Category: thiazole

A Double-Clicking Bis-Azide Fluorogenic Dye for Bioorthogonal Self-Labeling Peptide Tags was written by Demeter, Orsolya;Fodor, Eszter A.;Kallay, Mihaly;Mezo, Gabor;Nemeth, Krisztina;Szabo, Pal T.;Kele, Peter. And the article was included in Chemistry – A European Journal in 2016.Application of 2942-06-5 This article mentions the following:

Herein, the authors give the very first example for the development of a fluorogenic mol. probe that combines the two-point binding specificity of biarsenical-based dyes with the robustness of bioorthogonal click-chem. This proof-of-principle study reports on the synthesis and fluorogenic characterization of a new, double-quenched, bis-azide fluorogenic probe suitable for bioorthogonal two-point tagging of small peptide tags by double strain-promoted azide-alkyne cycloaddition The presented probe exhibits remarkable increase in fluorescence intensity when reacted with bis-cyclooctynylated peptide sequences, which could also serve as possible self-labeling small peptide tag motifs. In the experiment, the researchers used many compounds, for example, 6-Nitrobenzothiazole (cas: 2942-06-5Application of 2942-06-5).

6-Nitrobenzothiazole (cas: 2942-06-5) belongs to thiazole derivatives. The higher aromaticity of thiazole is due to delocalization of a lone pair of sulfur electrons across the ring, which is evidenced by chemical shifts of ring hydrogen at δ 7.27 and 8.77 ppm (C2 and C4), indicating diamagnetic ring current. Various laboratory methods exist for the organic synthesis of thiazoles. Prominent is the Hantzsch thiazole synthesis is a reaction between haloketones and thioamides.Application of 2942-06-5

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Pulmonary Delivery of Levamisole Nanoparticles as an Immunomodulator Affecting Th and a Potential ADAM10 Inhibitor to Ameliorate Severe Allergic Asthma was written by Fang, Liping;Nikfarjam, Nasser;Gharagozlou, Mohammad;Huang, Tao;Song, Yu;Islambulchilar, Ziba;Esmaeilzadeh, Abdolreza;Jafari, Davood;Athari, Seyyed Shamsadin. And the article was included in ACS Biomaterials Science & Engineering in 2022.Recommanded Product: (S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole This article mentions the following:

Asthma is a common chronic lung disease without absolute treatment, and hypersensitivity reactions and type 2 immune responses are responsible for asthma pathophysiol. ADAM10 as a metalloproteinase transmembrane protein is critical for development of Th2 responses, and levamisole as an anthelmintic drug has immunomodulatory effects, which not only regulates ADAM10 activity but also can suppress the bone marrow and neutrophil production Therefore, in the present study, nanoparticles were used as a levamisole delivery system to reduce bone marrow suppression, and the immunomodulatory and ADAM10 inhibitory effects of levamisole were studied in allergic asthma. Asthmatic mice were treated with PLGA-levamisole nanoparticles. Then, AHR, BALF, and blood cell counts, levels of the IgG1 subclass, total and OVA-specific IgE, IL2, IL-4, IL-5, IL-10, IL-13, IL-17, IL-25, IL-33, INF-γ, and TNF-α, gene expression of FoxP3, T-bet, RORγt, PU.1, GATA3, FcεRII, CysLT1R, eotaxin, and ADAM10, and lung histopathol. were evaluated. PLGA-LMHCl with considered characteristics could control airway hyper-responsiveness, eosinophils in the BALF, levels of Igs, Th2-, Th9-, and Th17-derived cytokines and pivotal genes, eosinophilic inflammation, hyperplasia of the goblet cell, and hyperprodn. of mucus and could increase Th1- and Treg-derived cytokines and also pivotal genes. It could also modulate the ADAM10 activity and had no effect on the number of neutrophils in the bloodstream. The novel safe nanodrug had no side effect on the bone marrow to produce neutrophils and could control the allegro-immuno-inflammatory response of asthma. In the experiment, the researchers used many compounds, for example, (S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole (cas: 14769-73-4Recommanded Product: (S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole).

(S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole (cas: 14769-73-4) belongs to thiazole derivatives. Thiazoles in peptides or their ability to bind proteins, DNA and RNA has led to many synthetic studies and new applications.Various laboratory methods exist for the organic synthesis of thiazoles. For example, 2,4-dimethylthiazole is synthesized from thioacetamide and chloroacetone.Recommanded Product: (S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Integrative multi-biomarker approach on caged rainbow trout: A biomonitoring tool for wastewater treatment plant effluents toxicity assessment was written by Beghin, Mahaut;Paris-Palacios, Severine;Mandiki, Syaghalirwa N. M.;Schmitz, Melodie;Palluel, Olivier;Gillet, Erin;Bonnard, Isabelle;Nott, Katherine;Robert, Christelle;Porcher, Jean-Marc;Ronkart, Sebastien;Kestemont, Patrick. And the article was included in Science of the Total Environment in 2022.Reference of 14769-73-4 This article mentions the following:

The complex mixtures of contaminants released in wastewater treatment plant (WWTP) effluents are a major source of pollution for aquatic ecosystems. The present work aimed to assess the environmental risk posed by WWTP effluents by applying a multi-biomarker approach on caged rainbow trout (Oncorhynchus mykiss) juveniles. Fish were caged upstream and downstream of a WWTP for 21 days. To evaluate fish health, biomarkers representing immune, reproductive, nervous, detoxification, and antioxidant functions were assayed. Biomarker responses were then synthesized using an Integrated Biomarker Response (IBR) index. The IBR highlighted similar response patterns for the upstream and downstream sites. Caged juvenile females showed increased activities of innate immune parameters (lysozyme and complement), histol. lesions and reduced glycogen content in the hepatic tissue, and higher muscle cholinergic metabolism However, the intensity of the observed effects was more severe downstream of the WWTP. The present results suggest that the constitutive pollution level of the Meuse River measured upstream from the studied WWTP can have deleterious effects on fish health condition, which are exacerbated by the exposure to WWTP effluents. Our results infer that the application of IBR index is a promising tool to apply with active biomonitoring approaches as it provides comprehensive information about the biol. effects caused by point source pollution such as WWTP, but also by the constitutive pollutions levels encountered in the receiving environment. In the experiment, the researchers used many compounds, for example, (S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole (cas: 14769-73-4Reference of 14769-73-4).

(S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole (cas: 14769-73-4) belongs to thiazole derivatives. Thiazole rings are planar and aromatic. Thiazoles are characterized by larger pi-electron delocalization than the corresponding oxazoles and have therefore greater aromaticity. Electrophilic attack at nitrogen depends on the presence of electron density at nitrogen as well as the position and nature of substituent linked to the thiazole ring.Reference of 14769-73-4

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Synthesis and study of novel benzothiazole derivatives with potential nonlinear optical properties was written by Sigmundova, Ivica;Zahradnik, Pavol;Loos, Dusan. And the article was included in Collection of Czechoslovak Chemical Communications in 2007.COA of Formula: C8H6N2O2S This article mentions the following:

The synthesis of new benzothiazole push-pull systems as candidates for NLO-phores is described. Spectral (UV/VIS and solvatochromic) and theor. studies (electronic properties based on semiempirical AM1 and PM3 methods) of the prepared compounds were carried out. The structure and physico-chem. parameters affecting the push-pull character and intramol. charge transfer (ICT) of the studied compounds have been investigated and compounds with enhanced hyperpolarizability β have been predicted. The benzothiazolium salts were found to be much more effective NLO-phores in comparison with the corresponding neutral benzothiazoles. The 4-NPh₂ group is the most effective donor. The extension of conjugated bridge improves the studied NLO characteristics. An addnl. acceptor group bonded to the heterocycle causes a red shift of λ_max but does not increase hyperpolarizability. In the experiment, the researchers used many compounds, for example, 2-Methyl-6-nitrobenzothiazole (cas: 2941-63-1COA of Formula: C8H6N2O2S).

2-Methyl-6-nitrobenzothiazole (cas: 2941-63-1) belongs to thiazole derivatives. Thiazoles frequently appear in peptide studies. Thiazoles can also be used as protected formyl groups, which can be released in later stages of complex natural product synthesis. There are numerous natural products that possess a thiazole ring with broad pharmacological activities. Thiamine, also known as vitamin B1, possesses a thiazole ring linked with 2-methylpyrimidine-4-amine as hydrochloride salt.COA of Formula: C8H6N2O2S

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Unlocking the full potential of voltammetric data analysis: A novel peak recognition approach for (bio)analytical applications was written by Van Echelpoel, Robin;de Jong, Mats;Daems, Devin;Van Espen, Piet;De Wael, Karolien. And the article was included in Talanta in 2021.Related Products of 14769-73-4 This article mentions the following:

Bridging the gap between complex signal data output and clear interpretation by non-expert end-users is a major challenge many scientists face when converting their scientific technol. into a real-life application. Currently, pattern recognition algorithms are the most frequently encountered signal data interpretation algorithms to close this gap, not in the least because of their straight-forward implementation via convenient software packages. Paradoxically, just because their implementation is so straight-forward, it becomes cumbersome to integrate the expert′s domain-specific knowledge. In this work, a novel signal data interpretation approach is presented that uses this domain-specific knowledge as its fundament, thereby fully exploiting the unique expertise of the scientist. The new approach applies data preprocessing in an innovative way that transcends its usual purpose and is easy to translate into a software application. Multiple case studies illustrate the straight-forward application of the novel approach. Ultimately, the approach is highly suited for integration in various (bio)anal. applications that require interpretation of signal data. In the experiment, the researchers used many compounds, for example, (S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole (cas: 14769-73-4Related Products of 14769-73-4).

(S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazole (cas: 14769-73-4) belongs to thiazole derivatives. Thiazole rings are planar and aromatic. Thiazoles are characterized by larger pi-electron delocalization than the corresponding oxazoles and have therefore greater aromaticity. There are numerous natural products that possess a thiazole ring with broad pharmacological activities. Thiamine, also known as vitamin B1, possesses a thiazole ring linked with 2-methylpyrimidine-4-amine as hydrochloride salt.Related Products of 14769-73-4

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Thiazolium as Single-Group Bifunctional Catalyst for Selectively Bulk Melt ROP of Cyclic Esters was written by Tian, Guo-Qiang;Liu, Wen;Chen, Li;Wu, Gang;Chen, Si-Chong;Wang, Yu-Zhong. And the article was included in ChemCatChem in 2019.Recommanded Product: 4209-18-1 This article mentions the following:

Novel single-group bifunctional hydrogen-bonding catalysts based on thiazolium were developed. The integration of hydrogen-bonding donor and acceptor in a single thiazolium ring not only amplified synergetic effect, but also enhanced the stability and the controllability for catalysis, and hence prompt thiazolium an efficient metal-free catalyst for melt ROP of cyclic esters. More interestingly, thiazolium may form a compacted active center with monomer and initiator (or propagating chain end), thus enabling it to selectively activate lower sterically encumbered substrates in ROP. In the experiment, the researchers used many compounds, for example, 3-Benzyl-4-methylthiazol-3-ium chloride (cas: 4209-18-1Recommanded Product: 4209-18-1).

3-Benzyl-4-methylthiazol-3-ium chloride (cas: 4209-18-1) belongs to thiazole derivatives. The thiazole ring has been identified as a central feature of numerous natural products, perhaps the most famous example of which is epothilone. Thiazole is a versatile building block for the construction and lead generation of new drug discoveries. Numerous diazole-based compounds are in clinical use as anticancer, antileukemic, antiinflammatory, antiviral, antifungal, antirheumatic, immunomodulator, and antiparasitic agents.Recommanded Product: 4209-18-1

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Diketopyrrolopyrrole based small molecular semiconductors containing thiazole units for solution-processed n-channel thin-film transistors was written by Tang, Meizhu;Wu, Sicheng;Xing, Weilong;Shen, Hongguang;Xiang, Lanyi;Liang, Yingying;Xu, Wei;Zhu, Daoben. And the article was included in Dyes and Pigments in 2019.Reference of 1452-16-0 This article mentions the following:

In this work, three diketopyrrolopyrrole-based conjugated small mol. semiconductors characterized by the combination of a diketopyrrolopyrrole (DPP) central core, thiazole π-conjugated moiety, and dicyanovinyl end group with different alkyl side chain substituents, 2TzDPPA1-2DCV, 2TzDPPA2-2DCV, and 2TzDPPA3-2DCV were synthesized. These small mols. have a similar narrow band gap of about 1.50 eV and deep LUMO energy level at -4.30 eV. Under ambient conditions, electron mobilities of 0.28 cm² V^-1 s^-1, 0.13 cm² V^-1 s^-1, 0.25 cm² V^-1 s^-1 for solution processed thin films of 2TzDPPA1-2DCV, 2TzDPPA2-2DCV, and 2TzDPPA3-2DCV were obtained, due to high crystallinity and well-organized mol. stacking. Compared with the other two materials, thin films of 2TzDPPA1-2DCV enable the best OFET performance with desirable Ion/Ioff rates exceeding of 10⁷, attribute to the coefficient of smoother film morphol. and stronger crystallinity. These results reveal that introducing the thiazole unit into the DPP-based conjugated skeleton is conducive to enhance the crystallinity and tailor LUMO energy levels which ensure good performance and excellent stability of these mols. as active materials for n-channel electronic devices. In the experiment, the researchers used many compounds, for example, 2-Cyanothiazole (cas: 1452-16-0Reference of 1452-16-0).

2-Cyanothiazole (cas: 1452-16-0) belongs to thiazole derivatives. The thiazole ring has been identified as a central feature of numerous natural products, perhaps the most famous example of which is epothilone. Various laboratory methods exist for the organic synthesis of thiazoles. Prominent is the Hantzsch thiazole synthesis is a reaction between haloketones and thioamides.Reference of 1452-16-0

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Lusutrombopag is effective and safe in patients with chronic liver disease and severe thrombocytopenia: a multicenter retrospective study was written by Nomoto, Hiroaki;Morimoto, Naoki;Miura, Kouichi;Watanabe, Shunji;Takaoka, Yoshinari;Maeda, Hiroshi;Sasaki, Takahiro;Koyashiki, Yohei;Kurata, Hidekazu;Numao, Norikatsu;Isoda, Norio;Yamamoto, Hironori. And the article was included in BMC Gastroenterology in 2020.Application of 1110766-97-6 This article mentions the following:

Chronic liver disease (CLD) is often complicated by severe thrombocytopenia (platelet count < 50,000/μL). Platelet transfusion has been a gold standard for increasing the platelet count to prevent hemorrhagic events in such patients. Lusutrombopag, a thrombopoietin receptor agonist, can increase the platelet count in such patients when invasive procedures are scheduled. Former studies on lusutrombopag included patients with a platelet count of > 50,000/μL at baseline: the proportions of patients who did not require platelet transfusion were 84-96%, which might be overestimated. The efficacy and safety of lusutrombopag were retrospectively investigated in CLD patients with platelet count of < 50,000/μL, a criterion for platelet transfusion, in real-world settings. We examined the proportion of patients who did not require platelet transfusion in 31 CLD patients, which exceeded a min required sample size (21 patients) calculated by 80% power at a significance level of 5%. Lusutrombopag, 3 mg once daily, was administered 8-18 days before scheduled invasive procedures. Among 31 patients who received lusutrombopag, 23 patients (74.2%) patients showed a platelet count of ≥ 50,000/μL (Group A) and did not require platelet transfusion. The remaining 8 patients (25.8%) did not reached platelet ≥ 50,000/μL (Group B). The means of platelet increase were 38,000/μL and 12,000/μL in groups A and B, respectivley. A low platelet count at baseline was a characteristic of patients in group B. Among 13 patients who repeatedly used lusutrombopag, lusutrombopag significantly increased the platelet count as the initial treatment. When all repeated uses of lusutrombopag were counted among these 13 patients, platelet transfusion was not required in 82.1% (23/28) of treatments. Although one patient showed portal thrombosis after lusutrombopag treatment, the thrombosis was disappeared by anticoagulant treatment for 35 days. The degree of platelet increase with lusutrombopag was larger than that in their previous platelet transfusion. The proportion of patients who did not require platelet transfusion was 74.2%, which is smaller than that in former studies which included CLD patients with a platelet count of > 50,000/μL. However, lusutrombopag is effective and safe for CLD patients with a platelet count of < 50,000/μL. In the experiment, the researchers used many compounds, for example, (S,E)-3-(2,6-Dichloro-4-((4-(3-(1-(hexyloxy)ethyl)-2-methoxyphenyl)thiazol-2-yl)carbamoyl)phenyl)-2-methylacrylic acid (cas: 1110766-97-6Application of 1110766-97-6).

(S,E)-3-(2,6-Dichloro-4-((4-(3-(1-(hexyloxy)ethyl)-2-methoxyphenyl)thiazol-2-yl)carbamoyl)phenyl)-2-methylacrylic acid (cas: 1110766-97-6) belongs to thiazole derivatives. Thiazoles are a class of five-membered rings containing nitrogen and sulfur with excellent antitumor, antiviral and antibiotic activities. The pyridine-type nitrogen in the thiazole ring deactivates the ring for electrophilic substitution reactions, which is further reduced in acid due to protonation of the thiazole ring.Application of 1110766-97-6

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Fatostatin suppresses growth and enhances apoptosis by blocking SREBP-regulated metabolic pathways in endometrial carcinoma was written by Gao, Shuhong;Shi, Zhengzheng;Li, Xin;Li, Wenzhi;Wang, Yiling;Liu, Zhiming;Jiang, Jie. And the article was included in Oncology Reports in 2018.Formula: C18H19BrN2S This article mentions the following:

Fatostatin, a chem. inhibitor of the sterol regu- latory element-binding protein (SREBP) pathway, has been reported to possess high antitumor activity against prostate and pancreatic cancer. The main aim of the present study was to investigate the effects and mechanism of fatostatin in endo- metrial carcinoma (EC). In the present study, we determined that fatostatin inhibited EC cell viability and colony formation capacity, decreased the invasive and migratory capacities of EC cells, induced EC cell cycle arrest at the G2/M phase and stimulated caspase-mediated apoptosis of EC cells. In addition, fatostatin significantly decreased the protein expression levels of nuclear SREBPs and their downstream genes and increased the protein expression levels of cleaved caspase-9, caspase-3 and PARP in EC cells. In addition, the mRNA expression levels of SREBP-controlled downstream genes were also significantly downregulated. The quantification assays of fatty acids and total cholesterol revealed that the levels of free fatty acids and total cholesterol in EC cells were decreased. The present study indicated that fatostatin exhibited antitumor effects by blocking SREBP-regulated metabolic pathways and inducing caspase-mediated apoptosis in EC and may be a potent therapeutic strategy for the treatment of EC. In the experiment, the researchers used many compounds, for example, 2-(2-Propylpyridin-4-yl)-4-(p-tolyl)thiazole hydrobromide (cas: 298197-04-3Formula: C18H19BrN2S).

2-(2-Propylpyridin-4-yl)-4-(p-tolyl)thiazole hydrobromide (cas: 298197-04-3) belongs to thiazole derivatives. The thiazole ring is notable as a component of the vitamin thiamine (B1). The nitrogen in thiazole is sp2 hybridized and the lone pair of electrons localized on the nitrogen is less reactive due to increased aromatic character and decreased basicity. It is protonated and alkylated/acylated at nitrogen forming hydrochloride and quaternary thiazolium salt.Formula: C18H19BrN2S

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica

Prevalence of colistin resistance gene mcr-1 in Escherichia coli isolated from chickens in central China, 2014 to 2019 was written by Zhang, Wenting;Zhang, Tengfei;Wang, Chen;Liang, Guixing;Lu, Qin;Wen, Guoyuan;Guo, Yunqing;Cheng, Yiluo;Wang, Zui;Shao, Huabin;Luo, Qingping. And the article was included in Journal of Global Antimicrobial Resistance in 2022.Safety of 2-((((Z)-1-(2-Aminothiazol-4-yl)-2-(((2S,3S)-2-methyl-4-oxo-1-sulfoazetidin-3-yl)amino)-2-oxoethylidene)amino)oxy)-2-methylpropanoic acid This article mentions the following:

This study investigated the prevalence and characteristics of mcr-1-harbouring Escherichia coli isolated from chickens in central China from 2014 to 2019.A total of 1132 E. coli isolated from 1647 chicken swabs were analyzed for colistin susceptibility by broth microdilution method and prevalence of mcr-1 gene by PCR. The colistin-resistant E. coli isolates were typed by multi-locus sequence typing (MLST) and tested with 12 antimicrobial agents. The transconjugation assay was conducted for the mcr-1-pos. isolates using the transconjugant E. coli C600.Of the 1132 E. coli isolated from chickens, 131 isolates (11.6%) exhibited colistin resistance, and 51 isolates (4.5%) were mcr-1 pos. The mcr-1-pos. rate was quite low in 2014 (2.3%) and 2015 (1.7%), increased to peak in 2016 (12.6%) and 2017 (11.4%), and then decreased significantly in 2018 (1.7%) and 2019 (0.9%). The 131 colistin resistant isolates were assigned to 66 unique sequence types (STs), 27 of which contained mcr-1-pos. isolates. Compared with mcr-1-neg. E. coli, mcr-1-pos. E. coli showed higher resistance rates to nalidixic acid, ciprofloxacin, ceftriaxone, cefotaxime, and tetracycline. Furthermore, 30 of the 51 mcr-1 pos. isolates transduced their mcr-1 gene into E. coli C600, and 13 of the 30 transconjugants carried more than one replicon types. The mcr-1 pos. rate varied enormously during 2014-2019 in central China. The ban on colistin likely decreased the dissemination of mcr-1 in E. coli isolates from chickens. Multidrug-resistant trait is observed in mcr-1 pos. E. coli isolates and can be transferred into other transconjugants. In the experiment, the researchers used many compounds, for example, 2-((((Z)-1-(2-Aminothiazol-4-yl)-2-(((2S,3S)-2-methyl-4-oxo-1-sulfoazetidin-3-yl)amino)-2-oxoethylidene)amino)oxy)-2-methylpropanoic acid (cas: 78110-38-0Safety of 2-((((Z)-1-(2-Aminothiazol-4-yl)-2-(((2S,3S)-2-methyl-4-oxo-1-sulfoazetidin-3-yl)amino)-2-oxoethylidene)amino)oxy)-2-methylpropanoic acid).

2-((((Z)-1-(2-Aminothiazol-4-yl)-2-(((2S,3S)-2-methyl-4-oxo-1-sulfoazetidin-3-yl)amino)-2-oxoethylidene)amino)oxy)-2-methylpropanoic acid (cas: 78110-38-0) belongs to thiazole derivatives. Thiazoles are a class of five-membered rings containing nitrogen and sulfur with excellent antitumor, antiviral and antibiotic activities. The pyridine-type nitrogen in the thiazole ring deactivates the ring for electrophilic substitution reactions, which is further reduced in acid due to protonation of the thiazole ring.Safety of 2-((((Z)-1-(2-Aminothiazol-4-yl)-2-(((2S,3S)-2-methyl-4-oxo-1-sulfoazetidin-3-yl)amino)-2-oxoethylidene)amino)oxy)-2-methylpropanoic acid

Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica