profile as an anti-browning agent. Hence, these results identify a new class of anti-tyrosinase and anti-browning agents for further investigation in the food industry.

Design, synthesis, biological evaluation, and docking study of chromone-based phenylhydrazone and benzoylhydrazone derivatives as antidiabetic agents targeting α-glucosidase.

To develop novel α-glucosidase inhibitors, a series of chromone-based phenylhydrazone and benzoylhydrazone derivatives were designed, synthesized, and evaluated their inhibitory effects on α-glucosidase. The target compounds were characterized using 1H NMR, 13C NMR, and high-resolution mass spectra. Some of the compounds showed a varying degree of α-glucosidase inhibitory activity with IC50 values ranging from 6.59 ± 0.09 to 158.55 ± 0.87 µM. Among them, compound 5c (IC50 = 6.59 ± 0.09 µM) was the most potent inhibitor by comparison with positive control acarbose (IC50 = 685.11 ± 7.46 µM). Enzyme kinetic, fluorescence analysis, circular dichroism spectra, and molecular docking techniques were employed to explain the underlying molecular mechanisms of 5c inhibition on α-glucosidase. In vivo sucrose-loading test showed that 5c could suppress the rise of blood glucose levels after loading sucrose in normal Kunming mice. The cytotoxicity assay indicated that 5c exhibited low cytotoxicity.

Chromone-based benzohydrazide derivatives as potential α-glucosidase inhibitor: Synthesis, biological evaluation and molecular docking study.

In order to find new α-glucosidase inhibitors with high efficiency and low toxicity, novel chromone-based benzohydrazide derivatives 6a-6s were synthesized and characterized through 1H NMR, 13C NMR, and HRMS. All the new synthesized compounds were tested for inhibitory activities against α-glucosidase. Compounds 6a-6s with IC50 values ranging from 4.51 ± 0.09 to 27.21 ± 0.83 µM, showed a potential α-glucosidase inhibitory activity as compared to the positive control (acarbose: IC50 = 790.40 ± 0.91 µM). Compound 6i exhibited the highest α-glucosidase inhibitory activity with an IC50 value of 4.51 ± 0.09 µM. Theinteractionbetween α-glucosidase and 6i was further confirmed by enzyme kinetic, fluorescence quenching, circular dichroism, and molecular docking study. In vivo experiment showed that 6i could suppress the rise of blood glucose levels after sucrose loading. The cytotoxicity result indicated that 6i exhibited low cytotoxicity in vitro.

An overview: metal-based inhibitors of urease.

Urease is a kind of nickel-dependent metalloenzyme, which exists in the biological world widely, and can catalyse the hydrolysis of urea into ammonia and carbon dioxide to provide a nitrogen source for organisms. Urease has important uses in agriculture and medicine because it can catalyse the production of ammonia. Therefore, in this review, metal-based inhibitors of urease will be summarised according to different transition metal ions. Including the urease inhibition, structure-activity relationship, and molecular docking. Importantly, among these reviewed effective urease inhibitors, most of copper metal complexes exhibited stronger urease inhibition with IC50 values ranging from 0.46 µM to 41.1 µM. Significantly, the collected comprehensive information looks forward to providing rational guidance and effective strategies for the development of novel, potent, and safe metal-based urease inhibitors, which are better for practical applications in the future.

Covalent Grafting of 5-Aminolevulinic Acid onto Polylactic Acid Films and Their Photodynamic Potency in Preserving Salmon.

A novel photodynamic inactivation (PDI)-mediated antimicrobial film of polylactic acid/5-aminolevulinic acid (PLA/ALA) was successfully fabricated by a covalent grafting method using low-temperature plasma. The chemical structure, surface morphology, hydrophilic ability, and mechanical and barrier properties of the films were characterized, and their antibacterial, anti-biofilm potency and preservation effects on ready-to-eat salmon were investigated during storage. Results showed that the amino group of ALA was covalently grafted with the carboxyl group on the surface of PLA after the plasma treatment, with the highest grafting rate reaching ∼50%. The fabricated PLA/ALA films displayed an enhanced barrier ability against water vapor and oxygen. Under blue light-emitting diode illumination, the PLA/ALA films generated massive reactive oxygen species from the endogenous porphyrins in cells induced by ALA and then fatally destroyed the cell wall of planktonic cells and the architectural structures of sessile biofilms of the pathogens (Listeria monocytogenes and Vibrio parahaemolyticus) and spoilage bacterium (Shewanella putrefaciens). More importantly, the PDI-mediated PLA/ALA films potently inhibited 99.9% native bacteria on ready-to-eat salmon and significantly suppressed the changes of its drip loss, pH, and lipid oxidation (MDA) during storage, and on this basis, the shelf life of salmon was extended by 4 days compared with that of the commercial polyethylene film. Therefore, the PDI-mediated PLA/ALA films are valid in inactivating harmful bacterial and preserving the quality of seafood.

Synthesis and biological evaluation of new kojic acid-1,3,4-oxadiazole hybrids as tyrosinase inhibitors and their application in the anti-browning of fresh-cut mushrooms.

In the food industry, inhibition of tyrosinase activity is considered as one of the main means to prevent browning. Therefore, fourteen kojic acid-1,3,4-oxadiazole hybrids (5a-5n) were prepared and tested for their tyrosinase inhibitory effects. Among them, 5f (IC50 = 5.32 ± 0.58 µM) has the best anti-tyrosinase activity and was 9 times higher than that of kojic acid (IC50 = 49.77 ± 1.19 µM). Additionally, the inhibitory mechanism was studied by copper-chelating assay, ultraviolet spectrophotometry, fluorescence quenching, molecular docking, etc. The results had shown that 5f could not only bind to the copper ion in the active region of tyrosinase but also change the secondary structure of tyrosinase. Combined with the outstanding anti-browning effect and low cytotoxicity of 5f, it is concluded that these title derivatives could be used as the leading molecules in the development of new anti-browning agents.

Recent advances in the synthetic thymidine phosphorylase inhibitors for cancer therapy.

Thymidine phosphorylase (TP) is an important enzyme for the synthesis and decomposition of pyrimidine, which can specifically catalyze the reversible phosphorolysis of thymidine to thymine and 2-deoxy-α-D-ribose-1-phosphate in the body. TP is highly expressed in many solid tumor tissues and can induce angiogenesis and anti-apoptotic effect, as well as tumor growth and metastasis. Therefore, TP inhibitors play a major role in the treatment. In recent years, a large number of synthetic TP inhibitors have been widely reported. In this article, the research progress of synthetic TP inhibitors was reviewed, including inhibitory activity, cytotoxicity, structure-activity relationship (SAR), inhibitory kinetics, mechanism of interaction and molecular docking. In our reviewed inhibitors, pyrimidine derivatives account for about a half, but it is a lack for research on other biological activities of pyrimidine derivatives and further exploration of the inhibitory mechanism of excellent inhibitors. Meanwhile, application of radiolabeled inhibitors to assess TP expression in tumors and prognosis of cancer chemotherapy in vivo is rarely reported. In addition, the study on the synergistic anticancer activity of TP inhibitors in combination with other anticancer drugs is less. Therefore, it is valuable to look forward to developing more and more potent TP inhibitors and applying them in the clinical treatment of cancer in the future.

Synthesis and antitumor activity of litseaone B analogues as tubulin polymerisation inhibitors.

A series of litseaone B analogues 4a∼4p were synthesised and antitumor activities of all compounds were screened. These compounds were designed by introducing different substituents on the B ring. Among these synthesised compounds, it was proved that 4k showed excellent activity against A549, HepG2, and HCT-15 cell lines, the IC50 values were 7.60 µM, 20.53 µM, and 4.59 µM, respectively. The results of tubulin polymerisation inhibition and immunofluorescence staining experiments displayed that 4k could act on tubulin and inhibit the polymerisation of tubulin. Moreover, the wound healing assay showed that 4k could inhibit the migration of A549 cells in a dose-dependent manner. Furthermore, the results of flow cytometry revealed that 4k was capable of blocking the cell cycle in the G2/M phase, inducing a decrease in the mitochondrial membrane potential and ultimately leading to apoptosis in A549 cells. Importantly, the possible binding model was also performed by molecular docking. Subject classification codes: short communication.

Metagenomic next-generation sequencing in diagnosing Pneumocystis jirovecii pneumonia: A case report.

It remains a huge challenge for clinicians to diagnose Pneumocystis jirovecii pneumonia (PJP) by a conventional method, which leads to delay in diagnosing PJP, accounting for higher mortality in patients with rheumatoid arthritis (RA). A 69-year-old woman, who suffered from RA for years, developed acute respiratory failure. The computed tomography scan showed diffused effusion and ground glass opacity in both lungs, which could not be differentiated from interstitial pneumonia. Metagenomic next-generation sequencing (mNGS) revealed P. jirovecii in both serum and bronchoalveolar lavage fluid with reads per million (RPM) of 17 and 437, while other diagnostic tests did not detect any pathogenic microorganism. The results were verified by quantitative polymerase chain reaction (mtSSU region) against the same samples. The DNA RPM of P. jirovecii declined notably after treatment with trimethoprim/sulfamethoxazole. The patient was discharged without treatment and finally passed away. This case fully highlights the sensitivity of mNGS in early diagnosis of PJP, which is of great significance for prognosis and treatment. Nonetheless, the clinical application of mNGS is worth further standardization and normalization.

Occurrence, synthesis and biological activity of 2-(2-phenyethyl)chromones.

2-(2-Phenylethyl)chromones (PECs) are a group of naturally occurring compounds, which are characterized as phenylethyl substituent at the C2 position of chromone. They have been isolated mainly from Aquilaria sinensis (Lour.) Gilg. This type of natural compound is correlative with anti-diabetes, anticancer, antioxidant, antibacterial, anticancer, and anti-inflammatory activities. Due to the versatile activities of PECs, more and more researchers use different improved methods to synthesize them and their derivatives. This review mainly focuses on the natural occurrence, chemical synthesis, and biological activities of PECs, which were published up until 2020.

An overview on the synthetic urease inhibitors with structure-activity relationship and molecular docking.

Urease is a kind of enzyme which could be found in various bacteria, fungi, plants, and algae, which can quickly catalyze the hydrolysis of urea into ammonia and carbon dioxide. With the ammonia concentration increasing, the activity of Helicobacter pylori has got an obvious enhancement and leads to mucosal damage in the stomach, gastroduodenal infection, peptic ulcers, and gastric cancer. The infectious diseases caused by Helicobacter pylori can be controlled to a certain extent by inhibiting urease activity with urease inhibitors. Hence, studies of urease inhibitors have attracted great attention all over the world and a variety of effective urease inhibitors have been synthesized in recent years. In this review, we will draw summaries for these inhibitors including urease inhibitory activity, inhibition kinetics, structure-activity relationship, and molecular docking. The collected information is expected to provide rational guidance and effective strategy to develop novel, potent, and safe urease inhibitors for better practical applications in the future.

Structural and functional properties of soluble Antarctic krill proteins covalently modified by rutin.

New polyphenol-protein conjugates were successfully prepared by covalently crosslinking soluble Antarctic krill proteins with rutin (SAKPs-rutin). The physico-chemical and functional properties of SAKPs-rutin conjugates were systematically evaluated by measuring the changes in interfacial tension, structural conformation, and emulsifying ability, etc. The results showed that SAKPs-rutin conjugates possessed higher surface hydrophobicity, surface charge, and thermal denaturation temperature, and lower ß-sheet conformation compared to native SAKPs. On this basis, the interfacial tension of SAKPs-rutin conjugates was reduced, which greatly contributed to the formation of denser and more ordered networks at the oil-water interface. Meanwhile, the emulsifier endowed the fabricated high internal phase emulsions (HIPEs) with excellent physical performance and oxidative stability, evidenced by low peroxide values (POV) and malondialdehyde (MDA) after the treatment of long-term storage (15d), heating (65 °C) and UV light treatment. These findings suggest that SAKPs-rutin conjugates are a novel and promising food resource for preparing food-grade emulsions.

Fenton reaction-assisted photodynamic inactivation of calcined melamine sponge against Salmonella and its application.

Photodynamic inactivation (PDI) is an effective alternative to traditional antibiotics to broadly kill bacteria. This study aimed to develop a potent PDI system by coupling calcinated melamine sponges (CMSs) with the Fenton reaction. The results showed that CMS calcined at 350 ℃ was successfully carbonized with intact and porous structures, and it possessed excellent hydrophilicity and photothermal conversion performance. When Fe2+ was added and internalized, the Fenton reaction in which Fe2+ reacted with H2O2 in cells occurred to produce reactive oxygen species (ROS) (OH, OOH, etc.) and O2, and notably, the O2 molecules could serve as a raw material to absorb the photothermal energy of CMS to generate highly reactive 1O2. Under synergistic effects, CMS-350 coupled with Fe2+ potently inactivated > 6 Log CFU/mL (>99.9999%) of Salmonella under 201.6 J/cm2 blue LED illumination by destroying Na+/K+-ATPase and Ca2+/Mg2+-ATPase, DNA synthesis-related enzymes, cell membranes, etc. Meanwhile, the composite photocatalyst was proven to be nontoxic and could inactivate Salmonella in various foods, including vegetables (Brassica chinensis L), eggs and fresh cucumber juice. As a result, CMS coupled with the Fenton reaction greatly improves the inactivation potency of PDI against harmful bacteria.