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  (12a)  binds strongly to both the hMT1 and hMT2 receptors, and shows a preference for the hMT2, as does Its propanamido counterpart  12b . The introduction of two methyl groups into their side chain, analogues  15a  and 1 5b,  leads to antagonism, in the case of the former, and drastically diminishes its hMT1 binding; an analogous profile is seen for  15b , which, however, is a partial agonist.. Introduction of chlorine or methoxyl 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 ,  36a  and  b , that bind strongly to the human receptors,  33 ,  36b  are 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

2-{2-[3-(1-Adamantyl)-4-fluorophenyl]thiazol-4-yl}ethan-1-amine (1a) and 2-{2-[4-(1-adamantyl)phenyl]thiazol-4-yl}ethan-1-amine (2a) exhibit activity against T. brucei in the range of IC₅₀ = 0.42 μM and IC₅₀ = 0.80 μM, respectively.

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.

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.

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[3.3.1.1^3,7 ]dec-1-yl)phenyl]-N'-[(5-nitrofuran-2-yl)methylene]acetohydrazide; EC₅₀ =11±0.9 nm, SI_Tb =770).

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.

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.

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). β-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 β-substituents.

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.

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.

Synthesis and anti-HIV Evaluation of Alkyl and Alkoxyethyl Phosphodiester AZT Derivatives

A series of new AZT conjugates with alkyl and oxyalkyl ether phospholipids was synthesized and evaluated for inhibitory activities against HIV-1 and HIV-2. The alkoxyethyl derivatives 6a-c proved 3- to 5-fold more active against HIV-1 and HIV-2 than the alkyl analogues 6d-f. A trend for higher activity with longer alkyl side-chains was observed. However, the analogues with the shortest chain possessed the most favourable therapeutic index.

New hydrazones of 5-nitro-2-furaldehyde with adamantanealkanohydrazides: synthesis and in vitro trypanocidal activity

A range of hydrazones of 5-nitro-2-furaldehyde with adamantane alkanohydrazides was synthesized and their trypanocidal activity was evaluated.

Novel 1-(2-aryl-2-adamantyl)piperazine derivatives with antiproliferative activity

Novel 1-(2-aryl-2-adamantyl)piperazine derivatives have been synthesized and evaluated in vitro for their antitumor properties against HeLa cervical carcinoma, MDA MB 231 breast cancer, MIA PaCa2 pancreatic cancer, and NCI H1975 non-small cell lung cancer. The parent piperazine 6 was found to exhibit a reasonable activity toward the HeLa and MDA MB 231 tumor cell lines (IC50= 9.2 and 8.4 μΜ, respectively). Concurrent benzene ring C4-fluorination and piperidine acetylation of the piperazino NH of compound 6 resulted in the most active compound 13 of the series in both of the above cell lines (IC50=8.4 and 6.8 μΜ, respectively). Noticeably, compounds 6 and 13 exhibited a significantly low cytotoxicity level over the normal human cells HUVEC (Human Umbilical Vein Endothelial Cells) and NHDF (Normal Human Dermal Fibroblasts).

New adamantane derivatives with sigma affinity and antiproliferative activity

The synthesis of 4-(1-adamantyl)-4,4-diarylbutylamines 1, 5-(1-adamantyl)-5,5-diarylpentylamines 2 and 6-(1-adamantyl)-6,6-diarylhexylamines 3 is described and the σ1, σ2-receptors and sodium channels binding affinity of compounds 1 were investigated. The in vitro activity of compounds 1, 2 and 3 against main cancer cell lines is significant. One of the most active analogs, 1a, had an interesting in vivo anticancer profile against the ovarian cancer cell line IGROV-1, which was associated with an anagelsic activity against the neuropathic pain induced by the main anticancer drugs.

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.

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.

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 new N1 and C3-substituted 4-fluoroindolic melatoninergics

A series of new C-3 and N1-substituted 4-fluorotryptamides have been prepared and tested for their ability to activate pigment granule aggregation in Xenopus laevis melanophores and bind to the recombinant human MT(1) and MT(2) melatonin receptor subtypes expressed in NIH 3T3 cells. Planar sp(2) geometry at C-3-betaC seems to decrease the population of the preferred conformation as it renders 4-fluoroindoles 4b-d weaker antagonists than their C-3-betaC-unsubstituted congeners 3a-e. This effect is not preclusively linked with the C-3 region, as the same geometry around N1 (compounds 5a-c) similarly leads to weak antagonistic action. Last, the new C-3 substituted 4-fluorotryptamides presented herein are substantially more potent than their respective N-OMe functionalized congeners, previously reported.

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.

C4-substituted isoquinolines: synthesis and cytotoxic action

A facile synthesis of the C4-substituted isoquinolines 5a-c and 6a-c is described. Commercially available 4-bromoisoquinoline is converted to the α,β-unsaturated esters 8 and 10 on treatment with the appropriate acrylate ester under Heck reaction conditions. The saturated amides 5a-c were obtained from the reaction of ester 9 with the requisite primary amine. Similarly the unsaturated analogues 6a-c were prepared by reacting ester 10 with the appropriate amine. The cytotoxicity of the target molecules was evaluated in two tumour cell lines in vitro. Two compounds, 6b and 6c, showed sufficient activity in the human non-small cell lung cancer line NSCLC-N16-L16 to be worthy of further study.

Design, synthesis and melatoninergic activity of new unsubstituted and β,β′-difunctionalised 2,3-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-6-alkanamides

A series of new 2,3-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-6-alkanamides, with and without alkyl and cycloalkyl moieties in the beta-position of the alkanamido side chain, have been prepared and tested for their ability to activate pigment granule aggregation in Xenopus laevis melanophores and bind to the recombinant human MT(1) and MT(2) melatonin receptor subtypes expressed in NIH 3T3 cells. An increase of the spacer's length in the side chain by a methylene unit (from 17d to 21d) leads to a six-fold decrease in antagonistic activity. On the other hand, the introduction of two methyl groups in the beta-position of the side chain of 17a induces agonist potency (compound 24), implying thus that the two beta-methyl groups are not only tolerated by the receptor, but constitute functional probes in its dynamic agonist-antagonist conformational equilibrium. The presence of more bulky beta-substituents, regardless of the size of the R group, compounds 24a,b, seems to lead to antagonism and to a noteworthy MT(2) subtype selectivity. Last, the new N1-C7 annulated derivatives presented herein are substantially more potent than their respective N1-C2 annulated counterparts, previously reported.

Design, synthesis and melatoninergic potency of new N-acyl 8,9-dihydro-4-methoxy-7H-2-benzo[de]quinolinalkanamines

A series of new N-acyl 8,9-dihydro-4-methoxy-7H-2-benzo[de]quinolinalkanamines have been prepared and tested for their ability to activate pigment granule aggregation in Xenopus laevis melanophores and bind to the recombinant human MT(1) and MT(2) melatonin receptor subtypes expressed in NIH 3T3 cells. Compounds with a single methylene spacer in the side chain (7) have no agonist activity, but are weak antagonists in the Xenopus melanophore assay, irrespectively of the size or shape of the R substituent (R=CH(3) to c-C(4)H(7)). In contrast, compounds with two (8) or three (9) methylene spacers show partial agonist activity, though this does vary with the nature of the R substituent. Interestingly, the cyclopropane and cyclobutane R substituents, which are usually linked with antagonism, render the cyclopropanecarboxamido analog 9d and its cyclobutanecarboxamido congener 9e weak agonists. It seems, therefore, that in these compounds the R substituent constitutes a functional probe in the dynamic agonist-antagonist conformational equilibrium. One of the new molecules, antagonist 8c, exhibits a noteworthy MT(2) subtype selectivity (13-fold), whereas the acetamido analog 9a (with a three methylene units spacer) also acts as an antagonist and is the only analog exhibiting MT(1) selectivity (>10-fold). In contrast to the analogous N1-C7 annulated indole derivatives, recently reported, the new C1-C8 condensed isoquinolines are not all pure antagonists. Despite their modest receptor affinity at the binding site these compounds demonstrate that the nature of the response (agonist or antagonist activity) is dependent, in this case, on both the side chain spacer's length and the size and shape of the R group.