Design, synthesis, and thrombin-inhibitory activity of pyridin-2-ones as P2/P3 core motifs

My 50-Plus Years of Academic Research Collaborations with Industry. A Retrospective

A retrospective is presented highlighting the synthesis of selected "first-in-kind" natural products, their synthetic analogues, structure elucidations, and rationally designed bioactive synthetic compounds that were accomplished because of collaborations with past and present pharmaceutical and agrochemical companies. Medicinal chemistry projects involving structure-based design exploiting cocrystal structures of small molecules with biologically relevant enzymes, receptors, and bacterial ribosomes with synthetic small molecules leading to marketed products, clinical candidates, and novel drug prototypes were realized in collaboration. Personal reflections, historical insights, behind the scenes stories from various long-term projects are shared in this retrospective article.

Cyanide-Free Synthesis of Air Stable N-Substituted Li and K Cyanamide Salts from Tetrazoles. Applications toward the Synthesis of Primary and Secondary Cyanamides as Precursors to Amidines

A practical two-step synthesis of N,N'-disubstituted cyanamides consists in the low-temperature metalation of N-substituted 5H-tetrazoles that undergo spontaneous cycloreversion at 0 °C releasing dinitrogen, and forming N-metalated cyanamides that can be reacted in situ with a variety of electrophiles. Remarkably, the N-substituted Li and K cyanamides are air stable white solids at room temperature. Addition of lithium organometallics to the N,N'-disubstituted cyanamides provides a new method for accessing N,N'-disubstituted amidines.

Influence of the drying method on the bioactive compounds and pharmacological activities of rhubarb

BACKGROUND

Raw rhubarb samples that have been subjected to different drying procedures will have different therapeutic effects, possibly due to processing-induced variations in the chemical composition. In the present work, the fresh materials were processed by smoking, sun-drying, shade-drying and oven-drying at low, moderate and high temperatures. To facilitate the selection of a suitable drying method for rhubarb, the quality of rhubarb processed under various drying conditions was evaluated based on the simultaneous determination of multiple bioactive constituents in combination with bioactivity assays.

RESULTS

The total concentrations of 12 compounds in smoked rhubarb were higher than the concentrations of the same components in raw rhubarb and rhubarb products processed using other drying techniques. Smoked rhubarb was found to substantially inhibit Na⁺ /K⁺ -ATPase and thrombin. In addition, higher content of anthraquinones led to higher Na⁺ /K⁺ -ATPase inhibitory activities, and higher gallic acid content increased the antithrombin capacity.

CONCLUSION

The results confirmed that post-harvest fresh plant materials, especially roots, were still physiologically active organs that could undergo series of anti-dehydration mechanisms, including the production of related secondary metabolites during the early stages of dehydration. Therefore, the proper design of drying processes could enhance the quality of rhubarb as well as other similar medicinal plants. © 2018 Society of Chemical Industry.

Identification of berberine as a direct thrombin inhibitor from traditional Chinese medicine through structural, functional and binding studies

Thrombin acts as a key enzyme in the blood coagulation cascade and represents a potential drug target for the treatment of several cardiovascular diseases. The aim of this study was to identify small-molecule direct thrombin inhibitors from herbs used in traditional Chinese medicine (TCM). A pharmacophore model and molecular docking were utilized to virtually screen a library of chemicals contained in compositions of traditional Chinese herbs, and these analyses were followed by in vitro bioassay validation and binding studies. Berberine (BBR) was first confirmed as a thrombin inhibitor using an enzymatic assay. The BBR IC₅₀ value for thrombin inhibition was 2.92 μM. Direct binding studies using surface plasmon resonance demonstrated that BBR directly interacted with thrombin with a K_D value of 16.39 μM. Competitive binding assay indicated that BBR could bind to the same argartroban/thrombin interaction site. A platelet aggregation assay demonstrated that BBR had the ability to inhibit thrombin-induced platelet aggregation in washed platelets samples. This study proved that BBR is a direct thrombin inhibitor that has activity in inhibiting thrombin-induced platelet aggregation. BBR may be a potential candidate for the development of safe and effective thrombin-inhibiting drugs.

An Improved Synthesis of 6-O-Methyl-Scutellarein through Selective Benzylation

An improved synthesis of 6-O-methyl-scutellarein is described. Benzyl bromide was selected to protect both the hydroxyl groups at C-4′ and C-7 in scutellarein. The product was then methylated and deprotected to produce the target compound in high yield in four steps.

Synthesis and biological evaluation of methylated scutellarein analogs based on metabolic mechanism of scutellarin in vivo

Scutellarin (1) could be hydrolyzed into scutellarein (2) in vivo and then converted into methylated, sulfated and glucuronidated forms. In order to investigate the biological activities of these methylated metabolites, eight methylated analogs of scutellarein (2) were synthesized via semi-synthetic methods. The antithrombotic activities of these compounds were evaluated through the analyzation of prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT) and fibrinogen (FIB). Their antioxidant activities were assessed by measuring their scavenging capacities toward 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and the ability to protect PC12 cells against H2O2-induced cytotoxicity. Furthermore, the physicochemical properties of these compounds including aqueous solubility and lipophilicity were also investigated. The results showed that 6-O-methylscutellarein (5) demonstrated potent antithrombotic activity, stronger antioxidant activity and balanced solubility and permeability compared with scutellarin (1), which warrants further development of 5 as a promising lead for the treatment of ischemic cerebrovascular disease.

A new and efficient synthesis of 6-O-methylscutellarein, the major metabolite of the natural medicine scutellarin

In this paper, a new and efficient synthesis of 6-O-methylscutellarein (3), the major metabolite of the natural medicine scutellarin, is reported. Two hydroxyl groups at C-4′ and C-7 in 2 were selectively protected by chloromethyl methyl ether after the reaction conditions were optimized, then 6-O-methyl-scutellarein (3) was produced in high yield after methylation of the hydroxyl group at C-6 and subsequent deprotection of the two methyl ether groups.

Mannich bases of scutellarein as thrombin-inhibitors: design, synthesis, biological activity and solubility

Two series of 8-aminomethylated derivatives were prepared by Mannich reaction of scutellarein (2) with appropriate aliphatic amines, alicyclic amines and formaldehyde. All the compounds were tested for their thrombin inhibition activity through the analyzation of prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT) and fibrinogen (FIB). The antioxidant activities of these target products were assessed by 1,1-diphenyl-2-picrylhydrazyl radical 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl (DPPH) assay using 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay method and the solubility were assessed by ultraviolet (UV). The results showed that morpholinyl aminomethylene substituent derivative (3d) demonstrated stronger anticoagulant activity, better water solubility and good antioxidant activity compared with scutellarein (2), which warrants further development as a agent for ischemic cerebrovascular disease treatment.

Metabolism-based synthesis, biologic evaluation and SARs analysis of O-methylated analogs of quercetin as thrombin inhibitors

In blood, quercetin is mainly found in metabolized forms. In order to study the activities of these quercetin metabolites in cardiovascular disease, 17 methylquercetin derivatives were synthesized based on metabolism in vivo, their thrombin inhibition activity were evaluated through the analyzation of prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT) and fibrinogen (FIB). The results showed that 6 methylquercetin derivatives had stronger inhibitory activities than that of quercetin. Preliminary SARs analysis showed that hydroxyl groups at C-3' and C-4' position in the B-ring and hydroxyl group at C-3 position in the C-ring played key roles in the thrombin inhibitory activity. The findings of this study would provide information for the exploitation and utilization of quercetin as thrombin inhibitor for thrombotic disease treatment.

Design, synthesis and biological evaluation of N-phenylsulfonylnicotinamide derivatives as novel antitumor inhibitors

A series of novel N-phenylsulfonylnicotinamide derivatives (1-24) have been synthesized and evaluated as potential EGFR tyrosine kinase (TK) inhibitors. Among all the compounds, compound 10 (5-bromo-N-(4-chlorophenylsulfonyl)nicotinamide) showed the most potent growth inhibitory activity against EGFR TK and antiproliferative activity of MCF-7 cancer cell line in vitro, with IC(50) value of 0.09 and 0.07 μM. Docking simulation was performed to insert compound 10 into the EGFR TK active site to determine the probable binding model. Based on the preliminary results, compound 10 with potent inhibitory activity to tumor growth may be a potential anticancer agent.

A series of natural flavonoids as thrombin inhibitors: structure-activity relationships

A series of natural flavonoids has been evaluated as potential inhibitors of thrombin using the optimized method of thrombin time. Myricetin and quercetin have shown to be the best thrombin inhibitors tested. In order to investigate the thrombin recognition of the most active and selective compounds, a molecular modeling study has been performed using available Protein Data Bank (PDB) structures as receptor models for docking experiments. Structure-activity relationships of flavonoids (SARs) on thrombin would facilitate the design of chemical compounds with higher potency to serve as potential thrombin inhibitors, and provide information for the exploitation and utilization of flavonoids as thrombin inhibitors for thrombotic disease treatment.

From natural products to achiral drug prototypes: potent thrombin inhibitors based on P2/P3 dihydropyrid-2-one core motifs

A series of dihydropyrid-2-ones was synthesized and tested for inhibitory activity against serine protease enzymes. Moderate to low nanomolar inhibitory activities were obtained against thrombin and excellent selectivity against trypsin was observed.

Structure-based synthesis: From natural products to drug prototypes

X-ray crystallographic data available from complexes of natural and synthetic molecules with the enzyme thrombin has led to the design and synthesis of truncated and hydrid molecules exhibiting excellent inhibition in vitro. The design element has also been extended to the synthesis and in vitro inhibition of a series of achiral molecules deploying aromatic and heterocyclic core motifs with appropriately functionalized appendages that provide excellent binding interactions at the S1, S2, and S3 sites of thrombin. Excellent selectivity for thrombin over trypsin has also been observed. Thus, studies in total synthesis of highly active natural aeruginosins have inspired further work toward truncated and hybrid analogs with excellent inhibitory activities. Structure-based organic synthesis has guided our research from natural products toward unnatural drug-like prototypes.