Tricyclic Moiety Research Articles

Tricyclic compounds inhibit the OATP1A2 transporter

BackgroundOATP1A2 is a membrane transporter potentially involved in the absorption of various drugs. Previous data demonstrated that the uptake of rosuvastatin through OATP1A2 can be inhibited by several β‐blockers, where carvedilol is the most potent inhibitor. Carvedilol structurally differs from the other β‐blockers tested by its tricyclic moiety. The goal of this study was to determine whether the tricyclic structure of carvedilol is responsible for its strong inhibitory effect on OATP1A2.MethodsA HEK293 cell line overexpressing OATP1A2 was used as model. They were co‐incubated in the presence of rosuvastatin and increasing concentrations of different tricyclic compounds. The amount of rosuvastatin transported in the cells was measured by HPLC.ResultsMost tricyclic compounds evaluated inhibited rosuvastatin uptake through OATP1A2 with different IC50. Our data show that the inhibition is competitive. Compound IC50 (μM) Compound IC50 (μM) carazolol 4.0 nortriptyline 14.8 amitriptyline 5.0 chlorpromazine 29.6 imipramine 12.6 desipramine 77.9 trimipramine 13.6 carbamazepine >;100 doxepin 14.0 carbazole No effect clomipramine 14.7 phenothiazine No effect ConclusionsThe inhibitory component is made up of the tricyclic ring with a short aliphatic chain. Consequently, drugs with a similar structure may strongly modulate the transport of OATP1A2 substrates.Funding: CIHR, FRSQ, Foundation CHUM

Equilibrium and structural characterization of ofloxacin–cyclodextrin complexation

The enantiomer-specific characterization of ofloxacin–cyclodextrin complexes was carried out by a set of complementary analytical techniques. The apparent stability constants of the ofloxacin enantiomers with 20 different cyclodextrins at two different pH values were determined to achieve good resolution capillary electrophoresis enantioseparation either to establish enantioselective drug analysis assay, or to interpret and design improved host–guest interactions at the molecular level. The cyclodextrins studied differed in the nature of substituents, degree of substitution (DS), charge and purity, allowing a systematic test of these properties on the complexation. The seven-membered beta-cyclodextrin and its derivatives were found to be the most suitable hosts. Highest stability and best enantioseparation were observed for the carboxymethylated-beta-cyclodextrin (DS ~ 3.5). The effect of substitution pattern (SP) was investigated by molecular modeling, verifying that SP greatly affects the complex stability. Induced circular dichroism was observed and found especially significant on carboxymethylated-beta-cyclodextrin. The complex stoichiometry and the geometry of the inclusion complexes were determined by 1H NMR spectroscopy, including 2D ROESY techniques. Irrespective of the kind of cyclodextrin, the complexation ratio was found to be 1:1. The alfa-cyclodextrin cavity can accommodate the oxazine ring only, whereas the whole tricyclic moiety can enter the beta- and gamma-cyclodextrin cavities. These equilibrium and structural information offer molecular basis for improved drug formulation.

Crystal Structure of Bis(<i>μ</i>-4-methylpiperidine-1-carbodithioato-1:2<i>κ</i><sup>3</sup><i>S</i>,<i>S</i>′:<i>S</i>′;2:1<i>κ</i><sup>3</sup><i>S</i>,<i>S</i>′:<i>S</i>′)bis[(4-methylpiperidine-1-carbodithioato-<i>k</i><sup>2</sup><i>S</i>,<i>S</i>′)cadmium(II)

The structure of the title compound features both bridging and chelating dithiocarbamate ligands, so that a tetragonal pyramidal S5 coordination geometry results. Each of the chelating ligands is bidentately coordinated to a cadmium atom, and forms a planar four-membered chelate ring [CdS2C]; However, a pair of tridentate bridging ligands combine two neigbouring cadmium atoms, forming extended eight-membered tricyclic moieties [Cd2S4C2], whose geometry can be approximated by a ‘chair’ conformation. The compound crystallizes in the triclinic space group P1 with the following unit-cell parameters: a = 8.5286(6), b = 11.4221(6), c = 11.4561(6)A, α = 112.632(2), β = 97.216(2), γ = 106.241(2)°, Z = 1. The crystal structure was solved by direct methods using single-crystal X-ray diffraction data collected at room temperature, and refined by full-matrix least-squares procedures to a final R-value of 0.0297 for 5115 observed reflections. Both of the piperidine rings exhibit a chair conformation. The structure has an intermolecular hydrogen bond of the type C-H…S, which helps to stabilize the crystal structure.

Three new fluorinatedN-phenyl-substituted pentacyclic ethanoanthracenedicarboximides

Diels-Alder reaction between maleimides featuring 3,5-di-, 2,4,6-tri- and pentafluorinated N-phenyl substituents and anthracene yields the corresponding pentacyclic ethanoanthracenedicarboximide compounds, namely N-(3,5-difluorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximide, C(24)H(15)F(2)NO(2), (IIa), N-(2,4,6-trifluorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximide, C(24)H(14)F(3)NO(2), (IIb), N-(2,3,4,5,6-pentafluorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximide, C(24)H(12)F(5)NO(2), (IIc). The crystal structures of (IIa)-(IIc) reveal an expected molecular geometry with a `V'-shape of the anthracene-derived tricyclic moiety. The crystal packings of (IIa) and (IIb) are dominated by π-π and C-H···O/F interactions, while F···F and C-H···π contacts are absent. In contrast, (IIc) shows F···F and C-H···O/F contacts, but no π-involved contacts of relevance.

Tuning G-Quadruplex vs Double-Stranded DNA Recognition in Regioisomeric Lysyl-Peptidyl-Anthraquinone Conjugates

Anthraquinone is a versatile scaffold to provide effective DNA binders. This planar system can be easily conjugated to protonable side chains: the nature of the lateral groups and their positions around the tricyclic moiety largely affect the DNA recognition process in terms of binding affinity and mode, as well as sequence and structure of the target nucleic acid. Starting from an anthracenedione system symmetrically functionalized with N-terminal lysyl residues, we incremented the length of side chains by introducing a Gly, Ala, or Phe spacer, characterized by different flexibility, lipophilicity, and bulkiness. Moreover, 2,6, 2,7, 1,8, and 1,5 regioisomers were examined to yield a small bis(lysyl-peptidyl) anthracenedione library. By merging spectroscopic, enzymatic, and cellular results, we showed that the proper combination of a basic aminoacid (Lys) with a more hydrophobic residue (Phe) can provide selective G-quadruplex recognition, in particular when side chains are located at positions 2,6 or 2,7. In fact, while these derivatives effectively bind G-quadruplex structures, they behave at the same time as rather poor double-stranded DNA intercalators. As a result, the Lys-Phe substituted anthraquinones are poorly cytotoxic but still able to promote a senescence mechanism in cancer cells. This combination of chemical and biological properties foresees potentially valuable applications in anticancer medicinal chemistry.

Total Synthesis of (±)-Cylindricine C

A concise synthesis of (±)-cylindricine C and its C(13)-epimer is described. Starting from 1-octyne, cylindricine C and 13-epi-cylindricine C were prepared in 11% and 15% yields, respectively. The synthesis involves the preparation of the central tricyclic moiety via a radical α-iodoketone carboazidation/bis-reductive amination sequence. Inversion of the stereochemistry at C(13) and C(5) was efficiently achieved on late stage intermediates.

On the Origin of the Solid-State Thermochromism and Thermal Fatigue of Polycyclic Overcrowded Enes

Aimed at unraveling the relative contribution of the folding, twisting and bending in the mechanism of the solid-state thermochromism of overcrowded polycyclic aromatic enes (PAEs), the structures of two typical heteromeric and homomeric representatives, 2-(thioxanthen-9-ylidene)indane-1,3-dione (1) and 9,9'-bi-9(10H)-anthracenylidene-10,10'-dione (bianthrone, 2), were studied by temperature-resolved single crystal X-ray diffraction (120-530 K) and solid-state UV-visible spectroscopy. Aside from negligibly small unfolding of the tricyclic moiety of 1, this first direct diffraction study of the high-temperature structures of solid PAEs did not unravel any significant and detectable changes in the time- and space-averaged intramolecular structures, thus, showing that the PAE-type thermochromism is not due to phase transitions or to major and permanent molecular distortions of a large portion of the material that would be caused by folding, twisting and/or bending. Instead, the experimental observations and theoretical modeling indicated that the color change is probably due to a dynamic process, where the absorption spectrum changes as a result of enhanced thermal oscillations of the two halves of the molecules around the central bridge. In addition to the reversible coloration, we also observed irreversible processes of thermal fatigue that afford stable chemical products that absorb in the visible region. We showed that the stable products are conductive and they act electrocatalytically toward oxidation of several biomarkers.

Studies toward the total synthesis of armatol F: stereoselective construction of the C6 and C7 stereocenters and formation of the A-ring skeleton

Armatol F, isolated from the red alga Chondria armata as a polyether triterpene, has a solitary oxepane (A-ring) and a fused tricyclic ether moiety (BCD-ring). The A-ring features a rare cis-relationship between the hydroxy group at the quaternary carbon C6 and the carbon chain at C7. As part of our program toward the total synthesis of armatol F, a new stereoselective method for the construction of the C6 and C7 stereocenters has been developed based on chirality-transferring Ireland-Claisen rearrangement. The A-ring skeleton has also been synthesized from the rearrangement product by a process including ring-closing olefin metathesis.

ChemInform Abstract: Selenium- and Tellurium-Bridged Overcrowded Homomerous Bistricyclic Aromatic Enes.

The effects of selenium and tellurium bridges on the conformations of overcrowded homomerous bistricyclic aromatic enes were studied. The structures of the target molecules 9,9′-bi(9H-selenoxanthen-9-ylidene) (7) and 9,9′-bi(9H-telluroxanthen-9-ylidene) (8) were established by 1H, 13C, 77Se, 125Te NMR spectroscopy, and by X-ray analysis. The molecules adopted anti-folded conformations with 53.6 (7) and 53.1° (8) folding dihedrals between pairs of benzene rings of the tricyclic moieties, whereas the corresponding folding dihedral in 9-methylene-9H-selenoxanthene 20 was considerably lower, 32.4°. An X-ray analysis of 9,9′-bi(9H-selenoxanthene) (9) indicated an anti-folded conformation with a folding dihedral of 49.2° and short Se10⋯H9′ and Se10′⋯H9 distances. Compounds 7 and 8 exhibited low degrees of overcrowding in the fjord regions. Considerable overcrowding was evident in the short Se10⋯C9 and Te10⋯C9 contact distances in 7 and 8. The high shielding of the protons in the fjord regions of 7 and 8 revealed anti-folded conformations in solution. The 13C NMR chemical shifts of 7 and 8 were characterized by low-field absorptions of C9 and C9′. Semi-empirical PM3 calculations of the anti-folded, syn-folded, and twisted conformations indicated that anti-folded-7 and syn-folded-8 were the most stable conformations, respectively. The special stability of syn-folded-8 was attributed to the short intramolecular Te10⋯Te10′ distance (3.06 A). Compounds 7 and 8 were synthesized by reductive “dimerizations” of 9H-selenoxanthene-9-thione (13) and 9H-telluroxanthene-9-thione (17) with copper in boiling toluene. Compound 7 was also synthesized by diazo–thione coupling between 13 and 9-diazo-9H-selenoxanthene (14), followed by elimination of sulfur from the intermediate thiirane 15. 9,9′-Bi(9H-selenoxanthene) (9) and 9,9′-bi(9H-telluroxanthene) (10) were prepared by low valent titanium induced reductive “dimerizations” of 9H-selenoxanthen-9-one (11) and 9H-telluroxanthen-9-one (12), respectively, using TiCl4/Zn/pyridine–THF.

Binding and Orientation of Tricyclic Antidepressants within the Central Substrate Site of the Human Serotonin Transporter

Tricyclic antidepressants (TCAs) have been used for decades, but their orientation within and molecular interactions with their primary target is yet unsettled. The recent finding of a TCA binding site in the extracellular vestibule of the bacterial leucine transporter 11 A above the central site has prompted debate about whether this vestibular site in the bacterial transporter is applicable to binding of antidepressants to their relevant physiological target, the human serotonin transporter (hSERT). We present an experimentally validated structural model of imipramine and analogous TCAs in the central substrate binding site of hSERT. Two possible binding modes were observed from induced fit docking calculations. We experimentally validated a single binding mode by combining mutagenesis of hSERT with uptake inhibition studies of different TCA analogs according to the paired mutation ligand analog complementation paradigm. Using this experimental method, we identify a salt bridge between the tertiary aliphatic amine and Asp(98). Furthermore, the 7-position of the imipramine ring is found vicinal to Phe(335), and the pocket lined by Ala(173) and Thr(439) is utilized by 3-substituents. These protein-ligand contact points unambiguously orient the TCA within the central binding site and reveal differences between substrate binding and inhibitor binding, giving important clues to the inhibition mechanism. Consonant with the well established competitive inhibition of uptake by TCAs, the resulting binding site for TCAs in hSERT is fully overlapping with the serotonin binding site in hSERT and dissimilar to the low affinity noncompetitive TCA site reported in the leucine transporter (LeuT).

Structural study of liposomes loaded with a GM3 lactone analogue for the targeting of tumor epitopes

Therapeutic vaccination with tumor antigens is a new approach in cancer treatment, which aims at inducing immune response while avoiding the side effects generally associated to many conventional therapies. To improve the efficacy of vaccines, suitable carriers may be used. Herein the insertion of a thioether analogue of GM3 lactone (SNeuAC-C14) into liposomes is reported. SNeuAC-C14 is a potential vaccine for the targeting of saccharide-based tumor epitopes. Different liposome formulations were designed to act as carriers and to generate recognition by tumor epitopes. The structural study of pure and loaded liposomes was carried out by synchrotron Small Angle X-ray Scattering and was complemented by Dynamic Light Scattering and Zeta potential measurements. This provided detailed information on relevant properties of the investigated host-guest structures and showed that the active unit of SNeuAC-C14, i.e. its spiro tricyclic moiety, was located in the polar head region of the liposome bilayer, which is an important requirement for recognition phenomena. Moreover, it was found that most of the SNeuAC-C14/liposome complexes were positively charged. The obtained results allow these systems to be considered as candidates to promote immunoresponse in tumor cells.

N-1-Naphthyl-3-oxobutanamide in Heterocyclic Synthesis: A Facile Synthesis of Nicotinamide, Thieno[2,3-b]pyridine, and Bi- or Tricyclic Annulated Pyridine Derivatives Containing Naphthyl Moiety

N-1-Naphthyl-3-oxobutanamide (1) reacts with arylidinecyanothioacetamide 2a–c in ethanol/piperidine solution under reflux to yield the pyridine-2(1H)-thiones 6a–c. Compound 6a reacts with α-haloketones 7a–e to give the 6-thio-N-1-naphthyl-nicotinamides derivatives 8a–e, which cyclized to thieno[2,3-b]pyridine derivatives 9a–e. The reaction of compound 9a with hydrazine hydrate and formamide gives the thieno[2,3-b]pyridine carbohydrazide derivative 10 and pyridothienopyrimidine derivative 11, respectively. Reaction of 9a with benzoyl isothiocyanate gave thiourea derivative 12. Compound 12, upon treatment with alcoholic NaOH, gave pyridothienopyrimidine 13. Saponifications of 9a gave the amino acid 15, which affords 16 when refluxed in Ac2O. Treatment of compound 16 with AcONH4/AcOH gave 17. Diazotization and self-coupling of 9b gave the pyridothienotriazine 18. Also, diazotization of the ortho-aminohydrazide 10 give the corresponding azide 19, which was subjected to Curtius rearrangement in boiling xylene to give imidazothienopyridine 20. Reaction of 10 with either formic acid or triethylorthoformate and phenyl isothiocyanate gave the corresponding pyridothienotriazepines 22 and 23, respectively. The interaction of 10 with acetylacetone furnished the pyrazolyl derivative 24. The structures of the synthesized compounds were established from their analytical and spectral data.

Identification of the Antioxidation Reaction Products from a Sinapic Ester in a Lipid Oxidation System

As a part of our research project on the elucidation of the chain-breaking antioxidation mechanism for natural phenols in food components, the antioxidation products from a sinapic acid methyl ester in lipid oxidation were identified. Sinapic acid is a potent antioxidative phenolic acid widely distributed in edible plants. The structural determination of the four isolated products revealed them each to have a tricyclic structure consisting of ethyl linoleate, methyl sinapate and molecular oxygen, and these were isomeric compounds for the substituents on the tricyclic moiety.

Discovery of a new PCC-mediated stereoselective oxidative spiroketalization process. An access to a new type of poly-THF spiroketal compound displaying anticancer activity

A new type of cytotoxic poly-tetrahydrofuran compound, embodying a novel tricyclic spiroketal moiety, has been obtained through an unprecedented PCC-mediated stereoselective oxidative spiroketalization process.

Synthesis of [14C]‐ and [13C6]‐labeled potent HIV non‐nucleoside reverse transcriptase inhibitor

Abstract5,11‐Dihydro‐11‐ethyl‐5‐methyl‐8‐{2‐{(1‐oxido‐4‐quinolinyl)oxy}ethyl}‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one, (1), labeled with carbon‐14 in the quinoline–benzene ring, in one of the pyridine rings of the dipyridodiazepinone tricyclic moiety, and in the side chain, was prepared in three different syntheses with specific activities ranging from 44 to 47 mCi/mmol (1.63–1.75 GBq/mmol). In the first synthesis, 5,11‐dihydro‐11‐ethyl‐8‐(2‐hydroxyethyl)‐5‐methyl‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one (2) was coupled to 4‐hydroxyquinoline, [benzene‐14C(U)]‐, using Mitsunobu's reaction conditions, followed by the oxidation of the quinoline nitrogen with 3‐chloroperoxybenzoic acid to give ([14C]‐(1a)) in 43% radiochemical yield. Second, 3‐amino‐2‐chloropyridine, [2,6‐14C]‐, was used to prepare 8‐bromo‐5,11‐dihydro‐11‐ethyl‐5‐methyl‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one (8), and then Stille coupled to allyl(tributyl)tin followed by ozonolysis of the terminal double bond and in situ reduction of the resulting aldehyde to alcohol (10). Mitsunobu etherification and oxidation as seen before gave ([14C]‐(1b)) in eight steps and in 11% radiochemical yield. Finally, carbon‐14 potassium cyanide was used to prepare isopropyl cyanoacetate (12), which was used to transform bromide (8) to labeled aryl acetic acid (13) under palladium catalysis. Trihydroborane reduction of the acid gave alcohol (14) labeled in the side chain, which was used as described above to prepare ([14C]‐(1c)) in 4.3% radiochemical yield. The radiochemical purities of these compounds were determined by radio‐HPLC and radio‐TLC to be more than 98%. To prepare [13C6]‐(1), [13C6]‐4‐hydroxyquinoline was prepared from [13C6]‐aniline and then coupled to (2) and oxidized as seen before. Copyright © 2008 John Wiley & Sons, Ltd.

Accommodation of physostigmine and its analogues by acetylcholinesterase is dominated by hydrophobic interactions

The role of the functional architecture of the HuAChE (human acetylcholinesterase) in reactivity toward the carbamates pyridostigmine, rivastigmine and several analogues of physostigmine, that are currently used or considered for use as drugs for Alzheimer's disease, was analysed using over 20 mutants of residues that constitute the interaction subsites in the active centre. Both steps of the HuAChE carbamylation reaction, formation of the Michaelis complex as well as the nucleophilic process, are sensitive to accommodation of the ligand by the enzyme. For certain carbamate/HuAChE combinations, the mode of inhibition shifted from a covalent to a noncovalent type, according to the balance between dissociation and covalent reaction rates. Whereas the charged moieties of pyridostigmine and rivastigmine contribute significantly to the stability of the corresponding HuAChE complexes, no such effect was observed for physostigmine and its analogues, phenserine and cymserine. Moreover, physostigmine-like ligands carrying oxygen instead of nitrogen at position -1 of the tricyclic moiety (physovenine and tetrahydrofurobenzofuran analogues) displayed comparable structure-function characteristics toward the various HuAChE enzymes. The essential role of the HuAChE hydrophobic pocket, comprising mostly residues Trp(86) and Tyr(337), in accommodating (-)-physostigmine and in conferring approximately 300-fold stereoselectivity toward physostigmines, was elucidated through examination of the reactivity of selected HuAChE mutations toward enantiomeric pairs of different physostigmine analogues. The present study demonstrates that certain charged and uncharged ligands, like analogues of physostigmine and physovenine, seem to be accommodated by the enzyme mostly through hydrophobic interactions.

Molecular Modeling of Benzothiazepine Binding in the L-type Calcium Channel

Benz(othi)azepine (BTZ) derivatives constitute one of three major classes of L-type Ca(2+) channel ligands. Despite intensive experimental studies, no three-dimensional model of BTZ binding is available. Here we have built KvAP- and KcsA-based models of the Ca(v)1.2 pore domain in the open and closed states and used multiple Monte Carlo minimizations to dock representative ligands. In our open channel model, key functional groups of BTZs interact with BTZ-sensing residues, which were identified in previous mutational experiments. The bulky tricyclic moiety occupies interface between domains III and IV, while the ammonium group protrudes into the inner pore, where it is stabilized by nucleophilic C-ends of the pore helices. In the closed channel model, contacts with several ligand-sensing residues in the inner helices are lost, which weakens ligand-channel interactions. An important feature of the ligand-binding mode in both open and closed channels is an interaction between the BTZ carbonyl group and a Ca(2+) ion chelated by the selectivity filter glutamates in domains III and IV. In the absence of Ca(2+), the tricyclic BTZ moiety remains in the domain interface, while the ammonium group directly interacts with a glutamate residue in the selectivity filter. Our model suggests that the Ca(2+) potentiation involves a direct electrostatic interaction between aCa(2+) ion and the ligand rather than an allosteric mechanism. Energy profiles indicate that BTZs can reach the binding site from the domain interface, whereas access through the open activation gate is unlikely, because reorientation of the bulky molecule in the pore is hindered.

Design, synthesis, and structure–affinity relationship studies in NK 1 receptor ligands based on azole-fused quinolinecarboxamide moieties

The substituent in position 2 of the quinoline nucleus of NK 1 receptor ligands 5 has been constrained into different five-membered heterocyclic moieties in order to obtain information on the binding site pocket interacting with this apparently critical portion of ligands 5. This structure–affinity relationship study led to the discovery of novel tricyclic NK 1 receptor ligands 6 showing affinity in the nanomolar range to the sub-micromolar one. The systematic structure variation suggests that electronic features of the tricyclic moiety play a role in modulating the interaction of these amide derivatives with their receptor.

Exploiting Protein Fluctuations at the Active-Site Gorge of Human Cholinesterases: Further Optimization of the Design Strategy to Develop Extremely Potent Inhibitors

Protein conformational fluctuations are critical for biological functions, although the relationship between protein motion and function has yet to be fully explored. By a thorough bioinformatics analysis of cholinesterases (ChEs), we identified specific hot spots, responsible for protein fluctuations and functions, and those active-site residues that play a role in modulating the cooperative network among the key substructures. This drew the optimization of our design strategy to discover potent and reversible inhibitors of human acetylcholinesterase and butyrylcholinesterase (hAChE and hBuChE) that selectively interact with specific protein substructures. Accordingly, two tricyclic moieties differently spaced by functionalized linkers were investigated as molecular yardsticks to probe the finest interactions with specific hot spots in the hChE gorge. A number of SAR trends were identified, and the multisite inhibitors 3a and 3d were found to be the most potent inhibitors of hBuChE and hAChE known to date.

Design, synthesis and biological evaluation of substituted dioxodibenzothiazepines and dibenzocycloheptanes as farnesyltransferase inhibitors

A new series of FTase inhibitors containing a tricyclic moiety—dioxodibenzothiazepine or dibenzocycloheptane—has been designed and synthesized. Among them, dioxodibenzothiazepine 18d displayed significant inhibitory FTase activity (IC 50 = 17.3 nM) and antiproliferative properties.