key: cord-0931777-roho2zde authors: Yamashkin, S. A.; Stepanenko, I. S. title: Synthesis and antimicrobial activity of N-(indol-5-yl)trifluoroacetamides and indol-5-ylaminium trifluoroacetates substituted in the pyrrole ring date: 2022-05-21 journal: Russ Chem Bull DOI: 10.1007/s11172-022-3506-2 sha: 42049c32f2d812f0957adf9dc3857c01e9e7fa46 doc_id: 931777 cord_uid: roho2zde Based on a series of 1H-indol-5-ylamines substituted in the pyrrole ring, the corresponding N-(indol-5-yl)trifluoroacetamides and indol-5-ylaminium trifluoroacetates were prepared. An in silico study showed a wide range of their biological activity, including antimicrobial, antiviral, antiprotozoal, anthelmintic, and antifungal effects. The results of in silico and in vitro screening for antimicrobial activity correlate with each other. All compounds are capable of inhibiting the growth of the tested microorganism strains. The dependence of minimum inhibitory concentrations on the nature of the substituents at the benzene and pyrrole rings of the indole system was revealed. Chemistry of indole derivatives retains its relevancy 1,2 as these compounds are involved in metabolic processes in living systems. A special attention in the indole chemistry is paid to indolylamines with an amino group in the benzene ring. We continue the studies devoted to compounds based on substituted 1H-indolylamines and possessing potential biological activity that were begun at the Lomonosov Moscow State University under the guidance of A. N. Kost. 3 Previously, we synthesized trifl uoromethylacetoacetamides and trifl uoroacetamides based on 4-, 5-, 6-, and 7-amino-1Нindoles, which effi ciently inhibited the growth of various strains of microorganisms. The dependence of antimicrobial activity on the nature of the substituents in the benzene and pyrrole rings of the indole system, as well as on the position of the amide group was revealed. 4-10 In our opinion, a signifi cant role in the emergence of biological activity belongs to the trifl uoromethyl group combined in these molecules with a substituted pharmacophore indole system. Therefore, the search for synthetic trifl uoromethyl-containing biologically active compounds is promising. In the present study, the behavior of substituted 1Н-indol-5-ylamines 1a-e in the trifl uoroacetylation reaction of indolylamines with ethyl trifl uoroacetate, which we previously 5 developed, is explored. Corresponding N-(1Н-indol-5-yl)-2,2,2-trifl uoroacetamides 2a-e were synthesized. Water soluble substituted 1Н-indol-5-ylaminium trifl uoroacetates 3a-e were also prepared from indolylamines 1a-e (Scheme 1). In addition to the formation of the corresponding indolylamides and indolylaminium trifl uoroacetates, electrophilic substitution of the H(3) atom of the indole moiety with the trifl uoroacetyl group could also be expected in the reactions of 1Н-indol-5-yl amines 1c-e with ethyl trifluoroacetate or trifluoroacetic acid. Previously, 9 the substitution of this type was observed when pyrroloquinoline quinones were prepared on the basis of 1-methyl-2-phenyl-1Н-indol-5-yl amine. However, it turned out that indolylamines 1c-e reacted similarly to 3-substituted indolylamines 1a,b. The structure of products 2a-e and 3a-e was confi rmed by 1 Н and 19 F NMR and UV spectroscopy and mass spectrometry. Mass spectra of compounds 2a,b and 3a-e (see the experimental part) do not give an idea of the structure of the fragment ions. Therefore, we present the schemes of fragmentation of compounds 2a,b and 3a-e under the conditions of high-tempera-ture electron ionization (Schemes 2-4). Schemes 2-4 show structures of the fragment ions and their m/z values and are based on the data on fragmentation of molecular ions of substituted indoles, aromatic amines, and carbon acids. 11- 14 The in silico prediction of biological activity of compounds 2a-e and 3a-e was carried out using a local version of the PASS program (version 9.1). [15] [16] [17] This program predicts the probability of the biological activity that a particular compound may exhibit, but does not indicate the level of this activity or the conditions necessary for its manifestation such as dose, method of administration, biological object, gender, age, etc. Thus, although the PASS program predicts the spectra of biological activity of specifi c compounds and, therefore, allows narrowing the scope of experimental tests, its predictions require experimental confi rmation. The results of the assessment of the spectra of biological activity of compounds 2a-e and 3a-e using the PASS program are shown in Table 1 . For compounds 2a-e and 3d, the program also predicted additional antiprotozoal, anthelmintic, and antifungal activity. According to in silico predicted interactions with molecular targets, the compounds under study can show an antimicrobial eff ect, 18-25 and the probability of their antiviral activity is high as well. In this connection, because of the current epidemiological situation in the world, the activity against the 3C-like protease (3CL pro ) is of particular interest since this protease belongs to the enzyme family found in the polyprotein of coronavirus. Protease 3CL pro (M pro , EC 3.4.22.69) 26 is the main protease of the SARS coronavirus that cleaves polyprotein at two self-cleavage sites. The prediction of antimicrobial activity made using the PASS program correlates with laboratory test results. We found that compounds 2a-e and 3a-e inhibited the growth of the tested microorganism strains at various minimum inhibitory concentrations (MICs) ( Table 2 ). The revealed antimicrobial activity of indolyl amides 2a-e and indolylaminium trifluoroacetates 3a-e Scheme 1 Reagents and conditions: i. AcOH (cat.), benzene, 80 °C; ii. benzene, 80 °C. Note. Fragment ions, which are formed during fragmentation of compounds 2a and 2b, are denoted by symbols * and **, respectively. exceeds the activity of dioxidine, 27 which was used as a comparator drug. Compounds 2d and 3b,d,e were the most active against the test strain of Staphylococcus aureus 6538-P. All compounds except 2b and 3a were effi cient against Escherichia coli 25922 АТСС. Compounds 2a,d and 3b,c were the most active against this strain. Compounds 2a,c,e and 3c-e showed the highest activity against Scheme 3 Note. Fragment ions, which are formed during fragmentation of compounds 3a, 3b, and 3c, are denoted by symbols *, **, and ***, respectively. Note. Fragment ions, which are formed during fragmentaion of compounds 3d и 3e, are denoted by symbols * and **, respectively. Pseudomonas aeruginosa 27853 АТСС. Substituted 1Н-indol-5-ylaminium trifl uoroacetates 3а-е were more active against all tested strains than corresponding trifl uoroacetamides 2а-е. It is apparently due to better water solubility of trifl uoroacetates. We have analyzed the dependence of antimicrobial activity on the structure of N-(indol-5-yl)trifl uoroacetamides 2a-e, which were synthesized during this study, and previously prepared N-(indol-6-yl)trifl uoroacetamides (4a-d) 7 and N-(indol-7-yl)trifl uoroacetamides (5a,b). 6 The MIC values of these compounds were used as a criterion for their antimicrobial effi ciency. It was found that the effi cacy of compounds 2a-e, 4a-d, and 5a,b depended on the position of the trifl uoroacetamide group and the substitution type. 5-Methoxy (4b,d 5 ) and 2-phenyl derivatives (2d,e) exhibit the highest activity. The antimicrobial activity of 1-methylsub stituted compounds is in general lower than that of derivatives unsubstituted at the nitrogen atom in the cycle. To sum up, we have carried out a study devoted to the search for synthetic biologically active compounds combining the trifl uoromethyl group and the pharmacophore substituted indole system. By the reactions of 1Н-indol-5-ylamines with ethyl trufl uoroacetate and trufl uoroacetic acid, a series of new substituted in the pyrrole ring 1Н-indol-5-yltrifl uoroacetamides and 1Н-indol-5-ylaminium trufl uoroacetates were synthesized. Computer screening of the prepared compounds using a local version of the PASS program predicted a wide spectrum of their biological activity, including an antimicrobial activity. The results of the performed experimental study of antimicrobial activity of the synthesized compounds correlate with the in silico prediction. All compounds inhibit the growth of the tested microorganism strains at various minimum inhibitory concentrations. The relationship between the structural features of the synthesized compounds and the effi cacy of their antimicrobial action was analyzed. Starting substituted 1Н-indol-5-ylamines 1a-e were prepared according to reported procedures. 28 1 Н NMR spectra were recorded in DMSO-d 6 on a JEOL JNM-ECX400 spectrometer (operating frequencies are 400.13 ( 1 H) and 376.50 ( 19 F) MHz). Chemical shifts in 1 Н and 19 F NMR spectra are given relative to the residual solvent signal (DMSO-d 6 : δ: 2.50) and relative to the C 6 H 5 CF 3 signal (δ: -60.94), respectively. Electronic absorption spectra were obtained using a LEKI SS2109UV spectrophotometer in ethanol. Mass spectra were recorded with the use of a Finnigan MAT INCOS-50 mass spectrometer with a direct sample introduction using 70 eV electron ionization. Elemental analysis was carried out using a vario MICRO cube analyzer. The reaction progress and the purity of the obtained compounds were monitored by TLC on Silufol UV-254 plates, spots of the compounds were visualized with iodine vapor. The PASS program (version 9.1) was used to predict biological activity of compounds. 2,3-Dimethyl-1Н-indol-5-ylammonium trifl uoroacetate (3a). Trifl uoroacetic acid (0.115 g, 1.01 mmol) in benzene (10 mL) was added to a refl uxing solution of 2,3-dimethyl-1Н-indol-5-ylamine (1a, 0.15 g, 0.94 mmol) in benzene (30 mL 1,2,3-Trimethyl-1Н-indol-5-ylammonium trifl uoroacetate (3b) was synthesized similarly to compound 3a from 1,2,3-trimethyl-1Н-indol-5-ylamine (1b, 0.31 g, 1.78 mmol) and trifl uoroacetic acid (0.21 g, 1.84 mmol). Yield 0.15 g (29%), Antibacterial activity of compounds 2a-e and 3a-e. In microbiological experiments, the synthesized compounds were used as the solutions. Dimexide for the preparation of solutions for external use (OJSC Marbiopharm) was used as a solvent for amides 2a-e, and disinfected distilled water was used as a solvent for salts 3a-e. The following museum strains obtained from the collection of the Museum of Living Cultures of the Federal State Budgetary Institution Scientifi c Center for Expertise of Medicinal Products of the Ministry of Health of Russian Federation were used in the study of antimicrobial activity of compounds 2a-e and 3a-e: S. aureus 6538-Р АТСС, E. coli 25922 АТСС, P. aeruginosa 27853 АТСС. The results obtained were compared with the known data 27 for the antimicrobial drug dioxidine (a derivative of di-N-oxyquinoxaline) (Biosintes, a solution for topical, endotracheal, and intravenous administration, 10 μg mL -1 ), which is widely used in medical practice. Determination of the antimicrobial activity of the prepared compounds was carried out by the method of serial dilutions in the cultural medium (the tube macromethod). 29-31 °С (decomp.). Found (%) 1 Hz); 7.36 (s, 1 Н, С(4)Н); 7.44 (d, 1 Н, С(7)Н, J = 9.1 Hz), 9.93 (br.s, 3 Н, С(5)NH 3 ). 19 F NMR, δ: -73.60 (s, 3 F, CF 3 ). MA, m/z (I rel 21). 2-Phenyl-1Н-indol-5-ylammonium trifl uoroacetate (3d) was synthesized similarly to compound 3a from 2-phenyl-1Н-indol-5-ylamine UV (EtОН) С(3)Н); 7.07 (d, 1 Н, С(6)Н, J = 8.0 Hz) 1-Methyl-2-phenyl-1Н-indol-5-ylammonium trifl uoroacetate (3e) was synthesized similarly to compound 3a from 1-methyl-2-phenyl-1Н-indol-5-ylamine (1e, 0.1 g, 0.45 mmol) and trifl uoroacetic acid (0.06 g, 0.53 mmol) )Н, С(2)С 6 Н 5 ) MS, m/z (I rel (%) Certifi cate of authorship 548608 USSR; Byul. Izobret Problemy Med. Micologii [Problems of Med Infektsiya i immunitet Mass-spectrometriya biologicheski activnykh azotistykh osnovaniy [Mass Spectrometry of Biologically Active Nitrogenous Bases Mass-spectrometriya v organicheskoy khimii [Mass Spectrometry in Organic Chemistry Mass-spectrometriya v organicheskoy khimii [Mass Spectrometry in Organic Chemistry Mass-spectrometriya v organicheskoy khimii [Mass Spectrometry in Organic Chemistry Chemoinformatics Approaches to Virtual Screening Infektsii i antimicrob. terapiya [Infections and Antimicrobial Therapy Sintez indol´nykh sistem Guidelines for Conducting Preclinical Studies of Medicinal Products Opredelenie chuvstvitel´nosti microorganismov k antimikrobnym preparatam: klinicheskie recomendatsii No human or animal subjects were used in this research.The authors declare no competing interests.