Rigid Analogues Research Articles

Synthesis of a Conformationally Rigid Analogue of 2-Aminoadipic Acid ­Containing an 8-Azabicyclo[3.2.1]octane Skeleton

A new, conformationally rigid analogue of 2-amino­adipic acid, 8-[(benzyloxy)carbonyl]-3-methylene-8-azabicyclo[3.2.1]octane-1,5-dicarboxylic acid, is synthesized from dimethyl rac-2,5-dibromohexanedioate. The key steps involve alkylation-cyclization of 1-benzyl 2,5-dimethyl pyrrolidine-1,2,5-tricarboxylate with 3-chloro-2-(chloromethyl)prop-1-ene to yield the 8-azabicyclo[3.2.1]octane skeleton.

Heterogeneous Wide Range pH-sensing Materials Allowing Ratiometric Fluorescence Detection Based on Structurally Rigid Analogs of 2,6-distyrylpyridine

The new sensing materials based on the microsized silica gel powder with non-covalently immobilized structurally rigid analogs of 2,6-distyrylpyrydine ((3E,5E)-3,5-dibenzylidene-8-phenyl-1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridines) were developed and tested. Most of the investigated compositions demonstrate linear ratiometric fluorescence response on pH in the physiologically important interval (pH 6-9). The compound with the greatest number of protolytic centers within the studied series demonstrated the widest pH sensitivity range, however in this case the analytical signal was the lowest. The prospects for the practical application of the investigated materials in the fiber optics sensing devices were outlined.

Pentaorganosilicates

AbstractIn this research report, we explore the emerging field of stable pentaorganosilicates, with the aim to show the development from transient species to stable and configurationally rigid analogues that may find application e.g. as novel chiral auxiliaries or in chiral ionic liquids.

1,3‐Dioxolane‐Based Ligands as Rigid Analogues of Naftopidil: Structure–Affinity/Activity Relationships at α1 and 5‐HT1A Receptors

Conformational restriction of naftopidil proved to be compatible with binding at alpha(1) adrenoceptor subtypes and 5-HT receptor 1A (5-HT(1A)), and led to the discovery of a new class of ligands with a 1,3-dioxolane (1,3-oxathiolane, 1,3-dithiolane) structure. Compound 7 shows the highest affinity toward alpha(1a) and alpha(1d) adrenoceptor subtypes (pK(i) alpha(1a) = 9.58, pK(i) alpha(1d) = 9.09) and selectivity over 5-HT(1A) receptors (alpha(1a)/5-HT(1A) = 100, alpha(1d)/5-HT(1A) = 26). In functional experiments it behaves as a potent competitive alpha(1a) and alpha(1d) adrenoceptor antagonist (pK(b) alpha(1A) = 8.24, pK(b) alpha(1D) = 8.14), whereas at 5-HT(1A) receptors it is a potent partial agonist (pD(2) = 8.30). Compounds 8 and 10 display high affinity (pK(i) = 8.29 and 8.26, respectively) and selectivity for 5-HT(1A) (5-HT(1A)/alpha(1) = 18 and 10). In functional experiments at the 5-HT(1A) receptor, compound 8 appears to be neutral antagonist (pK(b) = 7.29), whereas compound 10 is a partial agonist (pD(2) = 6.27). Therefore, 1,3-dioxolane-based ligands are a versatile class of compounds useful for the development of more selective ligands for one (alpha(1)) or the other (5-HT(1A)) receptor system.

A rigid GABA analog from a [4+3]-cycloaddition

A rigid GABA analog has been prepared from the adduct obtained from the [4+3]-cycloaddition of pentachloroacetone and a 2-substituted furan.

Synthesis of a 4′,4′-spirothietane-2′, N3-cycloadenosine as a highly constrained analogue of 5′-deoxy-5′-methylthioadenosine (MTA)

The synthesis of the highly constrained adenosine derivative 7 featuring at spirothietane at C-4 ′, which may be considered as a rigid analogue of MTA, is described.

ChemInform Abstract: Synthesis of Novel Rigid Analogues of Tryptamine as Potential Serotonin Ligands Through Pd(0)‐Catalyzed Diaryl Coupling Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and structure–activity relationships for biphenyl H 3 receptor antagonists with moderate anti-cholinesterase activity

The combination of antagonism at histamine H 3 receptors and inhibition of acetylcholinesterase has been recently proposed as an approach to devise putative new therapeutic agents for cognitive diseases. The 4,4′-biphenyl fragment has been reported by us as a rigid scaffold leading to potent and selective non-imidazole H 3-antagonists. Starting from these premises, the current work presents an expanded series of histamine H 3 receptor antagonists, characterized by a central 4,4′-biphenyl scaffold, where the structure–activity profile of both mono-basic and di-basic compounds is further explored and their ability to inhibit rat brain cholinesterase activity is determined. The steric properties and basicity of the terminal groups were modulated in symmetrical compounds, carrying identical substituents, and in asymmetrical compounds, having a piperidine ring at one end and different groups at the other. The length of the linker connecting the biphenyl scaffold to the terminal groups was also modulated. Binding studies at rat and human H 3 receptors evidenced the highest binding affinities for di-basic compounds, in the order of nM concentrations, and that the steric requirements for the two terminal groups are different. Many potent compounds showed good selectivity profiles over the other histamine receptors. Interestingly, some derivatives displayed a moderate ability to inhibit rat brain cholinesterase, for example compound 12 (1-[2-(4′-piperidinomethyl-biphenyl-4-yl)ethyl]piperidine) has a pIC 50 = 5.96 for cholinesterase inhibition and high H 3 receptor binding affinity and antagonist potency (p K i = 8.70; p K B = 9.28). These compounds can be considered as rigid analogs of a recently reported class of dual-acting compounds and as a promising starting point for the design of new H 3-antagonists with anti-cholinesterase activity.

A Combined Virtual Screening 2D and 3D QSAR Methodology for the Selection of New Anticonvulsant Candidates from a Natural Product Library

AbstractA virtual screening methodology combining a discriminant function (df) based on Dragon 2D‐descriptors, general ADME filters, and a pharmacophore identified through superposition of rigid analogs was applied in order to identify new anticonvulsant agents among 10 903 natural products. Fifty‐six compounds were selected from the application of this df, Lipinski's rule‐of‐five and other criteria for prediction of oral bioavailability, and the optimal value of log P for a compound to diffuse passively through the blood–brain barrier. Seven of these compounds were removed because they did not belong to descriptor space defined by the training set. The remaining 49 compounds were fitted to the pharmacophore structural constrains, selecting 7 structures with RMS distance value below 0.2. Systematic conformational analysis was performed to find the global minimum conformation, using the PM3 base included in Hyperchem 6.03. The global minimum conformations were further refined at a 6‐31G** level with Gaussian 03. Restricted optimization was then performed to determine the energy difference between the energy minimum conformation and the active conformation defined by the pharmacophore, retaining those structures whose energy differences were below 7 kcal/mol. Four new potential anticonvulsants which fulfill the df and the pharmacophore requisites were selected. One of these structures, 2‐(4,6‐dimethyl‐1‐benzofuran‐3‐yl)acetic acid, was acquired and assayed in the MES and Rotorod tests, confirming anticonvulsant activity in mice at 30 and 100 mg/kg (0.5 and 4 h, i.p.) and absence of neurotoxicity at the tested doses.

Synthesis of new 4-(phenylamino)thieno[2,3-b]pyridines and derivatives of the novel benzo[b]thieno[3,2-h][1,6]naphthyridine tetracyclic system

Recently 1-hydroxyacridone derivatives were described as a new class of non-nucleoside inhibitors of Herpes Simplex Virus-1 (HSV-1), the agent of the most common human diseases. Based on these molecules, we applied rigid analogue and isosteric replacement approaches to design and synthesize five new benzo(b)thieno(3,2-h)-1,6-naphthyridines derivatives 8a-e as feasible anti-HSV prototypes. Herein we described the synthesis of this series of compounds and a theoretical evaluation of the drug score and drug likeness of these compounds by using an in silico ADMET screening.

Synthesis of Novel Rigid Analogs of Tryptamine as Potential Serotonin Ligands through Pd(0)-Catalyzed Diaryl Coupling Reactions

A series of novel tetracyclic 6-thia-5a-aza-acephenanthrylene derivatives 7 were synthesized by rigidization of the arylsulfonyl/carbonyl/methyl moiety through C7 of indole, which was achieved under Heck conditions. The strategy of altering the palladium–bromine exchange site produced target products.

‘Hybrid’ benzofuran–benzopyran congeners as rigid analogs of hallucinogenic phenethylamines

Phenylalkylamines that possess conformationally rigidified furanyl moieties in place of alkoxy arene ring substituents have been shown previously to possess the highest affinities and agonist functional potencies at the serotonin 5-HT 2A receptor among this chemical class. Further, affinity declines when both furanyl rings are expanded to the larger dipyranyl ring system. The present paper reports the synthesis and pharmacological evaluation of a series of ‘hybrid’ benzofuranyl–benzopyranyl phenylalkylamines to probe further the sizes of the binding pockets within the serotonin 5-HT 2A agonist binding site. Thus, 4( a– b), 5( a– b), and 6 were prepared as homologs of the parent compound, 8-bromo-1-(2,3,6,7-tetrahydrobenzo[1,2- b:4,5- b′]difuran-4-yl)-2-aminopropane 2, and their affinity, functional potency, and intrinsic activity were assessed using cells stably expressing the rat 5-HT 2A receptor. The behavioral pharmacology of these new analogs was also evaluated in the two-lever drug discrimination paradigm. Although all of the hybrid isomers had similar, nanomolar range receptor affinities, those with the smaller furanyl ring at the arene 2-position ( 4a– b) displayed a 4- to 15-fold greater functional potency than those with the larger pyranyl ring at that position ( 5a– b). When the furan ring of the more potent agonist 4b was aromatized to give 6, a receptor affinity similar to the parent difuranyl compound 2 was attained, along with a functional potency equivalent to 2, 4a, and 4b. In drug discrimination experiments using rats trained to discriminate LSD from saline, 4b was more than two times more potent than 5b, with the latter having a potency similar to the classic hallucinogenic amphetamine 1 (DOB).

Tetrahydronaphthyl azole oxime ethers: The conformationally rigid analogues of oxiconazole as antibacterials

A series of novel ( Z)- and ( E)-2-imidazolo-/triazolo-methyl tetrahydronaphthyl oxime ethers ( 7– 28) were synthesized as conformationally constrained analogues of oxiconazole and evaluated for antifungal and antibacterial activities. Many of these derivatives exhibited potent antibacterial activity and surprisingly none of them was active against fungal strains. The SAR studies showed that imidazole oxime ethers were more active than the corresponding triazole oxime ethers. Imidazole derivatives 8, 11, 12, 15, 18, 19, 21 and 23 exhibited high inhibitory activity with 1.56–0.39 μg/mL MIC values against Klebsiella pneumoniae, Escherichia coli and Staphylococcus aureus. These compounds represent new structure scaffolds that can be further optimized to give new antibacterial agents with structures significantly different from those of existing classes of antibiotics.

Cannabinoid CB1 receptor antagonists in therapeutic and structural perspectives

The observed antiobesity effect of rimonabant (1) in a pharmacological rodent model 10 years ago has led to a surge in the search for novel cannabinoid CB1 antagonists as a new therapeutic target for the treatment of obesity. Rimonabant showed clinical efficacy in the treatment of obesity and also improved cardiovascular and metabolic risk factors. Cannabinoid CB1 receptor antagonists have also good prospects in other therapeutic areas, including smoking and alcohol addiction as well as cognitive impairment. Solvay's research achievements in this fast-moving field are reported in relation with the current state of the art. Several medicinal chemistry strategies have been pursued. The application of the concept of conformational constraint led to the discovery of more rigid analogs of the prototypic CB1 receptor antagonist rimonabant. Replacement of the central heterocyclic pyrazole ring in rimonabant yielded imidazoles, triazoles, and thiazoles as selective CB1 receptor antagonists. Dedicated medium-throughput screening efforts delivered one 3,4-diarylpyrazoline hit. Its poor pharmacokinetic properties were successfully optimized which led to the discovery of orally active and highly CB1/CB2 receptor selective analogs in this series. Regioisomeric 1,5-diarylpyrazolines, 1,2-diarylimidazolines, and water-soluble imidazoles have been designed as novel CB1 receptor antagonist structure classes.

SAR of a series of anti-HSV-1 acridone derivatives, and a rational acridone-based design of a new anti-HSV-1 3 H-benzo[ b]pyrazolo[3,4- h]-1,6-naphthyridine series

Herpes Simplex Virus (HSV) infections are among the most common human diseases. In this work, we assess the structural features and electronic properties of a series of ten 1-hydroxyacridone derivatives ( 1a– j) recently described as a new class of non-nucleoside inhibitors of Herpes Simplex Virus-1 (HSV-1). Based on these molecules, we applied rigid analogue and isosteric replacement approaches to design and synthesize nine new 3 H-benzo[ b]pyrazolo[3,4- h]-1,6-naphthyridine derivatives ( 2a– i). The biological and computational results of these new molecules were compared with 1-hydroxyacridones. An inhibitory profile was observed in 10-Cl substituted 3 H-benzo[ b]pyrazolo[3,4- h]-1,6-naphthyridine derivative ( 2f), which presents the same substituent at the analogous position of 1-hydroxyacridone derivative ( 1b). The structure–activity relationship (SAR) studies pointed out the 10-position next to nitrogen atom as important for the anti-HSV-1 profile in the pyrazolo-naphthyridine derivatives tested, which reinforced the promising profile for further experimental investigation. The most potent acridone and pyrazolo-naphthridine derivatives were also submitted to an in silico ADMET screening in order to determine their overall drug-score, which confirmed their potential antiviral profile.

Solid-Phase Synthesis and Insights into Structure−Activity Relationships of Safinamide Analogues as Potent and Selective Inhibitors of Type B Monoamine Oxidase

Safinamide, (S)-N2-{4-[(3-fluorobenzyl)oxy]benzyl}alaninamide methanesulfonate, which is in phase III clinical trials as an anti-Parkinson drug, and a library of alkanamidic analogues were prepared through an expeditious solid-phase synthesis and evaluated for their monoamine oxidase B (MAO-B) and monoamine oxidase A (MAO-A) inhibitory activity and selectivity. (S)-3-Chlorobenzyloxyalaninamide (8) and (S)-3-chlorobenzyloxyserinamide (13) derivatives proved to be more potent MAO-B inhibitors than safinamide (IC50 = 33 and 43 nM, respectively, vs 98 nM) but with a lower MAO-B selectivity (SI = 3455 and 1967, respectively, vs 5918). The highest MAO-B inhibitory potency (IC50 = 17 nM) and a good selectivity (SI = 2941) were displayed by (R)-21, a tetrahydroisoquinoline analogue of safinamide. Structure-affinity relationships and docking simulations pointed out strong negative steric effects of alpha-aminoamide side chains and para substituents of the benzyloxy groups and favorable hydrophobic interactions of meta substituents. The significantly diverse MAO-B affinities of a number of R and S alpha-aminoamide enantiomers, including the two rigid analogues (21) of safinamide, indicated likely enantioselective interactions at the enzymatic binding sites.

Rational design of a novel, potent, and orally bioavailable cyclohexylamine DPP-4 inhibitor by application of molecular modeling and X-ray crystallography of sitagliptin

Molecular modeling was used to design a rigid analog of sitagliptin 1. The X-ray crystal structure of sitagliptin bound to DPP-4 suggested that the central β-amino butyl amide moiety could be replaced with a cyclohexylamine group. This was confirmed by structural analysis and the resulting analog 2a was synthesized and found to be a potent DPP-4 inhibitor (IC 50 = 21 nM) with excellent in vivo activity and pharmacokinetic profile.

Preparation of novel anthranilic acids as antibacterial agents. Extensive evaluation of alternative amide bioisosteres connecting the A- and the B-rings

In the past few years, a significant effort has been devoted by Pharmacia toward the discovery of novel antibiotics. We have recently described the identification of an anthranilic acid lead 1 and the optimization resulting in the advanced lead 2. In this report, we describe the preparation of several selected amide bioisosteres connecting the A- and the B-rings. The E-alkene provided a rigid analog with equal potency to the corresponding amide. This indicates that the amide is not a recognition element rather acts as an appropriate spatial linker of the two important aryl A and B rings. The work here clearly demonstrates that the amide linker can be replaced with several functionalities without significant deterioration in the MIC activity.

Glutamine vinyl ester proteasome inhibitors selective for trypsin-like (β2) subunit

Here we report the study of a new series of peptide-based proteasome inhibitors with a vinyl ester moiety at C-terminal. The presence of Tic, a rigid analogue of phenylalanine, in the central portion of some derivatives is not favourable for the activity. The best analogue of the series shows a potent and selective inhibition for the β2 subunit and good enzymatic stability.

Synthesis of isoquinuclidine analogs of chloroquine: Antimalarial and antileishmanial activity

The isoquinuclidine (2-azabicyclo[2.2.2]octane) ring system may be viewed as a semi-rigid boat form of the piperidine ring and, when properly substituted, a scaffold for rigid analogs of biologically active ethanolamines and propanolamines. It is present in natural products (such as ibogaine and dioscorine) that display interesting pharmacological properties. In this study, we have expanded our continuing efforts to incorporate this ring system in numerous pharmacophores, by designing and synthesizing semirigid analogs of the antimalarial drug chloroquine. The analogs were tested in vitro against Plasmodium falciparum strains and Leishmania donovani promastigote cultures. Compounds 6 and 13 displayed potent antimalarial activity against both chloroquine-susceptible D6 and the -resistant W2 strains of P. falciparum. All analogs also demonstrated significant antileishmanial activity with compounds 6 and 13 again being the most potent. The fact that these compounds are active against both chloroquine-resistant and chloroquine-sensitive strains as well as leishmanial cells makes them promising candidates for drug development.