pKa, Log P and MedChem CLOGP Fragment Values of Acidic Heterocyclic Potential Bioisosteres

New thieno[3,2-d]pyrimidine-based derivatives: Design, synthesis and biological evaluation as antiproliferative agents, EGFR and ARO inhibitors inducing apoptosis in breast cancer cells

An array of newly synthesized thieno[3,2-d]pyrimidine-based derivatives and thienotriazolopyrimidines hybridized with some pharmacophoric anticancer fragments were designed, synthesized and assessed for their in vitro antiproliferative activity against MCF-7 and MDA-MB-231 breast cancer cell lines using erlotinib and pictilisib as reference standards in the MTT assay. In general, many compounds were endowed with considerable antiproliferative activity (IC₅₀ = 0.43-1.31 µM). Some of the tested compounds, namely 3c, 5b, 5c, 9d, 10, 11b and 13 displayed remarkable antiproliferative activity against both cell lines. Meanwhile, compounds 2c-e, 3b, 4a, 5a, 9c and 15b showed noticeable selectivity against MCF-7 cells while compounds 2b, 3a, 4b, 6a-c, 7, 8, 9b and 12 exhibited considerable selectivity against MDA-MB-231 cells. Further mechanistic evidences for their anticancer activities were provided by screening the most potent compounds against MCF-7 and/or MDA-MB-231 cells for EGFR and ARO inhibitory activities using erlotinib and letrozole as reference standards respectively. Results proved that, in general, tested compounds were better EGFRIs than ARIs. In addition, significant overexpression in caspase-9 level in treated MCF-7 breast cell line samples was observed for all tested compounds with the 4-fluorophenylhydrazone derivative 2d exhibiting the highest activation. In treated MDA-MB-231 breast cell line samples, 11b was found to highly induce caspase-9 level thereby inducing apoptosis. Cell cycle analysis and Annexin V-FITC/PI assay were also assessed for active compounds where results indicated that all tested compounds induced preG1 apoptosis and cell cycle arrest at G2/M phase. Compound 9d, as an inhibitor of ARO, was observed to downregulate the downstream signaling proteins HSP27 and p-ERK in MCF-7 cells. Furthermore, compound 11b downregulated EGFR expression as well as the downstream signaling protein p-AKT. Docking experiments on EGFR and ARO enzymes supported their in vitro results. Thus, the thienotriazolopyrimidines 11b and 12 showing good EGFR inhibition and the thieno[3,2-d]-pyrimidine derivatives 3b and 9d, eliciting the best ARO inhibition activity, can be considered as new candidates as anti-breast cancer agents that necessitate further development.

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).

Unearthing novel thiazolidinone building blocks as carboxylic acid bioisosteres

Aim: Thiazolidinones were prepared as building blocks for the replacement of carboxylic acids. Materials & methods: Chemical syntheses of thiazolidinones were developed. In addition, the drug-likeness of the target compounds was evaluated in silico. Results: The prepared compounds included the novel structure 4; 5-(3-Iodophenylmethylene)-2,4-thiazolidinedione. Conclusion: Exploration of the methods required to synthesize thiazolidinone building blocks was completed. This work allows future generation of bioisosteric analogs of drugs.

Identification of a New Zinc Binding Chemotype by Fragment Screening

The discovery of a new zinc binding chemotype from screening a nonbiased fragment library is reported. Using the orthogonal fragment screening methods of native state mass spectrometry and surface plasmon resonance a 3-unsubstituted 2,4-oxazolidinedione fragment was found to have low micromolar binding affinity to the zinc metalloenzyme carbonic anhydrase II (CA II). This affinity approached that of fragment sized primary benzenesulfonamides, the classical zinc binding group found in most CA II inhibitors. Protein X-ray crystallography established that 3-unsubstituted 2,4-oxazolidinediones bound to CA II via an interaction of the acidic ring nitrogen with the CA II active site zinc, as well as two hydrogen bonds between the oxazolidinedione ring oxygen and the CA II protein backbone. Furthermore, 3-unsubstituted 2,4-oxazolidinediones appear to be a viable starting point for the development of an alternative class of CA inhibitor, wherein the medicinal chemistry pedigree of primary sulfonamides has dominated for several decades.

Carboxylic acid (bio)isosteres in drug design

The carboxylic acid functional group can be an important constituent of a pharmacophore, however, the presence of this moiety can also be responsible for significant drawbacks, including metabolic instability, toxicity, as well as limited passive diffusion across biological membranes. To avoid some of these shortcomings while retaining the desired attributes of the carboxylic acid moiety, medicinal chemists often investigate the use of carboxylic acid (bio)isosteres. The same type of strategy can also be effective for a variety other purposes, for example, to increase the selectivity of a biologically active compound or to create new intellectual property. Several carboxylic acid isosteres have been reported, however, the outcome of any isosteric replacement cannot be readily predicted as this strategy is generally found to be dependent upon the particular context (i.e., the characteristic properties of the drug and the drug-target). As a result, screening of a panel of isosteres is typically required. In this context, the discovery and development of novel carboxylic acid surrogates that could complement the existing palette of isosteres remains an important area of research. The goal of this Minireview is to provide an overview of the most commonly employed carboxylic acid (bio)isosteres and to present representative examples demonstrating the use and utility of each isostere in drug design.

Heterocycles as nonclassical bioisosteres of α-amino acids

Bioisosterism of α-amino acids is often accomplished by replacing the α-carboxylate with one of the many known carboxylic acid bioisosteres. However, bioisosterism of the whole α-amino acid moiety is accomplished with heterocyclic bioisosteres that often display an acidic function. In this Minireview, we summarized the reported heterocycles as nonclassical bioisosteres of α-amino acids, which include quinoxaline-2,4(1H)-dione, quinoxaline-2,3(1H)-dione and quinolin-2(1H)-one, azagrevellin and azepine-derived structures. The binding mode of the crystalized bioisosteres were compared with those of the crystalized α-amino acids that bind in the same domain, and where no data on the crystal structure were available, the displacement studies of known orthosteric ligands were used. The reported bioisosteres share the following essential structural features for mimicking α-amino acids: an aromatic ring system joined to a lactam ring system with an acidic feature next to the lactam carbonyl, where this acidic feature together with the lactam carbonyl can mimic the α-carboxylate, and the lactam nitrogen together with the aromatic ring system can mimic the α-ammonium. The majority of these heterocycles can be prepared from three common corresponding starting materials: the corresponding anilines, isatins or anthranilic esters. The data collected here show the potential of this class of bioisosteres in the design of glutamate receptor ligands and beyond.

Investigation of the lipophilic behaviour of some thiazolidinediones. Relationships with PPAR-gamma activity

Various lipophilicity aspects of five well-known PPAR-gamma ligands, belonging to the thiazolidinedione (TZD) class, ciglitazone (CSZ), troglitazone (TGZ), netoglitazone (NGZ) and the ampholytic pioglitazone (PGZ) and rosiglitazone (RGZ), have been explored. The compounds were found to be highly lipophilic as assessed by direct octanol-water partitioning experiments and further confirmed by reversed phase HPLC measurements under different conditions. Immobilised artificial membrane (IAM) chromatographic indices were also determined as an alternative expression of lipophilicity. They were found to show less diversity forming two clusters. Experimental logD/logP values were compared to those predicted by three widely used calculation systems. For the two ampholytic TZDs, the lipophilicity and retention/pH profiles were established over a broad pH range and compared to the corresponding calculated profiles. Lipophilicity indices derived under the different conditions were further compared to biological activity, concerning in vitro transactivation (pEC(50)) and binding affinity (pK(i)) data, taken from literature. The most active TZD (RGZ) in both transactivation and binding assay proved to be the less lipophilic analogue. An equation relating pEC(50) data to experimental logD(7.4) or reversed-phase logk(w) values could be established, while pK(i) data did not lead to satisfactory correlation.

Interaction of ligands for the peroxisome proliferator-activated receptor gamma with the endocannabinoid system

BACKGROUND AND PURPOSE

There is good evidence that agents interacting with the endocannabinoid system in the body can also interact with the peroxisome proliferator-activated receptor gamma. The present study was designed to test whether the reverse is true, namely whether peroxisome proliferator-activated receptor gamma ligands have direct effects upon the activity of the endocannabinoid metabolizing enzyme fatty acid amide hydrolase.

EXPERIMENTAL APPROACH

Fatty acid amide hydrolase activity was measured in rat brain homogenates, C6 glioma and RBL2H3 basophilic leukaemia cells. Cellular uptake of anandamide was also assessed in these cells.

KEY RESULTS

Peroxisome proliferator-activated receptor gamma activators inhibited the metabolism of the endocannabinoid anandamide in rat brain homogenates with an order of potency MCC-555 > indomethacin approximately ciglitazone approximately 15-deoxy-Delta(12,14)-prostaglandin J(2) approximately pioglitazone > rosiglitazone > troglitazone. The antagonists BADGE, GW9662 and T0070907 were poor inhibitors of anandamide hydrolysis. The inhibition by ciglitazone was competitive and increased as the pH of the assay buffer was decreased; the K(i) value at pH 6.0 was 17 microM. In intact C6 glioma cells assayed at pH 6.2, significant inhibition of anandamide hydrolysis was seen at 3 microM ciglitazone, whereas 100 microM was required to produce significant inhibition at pH 7.4. Ciglitazone also interacted with monoacylglycerol lipase as well as with cannabinoid CB(1) and CB(2) receptors.

CONCLUSIONS AND IMPLICATIONS

Ciglitazone may be useful as a template for the design of novel dual action anti-inflammatory agents which are both inhibitors of fatty acid amide hydrolase and agonists at the peroxisome proliferator-activated receptor gamma.

Structure–activity relationships and molecular modelling of 5-arylidene-2,4-thiazolidinediones active as aldose reductase inhibitors

The structure-activity relationships (SARs) of 5-arylidene-2,4-thiazolidinediones active as aldose reductase inhibitors (ARIs) were extended by varying the substitution pattern on the 5-arylidene moiety and on N-3. In particular, the introduction of an additional aromatic ring or an H-bond donor group on the 5-benzylidene ring enhanced ALR2 inhibitory potency. Moreover, the presence of a carboxylic anionic chain on N-3 was shown to be an important, although not essential, structural requisite to produce high levels of ALR2 inhibition. The length of this carboxylic chain was critical and acetic acids 4 were the most effective inhibitors among the tested derivatives. Molecular docking simulations into the ALR2 active site accorded with the in vitro inhibition data. They allowed the rationalization of the observed SARs and provided a pharmacophoric model for this class of ARIs.

Synthesis and aldose reductase inhibitory activity of 5-arylidene-2,4-thiazolidinediones

Several (Z)-5-arylidene-2,4-thiazolidinediones were synthesized and tested as aldose reductase inhibitors (ARIs). The most active of the N-unsubstituted derivatives (2) exerted the same inhibitory activity of Sorbinil. The introduction of an acetic side chain on N-3 of the thiazolidinedione moiety led to a marked increase in lending inhibitory activity, conducting to the discovery of a very potent ARI (4c), whose activity level (IC50=0.13 microM) was in the same range of Tolrestat. Moreover, the corresponding methyl esters (3), devoid of any acidic functionality, showed appreciable inhibitory activity similar to that of the N-unsubstituted compounds. It was also found that the substitution pattern on the 5-benzylidene moiety markedly influenced the activity of N-unsubstituted 2,4-thiazolidinediones 2, compounds with substituents at the meta position being generally more effective than the para-substituted ones; however, this SAR was not evidenced in acetates 3 and acids 4.

Synthesis of a sulfahydantoin library

A five-step solid-phase synthesis of sulfahydantoins from alpha-amino acids and aldehydes was developed. The synthetic method allows the use of hindered amino acids, including Val, Phg, and Aib, and use of aromatic aldehydes substituted with electron-withdrawing and -donating groups. Some limitations were encountered with amino acids with reactive side chains. A small but diverse library of compounds was produced for biological testing.

Effects of log P and phenyl ring conformation on the binding of 5-phenylhydantoins to the voltage-dependent sodium channel

Binding to the neuronal voltage-dependent sodium channel (NVSC) was evaluated for 12 5-phenylhydantoins which systematically varied either log P and/or 5-phenyl ring orientation. The linear correlation of log P with in vitro sodium channel binding activity (log IC50) for hydantoins 1-12 and diphenylhydantoin (DPH) (r2 = 0.638) suggested that simple partitioning into the lipid phase is important but not sufficient to account for the effects of hydantoins on the NVSC. Comparisons among different hydantoins with the same log P but different low-energy phenyl ring orientations revealed that, in addition to log P, the correct 5-phenyl orientation is important for efficient binding.