Phenylthiomethyl Ketone-Based Fragments Show Selective and Irreversible Inhibition of Enteroviral 3C Proteases

Lead structure discovery mainly focuses on the identification of noncovalently binding ligands. Covalent linkage, however, is an essential binding mechanism for a multitude of successfully marketed drugs, although discovered by serendipity in most cases. We present a concept for the design of fragments covalently binding to proteases. Covalent linkage enables fragment binding unrelated to affinity to shallow protein binding sites and at the same time allows differentiated targeted hit verification and binding location verification through mass spectrometry. We describe a systematic and rational computational approach for the identification of covalently binding fragments from compound collections inhibiting enteroviral 3C protease, a target with high therapeutic potential. By implementing reactive groups potentially forming covalent bonds as a chemical feature in our 3D pharmacophore methodology, covalent binders were discovered by high-throughput virtual screening. We present careful experimental validation of the virtual hits using enzymatic assays and mass spectrometry unraveling a novel, previously unknown irreversible inhibition of the 3C protease by phenylthiomethyl ketone-based fragments. Subsequent synthetic optimization through fragment growing and reactivity analysis against catalytic and noncatalytic cysteines revealed specific irreversible 3C protease inhibition.

N-malonyl-1,2-dihydroisoquinoline as a novel carrier for specific delivery of drugs to the brain

N-Malonyl-1,2-dihydroisoquinoline derivatives were synthesized and investigated as a novel carrier system for site-specific and sustained delivery of drugs to the brain. Such carriers are expected to be stable against air oxidation due to the presence of the carbonyl group close to nitrogen of the dihydroisoquinoline. Reduction of the prepared isoquinolinium quaternary derivatives with sodium dithionite afforded a novel group of N-malonyl-1,2-dihydroisoquinoline chemical delivery systems (CDS). The synthesized N-malonyl-1,2-dihydroisoquinoline chemical delivery systems were subjected to various chemical and biological investigations to evaluate their ability to cross the blood-brain barrier (BBB), and to be oxidized biologically into their corresponding quaternary derivatives. The in-vitro oxidation studies showed that the designed N-malonyl-1,2-dihydroisoquinoline chemical delivery system could be oxidized into its corresponding quaternary derivatives at an adequate rate. The in-vivo distribution studies showed that these N-malonyl-1,2-dihydroisoquinoline chemical delivery systems were able to cross the blood-brain barrier at detectable concentrations.

Design, synthesis and biological investigation of certain pyrazole-3-carboxylic acid derivatives as novel carriers for nitric oxide

Some novel pyrazole-NO hybrid molecules 5a-e, 6, 8 and 10 were prepared through binding of the pyrazole-3-carboxylic acid derivatives with nitric oxide donor moiety like oxime or nitrate ester. The prepared compounds were evaluated for nitric oxide release, antibacterial and anti-inflammatory activities. The organic nitrate 10 exhibited the highest percentage of NO release using Griess diazotization method. Some of the prepared compounds exhibited remarkable antibacterial activity against Escherichia coli C-600, Pseudomonas aeruginosa, Bacillus subitilis and Staphylococcus aureus NCTC 6571 compared to ciprofloxacin. Most of the tested compounds showed significant anti-inflammatory activity compared to indomethacine using carrageenan induced paw edema method. In general, structural modification of compound 2 either to nitrate ester or oxime hybrids showed better anti-inflammatory with less ulcerogenic liability than their corresponding starting intermediates.

One Pot Synthesis of tetrahydroquinoline-5-thiones and Evaluation of their Antimicrobial Activities

One-pot syntheses of various tetrahydroquinoline-5-thiones are reported. The antimicrobial activity of the obtained products against various types of bacteria was estimated.

Microwave assisted synthesis of triazoloquinazolinones and benzimidazoquinazolinones

BACKGROUND

Benzimidazoquinazolinones and related quinazolines are classes of heterocycles that are of considerable interest because of the diverse range of their biological properties. Although numerous classes of quinazolines have been conventionally synthesized, their syntheses have been suffered due to the multiple steps that sometimes have described in their preparation and also their chemical transformations that have been taken hours or even days to be completed. However, microwave energy can offer numerous benefits for performing synthesis of organic compounds including reduced pollution, increased reaction rates, yield enhancements, and cleaner chemistries.

RESULTS

Synthesis of a series of triazoloquinazolinones and benzimidazoquinazolinones has been achieved under microwave irradiation. The products were obtained in nearly quantitative yields within few minutes during the reaction of aromatic aldehydes with 5-amino-1(H)-1,2,4-triazole (or 2-aminobenzimidazole) and dimedone in DMF.

CONCLUSION

Microwave irradiation can be used as a facile and general method for the construction of a wide variety of triazoloquinazolinones and benzimidazoquinazolinones. The reaction involves a three component condensation (with potential for combinatorial work) being carried out with almost productive yields by microwave irradiation and considerably shortened reaction time.

Brain delivery of HIV protease inhibitors

To overcome the problems of peptidomimetic drug delivery to the specific organs, the use of dihydropyridine <--> pyridinium chemical delivery systems to deliver peptides to the brain is considered in this work. An HIV protease inhibitor lead compound; KNI 279 was selected for the study. The N-alkylated dihydroisoquinoline derivatives of KNI-279 were synthesized and tested for their ability to be oxidized by brain homogenate and showed good results with reasonable half-life times specially for the N-alkoxycarbonyl-methyl derivative 8. The in-vivo distribution of compound 8 proved the brain delivery and locked in property of HIV PR inhibitors in the brain. All the prepared compounds (both quaternary and dihydro derivatives) showed between 51 and 86 % HIV PR inhibitory activity compared to the parent compound.

In vitro and in vivo evaluations of dihydroquinoline- and dihydroisoquinoline-based targetor moieties for brain-specific chemical delivery systems

Brain-targeted delivery of various drugs can be successfully achieved by chemical delivery systems (CDS) that contain a 1,4-dihydropyridine-based redox targetor moiety and undergo a sequential metabolism. However, the susceptibility of this moiety toward hydration in acidic media may limit the shelf-life of such compounds in aqueous formulation. Here, a systematic investigation of the chemical stability toward oxidation and hydration of ester and amide derivatives of 3-substituted 1,4-dihydropyridine, 1,4-dihydroquinoline, and 4-substituted 1,2-dihydroisoquinoline is reported, together with the in vitro stability and in vivo (rat) distribution of isoquinoline-based testosterone and hydrocortisone chemical delivery systems, which were selected as having the most suitable acid-resistant targetor moieties.

A tryptamine analog with high affinity to the heart tissues is a potential antiarrhythmic agent

A novel tryptamine analog, 1-methyl-3-[N-(3-indolyl)ethyl]carbamoyl-1,4-dihydropyridine (T-CDS) was synthesized and converted into a stable, solid complex with 2-hydroxypropyl-beta-cyclodextrin. An aqueous solution of the complex was given intravenously to dogs and the concentration of T-CDS and its corresponding quaternary (T-Q+) forms were monitored in the blood for 50 min. The effect of the drug on vital heart parameters was monitored throughout the studies. At the end of the experiment the dogs were sacrificed and the concentration of the quaternary pyridinium form (T-Q+) was determined in the different heart tissues, as well as in the kidney, liver, lung, brain, urine and cerebrospinal fluid. The compound was found to be selectively bound to the heart muscles and showed different concentrations in different heart tissues. The T-Q+ concentrations were much higher in the heart after administration of the dihydro form (T-CDS), than after administering T-Q+ directly. The compound was found to be active on certain vital signs of the cardiovascular system and could be an effective and safe antiarrhythmic agent.

Receptor binding studies of soft anticholinergic agents

Receptor binding studies were performed on 24 soft anticholinergic agents and 5 conventional anticholinergic agents using 4 cloned human muscarinic receptor subtypes. The measured pK(i) values of the soft anticholinergic agents ranged from 6.5 to 9.5, with the majority being in the range of 7.5 to 8.5. Strong correlation was observed between the pK(i) s determined here and the pA 2 values measured earlier in guinea pig ileum contraction assays. The corresponding correlation coefficients (r2) were 0.80, 0.73, 0.81, and 0.78 for pK(i) (m1), pK(i) (m2), pK(i) (m3), and pK(i) (m4), respectively. Quantitative structure-activity relationship (QSAR) studies were also performed, and good characterization could be obtained for the soft anticholinergics containing at least 1 tropine moiety in their structure. For these compounds, the potency as measured by the pK i values was found to be related to geometric, electronic, and lipophilicity descriptors. A linear regression equation using ovality (O(e)), dipole moment (D), and a calculated log octanol-water partition coefficient (QLogP) gave reasonably good descriptions (r = 0.88) for the pK(i) (m3) values.

Ocular-specific delivery of timolol by sequential bioactivation of its oxime and methoxime analogs

S-(-)- Timolol maleate was oxidized, using the modified Pfitzner-Mofatt method, to the corresponding keto analog, which was then coupled with either hydroxylamine or methoxyamine in the same reaction medium. The products separated, timolone oxime (TO) or timolone methoxime (TMO), were found to be a mixture of both E and Z isomers with the Z isomer in higher concentration. Both isomers could be separated on silica column. No isomerization of any of the isomers could be detected whether in buffers or biological fluids. TMO salts were found to be stable in slightly acidic buffer. The Z isomer of TMO is more stable than the E isomer. Both TO and TMO showed pronounced reduction of the intraocular pressure (IOP) in normotensive rabbits, when instilled into the conjunctival sac. Reduction of IOP caused by either TO or TMO was higher than the reduction produced with the same dose of timolol maleate. Equal doses of any of the TMO isomers or the mixture of isomers gave almost the same percent reduction of IOP. TMO and TO did not show cardiovascular effects when administered intravenously to rabbits or rats. Both are good candidates to be used for topical management of glaucoma without producing systemic side effects.

Ocular-specific chemical delivery systems of betaxolol for safe local treatment of glaucoma

Novel ketomethoxime (BMO) and oxime (BO) analogs of betaxolol (B) were prepared through the oxidation of betaxolol, followed by quenching of the ketone with the appropriate oxyamine. The Z isomers were kinetically favored and thermodynamically more stable. Isomerization to reach an equilibrium mixture of Z/E was observed for all pure isomers in buffers. Equilibration is much faster, however in biological fluids. Ocular administration of any of the oxime derivatives, delivers betaxolol specifically to the eye tissues, with the highest concentration in the iris ciliary body. Both BMO and BO, when applied topically, showed marked reduction of intraocular pressure (IOP) in normotensive rabbits. No effect on isoproterenol-induced tachycardia in rabbits and rats were observed, even after iv. administration. Very mild eye irritation, which was less than that of betaxolol hydrochloride, was observed particularly with BMO maleate, which is an excellent candidate for safe treatment of glaucoma.

Synthesis and investigation of N4-substituted cytarabine derivatives as prodrugs

Esters of Cytarabine-N4-carboxylates 2a-i and succinamates 3a-f were synthesized as prodrugs of cytarabine (Ara-C) with the aim of developing improved derivatives for oral or parentral administration. At pH 2 series 2 showed relative higher stability than 3, while both series of esters revealed matched stability at pH 7. All esters were susceptible to enzymatic hydrolysis by rat plasma and liver homogenate with half lives ranged from 0.14 h to 12 d, and showed improved stability against cytidine deaminase. A parabolic relation was shown between Kobs of enzymatic hydrolysis and Vw. All compounds are more lipophilic than the parent drug, Ara-C.

Synthesis and evaluation of a redox chemical delivery system for brain-enhanced dopamine containing an activated carbamate-type ester

A chemical delivery system (CDS) for enhanced delivery of dopamine to brain tissue, based on a dihydropyridine<==>pyridinium salt redox system, was modified to include an activated carbamate ester. The dihydronicotinate moiety was chemically attached to the amino group of dopamine (DA) by acylation with chloroethyl chloroformate, followed by condensation with sodium nicotinate under mild conditions. The product was selectively N-alkylated at the pyridine ring and subjected to regioselective reduction to the corresponding 1,4-dihydropyridine derivative, DA-CDSac. In vitro stability of the new compound was studied in phosphate buffers at mild acidic, physiological, and mild alkaline pH values. Oxidation studies showed facile conversion of the dihydronicotinate, DA-CDSac, is readily converted to the corresponding quaternary salt, both chemically and enzymatically. In vivo studies in rats did not detect sustained increases in brain levels of the quaternary salt after i.v. dosing with DA-CDSac. However, the new CDS appeared to change spontaneous locomotor activity in rats after i.v. administration which may be due to altered central DA neuronal activity.

Imidazo[2,1-b]benzothiazoles. II. Synthesis and antiinflammatory activity of some imidazo[2,1-b]benzothiazoles

3-[2-[p-(Un)substituted phenyl]imidazo [2,1-b]benzothiazol-3- yl]propionic acid derivatives (2a--e) were prepared via the interaction of the corresponding 2-[p-(un)substituted phenyl]imidazo[2,1-b]benzothiazoles (1a--e) with acrylic acid in the presence of acetic anhydride and acetic acid. Esterification of 2a--e produced methyl esters (3a--e). Upon the interaction of 3a with m-chloroperbenzoic acid, the S-dioxide (4a) was obtained. Compound 5a was prepared from 4a by alkaline hydrolysis. Vilsmeier formylation for 1a--e produced novel [2-[p-(un)substituted phenyl]imidazo[2,1-b]benzothiazol-3- yl]formaldehyde derivatives (6a--e). Derivatives 6a--e reacted with ethyl bromoacetate to give ethyl 3-hydroxy-3-[2-[p-(un)substituted phenyl]imidazo[2,1-b]benzothiazol- 3-yl]propionate esters (7a--e). Compound dl-7a was resolved with l-(+)-tartaric acid. Compounds 2a--e showed weak or no activity in the carrageein-induced paw edema assay. Compound 4a significantly inhibited the leakage of pontamine-sky blue dye into the peritoneal cavity of mice, in the capillary permeability inhibition assay. Compound 5a inhibited the writhing by 62% in the acetic acid-induced writhing assay.

Improved delivery through biological membranes XIV: Brain-specific, sustained delivery of testosterone using a redox chemical delivery system

The dihydropyridine in equilibrium pyridinium salt redox delivery system was used for the specific delivery and sustained release of testosterone in the brain. Administration of the N-methyl-1,4-dihydro nicotinate ester of testosterone in female rats gave high and sustained brain levels of the corresponding quaternary ester, testosterone trigonellinate. This contrasted with rapid elimination from the general circulation. Release of testosterone "locked into" brain as the quaternary salt was sustained, t1/2 = 20 h.

Improved delivery through biological membranes. 13. Brain-specific delivery of dopamine with a dihydropyridine in equilibrium with pyridinium salt type redox delivery system

The dihydropyridine in equilibrium with pyridinium salt type redox delivery system was used for the brain-specific delivery of dopamine. In vivo administration of the catechol-protected dopamine coupled with 1,4-dihydrotrigonelline as the carrier resulted in brain-specific, high and sustained concentrations of the 1-methyl-3-[N-[beta-(3,4-dihydroxyphenyl)ethyl]carbamoyl]pyridinium salt, the direct dopamine precursor, locked in the brain for many hours, while systemic concentration decreased fast, with a t 1/2 of less than 30 min. Significant dopaminergic activity was observed in the brain, which was sustained for hours.

Improved delivery through biological membranes. 11. A redox chemical drug-delivery system and its use for brain-specific delivery of phenylethylamine

A dihydropyridine in equilibrium pyridinium salt type redox system is described as a general and flexible method for site-specific and sustained delivery of drugs to the brain. According to this, a biologically active compound linked to a lipoidal dihydropyridine carrier easily penetrates the blood-brain barrier. Oxidation of the carrier part in vivo to the ionic pyridinium salt prevents its elimination from the brain, while elimination from the general circulation is accelerated. Subsequent cleavage of the quaternary carrier-drug species results in sustained delivery of the drug in the brain and facile elimination of the carrier part. The concept is illustrated with phenethylamine as the drug and trigonelline as the quaternary carrier. One injection to rats of 1-methyl-3-(N-phenethylcarbamoyl)-1,4-dihydropyridine resulted in continuous build up in the brain of the corresponding 1-methyl-3-(N-phenethylcarbamoyl)pyridinium salt, reaching a maximum at about 80 min. At this time, the general circulation was practically void of either compound, while the accumulated carrier-drug species provided a source for sustained drug delivery only in the brain.

Site-specific, sustained release of drugs to the brain

A dihydropyridine-pyridinium salt type of redox system is used in a general and flexible method for the site-specific or sustained delivery (or both) of drugs to the brain. A biologically active compound linked to a lipoidal dihydropyridine carrier easily penetrates the blood-brain barrier. Oxidation of the carrier part in vivo to the ionic pyridinium salt prevents its elimination from the brain, while elimination from the general circulation is accelerated. Subsequent cleavage of the quaternary carrier-drug species results in sustained delivery of the drug in the brain and facile elimination of the carrier part.

Synthesis of 3-(1-Methyl-5-nitro-2-benzimidazolyl)acrylic Acid Derivatives as Expected Antischistosomal Agents

Several ester and amide derivatives of 3-(1-methyl-5-nitro-2-benzimidazolyl)acrylic acid have been prepared for testing as potential antischistosomal agents. The starting acid was conveniently synthesized from the corresponding aldehyde derivative through the Knövenagel-Döbner reaction. The utility of EEDQ as a coupler for the synthesis of peptides has been successfully extended to the coupling of N-heterocyclic acrylic acid derivatives and various amines.