Synthesis of diphenoxyadamantane alkylamines with pharmacological interest.

In this work, the synthesis and the pharmacological evaluation of diphenoxyadamantane alkylamines Ia-f and IIa-f is described. The new diphenoxy-substituted adamantanes share structural features present in trypanocidal and antitubercular agents. 1-Methylpiperazine derivative Ia is the most potent against T. brucei compound, whilst its hexylamine congener IIf exhibits a significant antimycobacterial activity.

New Lipophilic Hydroxamates as Promising Trypanocidal Agents: Design, Synthesis, SAR, and Conformational Behavior Studies.

A series of novel hydroxamic acid derivatives was designed and synthesized, and their growth inhibitory activity against bloodstream form Trypanosoma brucei was evaluated. These compounds are based on conformationally constrained, lipophilic, spiro carbocyclic 2,6-diketopiperazine (2,6-DKP) scaffolds and bear a side pharmacophoric functionality that contains an acetohydroxamic acid moiety (CH2CONHOH) linked with the imidic nitrogen atom of the 2,6-DKP ring via an acetamido portion [CH2CON(R), R = H, CH3]. Most of these analogues were active in the midnanomolar to low micromolar range against T. brucei. (S)-Isobutyl- or (S)-benzyl-substitution on the methylene carbon located between the amine nitrogen atom and carbonyl of the 2,6-DKP ring was studied. The effect of the methyl-substitution on the nitrogen atom of the acetamido portion in the side pharmacophoric functionality was also examined. Compounds 22 and 23, bearing an isobutyl- or benzyl-substituent, respectively, and concurrently a methyl-substituent, were found to be the most potent hydroxamates of this series (IC50 = 34 and 53 nM, respectively). Both had promising selectivity over the parasite compared to mammalian cells (SI = 940 and 470, respectively). Moreover, an E/Z conformational behavior study on hydroxamic acid 18 and its methyl-substituted counterpart 21 was undertaken using NMR spectroscopy and theoretical calculations.

An E/Z conformational behaviour study on the trypanocidal action of lipophilic spiro carbocyclic 2,6-diketopiperazine-1-acetohydroxamic acids.

An explanation for the vast difference observed in the trypanocidal activity between the new secondary (N-methylated) hydroxamic acids 5 and 6, and their primary (nonmethylated) congeners 1a and 2, based on their E/Z conformational behaviour in DMSO, is presented.

Conformational analysis of two novel cytotoxic C2-substituted pyrrolo[2,3-f]quinolines in aqueous media, organic solvents, membrane bilayers and at the putative active site.

We have performed: (i) conformational analysis of two novel cytotoxic C2-substituted pyrrolo[2,3-f]quinolines 5e and 5g in deuterated dimethylsulfoxide (DMSO-d(6)) utilizing NOE results from NMR spectroscopy; (ii) molecular dynamics (MD) calculations in water, DMSO and dimyristoyl phosphatidylcholine bilayers and (iii) molecular docking and MD calculations on DNA nucleotide sequences. The obtained results for the two similar in structure molecules showed differences in: (i) their conformational properties in silico and in media that reasonably simulate the biological environment; (ii) the way they are incorporated into the lipid bilayers and therefore their diffusion ability and (iii) molecular docking capacity as it is depicted from their different binding scores.

Synthesis, σ1, σ2-receptors binding affinity and antiproliferative action of new C1-substituted adamantanes.

The synthesis of N-{4-[a-(1-adamantyl)benzyl]phenyl}piperazines 2a-e is described. The in vitro antiproliferative activity of most compounds against main cancer cell lines is significant. The σ(1), σ(2)-receptors and sodium channels binding affinity of compounds 2 were investigated. One of the most active analogs, 2a, had an interesting in vivo anticancer profile against the BxPC-3 and Mia-Paca-2 pancreas cancer cell lines with caspase-3 activation, which was associated with an anagelsic activity against the neuropathic pain.

Mapping the Melatonin Receptor. 8. Selective MT2 Agonists Derived from 5,6-Dihydroindolo[2,1-a]isoquinolines and Related Systems.

A series of substituted indolo[2,1-a]isoquinolines and indolo[1,2-a]benzoxazines have been prepared, as melatonin analogues, to investigate the nature of the binding site of the melatonin receptor. Agonist and antagonist potency of all the analogues was measured using the [35S]GTPγS binding assay protocol. The binding affinity of the analogues were measured by competition binding studies against the human MT1 (hMT1) and MT2 (hMT2) receptors stably transfected in Chinese Hamster Ovarian (CHO) cells, using 2-[125 I]-iodomelatonin, as a ligand. N-Acetyl 2-(10-methoxy-5,6-dihydroindolo[2,1-a]isoquinolin-12-yl)propyl-1-amine (12 a) binds strongly to both the hMT1 and hMT2 receptors, and shows a preference for the hMT2, as does its propanamido counterpart 12 b. The introduction of two methyl groups into their side chain, analogues 15 a and 15 b, leads to antagonism, in the case of the former, and drastically diminishes its hMT1 binding; an analogous profile is seen for 15 b, which, however, is a partial agonist. Introduction of chlorine or methoxy groups into ring 4 gives compounds, that are weakly binding, with a preference for MT2. Substitution of oxygen for carbon at position 5 gives the indolo[1,2-c]benzoxazines 33, 36 a and b, that bind strongly to the human receptors, 33, 36 b being potent agonists at the melatonin receptors, but do not discriminate between hMT1 and hMT2.

Synthesis and evaluation of novel 2,4-disubstituted arylthiazoles against T. brucei.

The design, synthesis and pharmacological evaluation of the 4-substituted-2-[3-(adamant-1-yl)-4-fluorophenyl]thiazoles 1a-j, the 4-substituted-2-[4-(adamant-1-yl)phenyl]thiazoles 2a-h, the 2-substituted-4-[4-(adamant-1-yl)phenyl]thiazoles 3a-e, the N-substituted 2-phenylthiazol-4-ethylamides 4a, b and the N-substituted 4-phenylthiazol-2-ethylamides 4c, d is described. Compounds 1a and 2a exhibit trypanocidal activity in the range of IC50 = 0.42 µM and IC50 = 0.80 µM, respectively. Both of these derivatives bear a lipophilic end, which consists of a 4-(1-adamantyl) phenyl or a 3-(1-adamantyl)phenyl moiety, a 1,3-thiazole ring and a functional end, which comprises of an alkylamine and can be considered as promising candidates for the treatment of Trypanosoma brucei infections.

Novel 2,6-diketopiperazine-derived acetohydroxamic acids as promising anti-Trypanosoma brucei agents.

Aim: Identification of new, effective and selective trypanocidal agents. Materials & methods: Twelve novel acetohydroxamic acid derivatives based on 2-alkyl-2-aryl-2,6-diketopiperazine scaffolds have been synthesized and evaluated in vitro for their growth inhibitory activity against bloodstream form Trypanosoma brucei. Results: All the analogs were remarkably potent inhibitors, with low micromolar to submicromolar activities. Structure-activity relationship studies demonstrated that the presence of an alkyl substituent at the N(4)-position of the 2,6-diketopiperazine ring portion was, in general, beneficial to trypanocidal activity in this series. Conclusion: The highest activity resulted from the introduction of a methyl, n-propyl or n-butyl substituent to the N(4)-position of the parent compound. Importantly, the most potent analogs were found to be highly selective against T. brucei with respect to mammalian cells.

Fluorine substituted methoxyphenylalkyl amides as potent melatonin receptor agonists.

A series of fluorine substituted methoxyphenylalkyl amides were prepared with different orientations of the fluorine and methoxy groups with respect to the alkylamide side chain and with alkyl sides of differing lengths (n = 1-3). ß-Dimethyl and α-methyl derivatives were also synthesised. The compounds were tested as melatonin agonists and antagonists using the pigment aggregation of Xenopus melanophores as the biological assay. A number of these compounds were potent melatonin agonists, the potency depending on the length of the alkyl chain, the orientation of the methoxy and fluorine substituents, the amide chain length and, for the ethyl side-chain analogues, the presence of ß-substituents.

Synthesis and Evaluation of Nifurtimox-Adamantane Adducts with Trypanocidal Activity.

The synthesis and pharmacological evaluation of C1-substituted adamantane hydrazones, their C2-substituted isomers, and C1-substituted adamantane furanoic carboxamides is described. These new adamantane derivatives exhibited an interesting pharmacological profile in terms of trypanocidal activity and selectivity. The most active adduct with the best selectivity in this study was found to be the phenylacetoxy hydrazone 1 b (2-[4-(tricyclo[3.3.1.13,7 ]dec-1-yl)phenyl]-N'-[(5-nitrofuran-2-yl)methylene]acetohydrazide; EC50 =11±0.9 nm, SITb =770).

Development and Characterization of Eudragit®-Based Electrospun Nanofibrous Mats and Their Formulation into Nanofiber Tablets for the Modified Release of Furosemide.

Furosemide, a chloride channel blocker ordinarily used as a high-ceiling or loop diuretic, is practically insoluble in water and dilute acids. Due to its acidic nature, furosemide is mostly absorbed in the stomach and in the upper small intestine. Efforts have focused on the development of sustained release systems of furosemide in order to improve the effectiveness of the drug, which exhibits poor aqueous solubility and poor permeability. Recently, electrospun nanofibrous drug delivery systems have emerged as promising alternative solid-dosage forms due to their advantages of high porosity, high surface to volume ratio, and high drug-loading efficacy. Herein, a number of nanofibrous mats composed of different types of Eudragit® polymers in various concentrations and combinations loaded with furosemide were designed, successfully electrospun, and characterized using SEM, FTIR, DSC, and TGA analyses. The nanofibrous nonwovens were formulated in nanofiber tablets and the release profile of furosemide from them was evaluated at pH 1.2 and 6.8 and compared to that of physical mixture matrix tablets of analogous composition as well as to that of a commercial formulation. It was found that the release of furosemide was compatible with the gastroretentive and slower intestinal release requirements with a well-defined absorption window, while some nanofiber formulations could act as furosemide carriers in emergency situations where a relatively fast onset of its action is required, as in the case of critically ill post-traumatic patients.

Modified In Vitro Release of Melatonin Loaded in Nanofibrous Electrospun Mats Incorporated Into Monolayered and Three-Layered Tablets.

Modified release tablet formulations with melatonin (MLT) are clinically more useful in initiating and maintaining sleep in elderly insomniacs, compared with those designed for immediate release. Aiming at the modified release of MLT, monolayered and 3-layered tablets, incorporating nanofibrous mats composed of cellulose acetate and polyvinylpyrrolidone loaded with MLT, were prepared and studied. In vitro dissolution profiles of MLT in gastrointestinal-like fluids revealed tableting pressure/pH-dependence. The release of the hormone from physical mixture tablets was generally slower from the nanofibers-based tablets, thus exhibiting in the latter case properties that are necessary for the control of both the sleep-onset and the maintenance dysfunctions. The nature of the excipients (hydroxypropylmethylcellulose or lactose monohydrate) used in this study to produce 3-layered tablets was also found to affect the release of MLT, adjusting it to the endogenous hormone's chronobiotic profile. The release of MLT from formulation F(nf)2 (nanofiber mats incorporated into 3-layered tablets containing lactose monohydrate both in the upper and lower layers) was found to be in closer alignment with these effects than the other delivery systems.

Fabrication and Characterization of Electrospun Nanofibers for the Modified Release of the Chronobiotic Hormone Melatonin.

OBJECTIVE: Aiming at the modified release of melatonin (MLT), electrospun-MLT loaded nanofibers, filled into hard gelatin and DRcapsTM capsules, were used as formulants. METHODS: Cellulose acetate, polyvinylpyrrolidinone and hydroxypropylmethylcellusose (HPMC 2910) were used for the preparation of the fiber matrices through electrospinning. The in vitro modified release profile of MLT from the fabricated matrices in gastrointestinal-like fluids was studied. At pH 1.2, the formulations CA1, CA2, PV1, HP1, HP2 and the composite formulations CAPV1-CAPV5 in hard gelatin capsules exhibited fast MLT release. RESULTS: In general, the same trend was observed at pH 6.8, with the exception of CAPV1 and CAPV2. These two composite formulations delivered 52.08% and 75.25% MLT, respectively at a slower pace (6 h) when encapsulated in DRcapsTM capsules. In all other cases, the release of MLT from DRcapsTM capsules filled with the MLT-loaded nanofibers reached 100% at 6h. CONCLUSION: These findings suggest that the MLT-loaded nanofibrous mats developed in this study exhibit a promising profile for treating sleep dysfunctions.

Design, synthesis, and trypanocidal activity of new aminoadamantane derivatives.

To develop functionalized adamantanes for treating African trypanosomiasis, we report on the synthesis of new 1-alkyl-2-aminoadamantanes 1a- i, 1-alkyltricyclo[3.3.1.1 (3,7)]decan-2-guanylhydrazones 2a- g, and their congeneric thiosemicarbazones 3a, b. The potency of these compounds against Trypanosoma brucei was compared to that of amantadine and rimantadine and found to be substantially higher. The most active analogues, 1c, 1d, 2c, 2g, and 3b, illustrate the synergistic effect of the lipophilic character of the C1 side chain and the C2 functionality on trypanocidal activity.

Design and synthesis of bioactive 1,2-annulated adamantane derivatives.

Adamantanopyrrolidines 8, 9 and 10, adamantanopyrrolidines 16 and 18, adamantanoxazolone 20, adamantanopyrazolone 23, adamantanopyrazolothione 24 and adamantanocyclopentanamine 32 were synthesized and tested for anti-influenza A virus and trypanocidal activity. The stereoelectronic requirements for optimal antiviral and trypanocidal potency were investigated. Pyrrolidine 16 proved to be the most active of the compounds tested against influenza A virus, being 4-fold more active than amantadine, equipotent to rimantadine and 19-fold more potent than ribavirin. Oxazolone 20 showed significant trypanocidal activity against bloodstream forms of the African trypanosome, Trypanosoma brucei, being approximately 3 times more potent than rimantadine and almost 50-fold more active than amantadine.

Design and synthesis of nitrate esters of aromatic heterocyclic compounds as pharmacological preconditioning agents.

Ischemic preconditioning (IPC) constitutes an endogenous protective mechanism in which one or more brief periods of myocardial ischemia and reperfusion render the myocardium resistant to a subsequent more-sustained ischemic insult. Pharmacological preconditioning represents an ideal alternative of IPC. We now describe the design and synthesis of indole, quinoline, and purine systems with an attached pharmacophoric nitrate ester group. The indole and quinoline derivatives 4 and 5 possess structural features of the nitrate containing K(ATP) channel openers. Purine analogues 11 and 12, substituted at the position 6 by a piperidine moiety and at position 9 by an alkyl nitrate, could combine the effects of the nitrate containing K(ATP) channel openers and those of adenosine. Compound 13 bears the nicotinamide moiety of nicorandil instead of nitrate ester. Compounds 4, 5, and 11 reduced infarction and the levels of malondialdehyde (MDA) at reperfusion in anesthetized rabbits. Compounds 12 and 13 did not significantly reduce the infarct size. Analogues 4 and 5 increased cGMP and MDA during ischemia, while combined analogue 4 and mitoK(ATP) blocker 5-hydroxydecanoic acid (5-HD) abrogated this benefit suggesting an action through mitoK(ATP) channel opening. Treatment with derivative 11 combined with 5-HD as well as treatment with 11 and adenosine receptor blocker 8-(p-sulfophenyl)theophylline (SPT) did not abrogate cardioprotection. Compound 11 is a lead molecule for the synthesis of novel analogues possessing a dual mode of action through cGMP-mitoK(ATP) channel opening-free radicals and through adenosine receptors.

Lipophilic conformationally constrained spiro carbocyclic 2,6-diketopiperazine-1-acetohydroxamic acid analogues as trypanocidal and leishmanicidal agents: An extended SAR study.

We have previously described a number of lipophilic conformationally constrained spiro carbocyclic 2,6-diketopiperazine (2,6-DKP)-1-acetohydroxamic acids as potent antitrypanosomal agents. In this report, we extend the SAR analysis in this class of compounds with respect to in vitro growth inhibition of Trypanosoma and Leishmania parasites. Introduction of bulky hydrophobic substituents at the vicinal position of the basic nitrogen atom in the spiro carbocyclic 2,6-DKP ring system can provide analogues which are potently active against bloodstream form Trypanosoma brucei and exhibit significant activities toward Trypanosoma cruzi epimastogotes and Leishmania infantum promastigotes and intracellular amastigotes. In particular, compounds possessing a benzyl or 4-chlorobenzyl substituent were found to be the most active growth inhibitors, with activities in the low nanomolar and low micromolar ranges for T. brucei and L. infantum, respectively. The benzyl-substituted (S)-enantiomer was the most potent derivative against T. brucei (IC50  = 6.8 nm), T. cruzi (IC50  = 0.21 µm), and L. infantum promastigotes (IC50  = 2.67 µm) and intracellular amastigotes (IC50  = 2.60 µm). Moreover, the (R)-chiral benzyl-substituted derivative and its racemic counterpart displayed significant activities against L. donovani. Importantly, the active compounds show high selectivity in comparison with two mammalian cell lines.

Design, synthesis, and melatoninergic activity of new azido- and isothiocyanato-substituted indoles.

To develop irreversibly binding ligands for the melatonin receptor(s) as tools for tracing the primary melatonin binding site, we report on the design and synthesis of new melatoninergic azido- and isothiocyanato-substituted indoles. All active compounds were partial agonists or antagonists in the Xenopus melanophore assay, the most potent being the 5-OMe C3-substituted azido 45 and isothiocyanato 46 analogues.

C1'-cycloalkyl side chain pharmacophore in tetrahydrocannabinols.

In earlier work we have provided evidence for the presence of a subsite within the CB1 and CB2 cannabinoid receptor binding domains of classical cannabinoids. This putative subsite corresponds to substituents on the C1'-position of the C3-alkyl side chain, a key pharmacophoric feature in this class of compounds. We have now refined this work through the synthesis of additional C1'-cycloalkyl compounds using newly developed approaches. Our findings indicate that the C1'-cyclopropyl and C1'-cyclopentyl groups are optimal pharmacophores for both receptors while the C1'-cyclobutyl group interacts optimally with CB1 but not with CB2. The C1'-cyclohexyl analogs have reduced affinities for both CB1 and CB2. However, these affinities are significantly improved with the introduction of a C2'-C3' cis double bond that modifies the available conformational space within the side chain and allows for a better accommodation of a six-membered ring within the side chain subsite. Our SAR results are highlighted by molecular modeling of key analogs.

Synthesis of compounds as melatonin agonists and antagonists.

The functions of melatonin, the hormone of the pineal gland, are of considerable current interest. Synthetic melatonin analogues as agonists and antagonists have been explored in some detail and the molecule can be considered as consisting of an indole core, acting mainly as a spacer, and the 5-methoxyl and 3-amidoethyl side chains acting as the functional components, as originally proposed by Heward and Hadley. This review focuses on the synthetic routes to these melatonin analogues, first of the core, then of the substituents that have been attached to the core, and finally those compounds with restricted conformations and those that are chiral. The importance of the various factors involved in the activity of the compounds as agonist or antagonists is indicated, as is the difference in activity of enantiomers.