Structure-activity Relationship Considerations Research Articles

The opioid receptor: emergence through millennia of pharmaceutical sciences.

Throughout history humanity has searched for an optimal approach to the use of opioids that maximizes analgesia while minimizing side effects. This review reflects upon the conceptualization of the opioid receptor and the critical role that the pharmaceutical sciences played in its revelation. Opium-containing formulations have been delivered by various routes of administration for analgesia and other therapeutic indications for millennia. The concept of a distinct site of opium action evolved as practitioners developed innovative delivery methods, such as intravenous administration, to improve therapeutic outcomes. The introduction of morphine and synthetic opioids engendered the prevalent assumption of a common opioid receptor. Through consideration of structure-activity relationships, spatial geometry, and pharmacological differences of known ligands, the idea of multiple opioid receptors emerged. By accessing the high-affinity property of naloxone, the opioid receptor was identified in central and peripheral nervous system tissue. The endogenous opioid neuropeptides were subsequently discovered. Application of mu-, delta-, and kappa- opioid receptor-selective ligands facilitated the pharmacological characterization and distinctions between the three receptors, which were later cloned and sequenced. Opioid receptor signal transduction pathways were described and attributed to specific physiological outcomes. The crystal structures of mu, delta, kappa, and nociceptin/orphanin FQ receptors bound to receptor-selective ligands have been elucidated. Comparison of these structures reveal locations of ligand binding and engagement of signal transduction pathways. Expanding knowledge regarding the structure and actions of the opioid receptor fuels contemporary strategies for driving the activity of opioid receptors toward maximizing therapeutic and minimizing adverse outcomes.

Survey on the Recent Advances in 4-Hydroxyphenylpyruvate Dioxygenase (HPPD) Inhibition by Diketone and Triketone Derivatives and Congeneric Compounds: Structural Analysis of HPPD/Inhibitor Complexes and Structure-Activity Relationship Considerations.

The serendipitous discovery of the HPPD inhibitors from allelopathic plants opened the way for searching new and effective herbicidal agents by application of classical hit-to-lead optimization approaches. A plethora of active and selective compounds were discovered that belong to three major classes of cyclohexane-based triketones, pyrazole-based diketones, and diketonitriles. In addition, to enhance inhibitory constant and herbicidal activity, many efforts were also made to gain broader weed control, crop safety, and eventual agricultural applicability. Moreover, HPPD inhibitors emerged as therapeutic agents for inherited and metabolic human diseases as well as vector-selective insecticides in the control of hematophagous arthropods. Given the large set of experimental data available, structure-activity relationship analysis could be used to derive suggestions for next generation optimized compounds.

New small molecule fluorescent probes for G protein-coupled receptors: valuable tools for drug discovery.

G protein-coupled receptors (GPCRs) are essential signaling proteins and tractable therapeutic targets. To develop new drug candidates, GPCR drug discovery programs require versatile, sensitive pharmacological tools for ligand binding and compound screening. With the availability of new imaging modalities and proximity-based ligand binding technologies, fluorescent ligands offer many advantages and are increasingly being used, yet labeling small molecules remains considerably more challenging relative to peptides. Focusing on recent fluorescent small molecule studies for family A GPCRs, this review addresses some of the key challenges, synthesis approaches and structure-activity relationship considerations, and discussesadvantages of using high-resolution GPCR structures to inform conjugation strategies. While no single approach guarantees successful labeling without loss of affinity or selectivity, the choice of fluorophore, linker type and site of attachment have proved to be critical factors that can significantly affect their utility in drug discovery programs, and as discussed, can sometimes lead to very unexpected results.

Pyrrolizidine alkaloids in food and phytomedicine: Occurrence, exposure, toxicity, mechanisms, and risk assessment - A review

Among naturally occurring plant constituents, the 1,2-unsaturated pyrrolizidine alkaloids (in the following termed ‘PAs’) play a distinct role because of the large number of congeners occurring in nature and the pronounced toxicity of some congeners. Several PAs are hepatotoxic in humans, experimental and farm animals and were shown to be potent hepatocarcinogens in laboratory rodents. Although the general mode of action leading to toxicity has been elucidated, i.e., being mediated by metabolic conversion of the parent molecule into a highly reactive electrophile capable of attacking cellular target molecules, major questions related to the risk assessment of PAs remain unresolved.It was the aim of a workshop held in September 2018 to shed more light on the occurrence, exposure, mode of action, toxicokinetics and –dynamics of PAs to improve the scientific basis for an advanced toxicological risk assessment. The contributions in nine chapters describe the scientific progress using advanced analytical methods, studies in subcellular fractions, cell culture, experimental animals and humans and the use of PBPK modeling and structure-activity relationship considerations aiming at a better understanding of PA toxicity and genotoxicity. Since PAs differ considerably in their toxic potencies and substantial species differences in sensitivity towards PA exposure exist, a special emphasis was placed on these issues.

Efficient synthetic methodology for the construction of dihydronaphthalene and benzosuberene molecular frameworks

Benzosuberene analogues (1 and 2) and dihydronaphthalene analogues (3 and 4) function as potent inhibitors of tubulin polymerization, demonstrate pronounced cytotoxicity (low nM to pM range) against human cancer cell lines, and are promising vascular disrupting agents (VDAs). As such, these compounds represent lead anticancer agents with potential translatability towards the clinic. Methodology previously established by us (and others) facilitated synthetic access to a variety of structural and functional group modifications necessary to explore structure activity relationship considerations directed towards the development of these (and related) molecules as potential therapeutic agents. During the course of these studies it became apparent that the availability of synthetic methodology to facilitate direct conversion of the phenolic-based compounds to their corresponding aniline congeners would be beneficial. Accordingly, modified synthetic routes toward these target phenols (benzosuberene 1 and dihydronaphthalene 3) were developed in order to improve scalability and overall yield [45-57% (1) and 32% (3)]. Moreover, benzosuberene-based phenolic analogue 1 and separately dihydronaphthalene-based phenolic analogue 3 were successfully converted into their corresponding aniline analogues 2 and 4 in good yield (>60% over three steps) using a palladium catalyzed amination reaction.

Medicinal chemistry insights in the discovery of novel LSD1 inhibitors.

LSD1 is an epigenetic modulator associated with transcriptional regulation of genes involved in a broad spectrum of key cellular processes, and its activity is often altered under pathological conditions. LSD1 inhibitors are considered to be candidates for therapy of cancer, viral diseases and neurodegeneration. Many LSD1 inhibitors with various scaffolds have been disclosed, and a few potent molecules are in different stages of clinical development. In this review, we summarize recent biological findings on the roles of LSD1 and the current understanding of the clinical significance of LSD1, and focus on the medicinal chemistry strategies used in the design and development of LSD1 inhibitors as drug-like epigenetic modulators since 2012, including a brief consideration of structure-activity relationships.

Bicyclic heterocyclic anthranilic diamides as ryanodine receptor modulators with insecticidal activity

The diamide insecticides act on the ryanodine receptor (RyR). The synthesis of various bicyclic anthranilic derivatives is reported. Their activity against the insect ryanodine receptor (RyR) and their insecticidal activity in the greenhouse is presented, as well as structure activity relationship considerations.

Vitamin K catabolite inhibition of ovariectomy‐induced bone loss: Structure–activity relationship considerations

The potential benefit of vitamin K as a therapeutic in osteoporosis is controversial and the vitamin K regimen being used clinically (45 mg/day) employs doses that are many times higher than required to ensure maximal gamma-carboxylation of the vitamin K-dependent bone proteins. We therefore tested the hypothesis that vitamin K catabolites, 5-carbon (CAN5C) and 7-carbon carboxylic acid (CAN7C) aliphatic side-chain derivatives of the naphthoquinone moiety exert an osteotrophic role consistent with the treatment of osteoporosis. Osteoblast-like MG63 cell cultures were challenged with lipopolysaccharide and the levels of interleukin-6, an osteoclastogenic cytokine, measured with and without catabolites; low concentrations of CAN7C significantly inhibited interleukin-6 release, but CAN5C did not. In models of bone loss induced by ovariectomy or sciatic neurectomy in C57BL/6 mice, we found that the rarer CAN7C catabolite markedly restricted ovariectomy-induced bone loss and possibly limited sciatic neurectomy-induced bone loss. CAN7C activity depends on a free carboxylic acid and its particular side-chain structure. These in vivo data indicate for the first time that the clinical utility of vitamin K for osteoporosis may reside in an unusual catabolite.

Structural basis of natural ligand binding and activation of the Class II G-protein-coupled secretin receptor

The secretin receptor is prototypic of Class II GPCRs (G-protein-coupled receptors), based on its structural and functional characteristics and those of its natural agonist ligand. Secretin represents a linear 27-residue peptide with diffuse pharmacophoric domain. The secretin receptor includes the typical signature sequences for this receptor family within its predicted transmembrane segments and the highly conserved six cysteine residues contributing to three intradomain disulfide bonds within its long N-terminus. This domain is critical for secretin binding based on receptor mutagenesis and photoaffinity labelling studies. Full agonist analogues of secretin incorporating a photolabile moiety at various positions throughout the pharmacophore covalently label residues within this region, while only N-terminal probes have labelled the core helical bundle domain. Combining insights coming from receptor structural studies, peptide structure-activity relationship considerations, photoaffinity labelling, and application of fluorescence techniques has resulted in the development of a working model of the secretin-receptor complex. This supports the initial docking of the peptide agonist within a cleft in the receptor N-terminus, providing the opportunity for an endogenous sequence within that domain to interact with the core of the receptor. This interaction is believed to be key in the molecular basis of conformational change associated with activation of this receptor. The site of action of this endogenous agonist could also provide a possible target for small molecule agonists to act.

Effects of ionic liquids on the acetylcholinesterase – a structure–activity relationship consideration

Ionic liquids are discussed as sustainable green solvents, but toxicity and ecotoxicity data are rare. In this paper we present our results for different ionic liquids with the acetylcholinesterase inhibition assay. The results show that the acetylcholinesterase can be inhibited by ionic liquids containing a cation with a positively charged nitrogen and a certain lipophilicity. We tested imidazolium ionic liquids with different alkyl chains at R1 and R2 as well as with different anions and compared these results with our findings for other cation structures such as pyridinium ionic liquids and phosphonium ionic liquids. According to our results imidazolium and pyridinium ionic liquids inhibit the purified enzyme with EC50 values as low as 13 μM. The bulky phosphonium ionic liquids were less inhibitory. These results can be rationalized by structure–activity relationship considerations.

Introduction of in vitro data into local irritation/corrosion testing strategies by means of SAR considerations: assessment of chemicals

The European legislation on control and evaluation of chemicals requires hazard and risk assessment of chemicals for human health and the environment. Technical guidance on carrying out this assessment includes the use of information based on results of testing with animals and on results of alternatives to animal testing. Within regulatory risk assessment the use of in vitro data for hazard and risk classification purposes is in the very beginning, because in vitro results do not mirror the total of effects observed in standardised animal tests, and hence cannot be easily related to current regulatory classification criteria. In vitro tests aim at the detection of only a few aspects considered crucial for the formation of a very complex health hazard observed in vivo. Therefore, they need a clear definition of the toxicological questions they can answer and of the limits of their evidence with respect to meeting regulatory classification criteria. In order to enhance the use of in vitro results within the regulatory classification procedure, the Organisation for Economic Co-operation and Development (OECD) developed tiered testing and assessment strategies that combine in vitro results and structure–activity relationship (SAR) considerations.

Development of a decision support system for the introduction of alternative methods into local irritancy/corrosivity testing strategies. Development of a relational database.

For new chemical substances that are notified within the European Union, data sets have to be submitted to the National Competent Authorities. The data submitted have to demonstrate the physicochemical and toxic properties of the new chemical, such as solubility, partition coefficients and spectra, as well as acute toxic properties and the potential to cause local irritant or corrosive effects. In order to minimise testing for notification purposes (for example, animal testing), it is necessary to develop stepwise assessment procedures, including structure-activity considerations, alternative methods (for example, in vitro tests), and computerised structure-activity relationship (SAR) models. An electronic database was developed which contains physicochemical and toxicological data on approximately 1300 chemical substances. It is used for regulatory structure-property relationship (SPR) and SAR considerations, and for the development of rules for a decision support system (DSS) for the introduction of alternative methods into local irritancy/corrosivity testing strategies. The information stored in the database is derived from proprietary data, so it is not possible to publish the data directly. Therefore, the database is evaluated by regulators, and the information derived from the data is used for the development of scientific information about SARs. This information can be published, for example, by means of tables correlating measured physicochemical values and specific toxic effects caused by the measured chemical. This information is introduced to the public by means of a DSS that predicts local irritant/corrosive potential of a chemical by listing so called exception rules of the kind IF (physicochemical property) A THEN not (toxic) Effect B and so-called structural rules of the kind IF Substructure A THEN Effect B. These DSS rules "translate" proprietary data into scientific knowledge that can be published.

Investigation of SAR requirements of SR 142801 through an indexed combinatorial library in solution

To rapidly gain information on structure-activity relationship (SAR) requirements of the human neurokinin 3 (hNK-3) receptor antagonist SR 142801, an indexed combinatorial library was synthesised in solution and screened on the hNK-3 receptor. SAR considerations drawn from binding affinity of combinatorial mixtures were confirmed through the synthesis and biological evaluation of some individual compounds.

Prediction of rodent carcinogenicity of further 30 chemicals bioassayed by the U.S. National Toxicology Program.

Recently the U.S. National Toxicology Program (NTP) sponsored a comparative exercise in which different prediction approaches (both biologically and chemically based) were challenged for their predictive abilities of rodent carcinogenicity of a common set of chemicals. The exercise enjoyed remarkable scientific success and stimulated NTP to sponsor a second challenging round of tests, inviting participants to present predictions relative to the rodent carcinogenicity of a further 30 chemicals; these are currently being tested. In this article, we present our predictions based on structure-activity relationship considerations. In our procedure, first each chemical was assigned to an activity mechanism class and then, with semiquantitative considerations, was assigned a probability carcinogenicity score, taking into account simultaneously the hypothesized action mechanism and physical chemical parameters.

Chiral dioxolane inhibitors of leukotriene biosynthesis: structure-activity relationships and syntheses using asymmetric dihydroxylation.

1,3-Dioxolanes have been described as chiral inhibitors of 5-lipoxygenase (5LO). In the present work, this series has been developed further to provide agents which showed comparable or superior potency in vivo to ZD2138, a methoxytetrahydropyran inhibitor of 5LO, which is currently undergoing clinical evaluation. An asymmetric synthesis was developed to these dioxolanes based on asymmetric dihydroxylation. (S)-N-Methyl-4'-[[4-(2,2,4- trimethyl-1,3-dioxolan-4-yl)thien-2-yl]thio]acetanilide ((S)-10d) inhibited leukotriene B4 (LTB4) synthesis in A23187-stimulated human whole blood in vitro with IC50 0.039 microM, 25-fold more potent than (R)-10d. In vivo, (S)-10d inhibited LTB4 synthesis by 70% in zymosan-inflamed air pouch exudate in rat 10 h after an oral dose of 1.5 mg/kg. Structure-activity relationship considerations suggested that the dioxolane and methoxytetrahydropyran series are related, a conclusion which can be supported by molecular modeling.

Synthesis and nidation inhibitory activity of a new class of ergoline derivatives

The synthesis and the nidation inhibitory activity (indirect evidence of prolactin activity) of a new class of ergolinyl-acylureas is described. Some structure—activity relationship considerations are also reported. N-[3-(Dimethyl-amino)propyl]- N-[(ethylamino)carbonyl]-6-(2-propenyl)ergoline-8β-carboxamide (laboratory code FCE 21336; international non-proprietary name cabergoline) was the most interesting compound of the series and is now under extensive clinical evaluation in treatment of hyperprolactinemic disorders.