Modified aqueous mobile phases: A way to improve retention behavior of active pharmaceutical compounds and their impurities in liquid chromatography

Most commonly used analytical technique for determination of active pharmaceutical ingredients and their impurities in quality control throughout all phases of drug research, development and manufacture is definitely reversed-phase high performance liquid chromatography (RP-HPLC). However, pharmaceutical industry professionals are often faced with various challenges in RP mode, which cannot be resolved with common variations in the composition of the mobile phase. These challenges often occur when analyzing compounds that contain basic ionizable groups, possess large differences in polarities and require consumption of high amounts of toxic organic solvents. Among available strategies for addressing the aforementioned issues, the most convenient one includes RP-HPLC mobile phase modifications by an addition of the proper chemical compounds. In that respect, RP-HPLC method can be easily adapted to the needs of the analysis without time-consuming and expensive equipment procurement. In this review the chaotropic chromatography, micellar liquid chromatography, and cyclodextrin modified RP-HPLC systems are presented and discussed in details. Special attention is devoted to the theoretical background, the possibility of retention modeling and applications in various fields of pharmacy, as well as their prospective in further research

Cyclodextrin-based supramolecular systems of emerging guests with pharmaceutical and environmental interest

L'objectiu de la present tesi és estudiar i caracteritzar les interaccions moleculars entre les ciclodextrines (CD) o materials a base de ciclodextrines, amb molècules hoste emergents com ara fàrmacs i toxines d'interès industrial. En general, la tesi presentada ha contribuït a ampliar el coneixement actual sobre lús de CD per a aplicacions farmacèutiques i mediambientals. Els estudis de caracterització i la investigació dels mecanismes dels complexos d'inclusió de CD amb l'inhibidor enzimàtic mesilat de nafamostat i la neurotoxina veratridina constitueixen els primers informes a la literatura de les interaccions de CD amb aquestes molècules hoste. A més, la síntesi i caracterització de nanoesponges de ciclodextrina (CD-NS) amb diferents agents reticulants de molècules d'anhídrid amplia l'estat de l'art actual sobre materials polimèrics basats en CD i representa un nou ús potencial de CD-NS com a absorbents passius de toxines marines.El objetivo de la presente tesis es estudiar y caracterizar las interacciones moleculares entre las ciclodextrinas (CD) o materiales a base de ciclodextrinas, con moléculas huésped emergentes tales como fármacos y toxinas de interés industrial. En general, la tesis presentada ha contribuido a ampliar el conocimiento actual sobre el uso de CD para aplicaciones farmacéuticas y medioambientales. Los estudios de caracterización y la investigación de los mecanismos de los complejos de inclusión de CD con el inhibidor enzimático mesilato de nafamostat y la neurotoxina veratridina, constituyen los primeros informes en la literatura de las interacciones de CD con estas moléculas huésped. Además, Spanish la síntesis y caracterización de nanoesponjas de ciclodextrina (CD-NS) con diferentes agentes reticulantes de moléculas de anhídrido amplía el estado del arte actual sobre materiales poliméricos basados en CD y representa un nuevo uso potencial de CD-NS como adsorbedores pasivos de toxinas marinas.The aim of the present thesis is to study and characterize the molecular interactions between cyclodextrins (CDs) or cyclodextrin-based materials with emerging guest molecules such as drugs or toxins of industrial interest. Overall, the presented thesis has contributed to expand the current knowledge on the use of CDs for pharmaceutical and environmental applications. The studies of characterization unveiled the mechanisms of CD inclusion complexes with serine protease inhibitor nafamostat mesylate and veratridine neurotoxin and constitute the first reports in the literature of CD interactions with these emerging guests. Furthermore, the synthesis and characterization of CD-NS with English different anhydride crosslinkers broadens the current state of the art on CD-based polymeric materials and represents a potential novel use of CD-NS as passive adsorbers for marine toxins

The formation of host–guest complexes between surfactants and cyclodextrins

Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host–guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host–guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD–surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature. In general, the surfactant–cyclodextrin association is treated without reference to the kinetics of the process. However, there are several examples where the kinetics of the process can be investigated, in particular those where volumes of the CD cavity and surfactant (either the tail or in special cases the head group) are similar in magnitude. This will also be critically reviewed

Computational approaches in supramolecular chemistry with a special focus on virtual screening

Within this thesis novel computational tools for the rational design of synthetic host-guest complexes (SHGC) were developed and applied that employ the concepts of efficient virtual screening (VS) approaches. The first part describes the development of a fast structure prediction tool for flexible SHGC. The tool was validated on a test dataset comprising crystallographically determined SHGC. In nine of ten cases near-native solutions were generated. The tool can be applied for VS. In the second part of the thesis computational techniques were applied for designing SHGC based on ß-cyclodextrins (ß-CD). We performed a structure-based inverse virtual screening for identifying modified ß-CDs as receptors for the anticancer drug camptothecin (CPT). Six of the proposed receptors exhibited binding affinities which were significantly higher than for any other CPT-receptor. Furthermore, we applied a combination of a similarity-based virtual screening technique with a regression model (RM) for identifying novel high affinity guest molecules of ß-CD. Ten of the proposed guest molecules exhibited a binding free energy of lower than -20 kJ/mol. The last chapter describes a comparison of regression methods regarding their ability to generate predictive RM for thermodynamical parameters (dG, dH and dS) of ß-CD-guest complexes. dG could be predicted in good agreement with experimental values, none of the methods led to comparably good predictive models for dH. dS appears almost unpredictable.Im Rahmen dieser Arbeit wurden rechnergestützte Verfahren (RGV) zum gezielten Entwurf von synthetischen Wirt-Gast Komplexen (SWGK) entwickelt und eingesetzt. Dabei wurde ein Fokus auf schnelle virtuelle Screening (VS) Verfahren gelegt. Der erste Teil beschreibt die Entwicklung eines Programms zur schnellen Strukturvorhersage von flexiblen SWGK. Das Programm wurde auf einem Testdatensatz an kristallographisch vermessenen SWGK validiert. Für neun von zehn SWGK wurden nativ-ähnliche Lösungen gefunden. Das Programm kann für VS eingesetzt werden. Der zweite Teil der Arbeit behandelt RGV zum gezielten Entwurf von ß-Cyclodextrin (ß-CD) Komplexen. Mit Hilfe eines strukturbasierten inversen VS wurden sechs modifizierte ß-CD-Rezeptoren für den Krebsarzneistoff Camptothecin (CPT) gefunden, die deutlich höhere Bindungsaffinitäten zu CPT aufwiesen als alle bislang bekannten CPT-Rezeptoren. Zur Identifizierung neuer hochaffiner Gäste von ß-CD wurde ein ähnlichkeitsbasiertes VS Verfahren in Kombination mit einem Regressionsmodell (RM) eingesetzt. Zehn der mit Hilfe dieses Verfahrens vorgeschlagenen Moleküle wiesen eine Bindungsenergie von unter -20 kJ/mol auf. Das letzte Kapitel beschreibt einen Vergleich von drei Regressionsverfahren. Es wurde die Fähigkeit untersucht, vorhersagekräftige RM für thermodynamische Parameter (dG, dH und dS) von ß-CD-Gast-Komplexen zu generieren. dG konnte mit allen Methoden sehr gut vorhergesagt werden, während dH nur begrenzt und dS unzureichend vorhersagbar war

Cyclodextrin Chemistry and Toxicology

This is a reprint of the Special Issue "Cyclodextrin Chemistry and Toxicology”. This is a collection of eleven articles and three reviews that was published in Molecules that provides an overview of the applications of cyclodextrins, implements the information regarding the use of cyclodextrins and their inclusion complexes, considering both experimental and theorists approaches and using various scientific and technological tools

Cyclodextrin supramolecular systems for oral antiretroviral drug delivery

The global pandemic of Human Immunodeficiency Virus (HIV) is responsible for the death of more than 39 million people. Currently, about 37 million people are infected with an estimated rate of 2.1 million new cases and 1.2 million HIV related deaths per annum. Over the past three decades, Antiretroviral Therapy (ART) has significantly improved HIV prognosis and health related quality of life. However, HIV still remains a significant public health and socio-economic concern due to the inability to cure or completely eradicate both long-lived latently infected cells and replication competent provirus from anatomical and lymphatic reservoirs. This has necessitated lifelong pharmacotherapy in order to keep the viral loads below detection and prevent progression of the infection to full blown Acquired Immune Deficiency Syndrome (AIDS). Presently, antiretroviral (ARVs) drugs used in the management of HIV are administered orally due to the volume and ambulatory nature of the lifelong therapeutic interventions. However, poor oral bioavailability, inadequate biodistribution and adverse side effects of many ARVs continue to preclude optimal therapeutic outcomes. In recent years, there has been an increased interest in the development of ARV delivery systems specifically tailored to improve HIV's therapeutic outcomes. Within this context, cyclodextrins (CyD) based drug delivery systems offer several possibilities for constructing an ARV drug delivery system with enhanced bioavailability, biodistribution and therapeutic performance. The traditional role of cyclodextrins (CyDs) in the pharmaceutical industry has been to enhance the aqueous solubility, physicochemical and physiological stability, the deliverability and therapeutic performance, and reduce the adverse side effects of several active pharmaceutical ingredients (APIs). Also, CyDs have been reported to modulate cytochrome P450 (CYP450) metabolism and p-glycoprotein (P-gp) efflux transport for enhanced drug pharmacokinetic profiles. Thus, this study was designed to explore the utility of CyD supramolecular systems in the development of an oral ARV delivery system with enhanced pharmacokinetic properties. Lopinavir (LPV), a potent inhibitor of HIV-1 protease and a Class 4 Biopharmaceutical Classification System (BSC) drug with poor oral bioavailability was chosen as our model drug. LPV's poor bioavailability is a combined effect of low aqueous solubility, P-gp efflux transport/low gastric permeability and CYP450 3A metabolism. Presently, LPV is clinically available as a co-formulation with suboptimal doses of ritonavir (RTV) which enhances oral bioavailability by inhibiting LPV's metabolism. The adverse side effects associated with RTV has made necessary the development of a RTV free LPV formulation. Also, paediatric formulations of LPV (even with RTV) is fraught with problems such as the presence of high quantities of ethanol and propylene glycol in the commercially available oral solution. Therefore, an in silico method was developed an validated experimentally (using ibuprofen as model drug) to study the host-guest molecular interaction between LPV and CyD, and to predict the best CyD molecule for developing a CyD based LPV delivery system. The predicted derivative of (2-hydroxyl)propyl-gamma-cyclodextrin (HP-γ-CyD) with a high degree of substitution (DS) that is, HP17-γ-CyD, was synthesized and evaluated comparatively with parent γ-CyD and commercially available HP-γ-CyD. The applicability of supercritical assisted spray drying (SASD), a non-toxic and cheap method for enhancing CyD complex formation was also evaluated. Then, polymer CyD (pCyD) sub-microcarriers were synthesized, loaded with LPV and evaluated for its ability to modulate drug release and enhance antiviral activity. The results suggests the application of in silico methodologies is a feasible approach for the rational and/or deductive development of CyD based drug delivery systems. The predicted HP17-γ-CyD facilitated a higher LPV amorphization and solubilization relative to the parent γ-CyD and commercially available HP-γ-CyD. Also, the application of SASD technique for preparing LPV-CyD complexes enhanced drug solubilization and complexation. With regards to the sub-microcarrier, results indicate the successful synthesis of a water soluble p(CyD) based on (2-hydroxyl)propyl-beta-cyclodextrin (HP-β-CyD) and methyl-beta-cyclodextrin (M-β-CyD) as monomers, and pyromellitic dianhydride as crosslinker. The physicochemical analysis of the LPV loaded pCyD revealed the successful preparation of sub-micron sized particles with good encapsulation efficiencies, a pCyD mediated amorphization of LPV and a significant increase in LPV solubilization and release. In vitro cytotoxicity of the pCyD and their LPV formulations revealed good safety profiles in Caco-2 and Sup-T1 cell lines. Results obtained from the in vitro antiviral assays revealed a dose independent HIV-1 inhibition by the synthesized pCyD and a CyD monomer dependent synergistic antiviral activity in their formulations. Overall, the study contributed to a better understanding of in silico methodologies as predictive tools for CyD selection in drug development. It was possible to completely avoid the tedious and time/resource consuming traditional approach of selecting CyD by calculating association constants from phase solubility studies or isothermal titration calorimetry. The application of SASD for drug-CyD complexation seems an interesting alternative to conventional spray drying and other methods of CyD solid complex formation. Also, considering the potential for drug dose reduction without a compromise on antiretroviral activity, the synthesized pCyDs represent a promising approach for formulating new alternatives to clinically available antiretroviral drugs. In conclusion, all the results obtained in this experimental work showed the interest of CyDs as promising vehicles for the development of ARV drug delivery systems with enhanced pharmacokinetic profiles

Nuevas aportaciones al desarrollo de modelos QSAR/QSPR para la predicción de la mutagenicidad de contaminantes ambientales y su interacción con sustancias activas presentes en el medio

Se estudió mediante modelos QSAR, la posible mutagenicidad de sustancias presentes en el medio ambiente como los ácidos haloacéticos (derivados de la cloración del agua) y los carbonilos alfa, beta insaturados (sobre todo los empleados como monómeros para la preparación de materiales dentales de restauración) y su posible interacción con la beta ciclodextrina, la cual está presente como excipiente en productos farmacéuticos y como estabilizador de aromas, colorantes y algunas vitaminas en alimentos. Como resultado de este estudio pudimos destacar: -El ácido fluoroiodoacético y difluoroiodoacético podrían ser mutagénicos debido a los valores de potencia mutagénica obtenidos con los modelos desarrollados. Sustancias que podrían encontrarse en aguas fluoradas ricas en ioduro/bromuro. Además es posible que estén presentes en aguas fluoradas ricas en bromuro/ioduro hecho que pondría en duda la necesidad de fluorar el agua potable. - Sustancias comúnmente empleadas como monómeros dentales presentaron predicciones negativas para el ensayo de Ames y un carácter mutagénico para el ensayo con células de mamífero, a excepción del UDMA (Uretil dimetacrilato). - Respecto a la posible interacción de estas sustancias con la beta-ciclodextrina, los ácidos haloacéticos presentan valores de complejación inferiores a los que normalmente presentan fármacos o componentes de los alimentos, por lo que es de esperar que la interacción entre los ácidos haloacéticos y la beta-CD sea de escasa importancia. En cuanto a los monómeros dentales hay que resaltar que sustancias como el TEGDMA, 1,6-ADMA, 1,8-ADMA, GMR, MEPC y 6-HHMA, predichos como mutagénicos, presentan valores de complejación superiores a los que presentan fármacos o componentes de los alimentos. Por lo tanto, estas sustancias podrían desplazar de sus complejos a fármacos o componentes de los alimentos pudiéndose llegar a algún tipo de interacción.Farmaci

Encapsulation of sulfamethazine drug by β-cyclodextrins and its adsorption on carbon nanotubes

Sulfonamides are preventive and therapeutic agents for certain infections caused by gram-positive and gram-negative microorganisms. At the same time, their widespread application is hindered by their low solubility in aqueous media. Since the water solubility of sulfonamide drugs is increased in the presence of cyclodextrins, the host-guest type complex formation of these antibiotics with cyclodextrins is an extensively studied field. Sulfamethazine is a representative member of the sulfonamide antibiotic drugs, it is still used in human and veterinary therapy. Previous studies described the ability of -cyclodextrin to increase the solubility of this drug in aqueous solution and studied the structure of the complexes by experimental and molecular modeling techniques. This work aims to examine the interactions of sulfamethazine with two β-cyclodextrin derivatives at different pH in the temperature range of 298-313 K. Results showed the formation of stable complexes of sulfamethazine with both native and randomly methylated β-cyclodextrin host molecules. Spectroscopic measurements and molecular modeling studies indicated the possible driving forces (hydrophobic interaction, hydrogen bonding, and electrostatic interaction) of the complex formation, and highlighted the importance of the reorganization of the solvent molecules during the entering of the guest molecule into the host’s cavity. Functionalization of the β-cyclodextrin molecule does not affect considerably the complex stabilities, therefore the native β-cyclodextrin molecule looks the simplest and most effective inclusion host to design a selective and sensitive tool for sulfamethazine detection. The protonation state of this drug affects not only its aqueous solubility but controls its inclusion complexes with -cyclodextrins. The pH-affected structures of the complexes explain previous contradictory findings based on the inclusion of the aniline moiety as well as the pyrimidine ring through the cyclodextrin cavity. Furthermore, surprisingly, the interaction between the neutral and anionic forms of the guest molecule and cyclodextrins with electron rich cavity is thermodynamically more favorable compared to the cationic guest. This property probably due to the enhanced formation of the zwitterionic form of sulfamethazine in the hydrophobic cavities of cyclodextrins, which affect significantly the stability of sulfamethazine - cyclodextrin complexes. Since sulfonamide antibiotics, including sulfamethazine, are poorly metabolized, they can be found in surface water, in wastewater and in meat-producing animals with considerable concentrations. Therefore, several studies have focused on the sulfonamide drugs adsorption on different kinds of natural and synthetic materials to remove them from the environment. Accordingly, in this work, the removal of sulfamethazine from water has also been tested. Based on the interaction between sulfamethazine and -cyclodextrin, a cyclodextrin containing insoluble polymer has been tested to extract sulfamethazine from aqueous solution. Furthermore, carbon nanotubes, successfully used for the adsorption of several antibiotics earlier, have also been investigated as possible sorbents to eliminate this drug from aqueous solution. Systematic analysis has been done to describe the effect of the number of layers of walls and the effect of the functionalization of the carbon nanotubes. Results showed that although insoluble -cyclodextrin bead polymer is not applicable for removing sulfamethazine from aqueous solution effectively, single-walled carbon nanotubes are suitable for extracting this antibiotic from aqueous media. These observations might be relevant for the preparation of orally administered products of sulfonamide-cyclodextrin complexes which can be useful in finding materials suitable for developing new sulfonamide drug binders to remove these drugs from contaminated beverages, e.g. from drink water