Filomena Corbo

Synthesis and Biological Evaluation of 2-Mercapto-1,3-benzothiazole Derivatives with Potential Antimicrobial Activity

The enhancement of bacterial resistance of pathogens to currently available antibiotics constitutes a serious public health threat. So, intensive efforts are underway worldwide to develop new antimicrobial agents. To identify compounds with a potent antimicrobial profile, we designed and synthesized low molecular weight 2‐mercaptobenzothiazole derivatives 2a–2l and 3a–3l. Both series were screened for in‐vitro antibacterial activity against the representative panel of Gram‐positive and Gram‐negative bacteria strains. The biological screening identified compounds 2e and 2l as the most active ones showing an interesting antibacterial activity with MIC values of 3.12 μg/mL against Staphylococcus aureus and 25 μg/mL against Escherichia coli, respectively. The replacement of the S‐H by the S‐Bn moiety resulted in considerable loss of the antibacterial action of the 3a–3l series. The antibiotic action of compounds 2e and 2l was also investigated by testing their activity against some clinical isolates with different antimicrobial resistance profile. Moreover, the involvement of the NorA efflux pump in the antibacterial activity of our molecules was evaluated. Finally, in this paper, we also describe the cytotoxic activity of the most interesting compounds by MTS assay against HeLa and MRC‐5 cell lines.

In Vitro Synergistic Action of Certain Combinations of Gentamicin and Essential Oils

The aim of this study was to verify the existence of synergistic antibacterial effect between four essential oils (Aniba rosaeodora, Melaleuca alternifolia, Origanum vulgare, and Pelargonium graveolens) individually combined with the antibacterial drug Gentamicin. We investigated the effectiveness in vitro of the association of essential oil/Gentamicin, against fifteen different strains of Gram positive and Gram negative bacteria. The antibacterial effects of these oils in combination with Gentamicin were evaluated by using the MHB microdilution method, while gas chromatography (GC) and GC/Mass spectrometry were used to analyze the chemical composition of the oils. A synergistic interaction was observed against all tested strains with the associations between the essential oils Aniba rosaeodora/Gentamicin and Pelargonium graveolens/Gentamicin. In particular a very strong synergistic interaction was observed against Acinetobacter baumannii ATCC 19606 (FIC index = 0.11). In contrast, the essential oils Origanum vulgare and Melaleuca alternifolia in association with Gentamicin were less effective on bacterial species growth. In vitro interaction can improve the antimicrobial effectiveness of the Gentamicin and may contribute to reduce its dose correlated to side effects.

EFFECTS OF A NEW POTENT ANALOG OF TOCAINIDE ON hNav1.7 SODIUM CHANNELS AND IN VIVO NEUROPATHIC PAIN MODELS

The role of voltage-gated sodium channels in the transmission of neuropathic pain is well recognized. For instance, genetic evidence recently indicate that the human Nav1.7 sodium channel subtype plays a crucial role in the ability to perceive pain sensation and may represent an important target for analgesic/anti-hyperalgesic drugs. In this study a newly synthesized tocainide congener, named NeP1, was tested in vitro on recombinant hNav1.4 and hNav1.7 channels using patch-clamp technique and, in vivo, in two rat models of persistent neuropathic pain obtained either by chronic constriction injury of the sciatic nerve or by oxaliplatin treatment. NeP1 efficiently blocked hNav1.4 and hNav1.7 channels in a dose- and use-dependent manner, being by far more potent than tocainide. Importantly, the new compound displayed a remarkable use-dependent effect, which likely resulted from a very high affinity for inactivated compared to closed channels. In both models of neuropathic pain, NeP1 was greatly more potent than tocainide in reverting the reduction of pain threshold in vivo. In oxaliplatin-treated rats, NeP1 even produced greater and more durable anti-hyperalgesia than the reference drug tramadol. In addition, in vivo and in vitro studies suggest a better toxicological and pharmacokinetic profile for NeP1 compared to tocainide. Overall, these results indicate NeP1 as a new promising lead compound for further development in the treatment of chronic pain of neuropathic origin.

2-Aminobenzothiazole derivatives: Search for new antifungal agents

A new series of 6-substituted 2-aminobenzothiazole derivatives were synthesized and screened in vitro as potential antimicrobials. Almost all the compounds showed antifungal activity. In particular, compounds 1n,o, designed on the basis of molecular modeling studies, were the best of the series, showing MIC values of 4-8 μg/mL against Candida albicans, Candida parapsilosis and Candida tropicalis. None of the two compounds did show any cytotoxicity effect on human THP-1 cells.

Stereospecific synthesis of mexiletine and related compounds: Mitsunobu versus Williamson reaction

Abstract Mexiletine [1-(2,6-dimethylphenoxy)-2-propanamine], a chiral, orally effective antiarrhythmic agent, and several analogues substituted on either the stereogenic centre or the xylyloxy moiety, were prepared in both, highly enriched, optically active forms. According to the ‘chiral pool’ approach, the appropriate amino alcohols, protected as the corresponding phthalimide derivatives, were condensed with the desired phenols under either Mitsunobu (method A) or Williamson (method B) conditions. Generally, method A provided the most efficient route, both in terms of yields and number of steps necessary. Only when an isopropyl group was present on the stereogenic centre, i.e. when 2-amino-3-methylbutanol was used as the starting alcohol, method B proved to be the only available route, method A giving no product other than the starting phthalimide derivative. Regardless of the method used, enantiomeric excesses ranged from 91 to 99%. Given the availability of both variously substituted phenols and optically active amino alcohols, the two methods described herein, taken together, may serve as a versatile approach, useful to meet the needs of new chiral, optically active mexiletine analogues, possibly endowed with higher potency in exerting a use-dependent block on sodium channels and/or more resistant to biotransformations.

Constrained analogues of tocainide as potent skeletal muscle sodium channel blockers towards the development of antimyotonic agents

1-Benzyl-N-(2,6-dimethylphenyl)piperidine-3-carboxamide and 4-benzyl-N-(2,6-dimethylphenyl)piperazine-2-carboxamide, two conformationally restricted analogues of tocainide, were designed and synthesized as voltage-gated skeletal muscle sodium channel blockers. They showed, with respect to tocainide, a marked increase in both potency and use-dependent block.

New potent mexiletine and tocainide analogues evaluated in vivo and in vitro as antimyotonic agents on the myotonic ADR mouse.

The antimyotonic activity of chiral derivatives of mexiletine and tocainide, selected as potent use-dependent blockers of skeletal muscle sodium channels, was evaluated in vivo acutely in myotonic ADR mice. The compounds had either aromatic (Me4 and Me6) or branched isopropyl groups (Me5 and To1) on the asymmetric centre, or had this latter one methylene apart from the amino group (Me2). Therapeutic doses of mexiletine (5-10 mg/kg) and tocainide (7-20 mg/kg) significantly reduced the long time of righting reflex (TRR), typical of ADR mice. Me4, Me5 and Me6 were 2-fold more potent than mexiletine. To1 fully normalised the TRR at 7 mg/kg. The electromyographic analysis confirmed a muscle-based activity for drug effectiveness on TRR. All the compounds reduced the myotonic hyperexcitability of intercostal muscle fibres when tested in vitro by current-clamp recordings, with a potency correlated with their action on sodium channels. On stimulus-evoked firing, the isopropyl analogues were 2-4-fold more potent than parent compounds, while the aromatic analogues were about 10-fold more potent than mexiletine. Patch-clamp recordings confirmed a normal-like pharmacological sensitivity of sodium channels of native ADR muscle fibres. Finally, the in vivo antimyotonic activity is due to the block of sodium channels and divergences with in vitro potency can be related to structure-based changes in drug pharmacokinetics.

4H-1,4-Benzothiazine, Dihydro-1,4-benzothiazinones and 2-Amino-5-fluorobenzenethiol Derivatives: Design, Synthesis and In Vitro Antimicrobial Screening

As part of our studies focused on the design and synthesis of new antimicrobial agents a series of 7‐fluoro‐3,4‐dihydro‐2H‐1,4‐benzothiazine derivatives (4a–4f, 4h) and 7‐fluoro‐2H‐1,4‐benzothiazin‐3(4H)‐one analogues (4j–4o) were synthesized and evaluated for their in vitro inhibitory activity against a representative panel of Gram‐positive and Gram‐negative bacteria strains and also toward selected fungi species. These compounds were prepared in one step from chloro‐substituted‐2‐amino‐5‐fluorobenzenethiol 6a–6c. The biological screening identified in compounds 4a, 4j and 4l the most promising results of both series showing an interesting antimicrobial activity. Our antibiotic investigation was also completed by testing the key intermediates 6a–6c. Surprisingly, 6a–6c emerged as the compounds exhibiting the highest antimicrobial activity by possessing a remarkable antibacterial effect against the Gram‐positive strains with MIC (minimal inhibitory concentration) values between 2 and 8 µg/mL and the fungi panel with MIC values between 2 and 8 µg/mL. These results may prove useful in the design of a novel pool of antimicrobial agents.

Increased rigidity of the chiral centre of tocainide favours stereoselectivity and use-dependent block of skeletal muscle Na+ channels enhancing the antimyotonic activity in vivo

Searching for the structural requirements improving the potency and the stereoselectivity of Na+ channel blockers as antimyotonic agents, new derivatives of tocainide, in which the chiral carbon atom is constrained in a rigid α‐proline or pyrrolo‐imidazolic cycle, were synthesized as pure enantiomers. Their ability to block Na+ currents, elicited from −100 to −20 mV at 0.3 Hz (tonic block) and 2 – 10 Hz (use‐dependent block) frequencies, was investigated in vitro on single fibres of frog semitendinosus muscle using the vaseline‐gap voltage‐clamp method. The α‐proline derivative, To5, was 5 and 21 fold more potent than tocainide in producing tonic and 10 Hz‐use‐dependent block, respectively. Compared to To5, the presence of one methyl group on the aminic (To6) or amidic (To7) nitrogen atom decreased use‐dependence by 2‐ and 6‐times, respectively. When methylene moieties were present on both nitrogen atoms (To8), both tonic and use‐dependent block were reduced. Contrarily to tocainide, all proline derivatives were stereoselective in relation to an increased rigidity. A further increase in the molecular rigidity as in pyrrolo‐imidazolic derivatives markedly decreased the drug potency with respect to tocainide. Antimyotonic activity, evaluated as the shortening of the time of righting reflexes of myotonic adr/adr mice upon acute drug in vivo administration was 3 fold more effective for R‐To5 than for R‐Tocainide. Thus, constraining the chiral centre of tocainide in α‐proline cycle leads to more potent and stereoselective use‐dependent Na+ channel blockers with improved therapeutic potential.

Bemiparin, an effective and safe low molecular weight heparin: A review

Bemiparin is a low molecular weight heparin (LMWH) indicated for the acute treatment of deep vein thrombosis with or without pulmonary embolism, for the prophylaxis of venous thromboembolism in surgical and non-surgical patients and for the prevention of clotting in the extracorporeal circuit during hemodialysis. Due to its excellent pharmacological profile-the second-generation LMWH with the lowest molecular weight, the longest half-life and the highest anti-Factor Xa/anti-Factor IIa activity ratio-it can be safely used in special categories of patients (children, elderly, patients with renal impairment and congestive heart failure). Several studies demonstrated its safety and efficacy, while cost analyses show the economic benefits of bemiparin treatment as compared to other heparins. Recent evidences suggested the application of bemiparin even in the management of diabetic foot ulcers. The aim of this narrative review was to evaluate literature according to results coming from studies involving bemiparin administration in various clinical conditions.