Physicochemical Properties of Zwitterionic Drugs in Therapy

Discovery of BI-9787, a potent zwitterionic ketohexokinase inhibitor with oral bioavailability

Fructose metabolism by ketohexokinase (KHK) is implicated in a variety of metabolic disorders. KHK inhibition is a potential therapeutic strategy for the treatment of diseases including diabetes, non-alcoholic fatty liver disease, and non-alcoholic steatohepatitis. The first small-molecule KHK-inhibitors have entered clinical trials, but it remains unclear if systemic inhibition of KHK by small-molecules will eventually benefit patients. Here we report the discovery of BI-9787, a potent, zwitterionic KHK inhibitor characterized by high permeability and favorable oral rat pharmacokinetics. BI-9787 was identified by optimizing chemical starting points generated via a ligand-based virtual screening of Boehringer's virtual library of synthetically accessible compounds (BICLAIM). It serves as a high-quality in vitro and in vivo tool compound for investigating the role of fructose metabolism in disease.

Can membrane permeability of zwitterionic compounds be predicted by the solubility-diffusion model?

Zwitterions contain both positively and negatively charged functional groups, resulting in an overall net neutral charge. Nevertheless, the membrane permeability of the zwitterionic form of a compound is assumed to be much lower than the permeability of the uncharged neutral form. Although a significant proportion of pharmaceuticals are zwitterionic, it has not been clear so far whether their permeability is dominated by the permeation of the zwitterionic or the neutral form, since neutral fractions are often quite low as compared to the zwitterionic fraction. This complicates the in silico prediction of the permeability of zwitterionic compounds. In this work, we re-evaluated existing in vitro permeability data from literature measured with Caco-2/MDCK cell assays, using more strict exclusion criteria for effects like diffusion limitation by the aqueous boundary layers, paracellular transport, active transport and retention. Using this re-evaluated data set, we show that extracted intrinsic permeabilities of the neutral fraction are well predicted by the solubility-diffusion model (RMSE = 1.21; n = 18) if the permeability of the zwitterionic species is assumed negligible. Our work thus suggests that only the neutral species is relevant for the membrane permeability of zwitterionic compounds, and that membrane permeability of zwitterionic compounds is indeed predictable by the solubility-diffusion model.

Nonclassical Zwitterions as a Design Principle to Reduce Lipophilicity without Impacting Permeability

The ionization of bioactive molecules impacts many ADME-relevant physicochemical properties, in particular, solubility, lipophilicity, and permeability. Ampholytes contain both acidic and basic groups and are distinguished as ordinary ampholytes and zwitterions. An influential review states that zwitterions only exist if the acidic pKa is significantly lower than the basic pKa. Through concordance of measured and calculated pKa and log P, we show that the zwitterionic behavior of several marketed drugs and natural products occurs despite a low or negative ΔpKa. These nonclassical zwitterions are characterized by a weak acidic and basic pKa and conjugation through an extended aromatic system, often including pseudorings via intramolecular hydrogen bonds. In contrast to most classical zwitterions, nonclassical zwitterions can exhibit excellent permeability. As permeability and lipophilicity are typically correlated, the combination of low lipophilicity and high permeability makes nonclassical zwitterions an attractive design principle in medicinal chemistry.

Gold nanoclusters conjugated berberine reduce inflammation and alleviate neuronal apoptosis by mediating M2 polarization for spinal cord injury repair

Spinal cord injury (SCI) leads to nerve cell apoptosis and loss of motor function. Herein, excessive activation of the M1 phenotype macrophages/microglia is found to be the main reason for the poor prognosis of SCI, but the selective activation phenotype (M2) macrophages/microglia facilitates the recovery of SCI. Thereafter, we used gold nanoclusters loaded berberine (BRB-AuNCs) to reduce inflammation by inhibiting the activation of M1 phenotype macrophages/microglia, which simultaneously inhibited neuronal apoptosis after SCI. In vitro and in vivo experiments showed that BRB-AuNCs reduced M1 protein marker CD86, increased M2 protein marker CD206, reduced inflammation and apoptotic cytokines (IL-1β, IL-6, TNF-α, Cleaved Caspase-3 and Bax). These results indicate that BRB-AuNCs have excellent anti-inflammatory and anti-apoptotic effects by inducing the polarization of macrophages/microglia from M1 phenotype to M2 phenotype. Thereafter, the motor functions of SCI rats were significantly improved after treatment with BRB-AuNCs. This work not only provides a new way for the treatment of SCI but also broadens BRB utilization strategies.

Stability of high concentrated triple intrathecal therapy for pediatrics and mitigation strategies

Stringent formulation requirements are defined to intrathecally administer drug substances, avoiding neurological complications. In case of pediatric patients, these are further complicated due to the limited volumes of the celebrospinal fluid and, therefore, high concentrated solutions of methotrexate (MTX), cytarabine and corticosteroids (i.e., methylprednisolone or hydrocortisone) are prepared based on the patient's age. This work aims to assess the chemical and physical stability of triple intrathecal mixtures differing in volume and composition by a bracketing approach and to identify possible stress causes and mitigation strategies. Low solubility of MTX was the main factor limiting the physical stability of triple mixtures. Regarding solutions containing methylprednisolone, the amount of MTX remaining was about 95% in the solution at highest concentrations with the concomitant formation of a visible particulate sizing bigger than 1 µm after 24 h of storage at 25 °C. This behavior was mainly driven by the pH reduction due to the pH value of the cytarabine solution used; the shear stress also induced drug precipitation. In the case of the hydrocortisone based mixtures, the precipitate formation occurred at a slow rate. To improve the physical stability, a better control of the mixture pH (optimal value ≈ 7) is required or, as an alternative, the addition of the cytarabine solution to a pre-mixed binary mixture containing MTX and a corticosteroid should be preferred.

Low-temperature partitioning extraction followed by liquid chromatography tandem mass spectrometry determination of multiclass antibiotics in solid and soluble wastewater fractions

An analytical method based on low-temperature partitioning extraction (LTPE) followed by high performance liquid chromatography coupled to triple quadrupole mass spectrometry analysis was developed and validated for the determination of eight multiclass antibiotics in wastewater. The analyzed target antibiotics included one β-lactam, two sulfonamides, three fluoroquinolones, one macrolide and one diaminopyrimidine. LTPE parameters such as sample pH, volume ratio between sample and extractor solvent, ultra-sonic extraction time, extraction tube material, solvent and volume to reconstitute the sample extracts, were optimized. Additionally, the influence of solids on extraction efficiency was evaluated. Quantification of the target antibiotics was performed by double consecutive injection method, without the use of a labeled compound, in order to correct matrix effects. The whole samples were analyzed, including, liquid and solid fractions of wastewater. The results revealed that the filtration step can underestimate the total antibiotics concentration, particularly to the hydrophobic compounds that have higher affinity for solids, indicating that the suspended wastewater particulate should not be neglected. The method detection limit ranged from 18.54 ng L^-1 (trimethoprim) to 78.49 ng L^-1 (ciprofloxacin). Intra-day precision of less than 12.3% was achieved. The recoveries values ranged from 13.9% (sulfadiazine) to 48.9% (erythromycin) in influent samples and from 19.1% (sulfadiazine) to 57.2% (ciprofloxacin) in effluent samples. The method was applied to the measurement of antibiotic residues in influent and effluent from wastewater treatment plants. The majority target antibiotics were detected in wastewater samples. Their concentrations ranged from 237 to 9553 ng L^-1 in influent and from 212 to 1660 ng L^-1 in effluent. This work provides new insights on the applicability of LTPE for antibiotic residues extraction from wastewater. In addition, the performed analysis highlights the importance of measuring total concentrations of analytes in whole sample.

Structure-Activity Relationship of Heterocyclic P2Y14 Receptor Antagonists: Removal of the Zwitterionic Character with Piperidine Bioisosteres

A known zwitterionic, heterocyclic P2Y14R antagonist 3a was substituted with diverse groups on the central phenyl and terminal piperidine moieties, following a computational selection process. The most potent analogues contained an uncharged piperidine bioisostere, prescreened in silico, while an aza-scan (central phenyl ring) reduced P2Y14R affinity. Piperidine amide 11, 3-aminopropynyl 19, and 5-(hydroxymethyl)isoxazol-3-yl) 29 congeners in the triazole series maintained moderate receptor affinity. Adaption of 5-(hydroxymethyl)isoxazol-3-yl gave the most potent naphthalene-containing (32; MRS4654; IC50, 15 nM) and less active phenylamide-containing (33) scaffolds. Thus, a zwitterion was nonessential for receptor binding, and molecular docking and dynamics probed the hydroxymethylisoxazole interaction with extracellular loops. Also, amidomethyl ester prodrugs were explored to reversibly block the conserved carboxylate group to provide neutral analogues, which were cleavable by liver esterase, and in vivo efficacy demonstrated. We have, in stages, converted zwitterionic antagonists into neutral molecules designed to produce potent P2Y14R antagonists for in vivo application.

Two Faces of Water in the Formation and Stabilization of Multicomponent Crystals of Zwitterionic Drug-Like Compounds

Two new hydrated multicomponent crystals of zwitterionic 2-aminonicotinic acid with maleic and fumaric acids have been obtained and thoroughly characterized by a variety of experimental (X-ray analysis and terahertz Raman spectroscopy) and theoretical periodic density functional theory calculations, followed by Bader analysis of the crystalline electron density) techniques. It has been found that the Raman-active band in the region of 300 cm−1 is due to the vibrations of the intramolecular O-H...O bond in the maleate anion. The energy/enthalpy of the intermolecular hydrogen bonds was estimated by several empirical approaches. An analysis of the interaction networks reflects the structure-directing role of the water molecule in the examined multicomponent crystals. A general scheme has been proposed to explain the proton transfer between the components during the formation of multicomponent crystals in water. Water molecules were found to play the key role in this process, forming a “water wire” between the COOH group of the dicarboxylic acid and the COO– group of the zwitterion and the rendering crystal lattice of the considered multicomponent crystals.

Into the Fray! A Beginner's Guide to Medicinal Chemistry

Modern medicinal chemistry is a complex, multidimensional discipline that operates at the interface of the chemical and biological sciences. The medicinal chemistry contribution to drug discovery is typically described in the context of the well-recited linear progression of the drug discovery pipeline. However, compound optimization is idiosyncratic to each project, and clear definitions of hit and lead molecules and the subsequent progress along the pipeline becomes easily blurred. In addition, this description lacks insight into the entangled relationship between chemical and pharmacological properties, and thus provides limited guidance on how innovative medicinal chemistry strategies can be applied to solve optimization problems, regardless of the stage in the pipeline. Through discussion and illustrative examples, this article seeks to provide insights into the finesse of medicinal chemistry and the subtlety of balancing chemical properties pharmacology. In so doing, it aims to serve as an accessible and simple-to-digest guide for anyone who wishes to learn about the underlying principles of medicinal chemistry, in a context that has been decoupled from the pipeline description.