Nejvíce citovaný článek - PubMed ID 26079401
Salicylanilide carbamates: Promising antibacterial agents with high in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA)
A series of eleven benzylated intermediates and eleven target compounds derived from salicylanilide were tested against Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212 as reference strains and against three clinical isolates of methicillin-resistant S. aureus (MRSA) and three isolates of vancomycin-resistant E. faecalis. In addition, the compounds were evaluated against Mycobacterium tuberculosis H37Ra and M. smegmatis ATCC 700084. The in vitro cytotoxicity of the compounds was assessed using the human monocytic leukemia cell line THP-1. The lipophilicity of the prepared compounds was experimentally determined and correlated with biological activity. The benzylated intermediates were found to be completely biologically inactive. Of the final eleven compounds, according to the number of amide groups in the molecule, eight are diamides, and three are triamides that were inactive. 5-Chloro-2-hydroxy-N-[(2S)- 4-(methylsulfanyl)-1-oxo-1-{[4-(trifluoromethyl)phenyl]amino}butan-2-yl]benzamide (3e) and 5-chloro-2-hydroxy-N-[(2S)-(4-methyl-1-oxo-1-{[4-(trifluoromethyl)phenyl]amino)pentan-2-yl)benzamide (3f) showed the broadest spectrum of activity against all tested species/isolates comparable to the used standards (ampicillin and isoniazid). Six diamides showed high antistaphylococcal activity with MICs ranging from 0.070 to 8.95 μM. Three diamides showed anti-enterococcal activity with MICs ranging from 4.66 to 35.8 μM, and the activities of 3f and 3e against M. tuberculosis and M. smegmatis were MICs of 18.7 and 35.8 μM, respectively. All the active compounds were microbicidal. It was observed that the connecting linker between the chlorsalicylic and 4-CF3-anilide cores must be substituted with a bulky and/or lipophilic chain such as isopropyl, isobutyl, or thiabutyl chain. Anticancer activity on THP-1 cells IC50 ranged from 1.4 to >10 µM and increased with increasing lipophilicity.
- Klíčová slova
- antimicrobial activity, cytotoxicity, lipophilicity, peptidomimetics, salicylamide, structure–activity relationships,
- MeSH
- ampicilin MeSH
- anilidy MeSH
- antibakteriální látky farmakologie MeSH
- benzamidy MeSH
- isoniazid MeSH
- lidé MeSH
- methicilin rezistentní Staphylococcus aureus * MeSH
- mikrobiální testy citlivosti MeSH
- Mycobacterium tuberculosis * MeSH
- peptidomimetika * MeSH
- salicylanilidy farmakologie MeSH
- vankomycin MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- ampicilin MeSH
- anilidy MeSH
- antibakteriální látky MeSH
- benzamidy MeSH
- isoniazid MeSH
- peptidomimetika * MeSH
- salicylanilide MeSH Prohlížeč
- salicylanilidy MeSH
- vankomycin MeSH
Pattern 1-hydroxy-N-(2,4,5-trichlorophenyl)-2-naphthamide and the thirteen original carbamates derived from it were prepared and characterized. All the compounds were tested against Staphylococcus aureus ATCC 29213 as a reference and quality control strain and in addition against three clinical isolates of methicillin-resistant S. aureus (MRSA). Moreover, the compounds were evaluated against Enterococcus faecalis ATCC 29212, and preliminary in vitro cytotoxicity of the compounds was assessed using the human monocytic leukemia cell line (THP-1). The lipophilicity of the prepared compounds was experimentally determined and correlated with biological activity. While pattern anilide had no antibacterial activity, the prepared carbamates demonstrated high antistaphylococcal activity comparable to the used standards (ampicillin and ciprofloxacin), which unfortunately were ineffective against E. feacalis. 2-[(2,4,5-Trichlorophenyl)carba- moyl]naphthalen-1-yl ethylcarbamate (2) and 2-[(2,4,5-trichlorophenyl)carbamoyl]naphthalen-1-yl butylcarbamate (4) expressed the nanomolar minimum inhibitory concentrations (MICs 0.018−0.064 μM) against S. aureus and at least two other MRSA isolates. Microbicidal effects based on the minimum bactericidal concentrations (MBCs) against all the tested staphylococci were found for nine carbamates, while 2-[(2,4,5-trichlorophenyl)carbamoyl]naphthalen-1-yl heptylcarbamate (7) and 2-[(2,4,5-trichlorophenyl)carbamoyl]naphthalen-1-yl (4-phenylbutyl)carbamate (14) demonstrated MBCs in the range of 0.124−0.461 μM. The selectivity index (SI) for most investigated carbamates was >20 and for some derivatives even >100. The performed tests did not show an effect on the damage to the bacterial membrane, while the compounds were able to inhibit the respiratory chain of S. aureus.
- Klíčová slova
- antistaphylococcal activity, carbamates, cytotoxicity, hydroxynaphthalenes, lipophilicity, structure–activity relationships,
- Publikační typ
- časopisecké články MeSH
A series of eighteen 4-chlorocinnamanilides and eighteen 3,4-dichlorocinnamanilides were designed, prepared and characterized. All compounds were evaluated for their activity against gram-positive bacteria and against two mycobacterial strains. Viability on both cancer and primary mammalian cell lines was also assessed. The lipophilicity of the compounds was experimentally determined and correlated together with other physicochemical properties of the prepared derivatives with biological activity. 3,4-Dichlorocinnamanilides showed a broader spectrum of action and higher antibacterial efficacy than 4-chlorocinnamanilides; however, all compounds were more effective or comparable to clinically used drugs (ampicillin, isoniazid, rifampicin). Of the thirty-six compounds, six derivatives showed submicromolar activity against Staphylococcus aureus and clinical isolates of methicillin-resistant S. aureus (MRSA). (2E)-N-[3,5-bis(trifluoromethyl)phenyl]- 3-(4-chlorophenyl)prop-2-enamide was the most potent in series 1. (2E)-N-[3,5-bis(Trifluoromethyl)phenyl]-3-(3,4-dichlorophenyl)prop-2-enamide, (2E)-3-(3,4-dichlorophenyl)-N-[3-(trifluoromethyl)phenyl]prop-2-enamide, (2E)-3-(3,4-dichloro- phenyl)-N-[4-(trifluoromethyl)phenyl]prop-2-enamide and (2E)-3-(3,4-dichlorophenyl)- N-[4-(trifluoromethoxy)phenyl]prop-2-enamide were the most active in series 2 and in addition to activity against S. aureus and MRSA were highly active against Enterococcus faecalis and vancomycin-resistant E. faecalis isolates and against fast-growing Mycobacterium smegmatis and against slow-growing M. marinum, M. tuberculosis non-hazardous test models. In addition, the last three compounds of the above-mentioned showed insignificant cytotoxicity to primary porcine monocyte-derived macrophages.
- Klíčová slova
- antimicrobial activity, cinnamamides, cytotoxicity, lipophilicity, structure-activity relationships,
- MeSH
- ampicilin farmakologie MeSH
- antibakteriální látky farmakologie MeSH
- methicilin rezistentní Staphylococcus aureus * MeSH
- mikrobiální testy citlivosti MeSH
- Mycobacterium tuberculosis * MeSH
- prasata MeSH
- savci MeSH
- stafylokokové infekce * MeSH
- Staphylococcus aureus MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- ampicilin MeSH
- antibakteriální látky MeSH
A series of 1,3,5-triazinyl aminobenzenesulfonamides substituted by aminoalcohol, aminostilbene, and aminochalcone structural motifs was synthesized as potential human carbonic anhydrase (hCA) inhibitors. The compounds were evaluated on their inhibition of tumor-associated hCA IX and hCA XII, hCA VII isoenzyme present in the brain, and physiologically important hCA I and hCA II. While the test compounds had only a negligible effect on physiologically important isoenzymes, many of the studied compounds significantly affected the hCA IX isoenzyme. Several compounds showed activity against hCA XII; (E)-4-{2-[(4-[(2,3-dihydroxypropyl)amino]-6-[(4-styrylphenyl)amino]-1,3,5-triazin-2-yl)amino]ethyl}benzenesulfonamide (31) and (E)-4-{2-[(4-[(4-hydroxyphenyl)amino]-6-[(4-styrylphenyl)amino]-1,3,5-triazin-2-yl)amino]ethyl}benzenesulfonamide (32) were the most effective inhibitors with KIs = 4.4 and 5.9 nM, respectively. In addition, the compounds were tested against vancomycin-resistant Enterococcus faecalis (VRE) isolates. (E)-4-[2-({4-[(4-cinnamoylphenyl)amino]-6-[(4-hydroxyphenyl)amino]-1,3,5-triazin-2-yl}amino)ethyl]benzenesulfonamide (21) (MIC = 26.33 µM) and derivative 32 (MIC range 13.80-55.20 µM) demonstrated the highest activity against all tested strains. The most active compounds were evaluated for their cytotoxicity against the Human Colorectal Tumor Cell Line (HCT116 p53 +/+). Only 4,4'-[(6-chloro-1,3,5-triazin-2,4-diyl)bis(iminomethylene)]dibenzenesulfonamide (7) and compound 32 demonstrated an IC50 of ca. 6.5 μM; otherwise, the other selected derivatives did not show toxicity at concentrations up to 50 µM. The molecular modeling and docking of active compounds into various hCA isoenzymes, including bacterial carbonic anhydrase, specifically α-CA present in VRE, was performed to try to outline a possible mechanism of selective anti-VRE activity.
- Klíčová slova
- benzenesulfonamide, carbonic anhydrase, chalcone, inhibition, stilbene, triazine, vancomycin-resistant enterococci,
- MeSH
- antibakteriální látky farmakologie MeSH
- enterokoky rezistentní vůči vankomycinu účinky léků MeSH
- HCT116 buňky MeSH
- inhibitory karboanhydras farmakologie MeSH
- karboanhydrasa I antagonisté a inhibitory MeSH
- karboanhydrasa II antagonisté a inhibitory MeSH
- karboanhydrasa IX antagonisté a inhibitory MeSH
- karboanhydrasy účinky léků MeSH
- lidé MeSH
- nádory farmakoterapie MeSH
- protinádorové látky farmakologie terapeutické užití MeSH
- simulace molekulární dynamiky MeSH
- simulace molekulového dockingu MeSH
- sulfonamidy farmakologie MeSH
- vztahy mezi strukturou a aktivitou MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- antibakteriální látky MeSH
- carbonic anhydrase XII MeSH Prohlížeč
- inhibitory karboanhydras MeSH
- karboanhydrasa I MeSH
- karboanhydrasa II MeSH
- karboanhydrasa IX MeSH
- karboanhydrasy MeSH
- protinádorové látky MeSH
- sulfonamidy MeSH
A series of new tertiary phenothiazine derivatives containing a quinoline and a pyridine fragment was synthesized by the reaction of 1-methyl-3-benzoylthio-4-butylthioquinolinium chloride with 3-aminopyridine derivatives bearing various substituents on the pyridine ring. The direction and mechanism of the cyclization reaction of intermediates with the structure of 1-methyl-4-(3-pyridyl)aminoquinolinium-3-thiolate was related to the substituents in the 2- and 4-pyridine position. The structures of the compounds were analyzed using 1H, 13C NMR (COSY, HSQC, HMBC) and X-ray analysis, respectively. Moreover, the antiproliferative activity against tumor cells (A549, T47D, SNB-19) and a normal cell line (NHDF) was tested. The antibacterial screening of all the compounds was conducted against the reference and quality control strain Staphylococcus aureus ATCC 29213, three clinical isolates of methicillin-resistant S. aureus (MRSA). In silico computation of the intermolecular similarity was performed using principal component analysis (PCA) and hierarchical clustering analysis (HCA) on the pool of structure/property-related descriptors calculated for the novel tetracyclic diazaphenothiazine derivatives. The distance-oriented property evaluation was correlated with the experimental anticancer activities and empirical lipophilicity as well. The quantitative shape-based comparison was conducted using the CoMSA method in order to indicate the potentially valid steric, electronic and lipophilic properties. Finally, the numerical sampling of similarity-related activity landscape (SALI) provided a subtle picture of the SAR trends.
- Klíčová slova
- antibacterial activity, antiproliferative activity, azaphenothiazines, lipophilicity, pharmacophore mapping, phenothiazine, similarity-activity landscape index,
- MeSH
- antibakteriální látky chemie farmakologie MeSH
- fenothiaziny chemie MeSH
- heterocyklické sloučeniny chemie MeSH
- lidé MeSH
- mikrobiální testy citlivosti MeSH
- nádorové buňky kultivované MeSH
- nádory farmakoterapie MeSH
- protinádorové látky chemie farmakologie MeSH
- Staphylococcus aureus účinky léků MeSH
- vztahy mezi strukturou a aktivitou MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- antibakteriální látky MeSH
- fenothiaziny MeSH
- heterocyklické sloučeniny MeSH
- protinádorové látky MeSH
A series of nineteen novel ring-substituted N-arylcinnamanilides was synthesized and characterized. All investigated compounds were tested against Staphylococcus aureus as the reference strain, two clinical isolates of methicillin-resistant S. aureus (MRSA), and Mycobacterium tuberculosis. (2E)-N-[3-Fluoro-4-(trifluoromethyl)phenyl]-3-phenylprop-2-enamide showed even better activity (minimum inhibitory concentration (MIC) 25.9 and 12.9 µM) against MRSA isolates than the commonly used ampicillin (MIC 45.8 µM). The screening of the cell viability was performed using THP1-Blue™ NF-κB cells and, except for (2E)-N-(4-bromo-3-chlorophenyl)-3-phenylprop-2-enamide (IC50 6.5 µM), none of the discussed compounds showed any significant cytotoxic effect up to 20 μM. Moreover, all compounds were tested for their anti-inflammatory potential; several compounds attenuated the lipopolysaccharide-induced NF-κB activation and were more potent than the parental cinnamic acid. The lipophilicity values were specified experimentally as well. In addition, in silico approximation of the lipophilicity values was performed employing a set of free/commercial clogP estimators, corrected afterwards by the corresponding pKa calculated at physiological pH and subsequently cross-compared with the experimental parameters. The similarity-driven property space evaluation of structural analogs was carried out using the principal component analysis, Tanimoto metrics, and Kohonen mapping.
- Klíčová slova
- IVE-PLS, MTT assay, PCA, antistaphylococcal activity, cinnamamides, cytotoxicity, lipophilicity, quantitative structure-property relationships, synthesis,
- MeSH
- ampicilin farmakologie MeSH
- analýza hlavních komponent MeSH
- antiflogistika farmakologie MeSH
- cinnamáty chemická syntéza MeSH
- inhibiční koncentrace 50 MeSH
- koncentrace vodíkových iontů MeSH
- lidé MeSH
- methicilin rezistentní Staphylococcus aureus účinky léků MeSH
- mikrobiální testy citlivosti MeSH
- mikrovlny MeSH
- molekulární modely MeSH
- Mycobacterium tuberculosis účinky léků MeSH
- NF-kappa B metabolismus MeSH
- Staphylococcus aureus účinky léků MeSH
- THP-1 buňky MeSH
- viabilita buněk účinky léků MeSH
- vztahy mezi strukturou a aktivitou MeSH
- zánět MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- ampicilin MeSH
- antiflogistika MeSH
- cinnamamide MeSH Prohlížeč
- cinnamáty MeSH
- NF-kappa B MeSH
A series of twenty-two novel N-(disubstituted-phenyl)-3-hydroxynaphthalene- 2-carboxamide derivatives was synthesized and characterized as potential antimicrobial agents. N-[3,5-bis(trifluoromethyl)phenyl]- and N-[2-chloro-5-(trifluoromethyl)phenyl]-3-hydroxy- naphthalene-2-carboxamide showed submicromolar (MICs 0.16-0.68 µM) activity against methicillin-resistant Staphylococcus aureus isolates. N-[3,5-bis(trifluoromethyl)phenyl]- and N-[4-bromo-3-(trifluoromethyl)phenyl]-3-hydroxynaphthalene-2-carboxamide revealed activity against M. tuberculosis (both MICs 10 µM) comparable with that of rifampicin. Synergistic activity was observed for the combinations of ciprofloxacin with N-[4-bromo-3-(trifluoromethyl)phenyl]- and N-(4-bromo-3-fluorophenyl)-3-hydroxynaphthalene-2-carboxamides against MRSA SA 630 isolate. The similarity-related property space assessment for the congeneric series of structurally related carboxamide derivatives was performed using the principal component analysis. Interestingly, different distribution of mono-halogenated carboxamide derivatives with the -CF3 substituent is accompanied by the increased activity profile. A symmetric matrix of Tanimoto coefficients indicated the structural dissimilarities of dichloro- and dimetoxy-substituted isomers from the remaining ones. Moreover, the quantitative sampling of similarity-related activity landscape provided a subtle picture of favorable and disallowed structural modifications that are valid for determining activity cliffs. Finally, the advanced method of neural network quantitative SAR was engaged to illustrate the key 3D steric/electronic/lipophilic features of the ligand-site composition by the systematic probing of the functional group.
- Klíčová slova
- CoMSA, IVE-PLS, MIC, MTT assay, antistaphylococcal activity, antitubercular activity, hydroxynaphthalenecarboxamides, lipophilicity, similarity-activity landscape index,
- MeSH
- antiinfekční látky chemická syntéza MeSH
- methicilin rezistentní Staphylococcus aureus * MeSH
- mikrobiální testy citlivosti MeSH
- Mycobacterium tuberculosis * MeSH
- naftaleny chemie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- antiinfekční látky MeSH
- naftaleny MeSH
- naphthalene-2-carboxamide MeSH Prohlížeč
Ring-substituted 1-hydroxynaphthalene-2-carboxanilides were previously investigated for their antimycobacterial properties. In our study, we have shown their antiproliferative and cell death-inducing effects in cancer cell lines. Cell proliferation and viability were assessed by WST-1 assay and a dye exclusion test, respectively. Cell cycle distribution, phosphatidylserine externalization, levels of reactive oxygen or nitrogen species (RONS), mitochondrial membrane depolarization, and release of cytochrome c were estimated by flow cytometry. Levels of regulatory proteins were determined by Western blotting. Our data suggest that the ability to inhibit the proliferation of THP-1 or MCF-7 cells might be referred to meta- or para-substituted derivatives with electron-withdrawing groups -F, -Br, or -CF3 at anilide moiety. This effect was accompanied by accumulation of cells in G1 phase. Compound 10 also induced apoptosis in THP-1 cells in association with a loss of mitochondrial membrane potential and production of mitochondrial superoxide. Our study provides a new insight into the action of salicylanilide derivatives, hydroxynaphthalene carboxamides, in cancer cells. Thus, their structure merits further investigation as a model moiety of new small-molecule compounds with potential anticancer properties.
- Klíčová slova
- antiproliferative effect, apoptosis, cell cycle, hydroxynaphthalene carboxamides, salicylanilides,
- MeSH
- anilidy chemie farmakologie MeSH
- apoptóza účinky léků MeSH
- buněčný cyklus účinky léků MeSH
- lidé MeSH
- membránový potenciál mitochondrií účinky léků MeSH
- MFC-7 buňky MeSH
- mitochondrie účinky léků metabolismus MeSH
- molekulární struktura MeSH
- naftoly chemie MeSH
- proliferace buněk účinky léků MeSH
- protinádorové látky chemie farmakologie MeSH
- reaktivní formy kyslíku metabolismus MeSH
- salicylanilidy chemie farmakologie MeSH
- superoxidy metabolismus MeSH
- THP-1 buňky MeSH
- viabilita buněk účinky léků MeSH
- vztahy mezi strukturou a aktivitou MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- anilidy MeSH
- naftoly MeSH
- protinádorové látky MeSH
- reaktivní formy kyslíku MeSH
- salicylanilide MeSH Prohlížeč
- salicylanilidy MeSH
- superoxidy MeSH
1-[2-[({[2-/3-(Alkoxy)phenyl]amino}carbonyl)oxy]-3-(dipropylammonio)propyl]pyrrolidinium/azepan- ium oxalates or dichlorides (alkoxy = butoxy to heptyloxy) were recently described as very promising antimycobacterial agents. These compounds were tested in vitro against Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212 (reference and control strains), three methicillin-resistant isolates of S. aureus, and three isolates of vancomycin-resistant E. faecalis. 1-[3-(Dipropylammonio)-2-({[3-(pentyloxy-/hexyloxy-/heptyloxy)phenyl]carbamoyl}oxy)propyl]pyrrolidinium dichlorides showed high activity against staphylococci and enterococci comparable with or higher than that of used controls (clinically used antibiotics and antiseptics). The screening of the cytotoxicity of the compounds as well as the used controls was performed using human monocytic leukemia cells. IC50 values of the most effective compounds ranged from ca. 3.5 to 6.3 µM, thus, it can be stated that the antimicrobial effect is closely connected with their cytotoxicity. The antibacterial activity is based on the surface activity of the compounds that are influenced by the length of their alkoxy side chain, the size of the azacyclic system, and hydro-lipophilic properties, as proven by in vitro experiments and chemometric principal component analyses. Synergistic studies showed the increased activity of oxacillin, gentamicin, and vancomycin, which could be explained by the direct activity of the compounds against the bacterial cell wall. All these compounds demonstrate excellent antibiofilm activity, when they inhibit and disrupt the biofilm of S. aureus in concentrations close to minimum inhibitory concentrations against planktonic cells. Expected interactions of the compounds with the cytoplasmic membrane are proven by in vitro crystal violet uptake assays.
- Klíčová slova
- antibacterial, antibiofilm activity, carbamate, structure–activity relationships, synergy,
- Publikační typ
- časopisecké články MeSH
A series of sixteen ring-substituted N-arylcinnamanilides, previously described as highly antimicrobially effective against a wide spectrum of bacteria and fungi, together with two new derivatives from this group were prepared and characterized. Moreover, the molecular structure of (2E)-N-(2-bromo-5-fluorophenyl)-3-phenylprop-2-enamide as a model compound was determined using single-crystal X-ray analysis. All the compounds were tested for their anti-inflammatory potential, and most tested compounds significantly attenuated the lipopolysaccharide-induced NF-κB activation and were more potent than the parental cinnamic acid. (2E)-N-[2-Chloro-5-(trifluoromethyl)phenyl]-3-phenylprop-2-enamide, (2E)-N-(2,6-dibromophenyl)- 3-phenylprop-2-enamide, and (2E)-N-(2,5-dichlorophenyl)-3-phenylprop-2-enamide demonstrated the highest inhibition effect on transcription factor NF-κB at the concentration of 2 µM and showed a similar effectiveness as the reference drug prednisone. Several compounds also decreased the level of TNF-α. Nevertheless, subsequent tests showed that the investigated compounds affect neither IκBα level nor MAPKs activity, which suggests that the N-arylcinnamanilides may have a different mode of action to prednisone. The modification of the C(2,5)' or C(2,6)' positions of the anilide core by rather lipophilic and bulky moieties seems to be preferable for the anti-inflammatory potential of these compounds.
- Klíčová slova
- X-ray structure, anti-inflammatory potential, cinnamamides, polypharmacology,
- MeSH
- antiflogistika chemická syntéza chemie farmakologie MeSH
- cinnamáty chemická syntéza chemie farmakologie MeSH
- krystalografie rentgenová MeSH
- lidé MeSH
- lipopolysacharidy škodlivé účinky MeSH
- molekulární modely MeSH
- molekulární struktura MeSH
- NF-kappa B metabolismus MeSH
- regulace genové exprese účinky léků MeSH
- signální transdukce účinky léků MeSH
- THP-1 buňky MeSH
- TNF-alfa metabolismus MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- antiflogistika MeSH
- cinnamáty MeSH
- lipopolysacharidy MeSH
- NF-kappa B MeSH
- TNF protein, human MeSH Prohlížeč
- TNF-alfa MeSH