Sequential Selective C-H and C(sp3 )-+ P Bond Functionalizations: An Entry to Bioactive Arylated Scaffolds.

Organophosphonium salts containing C(sp3 )-+ P bonds are among the most utilized reagents in organic synthesis for constructing C-C double bonds. However, their use as C-selective electrophilic groups is rare. Here, we explore an efficient and general transition-metal-free method for sequential chemo- and regioselective C-H and C(sp3 )-+ P bond functionalizations. In the present study, C-H alkylation resulting in the synthesis of benzhydryl triarylphosphonium salts was achieved by one-pot, four-component cross-coupling reactions of simple and commercially available starting materials. The utility of the resulting phosphonium salt building blocks was demonstrated by the chemoselective post-functionalization of benzylic C(sp3 )-+ PPh3 groups to achieve aminations, thiolations, and arylations. In this way, benzhydrylamines, benzhydrylthioethers, and triarylmethanes, structural motifs that are present in many pharmaceuticals and agrochemicals, are readily accessed. These include the synthesis of two anticancer agents from simple materials in only two to three steps. Additionally, a protocol for late-stage functionalization of bioactive drugs has been developed using benzhydrylphosphonium salts. This new approach should provide novel transformations for application in both academic and pharmaceutical research.

Synthesis and biological evaluation of benzhydryl-based antiplasmodial agents possessing Plasmodium falciparum chloroquine resistance transporter (PfCRT) inhibitory activity.

Due to the surge in resistance to common therapies, malaria remains a significant concern to human health worldwide. In chloroquine (CQ)-resistant (CQ-R) strains of Plasmodium falciparum, CQ and related drugs are effluxed from the parasite's digestive vacuole (DV). This process is mediated by mutant isoforms of a protein called CQ resistance transporter (PfCRT). CQ-R strains can be partially re-sensitized to CQ by verapamil (VP), primaquine (PQ) and other compounds, and this has been shown to be due to the ability of these molecules to inhibit drug transport via PfCRT. We have previously developed a series of clotrimazole (CLT)-based antimalarial agents that possess inhibitory activity against PfCRT (4a,b). In our endeavor to develop novel PfCRT inhibitors, and to perform a structure-activity relationship analysis, we synthesized a new library of analogues. When the benzhydryl system was linked to a 4-aminoquinoline group (5a-f) the resulting compounds exhibited good cytotoxicity against both CQ-R and CQ-S strains of P. falciparum. The most potent inhibitory activity against the PfCRT-mediated transport of CQ was obtained with compound 5k. When compared to the reference compound, benzhydryl analogues of PQ (5i,j) showed a similar activity against blood-stage parasites, and a stronger in vitro potency against liver-stage parasites. Unfortunately, in the in vivo transmission blocking assays, 5i,j were inactive against gametocytes.

A Novel Prodrug of a nNOS Inhibitor with Improved Pharmacokinetic Potential.

Under different pathological conditions, aberrant induction of neuronal nitric oxide synthase (nNOS) generates overproduction of NO that can cause irreversible cell damage. The aim of this study was to develop an amidoxime prodrug of a potent nNOS inhibitor, the benzhydryl acetamidine. We synthesized the benzhydryl acetamidoxime, which was evaluated in vitro to ascertain the potential NOS inhibitory activity, as well as conducting bioconversion into the parent acetamidine. The prodrug was also profiled for in vitro physicochemical properties, by determining the lipophilicity, passive permeation through the human gastrointestinal tract and across the blood-brain barrier by PAMPA, and chemical, enzymatic, and plasma stability. The obtained data demonstrate that the amidoxime prodrug shows an improved pharmacokinetic profile with respect to the acetamidine nNOS inhibitor, thus suggesting that it could be a promising lead compound to treat all those pathological conditions in which nNOS activity is dysregulated.

Discovery of new benzhydrol biscarbonate esters as potent and selective apoptosis inducers of human melanomas bearing the activated ERK pathway: SAR studies on an ERK MAPK signaling modulator, ACA-28.

The recent discovery that an ERK signaling modulator [ACA-28 (2a)] preferentially kills human melanoma cell lines by inducing ERK-dependent apoptosis has generated significant interest in the field of anti-cancer therapy. In the first SAR study on 2a, here, we successfully developed candidates (2b, 2c) both of which induce more potent and selective apoptosis towards ERK-active melanoma cells than 2a, thus revealing the structural basis for inducing the ERK-dependent apoptosis and proposing the therapeutic prospect of these candidates against ERK-dependent cancers represented by melanoma.

An Efficient Metal-Free Oxidative Esterification and Amination of Benzyl C-H Bond.

An esterification and amination of benzylic C-H bonds was developed by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) under metal- and iodide-free conditions. Both carboxylic acids and amines could be used as ideal coupling partners for the oxidative coupling reactions with various diarylmethanes. A close to equal amount of coupling reagents was enough to afford the product in good to high yields.

Synthesis of Bisphenol Neolignans Inspired by Honokiol as Antiproliferative Agents.

Honokiol (2) is a natural bisphenol neolignan showing a variety of biological properties, including antitumor activity. Some studies pointed out 2 as a potential anticancer agent in view of its antiproliferative and pro-apoptotic activity towards tumor cells. As a further contribution to these studies, we report here the synthesis of a small library of bisphenol neolignans inspired by honokiol and the evaluation of their antiproliferative activity. The natural lead was hence subjected to simple chemical modifications to obtain the derivatives 3-9; further neolignans (12a-c, 13a-c, 14a-c, and 15a) were synthesized employing the Suzuki-Miyaura reaction, thus obtaining bisphenols with a substitution pattern different from honokiol. These compounds and the natural lead were subjected to antiproliferative assay towards HCT-116, HT-29, and PC3 tumor cell lines. Six of the neolignans show GI50 values lower than those of 2 towards all cell lines. Compounds 14a, 14c, and 15a are the most effective antiproliferative agents, with GI50 in the range of 3.6-19.1 µM, in some cases it is lower than those of the anticancer drug 5-fluorouracil. Flow cytometry experiments performed on these neolignans showed that the inhibition of proliferation is mainly due to an apoptotic process. These results indicate that the structural modification of honokiol may open the way to obtaining antitumor neolignans more potent than the natural lead.

K2S2O8-HFIP synergistically promoted para-selective sp3 C-H bond diarylation of glycine esters.

A metal-free K2S2O8-HFIP synergistically promoted double Friedel-Crafts alkylation between a glycine derivative and N-substituted aniline was developed to efficiently synthesize diarylmethane derivatives with high para-selectivity. The reaction proceeded smoothly in the absence of any metal and ligand, and exhibited a good tolerance of functional groups.

Bisphenol AF: Halogen bonding effect is a major driving force for the dual ERα-agonist and ERß-antagonist activities.

17ß-Estradiol (E2) is a natural steroid ligand for the structurally and physiologically independent estrogen receptors (ERs) ERα and ERß. We recently observed that CF3-containing bisphenol AF (BPAF) works as an agonist for ERα but as an antagonist for ERß. Similar results were also observed for the CCl3-containing bisphenol designated as HPTE. Both BPAF and HPTE are comprised of a tri-halogenated methyl group in the central alkyl moiety of their bisphenol structures, which strongly suggests that halogens contribute directly to the agonist/antagonist dual biological functions. We conducted this study to investigate the structure-activity relationships by assessing together newly synthesized CF3- and CBr3-containing bisphenol E analogs (BPE-X). We first tested bisphenols for their receptor binding ability and then for their transcriptional activities. Halogen-containing bisphenols were found to be fully active for ERα, but almost completely inactive for ERß. When we examined these bisphenols for their inhibitory activities for E2 in ERß, we observed that they worked as distinct antagonists. The ascending order of agonist/antagonist dual biological functions was BPE-F < BPE-Cl (HPTE) ≤ BPAF < BPE-Br, demonstrating that the electrostatic halogen bonding effect is a major driving force of the bifunctional ERα agonist and ERß antagonist activities of BPAF.

Nonstationary Two-Dimensional Nuclear Magnetic Resonance: A Method for Studying Reaction Mechanisms in Situ.

Nuclear magnetic resonance spectroscopy (NMR) is a versatile tool of chemical analysis allowing one to determine structures of molecules with atomic resolution. Particularly informative are two-dimensional (2D) experiments that directly identify atoms coupled by chemical bonds or a through-space interaction. Thus, NMR could potentially be powerful tool to study reactions in situ and explain their mechanisms. Unfortunately, 2D NMR is very time-consuming and thus often cannot serve as a "snapshot" technique for in situ reaction monitoring. Particularly difficult is the case of spectra, in which resonance frequencies vary in the course of reaction. This leads to resolution and sensitivity loss, often hindering the detection of transient products. In this paper we introduce a novel approach to correct such nonstationary 2D NMR signals and raise the detection limits over 10 times. We demonstrate success of its application for studying the mechanism of the reaction of AgSO4-induced synthesis of diphenylmethane-type compounds. Several reactions occur in the studied mixture of benzene and toluene, all with rather low yield and leading to compounds with similar chemical shifts. Nevertheless, with the use of a proposed 2D NMR approach we were able to describe complex mechanisms of diphenylmethane formation involving AgSO4-induced toluene deprotonation and formation of benzyl carbocation, followed by nucleophilic attacks.

Design, synthesis and biological evaluation of 6-deoxy O-spiroketal C-arylglucosides as novel renal sodium-dependent glucose cotransporter 2 (SGLT2) inhibitors for the treatment of type 2 diabetes.

In this work, aiming at finding a novel, potent, and selective sodium-dependent glucose cotransporter 2 (SGLT2) inhibitor with good pharmacokinetic profiles for the treatment of diabetes, we focus on modifying the sugar moiety of SGLT2 inhibitors, which dominates the binding with glucose binding site of hSGLT, via removing the C-6 hydroxy group to adjust the physicochemical properties and target-recognition manners of SGLT2 inhibitors. In addition, tofogliflozin containing a special O-spiroketal C-arylglucoside scaffold, displayed good efficacy and bioavailability both in animals and in humans. Therefore, a series of 6-deoxy O-spiroketal C-arylglucosides as novel SGLT2 inhibitors were designed, synthesized, and evaluated in this work. The structure-activity relationship (SAR) research on this novel series and a comprehensive in vitro and in vivo biological evaluation afforded compound 39 with high in vitro hSGLT2 inhibitory activity (IC50 = 4.5 nM), good pharmacokinetic profiles, and more remarkable efficacy in C57BL/6J mice and Sprague-Dawley rats than marketed drug tofogliflozin.

Fast and Reversible "Turn on" Fluorescent Sensors Based on Bisphenol-a for Zn2+ in Aqueous Solution.

Two novel bisphenol-A derivatives (R1 and R2) linked pyrene and napthylthiazole moieties were synthesized via condensation reaction, and positively applied for the selective recognition of Zn2+ ion in EtOH/H2O. Their optical properties were observed by using UV-vis and fluorescence measurements. R1 and R2 exhibited high selectivity and sensitivity towards Zn2+ over other metal ions. This fluorescence selectivity may be owing to inhibited excited-state intramolecular proton transfer (ESIPT) and photoinduced electron transfer (PET). The fluorescence titration analysis indicated detection limits of R1 and R2 for Zn2+ at 17.5 nM and 0.94 µM, respectively. Moreover, R1 and R2 were successfully applied to the detection of Zn2+ with different concentrations in water samples.

Design, synthesis, and biological evaluation of lipophilically modified bisphenol Z derivatives.

In the present study, a small library of bisphenol Z (BPZ) derivatives was synthesized and investigated for anti-proliferative effects in cultured breast and glioblastoma cell lines. Synthesized BPZ derivatives varied in molecular size, polarity, and lipophilicity. Of the 8 derivatives tested, compounds 4 and 6, both of which displayed the highest degree of lipophilicity, were most active at inducing cell death as determined by the XTT assay. Cell membranes were interrogated using trypan blue staining and were shown to remain intact during treatments with 4 and 6. Activation of caspase enzymes (3 and/or 7) was noted to occur following treatment with compound 4. Polar BPZ derivatives, those with a substituted amine or alcohol, were devoid of any inhibitory or proliferative effects. The remaining derivatives seem to lack sufficient lipophilicity to execute an overt toxic effect. Our results suggest that increasing the lipophilic character of BPZ enhances the cytotoxic effects.

Excellent Temperature-Control Based on Reversible Thermochromic Materials for Light-Driven Phase Change Materials System.

Light-driven phase change materials (PCMs) have received significant attention due to their capacity to convert visible light into thermal energy, storing it as latent heat. However, continuous photo-thermal conversion can cause the PCMs to reach high thermal equilibrium temperatures after phase transition. In our study, a novel light-driven phase change material system with temperature-control properties was constructed using a thermochromic compound. Thermochromic phase change materials (TC-PCMs) were prepared by introducing 2-anilino-6-dibutylamino-3-methylfluoran (ODB-2) and bisphenol A (BPA) into 1-hexadecanol (1-HD) in various proportions. Photo-thermal conversion performance was investigated with solar radiation (low power of 0.09 W/cm2) and a xenon lamp (at a high power of 0.14 W/cm2). The TC-PCMs showed a low equilibrium temperature due to variations in absorbance. Specifically, the temperature of TC-PCM180 (ODB-2, bisphenol A and 1-HD ratio 1:2:180) could stabilize at 54 °C approximately. TC-PCMs exhibited reversibility and repeatability after 20 irradiation and cooling cycles.

Synthesis of NSC 106084 and NSC 14778 and evaluation of their DNMT inhibitory activity.

DNA methylation is an epigenetic modification that is performed by DNA methyltransferases (DNMTs) and that leads to the transfer of a methyl group from S-adenosylmethionine (SAM) to the C5 position of cytosine. This transformation results in hypermethylation and silencing of genes such as tumor suppressor genes. Aberrant DNA methylation has been associated with the development of many diseases, including cancer. Inhibition of DNMTs promotes the demethylation and reactivation of epigenetically silenced genes. NSC 106084 and 14778 have been reported to inhibit DNMTs in the micromolar range. We report herein the synthesis of NSC 106084 and 14778 and the evaluation of their DNMT inhibitory activity. Our results indicate that while commercial NSC 14778 is moderately active against DNMT1, 3A/3L and 3B/3L, resynthesized NSC 14778 is inactive under our assay conditions. Resynthesized 106084 was also found to be inactive.

Development of New Epoxy Resin Monomers - A Delicate Balance between Skin Allergy and Polymerization Properties.

Epoxy resin monomers (ERMs) are used as building blocks for thermosetting polymers in applications where strong, flexible, and lightweight materials are required. Most epoxy resins are polymers of diglycidyl ether of bisphenol A (DGEBA). It is highly allergenic and causes occupational allergic contact dermatitis and contact allergy in the general population. Thus, measures to prevent exposure by protective clothing and education are not enough. This work describes a continuation of our research aiming at reducing the skin-sensitizing potency of ERMs while maintaining the ability to form polymers. Alternative ERMs were designed and synthesized whereafter the sensitizing potency was determined using the murine local lymph node assay (LLNA). The reactivity of the diepoxides toward a nucleophilic peptide was investigated, and the differences in reactivity explained using computational studies. The diepoxides were reacted with triethylenetetramine, and the formed polymers were tested for technical applicability using thermogravimetric analysis. We had previously shown that the absence of an oxygen atom in the side chains or removal of aromaticity reduced the sensitizing potency compared to that of DGEBA. Thus, a cycloaliphatic analogue 1 of DGEBA without ether oxygen in the side chains was considered promising and was synthesized. As predicted, the sensitizing potency was considerably reduced (10 times) compared to that of DGEBA. However, the technical properties of the polymer of this compound were not considered sufficient. More polar aromatic analogues were investigated, but they could not compete with our previously described ERMs regarding polymerization properties and with 1 regarding low skin sensitization properties. Development of alternative epoxy materials is a delicate balance between allergenic activity and polymerization properties. Tuning of structural properties together with investigation of polymerization conditions combined with skin sensitization studies should be used in industrial research and development. ERM 1 could be used as a lead compound for further studies of aliphatic ERMs.

Design, synthesis and biological evaluation of nitric oxide releasing derivatives of dapagliflozin as potential anti-diabetic and anti-thrombotic agents.

The cardiovascular complications were highly prevalent in type 2 diabetes mellitus (T2DM), even at the early stage of T2DM or the state of intensive glycemic control. Therefore, there is an urgent need for the intervention of cardiovascular complications in T2DM. Herein, the new hybrids of NO donor and SGLT2 inhibitor were design to achieve dual effects of anti-hyperglycemic and anti-thrombosis. As expected, the preferred hybrid 2 exhibited moderate SGLT2 inhibitory effects and anti-platelet aggregation activities, and its anti-platelet effect mediated by NO was also confirmed in the presence of NO scavenger. Moreover, compound 2 revealed significantly hypoglycemic effects and excretion of urinary glucose during an oral glucose tolerance test in mice. Potent and multifunctional hybrid, such as compound 2, is expected as a potential candidate for the intervention of cardiovascular complications in T2DM.

Synthesis, biological evaluation, and molecular docking investigation of benzhydrol- and indole-based dual PPAR-γ/FFAR1 agonists.

Type-2 diabetes mellitus is a progressive cluster of metabolic disorders, representing a global public health burden affecting more than 366 million people worldwide. We recently reported the discovery of three series of novel agents showing balanced activity on two metabolic receptors, peroxisome proliferator activated receptor-γ (PPAR-γ) and free fatty acid receptor 1 (FFAR1), also known as GPCR40. Our designing strategy relied on linking the thiazolidinedione head with known GPCR privilege structures. To further investigate this concept, two new scaffolds, the benzhydrol- and indole-based chemotypes, were introduced here in. Our optimization campaign resulted in three compounds; 15a, 15c, and 15d, with affinities in the low micromolar range on both targets. In vivo study of selected test compounds, revealed that 15c possesses a significant anti-hyperglycemic and anti-hyperlipidemic activities superior to rosiglitazone in fat-fed animal models. Molecular docking analysis was conducted to explain the binding modes of both series. These compounds could lead to the development of the unique antidiabetic agent acting as insulin sensitizer as well as insulin secretagogue.

Chemical Identity and Mechanism of Action and Formation of a Cell Growth Inhibitory Compound from Polycarbonate Flasks.

This paper reports the chemical identity and mechanism of action and formation of a cell growth inhibitory compound leached from some single-use Erlenmeyer polycarbonate shaker flasks under routine cell culture conditions. Single-use cell culture vessels have been increasingly used for the production of biopharmaceuticals; however, they often suffer from issues associated with leachables that may interfere with cell growth and protein stability. Here, high-performance liquid-chromatography preparations and cell proliferation assays led to identification of a compound from the water extracts of some polycarbonate flasks, which exhibited subline- and seeding density-dependent growth inhibition of CHO cells in suspension culture. Mass spectroscopy, nuclear magnetic resonance spectroscopy, and chemical synthesis confirmed that this compound is 3,5-dinitro-bisphenol A. Cell cycle analysis suggests that 3,5-dinitro-bisphenol A arrests CHO-S cells at the G1/Go phase. Dynamic mass redistribution assays showed that 3,5-dinitro-bisphenol A is a weak GPR35 agonist. Analysis of the flask manufacturing process suggests that 3,5-dinitro-bisphenol A is formed via the combination of molding process with γ-sterilization. This is the first report of a cell culture/assay interfering leachable compound that is formed through γ-irradiation-mediated nitric oxide free radical reaction.

Ni-Catalyzed Carbon-Carbon Bond-Forming Reductive Amination.

This report describes a three-component, Ni-catalyzed reductive coupling that enables the convergent synthesis of tertiary benzhydryl amines, which are challenging to access by traditional reductive amination methodologies. The reaction makes use of iminium ions generated in situ from the condensation of secondary N-trimethylsilyl amines with benzaldehydes, and these species undergo reaction with several distinct classes of organic electrophiles. The synthetic value of this process is demonstrated by a single-step synthesis of antimigraine drug flunarizine (Sibelium) and high yielding derivatization of paroxetine (Paxil) and metoprolol (Lopressor). Mechanistic investigations support a sequential oxidative addition mechanism rather than a pathway proceeding via α-amino radical formation. Accordingly, application of catalytic conditions to an intramolecular reductive coupling is demonstrated for the synthesis of endo- and exocyclic benzhydryl amines.

Kinetics of Thermal Polymerization Can Be Studied during Continuous Cooling.

It is demonstrated that differential scanning calorimetry can measure the kinetics of the thermally initiated polymerization during continuous cooling. The measurements are accomplished by switching from fast heating to much slower cooling. The study is exemplified by crosslinking polymerization (curing) of diglycidyl ether of bisphenol A epoxy and m-phenylenediamine taken in stoichiometric and nonstoichiometric ratios and measured under heating and cooling conditions. An advanced isoconversional method reveals that the reaction in the nonstoichiometric system follows the kinetics of the single-step type. Its activation energy is constant and the same for heating and cooling conditions. The stoichiometric system exhibits the multistep kinetics characterized by the dependencies of the activation energy on temperature that differ qualitatively for cooling and heating runs. The discovered differences emphasize the need for further systematic studies of the thermal polymerization during continuous cooling.