Molecular design, synthesis, and hypoglycemic activity of a series of thiazolidine-2,4-diones

Synthetic Strategies of Thiazolidine-2,4-dione Derivatives for the Development of New Anti-diabetic Agents: Compressive Review

BACKGROUND

Thiazolidine-2,4-dione (2,4-TZD) is a flexible pharmacophore and a privileged platform and contains a five-membered ring with a 2-oxygen atom with double bond 2,4- position and one nitrogen atom as well as sulphur containing in the heterocyclic compound. A famous electron-rich nitrogen transporter combines invigorating electronic properties with the prospective for elemental applications. Thiazolidine-2,4-dione analogues have been synthesized using a variety of methods, all of which have shown to have a strong biological effect.

OBJECTIVES

The study of the biological activity of Thiazolidine-2,4-dione derivatives has been a fascinating field of pharmaceutical chemistry and has many purposes. This derivative described in the literature between 1995 to 2023 was the focus of this study. Thiazolidine-2,4-diones have been discussed in terms of their introduction, general method, synthetic scheme and antidiabetic significance in the current review.

CONCLUSION

Thiazolidine-2,4-diones are well-known heterocyclic compounds. The synthesis of Thiazolidine-2,4-diones has been described using a variety of methods. Antidiabetic activity has been discovered in several Thiazolidine-2,4-dione derivatives, which enhance further research. The use of Thiazolidine-2,4-diones to treat antidiabetics has piqued researchers' interest in learning more about thiazolidine-2,4-diones.

Peroxisome Proliferator-Activated Receptors as Superior Targets for Treating Diabetic Disease, Design Strategies - Review Article

Thiazolidinedione (TZD), a class of drugs that are mainly used to control type 2 diabetes mellitus (T2DM), acts fundamentally as a ligand of peroxisome proliferator-activated receptors (PPARs). Besides activating pathways responsible for glycemic control by enhancing insulin sensitivity and lipid homeostasis, activating PPARs leads to exciting other pathways related to bone formation, inflammation, and cell proliferation. Unfortunately, this diverse effect of activating several pathways may show in some studies adverse health outcomes as osteological, hepatic, cardiovascular, and carcinogenic effects. Thus, a silver demand is present to find and develop new active and potent antiglycemic drugs for treating T2DM. To achieve this goal, the structure of TZD for research is considered a leading structure domain. This review will guide future research in the design of novel TZD derivatives by highlighting the general modifications conducted on the structure component of TZD scaffold affecting their potency, binding efficacy, and selectivity for the control of T2DM.

Anti-Diabetic Potentials of Thiazolidinedione Analogues with Efficient Synthetic Procedures: A Review of Literature

Background::

Diabetes mellitus refers to one of the leading cause of diseases that affect large populations of human and is characterized by a high glucose level in the blood (also known as hyperglycemia). Thiazolidinedione (TZD) is a five-member heterocyclic compound consisting of three carbons, nitrogen and sulfur. It is also known as glitazones, can be used as potent hypoglycemic agents and is also reduce many other cardiovascular risk factors including percutaneous coronary intervention, carotid and coronary atherosclerosis. As it plays a very important role in the field of medicinal chemistry or pharmaceutical sciences, novel medicine developed and many are on underdevelopment, these derivatives have thiazolidinedione as their primary nucleus.

Objective::

This article has discussed the different synthetic procedures of thiazolidinediones that exhibited potential antidiabetic activity by the activation of PPAR-γ, by reducing the blood glucose levels and by different metabolic process incorporation.

Conclusion::

Thiazolidinediones has effective profile as the future investigational drug and can be processed in drug discovery because of its efficient anti-diabetic potential.

Thiazolidinediones: An In-Depth Study of Their Synthesis and Application to Medicinal Chemistry in the Treatment of Diabetes Mellitus

2,4-Thiazolidinedione (TZD) is a privileged and highly utilised scaffold for the development of pharmaceutically active compounds. This sulfur-containing heterocycle is a versatile pharmacophore that confers a diverse range of pharmacological activities. TZD has been shown to exhibit biological action towards a vast range of targets interesting to medicinal chemists. In this review, we attempt to provide insight into both the historical conventional and the use of novel methodologies to synthesise the TZD core framework. Further to this, synthetic procedures utilised to substitute the TZD molecule at the activated methylene C5 and N3 position are reviewed. Finally, research into developing clinical agents, which act as modulators of peroxisome proliferator-activated receptors gamma (PPARγ), protein tyrosine phosphatase 1B (PTP1B) and aldose reductase 2 (ALR2), are discussed. These are the three most targeted receptors for the treatment of diabetes mellitus (DM).

The Journey of Thiazolidinediones as Modulators of PPARs for the Management of Diabetes: A Current Perspective

Peroxisome Proliferator-Activated Receptors (PPARs) also known as glitazone receptors are a family of receptors that regulate the expression of genes and have an essential role in carbohydrate, lipid and protein metabolism apart from other functions. PPARs come in 3 sub-types: PPAR-α, PPAR-β/δ and PPAR-γ - with PPAR-γ having 2 isoforms - γ1 and γ2. Upon activation, the PPARs regulate the transcription of various genes involved in lipid and glucose metabolism, adipocyte differentiation, increasing insulin sensitivity, prevention of oxidative stress and to a certain extent, modulation of immune responses via macrophages that have been implicated in the pathogenesis of insulin resistance. Hence, PPARs are an attractive molecular target for designing new anti-diabetic drugs. This has led to a boost in the research efforts directed towards designing of PPAR ligands - particularly ones that can selectively and specifically activate one or more of the PPAR subtypes. Though, PPAR- γ full agonists such as Thiazolidinediones (TZDs) are well established agents for dyslipidemia and type 2 diabetes mellitus (T2D), the side effect profile associated with TZDs has potentiated an imminent need to come up with newer agents that act through this pathway. Several newer derivatives having TZD scaffold have been designed using structure based drug designing technique and computational tools and tested for their PPAR binding affinity and efficacy in combating T2D and some have shown promising activities. This review would focus on the role of PPARs in the management of T2D; recently reported TZD derivatives which acted as agonists of PPAR- γ and its subtypes and are potentially useful in the new drug discovery for the disease.

An overview on medicinal perspective of thiazolidine-2,4-dione: A remarkable scaffold in the treatment of type 2 diabetes

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TZDs, an important pharmacophore in the treatment of diabetes.

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Various analog-based synthetic strategies and biological significance are discussed.

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Clinical studies using TZDs along with other antidiabetic agents are also highlighted.

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SAR has been discussed to suggest the interactions between derivatives and receptor sites.

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Pyrazole, chromone, and acid-based TZDs can be considered as potential lead molecules.

Diabetes or diabetes mellitus is a complex or polygenic disorder, which is characterized by increased levels of glucose (hyperglycemia) and deficiency in insulin secretion or resistance to insulin over an elongated period in the liver and peripheral tissues. Thiazolidine-2,4-dione (TZD) is a privileged scaffold and an outstanding heterocyclic moiety in the field of drug discovery, which provides various opportunities in exploring this moiety as an antidiabetic agent. In the past few years, various novel synthetic approaches had been undertaken to synthesize different derivatives to explore them as more potent antidiabetic agents with devoid of side effects (i.e., edema, weight gain, and bladder cancer) of clinically used TZD (pioglitazone and rosiglitazone). In this review, an effort has been made to summarize the up to date research work of various synthetic strategies for TZD derivatives as well as their biological significance and clinical studies of TZDs in combination with other category as antidiabetic agents. This review also highlights the structure-activity relationships and the molecular docking studies to convey the interaction of various synthesized novel derivatives with its receptor site.

Synthesis and Investigation on the Antidiabetic Effect of 3-aryl-1-(5-methylisoxazol-3-ylamino)-1-(4-nitrophenyl) Propan-1-one

Background:

Diabetes mellitus is the third-largest non-communicable chronic disease worldwide. There are many effective drugs, but the long-term use of these clinical drugs may cause various side effects. Therefore, it is urgent to develop new antidiabetic molecules with higher efficacy and lower toxicity.

Methods:

Fifteen new 3-aryl-1-(5-methylisoxazol-3-ylamino)-1-(4-nitrophenyl)propan-1-one were synthesized directly through the Mannich reaction of 4-nitroacetophenone, 3-amino-5- methylisoxazole and aromatic aldehydes catalyzed by concentrated hydrochloric acid. The molecular structures of the products were fully characterized by 1H NMR, 13C NMR, ESI MS and HRMS. The peroxisome proliferator-activated receptor (PPAR) response element and α-glucosidase inhibitory activity of these compounds were evaluated in vitro. Molecular docking, molecular physical parameters calculation, and molecular toxicity prediction were performed to analyze the structure- activity relationship and evaluate the druggability of these compounds theoretically.

Results:

All compounds exhibited weak antidiabetic activities, but compound 15 showed promising as a high performance, dual-target antidiabetic lead compound with peroxisome proliferatoractivated receptor (PPAR) response element relative agonist activity of 99.55% at 27.2 nmol·mL−1 and α-glucosidase inhibitory activity of 35.21% at 13.6 nmol·mL−1. All compounds obtained may have no cardiotoxicity, no acute toxicity, no carcinogenic, and within safe range of mutagenic risk.

Conclusion:

This study identified a potential PPAR lead molecule and presented an unusual strategy for antidiabetic drug development.

New N-phenyl-4,5-dibromopyrrolamides as DNA gyrase B inhibitors

Due to the rapid development of antimicrobial resistance, the discovery of new antibacterials is essential in the fight against potentially lethal infections. The DNA gyrase B (GyrB) subunit of bacterial DNA gyrase is an excellent target for the design of antibacterials, as it has been clinically validated by novobiocin. However, there are currently no drugs in clinical use that target GyrB. We prepared a new series of N-phenyl-4,5-dibromopyrrolamides and evaluated them against DNA gyrase and against the structurally and functionally similar enzyme, topoisomerase IV. The most active compound, 28, had an IC₅₀ of 20 nM against Escherichia coli DNA gyrase. The IC₅₀ values of 28 against Staphylococcus aureus DNA gyrase, and E. coli and S. aureus topoisomerase IV were in the low micromolar range. However, the compounds evaluated did not show significant antibacterial activities against selected Gram-positive and Gram-negative bacteria. Our results indicate that for potent inhibition of DNA gyrase, a combination of polar groups on the carboxylic end of the molecule and substituents that reach into the 'lipophilic floor' of the enzyme is required.

Targeting Peroxisome Proliferator-Activated Receptors Using Thiazolidinediones: Strategy for Design of Novel Antidiabetic Drugs

Thiazolidinediones are a class of well-established antidiabetic drugs, also named as glitazones. Thiazolidinedione structure has been an important structural domain of research, involving design and development of new drugs for the treatment of type 2 diabetes. Extensive research on the mechanism of action and the structural requirements has revealed that the intended antidiabetic activity in type 2 diabetes is due to their agonistic effect on peroxisome proliferator-activated receptor (PPAR) belonging to the nuclear receptor super family. Glitazones have specific affinity to PPARγ, one of the subtypes of PPARs. Certain compounds under development have dual PPARα/γ agonistic activity which might be beneficial in obesity and diabetic cardiomyopathy. Interesting array of hybrid compounds of thiazolidinedione PPARγ agonists exhibited therapeutic potential beyond antidiabetic activity. Pharmacology and chemistry of thiazolidinediones as PPARγ agonists and the potential of newer analogues as dual agonists of PPARs and other emerging targets for the therapy of type 2 diabetes are presented. This review highlights the possible modifications of the structural components in the general frame work of thiazolidinediones with respect to their binding efficacy, potency, and selectivity which would guide the future research in design of novel thiazolidinedione derivatives for the management of type 2 diabetes.

A 2,7-diamino-1,4,8-triazanaphthalene derivative selectively binds to cytosine bulge DNA only at a weakly acidic pH

The synthesis and properties of 2,7-diamino-1,4,8-triazanaphthalene (azaDANP) are described. AzaDANP is protonated only at a weakly acidic pH to bind to the cytosine bulge DNA duplex selectively. Upon binding of azaDANP to the cytosine bulge DNA, a new absorption band at 407 nm appears, and the absorption change of azaDANP on binding to the target is very sensitive to environmental pH with a bell-shaped pH-absorption profile.

Design, synthesis, molecular modeling and anti-hyperglycemic evaluation of novel quinoxaline derivatives as potential PPARγ and SUR agonists

In our effort to develop potent anti-hyperglycemic agents with potential agonistic activities toward PPARγ and SUR, three novel series of quinoxaline derivatives bearing sulfonylurea or sulfonylthiourea moieties with different linkers were designed and synthesized. Some of the newly synthesized compounds were evaluated in vivo for their anti-hyperglycemic activities in STZ-induced hyperglycemic rats. Compounds 15_a, 15_e, 19_b and 24_a exhibited the highest anti-hyperglycemic activities with % reduction in blood glucose level of (50.58, 43.84, 45.10 and 49.62, respectively). Additionally, eight compounds revealed potent anti-hyperglycemic activities were further evaluated in vitro for their PPARγ binding affinity and insulin-secreting ability as potential mechanisms for anti-hyperglycemic activity. Four compounds (15_a, 15_b, 15_d and 15_e) significantly bound to PPARγ with IC₅₀ values of 0.482, 0.491, 0.350 and 0.369μM, respectively. Moreover, Compounds 15_a and 15_b have demonstrated induction of insulin-secretion with EC₅₀ values of 0.92 and 0.98μM, respectively. Furthermore, molecular docking and pharmacophore generation techniques were carried out to investigate binding patterns and fit values of the designed compounds with PPARγ and SUR, respectively.

Thiazolidinediones and PPAR orchestra as antidiabetic agents: From past to present

Thiazolidinediones a class of drug, that provided a major breakthrough in the management of type 2 diabetes since 1990. Following the discovery of PPARs, TZDs were the first class to be reported as PPARγ modulators. This review is an attempt to summarize the chemical modifications around TZDs in past two decades to obtain a potent antidiabetic molecule. TZDs literature were initially dominated by their hypoglycemic & hypolipidemic activities, later PPARγ activity was also been incorporated. Moreover, in some cases, both benzyl and benzylidene derivatives were reported in the same manuscript for the sake of comparison. We thought of presenting the review on the basis of the variation in the linker region. Optimal linker at the time of discovery of the Ciglitazone was oxymethyl and it went on to evolve as oxyethyl (Pioglitazone) and oxyethylamino (Rosiglitazone). Few attempts were made to restrict the flexibility of the linker by introducing the cyclic structures and were summarized immediately after the respective linker class.

Solvent-free synthesis of novel vanillidene derivatives of Meldrum's acid: biological evaluation, DNA and BSA binding study

A series of novel O-alkyl vanillidene derivatives containing Meldrum's acid scaffold under solvent-free conditions were synthesized.

Tautomerization, molecular structure, transition state structure, and vibrational spectra of 2-aminopyridines: a combined computational and experimental study

Background

2-amino pyridine derivatives have attracted considerable interest because they are useful precursors for the synthesis of a variety of heterocyclic compounds possessing a medicinal value. In this work we aim to study both structural and electronic as well as high quality vibrational spectra for 2-amino-3-methylpyridine (2A3MP) and 2-amino-4-methylpyridine (2A4MP).

Results

Møller–Plesset perturbation theory (MP2/6-31G(d) and MP2/6-31++G(d,p) methods were used to investigate the structure and vibrational analysis of (2A3MP) and (2A4MP). Tautomerization of 2A4MP was investigated by Density Functional Theory (DFT/B3LYP) method in the gas phase. For the first time, all tautomers including NH → NH conversions as well as those usually omitted, NH → CH and CH → CH, were considered. The canonical structure (2A4MP1) is the most stable tautomer. It is 13.60 kcal/mole more stable than the next (2A4MP2). Transition state structures of pyramidal N inversion and proton transfer were computed at B3LYP/6-311++G(d,p). Barrier to transition state of hydrogen proton transfer is calculated as 44.81 kcal/mol. Transition state activation energy of pyramidal inversion at amino N is found to be 0.41 kcal/mol using the above method. Bond order and natural atomic charges were also calculated at the same level. The raman and FT-IR spectra of (2A3MP) and (2A4MP) were measured (4000–400 cm⁻¹). The optimized molecular geometries, frequencies and vibrational bands intensity were calculated at ab initio (MP2) and DFT(B3LYP) levels of theory with 6-31G(d), 6-31++G(d,p) and 6-311++G(d,p) basis sets. The vibrational frequencies were compared with experimentally measured FT-IR and FT-Raman spectra.

Conclusion

Reconsidering the vibrational analysis of (2A3MP) and (2A4MP) with more accurate FT-IR machine and highly accurate animation programs result in new improved vibrational assignments. Sophisticated quantum mechanics methods enable studying the transition state structure for different chemical systems.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-015-1363-2) contains supplementary material, which is available to authorized users.

N-Phenyl-4,5-dibromopyrrolamides and N-Phenylindolamides as ATP Competitive DNA Gyrase B Inhibitors: Design, Synthesis, and Evaluation

Bacterial DNA gyrase is a well-known and validated target in the design of antibacterial drugs. However, inhibitors of its ATP binding subunit, DNA gyrase B (GyrB), have so far not reached clinical use. In the present study, three different series of N-phenyl-4,5-dibromopyrrolamides and N-phenylindolamides were designed and prepared as potential DNA gyrase B inhibitors. The IC50 values of compounds on DNA gyrase from Escherichia coli were in the low micromolar range, with the best compound, (4-(4,5-dibromo-1H-pyrrole-2-carboxamido)benzoyl)glycine (18a), displaying an IC50 of 450 nM. For this compound, a high-resolution crystal structure in complex with E. coli DNA gyrase B was obtained, revealing details of its binding mode within the active site. The binding affinities of three compounds with GyrB were additionally evaluated by surface plasmon resonance, and the results were in good agreement with the determined enzymatic activities. For the most promising compounds, the inhibitory activities against DNA gyrase from Staphylococcus aureus and topoisomerases IV from E. coli and S. aureus were determined. Antibacterial activities of the most potent compounds of each series were evaluated against two Gram-positive and two Gram-negative bacterial strains. The results obtained in this study provide valuable information on the binding mode and structure-activity relationship of N-phenyl-4,5-dibromopyrrolamides and N-phenylindolamides as promising classes of ATP competitive GyrB inhibitors.

Design and synthesis of heterocyclic cations for specific DNA recognition: from AT-rich to mixed-base-pair DNA sequences

The compounds synthesized in this research were designed with the goal of establishing a new paradigm for mixed-base-pair DNA sequence-specific recognition. The design scheme starts with a cell-permeable heterocyclic cation that binds to AT base pair sites in the DNA minor groove. Modifications were introduced in the original compound to include an H-bond accepting group to specifically recognize the G-NH that projects into the minor groove. Therefore, a series of heterocyclic cations substituted with an azabenzimidazole ring has been designed and synthesized for mixed-base-pair DNA recognition. The most successful compound, 12a, had an azabenzimidazole to recognize G and additional modifications for general minor groove interactions. It binds to the DNA site -AAAGTTT- more strongly than the -AAATTT- site without GC and indicates the design success. Structural modifications of 12a generally weakened binding. The interactions of the new compound with a variety of DNA sequences with and without GC base pairs were evaluated by thermal melting analysis, circular dichroism, fluorescence emission spectroscopy, surface plasmon resonance, and molecular modeling.

K10 montmorillonite clays as environmentally benign catalysts for organic reactions

This perspective summarizes the catalytic activity of K10 montmorillonite as a multifunctional catalyst for organic reactions.

Recent pharmacological developments on rhodanines and 2,4-thiazolidinediones

Thiazolidines are five-member heterocyclic having sulfur, nitrogen, and oxygen atoms in their ring structure and exhibiting potent as well as wide range of pharmacological activities. In this minireview, recent updates on synthesis and pharmacological evaluations of molecules based on 2,4-thiazolidine and rhodanine are discussed.

SAR and Computer-Aided Drug Design Approaches in the Discovery of Peroxisome Proliferator-Activated Receptor γ Activators: A Perspective

Activators of PPARγ, Troglitazone (TGZ), Rosiglitazone (RGZ), and Pioglitazone (PGZ) were introduced for treatment of Type 2 diabetes, but TGZ and RGZ have been withdrawn from the market along with other promising leads due cardiovascular side effects and hepatotoxicity. However, the continuously improving understanding of the structure/function of PPARγ and its interactions with potential ligands maintain the importance of PPARγ as an antidiabetic target. Extensive structure activity relationship (SAR) studies have thus been performed on a variety of structural scaffolds by various research groups. Computer-aided drug discovery (CADD) approaches have also played a vital role in the search and optimization of potential lead compounds. This paper focuses on these approaches adopted for the discovery of PPARγ ligands for the treatment of Type 2 diabetes. Key concepts employed during the discovery phase, classification based on agonistic character, applications of various QSAR, pharmacophore mapping, virtual screening, molecular docking, and molecular dynamics studies are highlighted. Molecular level analysis of the dynamic nature of ligand-receptor interaction is presented for the future design of ligands with better potency and safety profiles. Recently identified mechanism of inhibition of phosphorylation of PPARγ at SER273 by ligands is reviewed as a new strategy to identify novel drug candidates.

Efficient α-chlorination of 2-[(1-oxocyclohex-2-en-2-yl)methyl]-1,3-dicarbonyl Compounds Using Sodium Hypochlorite

A rapid and efficient regioselective α-chlorination of a new series of β-dicarbonyl compounds using a commercial solution of sodium hypochlorite in the presence of K2CO3 in THF at 0 °C, is reported. With prolonged reaction times, α-chloro β-keto esters, bearing an acyl moiety, undergo a tandem chlorination–deacylation reaction, affording the corresponding α-chlorinated esters.

A Solvent-Free Protocol for the Green Synthesis of 5-Arylidene-2,4-thiazolidinediones Using Ethylenediamine Diacetate as Catalyst

A simple and efficient synthesis of 5-arylidene-2,4-thiazolidinediones by the Knoevenagel condensation of aromatic aldehydes with 2,4-thiazolidinedione catalyzed by ethylenediamine diacetate under solvent-free conditions is described. The major advantages of this method are simple experimental and work-up procedures, solvent-free reaction conditions, small amount of catalyst, short reaction time, high yields, and utilization of an inexpensive and reusable catalyst.

Investigation of the insulin-like properties of zinc(II) complexes of 3-hydroxy-4-pyridinones: identification of a compound with glucose lowering effect in STZ-induced type I diabetic animals

Results from an investigation in an in vivo model of STZ-induced diabetic rats demonstrate that compound bis(1,2-dimethyl-3-hydroxy-4(1H)-pyridinonate)zinc(II), Zn(dmpp)(2), significantly lowers the blood glucose levels of individuals, thus showing evidence of glucose lowering activity. The compound was selected from a set of eight zinc(II) complexes of 3-hydroxy-4-pyridinones with diverse lipophilicity that were prepared and characterized in our laboratory. Assessment of insulin-like activity of the complexes was firstly performed in vitro by measuring the inhibition of FFA release in isolated rat adipocytes. The results indicate that compounds bis(2-methyl-3-hydroxy-4-pyridinonate)zinc(II), Zn(mpp)(2) and Zn(dmpp)(2) display significantly higher activity than that of the respective positive control thus suggesting its selection for in vivo tests. Safety evaluation of the active zinc(II) compounds was performed in freshly isolated rat hepatocytes. The results support that cell viability is not significantly different from the control set after 1 and 2h of incubation with both zinc(II) complexes.

The design and synthesis of potent and cell-active allosteric dual Akt 1 and 2 inhibitors devoid of hERG activity

This letter details the attenuation of hERG in a class of Akt inhibitors through heteroatom insertions into aromatic rings. The development of a cell-active dual Akt 1 and 2 inhibitors devoid of hERG activity is discussed using structure-activity relationships.

QSAR analysis of PPAR-γ agonists as anti-diabetic agents

QSAR studies have been performed on some PPAR-gamma agonists using TATA-BioSuite software to identify the essential structural and physico-chemical features for their PPAR-gamma agonistic activity. The 23 compounds were divided into training set of 18 and test set of five compounds using k-nearest neighbor (kNN) clustering. The steric, electronic and topological descriptors were found to have an important role in governing the variation in agonistic activity. The predicted activities by the developed models were in good accordance with the observed activities.

A consideration of PPAR-gamma ligands with respect to lipophilicity: current trends and perspectives

The fact that PPAR-gamma is expressed dramatically higher in fat, regulating gene transcription in response to small lipophilic ligands, supports an essential role of increased lipophilicity for those ligands. On the other hand, the skepticism concerning high lipophilicity as a characteristic associated with undesirable effects and formulation problems raises the question of how much lipophilicity should be incorporated in the ligand molecules so that they comply with generally accepted guidelines. A survey on the lipophilic behavior of thiazolidinediones and tyrosine-based derivatives with well-established PPAR-gamma affinity and functional activity suggests that excessive lipophilicity may not be favorable for their action.