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The work aimed to develop the Absorption Driven Drug Formulation (ADDF) concept, which is a new approach in formulation development to ensure that the drug product meets the expected absorption rate. The concept is built on the solubility-permeability interplay and the rate of supersaturation as the driving force of absorption. This paper presents the first case study using the ADDF concept where not only dissolution and solubility but also permeation of the drug is considered in every step of the formulation development. For that reason, parallel artificial membrane permeability assay (PAMPA) was used for excipient selection, small volume dissolution-permeation apparatus was used for testing amorphous solid dispersions (ASDs), and large volume dissolution-permeation tests were carried out to characterize the final dosage forms. The API-excipient interaction studies on PAMPA indicated differences when different fillers or surfactants were studied. These differences were then confirmed with small volume dissolution-permeation assays where the addition of Tween 80 to the ASDs decreased the flux dramatically. Also, the early indication of sorbitol’s advantage over mannitol by PAMPA has been confirmed in the investigation of the final dosage forms by large-scale dissolution-permeation tests. This difference between the fillers was observed in vivo as well. The presented case study demonstrated that the ADDF concept opens a new perspective in generic formulation development using fast and cost-effective flux-based screening methods in order to meet the bioequivalence criteria.

Purpose The aim of our work was to develop a biorelevant dissolution method for a better understanding of the in vivo performance of delayed-release tablet formulations. Methods The typical pH profile and residence times in the stomach and small intestine were determined in fasted conditions based on the published results of swallowable monitoring devices. Then, a multi-stage pH shift dissolution method was developed by adding different amounts of phosphate-based buffer solutions to the initial hydrochloric acid solution. Because of the highly variable in vivo residence times in the stomach, two alternatives of the method were applied, modeling rapid and slow gastric emptying as well. This approach provided an opportunity to study the effect of the acidic treatment on post gastric release. Six enteric-coated low-dose acetylsalicylic acid (ASA) formulations including the reference Aspirin Protect were tested as a model compound. Moreover, the thickness of the coating of each formulation was investigated by scanning electron microscope. Results Comparing the in vitro results to the known properties of the formulations, the new method was found to be more discriminative than the USP dissolution method. Ingredients affecting the in vitro dissolution, and thus probably the in vivo performance, were identified in both the tablet core and the coating of the tested formulations. The limited available in vivo data also indicated an increased predictivity. Conclusion Overall, the presented method may be an efficient tool to support the development of enteric coated generic formulations. Graphical abstract

Absorption through the skin of topically applied chemicals is relevant for both formulation development and safety assessment, especially in the early stages of development. However, the supply of human skin is limited, and the traditional in vitro methods are of low throughput. As an alternative, an artificial membrane-based Skin Parallel Artificial Membrane Permeability Assay (Skin-PAMPA) has been developed to mimic the permeability through the stratum corneum. In this study, this assay was used to measure the permeability of a model compound, 4-phenylethyl-resorcinol (PER), dissolved in 13 different solvents that are commonly used in cosmetic formulation development. The study was performed at concentrations close to the saturated solution of PER in each solvent to investigate the maximum thermodynamic potential of the solvents. The permeability of PER in selected solvents was also measured on ex vivo pig skin for comparison. Pig ear skin is an accepted alternative model of human skin. The permeability coefficient, which is independent of the concentration of the applied solution, showed a good correlation (R2 = 0.844) between the Skin-PAMPA and the pig skin permeation data. Our results support the use of the Skin-PAMPA to screen the suitability of different solvents for non-polar compounds at an early stage of formulation development.

Isoflavonoids with various structural elements show a promising potential effect on central nervous system activities. Despite their favorable medicinal properties, the pharmacokinetic characteristics of this thoroughly investigated group of natural phenolics have only been described to a limited extent. Regarding the lack of information about the BBB permeability of isoflavones, isoflavanones, and pterocarpans found in Ononis species, the aim of our study was to investigate their physico-chemical properties influencing their absorption and distribution. Furthermore, we aimed to characterize the possible MAO-B inhibiting features of Ononis isoflavonoids in silico. Octanol-water partitioning and BBB-PAMPA permeability of formononetin, calycosin D, onogenin, sativanone, medicarpin and maackiain were assessed for the first time in our study. The log P values ranged from 2.21 to 3.03 and log D7.4 values from 2.48 to 3.03, respectively, indicating optimal polarity for BBB permeation. The results of PAMPA-BBB expressed as log Pe values fell between -5.60 and -4.45, predicting their good permeation capability as well. The effective permeability values showed structure-dependent differences, indicating that the pterocarpan type skeleton was the most preferred type, followed by isoflavanones, then isoflavones. The methoxy or methylenedioxy substitution of the same skeleton did not influence the permeability significantly, contrary to an additional hydroxyl group. Membrane retention showed a similar structure dependent pattern to that of effective permeability, ranging from 16% to 70%. For the identification of volumes of chemical space related to particular biological activities the ChemGPS-NP framework was used. The MAO-B inhibitory potency and selectivity were also predicted and validated. Based on our results, MAO-B inhibitory potency could be predicted with good precision, but in the case of selectivity, only the direction could be concluded (favors MAO-B or MAO-A), not the magnitude. Our finding reflects that Ononis isoflavonoid aglycones show an excellent fit with the suggested parameters for BBB permeability and this is the first study to confirm the highly favorable position of these natural products for MAO-B inhibition.

The work aimed to develop the Absorption Driven Drug Formulation (ADDF) concept, which is a new approach in formulation development to ensure that the drug product meets the expected absorption rate. The concept is built on the solubility-permeability interplay and the rate of supersaturation as the driving force of absorption. This paper presents the first case study using the ADDF concept where not only dissolution and solubility but also permeation of the drug is considered in every step of the formulation development. For that reason, parallel artificial membrane permeability assay (PAMPA) was used for excipient selection, small volume dissolution-permeation apparatus was used for testing amorphous solid dispersions (ASDs), and large volume dissolution-permeation tests were carried out to characterize the final dosage forms. The API-excipient interaction studies on PAMPA indicated differences when different fillers or surfactants were studied. These differences were then confirmed with small volume dissolution-permeation assays where the addition of Tween 80 to the ASDs decreased the flux dramatically. Also, the early indication of sorbitol's advantage over mannitol by PAMPA has been confirmed in the investigation of the final dosage forms by large-scale dissolution-permeation tests. This difference between the fillers was observed in vivo as well. The presented case study demonstrated that the ADDF concept opens a new perspective in generic formulation development using fast and cost-effective flux-based screening methods in order to meet the bioequivalence criteria. Graphical Abstract.

In this work, two different approaches have been developed to predict the food effect and the bioequivalence of marketed itraconazole (ITRA) formulations. Kinetic solubility and simultaneous dissolution-permeation tests of three (ITRA) formulations (Sporanox capsules and solution and SUBA-ITRA capsules) were carried out in simulated fasted and fed states. Fraction of dose absorbed ratios estimating food effect and bioequivalence were calculated based on these results and were compared to the in vivo study results published by Medicines Agencies. The comparison demonstrated that kinetic solubility and flux values could be used as input parameters for biopharmaceutics modeling and simulations to estimate food effect and bioequivalence. Both prediction methods were able to determine a slightly negative food effect in the case of the Sporanox solution and also a pronounced positive food effect for the Sporanox capsule. Superior bioavailability was predicted when the Sporanox solution was compared to the Sporanox capsule (in agreement with in vivo data).

Aims: The aqueous solubility of two polymorphic forms of venlafaxine hydrochloride was investigated. Methods: The pH-dependent solubility (SpH) over a wide pH range was measured by saturation shake-flask (SSF) method at 25 °C. The solubility of the free base form was depicted by the intrinsic solubility (So). To identify the solid form present at the solubility equilibrium, X-ray powder diffraction (XRPD) and Raman spectroscopy was carried out. The dissolution was studied using real time concentration monitoring applying fiber optic UV probes. Results: No difference was found in the SpH values of Form I and Form II, in the pH range 7.5-12. Solid phase isolated from pH 10-12 suspensions was identified as free base by XRPD and Raman spectroscopy. Precipitates separated from pH 7-8 samples were also identical product. The transition of polymorphs to the free base was supported by the real time dissolution analysis. Conclusion: In this study we demonstrated a good agreement of equilibrium solubility measured by SSF method and in-situ UV fiber optic method. µDISS ProfilerTM has the advantage to provide much more information about dissolution process; with this approach the dissolution kinetic, the supersaturation and the time needed to reach the equilibrium can be easily monitored.

The aim of this research was to investigate the driving force of membrane transport through size-exclusion membranes and to provide a concentration-based mathematical description of it to evaluate whether it can be an alternative for lipophilic membranes in the formulation development of amorphous solid dispersions. Carvedilol, an antihypertensive drug, was chosen and formulated using solvent-based electrospinning to overcome the poor water solubility of the drug. Vinylpyrrolidone-vinyl acetate copolymer (PVPVA64) and Soluplus were used to create two different amorphous solid dispersions of the API. The load-dependent effect of the additives on dissolution and permeation through regenerated cellulose membrane was observed by a side-by-side diffusion cell, μFLUX. The solubilizing effect of the polymers was studied by carrying out thermodynamic solubility assays. The supersaturation ratio (SSR, defined as the ratio of dissolved amount of the drug to its thermodynamic solubility measured in exactly the same medium) was found to be the driving force of membrane transport in the case of size-exclusion membranes. Although the transport through lipophilic and size-exclusion membranes is mechanistically different, in both cases, the driving force of membrane transport in the presence of polymer additives was found to be the same. This finding may enable the use of size-exclusion membranes as an alternative to lipid membranes in formulation development of amorphous solid dispersions.

Incubation time plays a critical role in the accurate measurement of equilibrium solubility of compounds. Substances which dissolve very slowly generally need long incubation times (days or weeks) to reach equilibrium. However, long times may pose several problems, such as decomposition of solute, molding of buffer, and drifting of pH. Higuchi in 1979 proposed the Facilitated Dissolution Method (FDM) to dramatically reduce incubation time. It employs a small volume of water-immiscible organic solvent to partly solubilize the sample and thereby increase the surface area available for dissolution. The method has been used only rarely. In this study we performed a systematic validation of FDM using progesterone as model compound. The reference solubility value, 7.95±0.21μg/mL (p0.05, n=5), was determined in Britton-Robinson buffer solution (pH7.4) at 25.0°C by the standardized protocol of Saturation Shake-Flask (SSF) method. Also, the solubility was measured by the FDM approach under varied experimental conditions (e.g., type and volume of organic solvent, time of agitation, and amount of solid excess), and compared to the reference value. It was demonstrated that the small amount of organic solvent used in the FDM does not impact the measured solubility, compared to the reference value. Additionally, four compounds of low dissolution rate (dexamethasone, digoxin, haloperidol and cosalane) were used to demonstrate that FDM can reduce the long equilibration time to the standardized 24h (6h stirring and 18h sedimentation). The time dependence of solubility equilibrium was measured by SSF, and the results were compared with those obtained by FDM. Our study, based on200 solubility experiments, supports the validity of Higuchi's method. In this study we propose a standardized protocol for the FDM, where 1% v/v of organic solvent is used. Octane (or isooctane) was found to be suitable for highly hydrophobic compounds. Alternatively, octanol or 1,2-dichloroethane can be used for less lipophilic compounds.

In the literature the therapeutic nonequivalence of oxytetracycline hydrochloride (OTCH) capsules and tablets was attributed to the different aqueous solubility of polymorphs without their comprehensive study. Our aim was to reveal the effects of polymorphism on equilibrium solubility, dissolution kinetics and the supersaturation of two OTCH polymorphs (stable Form A and metastable Form B).The equilibrium solubility was measured in biorelevant pH range 4-7.4 by the standardized saturation shake-flask method. We also studied the solubility in SGF at pH 1.2 and the effect of the pH change from 1.2 to 5.0 on solubility. The dissolution was studied using real-time concentration monitoring with an ATR probe attached to a UV spectrophotometer (µDISS Profiler). A wide spectrum of solid phase analysis methods (SEM, IR, XRPD, Raman) was applied for characterization of polymorphs and to identify which form is present at the equilibrium solubility. Identical equilibrium solubility values were obtained at the same pHs in region 4.0-7.4 using the two polymorphs as starting materials. The XRPD analysis of the isolated solid phases proved that both polymorphic forms were converted to dihydrate form. In situ monitoring of the dissolution at pH 5.0 showed immediate dissolution, no difference in supersaturation, and short equilibration time for both forms indicating the immediate conversion. In SGF (pH 1.2) Form B dissolved better than Form A and showed significantly different dissolution kinetic and stability. A long-lasting, false chain-citation stating that Form B dissolves 28x better in water than Form A, was cut by the present study (i) revealing that the cited data was measured in IPA not in water, and (ii) proving that only the intrinsic solubility of OTC dihydrate can be measured in water due to conversion of polymorphs under the experimental conditions of solubility measurement. However this conversion is inhibited below pH 1.5, so the differences in solubility and dissolution kinetic found at pH 1.2 may contribute to the interpretation of the different serum-levels reported at solid formulations.

The phase separation is a crucial step in equilibrium solubility measurements. In the standardized protocol of saturation shake-flask method, sedimentation is proposed as the safest technique. However filtration is widely used in pharma practice. In this paper the effect of the filtration on the measured equilibrium solubility results is presented. The equilibrium solubility values of four model compounds, namely diclofenac sodium, hydrochlorothiazide, papaverine hydrochloride and progesterone were determined at various pH values using the saturation shake-flask method. Two phase separation techniques (sedimentation and filtration) were applied for the separation of the solid from the saturated solution. Four membrane filters, polyvinylidene fluoride (PVDF), polyether sulfone (PES), polytetrafluoroethylene (PTFE) and nylon, as well as an analytical filter paper were investigated. The results obtained by filtration were compared with those measured by sedimentation and the distortion effect of the filter (DEF) on solubility results was expressed in %. The results showed that the filter material type is able to remarkably influence the results in solubility measurements. In several cases, the significant adsorption to the filter caused high inaccuracy in the measured concentration value, more over in some cases failed to work at all. As a main conclusion of this work, if the step of filtration is inevitable, the adsorption to the filter can be mitigated with the appropriate filter type selection what needs some experiences and knowledge about the acid-base chemistry and polar/apolar nature of the sample.

The purpose of this work was to investigate the temperature dependence of permeability measured by PAMPA method. The effective permeability (log Pe) of seven drugs representing diverse structures and different acid–base properties was determined on three membrane models (GIT, BBB, Skin). The incubation temperature was varied in the range of 15–55 °C with ten degree steps. The intrinsic permeability (log P0) of the compounds is in linear relation with temperature (T). The slope of the log P0 = aT + b regression equation is a good measure of the temperature effect on permeability. Results show intensive and significant temperature dependence of permeability influenced by the properties of the compounds and also by the selected PAMPA model. The Skin PAMPA™ proved to be the most sensitive on temperature alteration, though GIT and BBB PAMPA results were also affected. The compound with acid function showed the lowest temperature dependence, while the permeability of bases increased considerably in response to the increasing temperature. The importance of human-relevant incubation conditions at in vitro assays is concluded for the better in vivo prediction.

The following paragraphs describe the options of applying artificial membranes for the prediction of transdermal penetration, focusing mostly on the PAMPA method. A model membrane of PAMPA mimicking skin penetration was first described in 2006, but the need for a more bio-mimetic system has arisen with new industrial tendencies, and a more bio-relevant system was published in 2012. Since its first publication, Skin PAMPA has already been applied by several universities and industrial groups successfully and the first articles, podium, and poster presentations have appeared. Application of the Skin PAMPA model has been extended and examples for testing of semi-solid formulations and transdermal patches are available, besides the standard solution applications.

Besides the opioids the standard management of the World Health Organization suggests NSAIDs (non-steroidal anti-inflammatory drugs) alone or in combination to enhance analgesia in malignant and non-malignant pain therapy. The applicability of NSAIDs in a nasal formulation is a new approach in pharmaceutical technology. In order to enhance the nasal absorption of meloxicam (MX) as an NSAID, its salt form, meloxicam potassium monohydrate (MXP), registered by Egis Plc., was investigated in comparison with MX. The physico-chemical properties of the drugs (structural analysis, solubility and dissolution rate) and the mucoadhesivity of nasal formulations were controlled. In vitro and in vivo studies were carried out to determine the nasal applicability of MXP as a drug candidate in pain therapy. It can be concluded that MX and MXP demonstrated the same equilibrium solubility at the pH5.60 of the nasal mucosa (0.017mg/ml); nonetheless, MXP indicated faster dissolution and a higher permeability through the synthetic membrane. The animal studies justified the short Tmax value (15min) and the high AUC of MXP, which is important in acute pain therapy. It can be assumed that the low mucoadhesivity of MXP spray did not increase the residence time in the nasal cavity, and the elimination from the nasal mucosa was therefore faster than in the case of MX. Further experiments are necessary to prove the therapeutic relevance of this MXP-containing innovative intranasal formulation.

The purposes of this study are to evaluate if the PAMPA (Parallel Artificial Membrane Permeability Assay) permeability and the true partition coefficient could be useful for predicting AUC and MIC data of a group of antibacterial fluoroquinolones (FQs). The protonation macro- and microconstants, the n-octanol/water partition coefficients at isoelectric pHs, and the PAMPA permeability of 11 selected FQs were determined, and used to calculate the true partition coefficient, the interactivity parameter between the acidic and basic group, and the apparent intrinsic permeability. It has been shown that the apparent intrinsic permeability correlates well with the AUC in human, whereas the true partition coefficient and the interactivity parameter correlate with 1/MIC values on two Gram-positive bacteria, namely Streptococcus pneumonia and Staphylococcus aureus (methicillin-susceptible). The AUC/MIC ratios predicted from these correlations have shown to be in good agreement with the literature values. It is envisaged that the models described in this study could be useful in the development of new FQs by enabling an early prediction of AUC/MIC ratios based on physicochemical properties.

Cyclic chalcone analogues (2–5) and their ferrocenyl counterparts (6–10) were synthesized and their logP and P388 cyctotoxity were investigated. The structures of the newly synthesized compounds were confirmed by IR 1H and 13NMR spectroscopy. Comparison of conjugation and stereochemistry of the respective derivatives showed similar characteristics compared to ones with some higher degree of conjugation in the ferrocenyl series. Comparison of logP of the ferrocenyl derivatives determined by a validated RP-TLC method showed the ferrocenyl derivatives to have higher logP TLC. The results demonstrate that the differences in three dimensional shape, conjugation and lipophilicity do not have strong influence on the P388 cytotoxicity of the investigated phenyl (1−5) and ferrocenyl (6−10) enones.

A series of new spiro[naphto[2,1-c][2,7]naphtiridine-5,4'-piperidine] derivatives was prepared. Biochemical investigations revealed that all members of this series were potent inhibitors of both NADPH- and Fe(2+)-dependent lipid peroxidation (IC50 < 10 mumol/l) in rat brain microsomes and rat brain homogenate, respectively.

A potentiometric titration study of organic base hydrohalides and quaternary ammonium salts using perchloric acid as the titrant and a mixture of acetic anhydride and acetic acid as the solvent was carried out and the titration mixture was analysed by NMR in order to clarify the chemistry of the reactions involved. It was found that in contrast to the general belief the formation of acetyl halides and titratable free acetate ion does not take place prior to the titration but NMR spectra proved the formation of acetyl halides in the course of the titration. This observation and the fact that the shape of the titration curves depends on the nature of the hydrohaloic acid bound to the base or of the anion in the quaternary ammonium salts led to the conclusion that the titrating agent is acetyl perchlorate formed in situ during the titration. Equations of the reactions involved in the titration process are shown in the paper.

This commentary addresses data quality in equilibrium solubility measurement in aqueous solution. Broadly discussed is the “gold standard” shake-flask (SF) method used to measure equilibrium solubility of ionizable drug-like molecules as a function of pH. Many factors affecting the quality of the measurement are recognized. Case studies illustrating the analysis of both solution and solid state aspects of solubility measurement are presented. Coverage includes drug aggregation in solution (sub-micellar, micellar, complexation), use of mass spectrometry to assess aggregation in saturated solutions, solid state characterization (salts, polymorphs, cocrystals, polymorph creation by potentiometric method), solubility type (water, buffer, intrinsic), temperature, ionic strength, pH measurement, buffer issues, critical knowledge of the pKa, equilibration time (stirring and sedimentation), separating solid from saturated solution, solution handling and adsorption to untreated surfaces, solubility units, and tabulation/graphic presentation of reported data. The goal is to present cohesive recommendations that could lead to better assay design, to result in improved quality of measurements, and to impart a deeper understanding of the underlying solution chemistry in suspensions of drug solids.

A mixture of cosolvents is described that significantly improves the solubility of most pharmaceutical compounds. The mixture consists of equal volumes of MeOH, 1,4-dioxane, and MeCN, thereby containing polar and nonpolar solvents, and is referred to as MDM (from MeOH, dioxane, and MeCN). MDM is mixed with H2O until the required composition is reached. The utility of this system is that it enables analytical measurements to be performed on a wide range of compounds where measurements would be impaired in aqueous solution. We present the physicochemical characteristics of MDM/H2O mixtures (density, dielectric constant, psKw) and the principles of pKa measurement in this solvent/H2O mixture. We also present pKa values in H2O of several drug compounds determined from values measured in MDM/H2O mixtures.

The aim of this study was to investigate the behavior of promising penetration enhancers through the use of 2 different skin test systems. Hydrogel-based transdermal formulations were developed with ibuprofen as a nonsteroidal anti-inflammatory drug. Transcutol and sucrose esters were used as biocompatible penetration enhancers. The permeability measurements were performed with ex vivo Franz diffusion cell methods and a newly developed Skin Parallel Artificial Membrane Permeability Assays (PAMPA) model. Franz diffusion measurement is commonly used as a research tool in studies of diffusion through synthetic membranes in vitro or penetration through ex vivo human skin, whereas Skin PAMPA involves recently published artificial membrane-based technology for the fast prediction of skin penetration. It is a 96-well plate-based model with optimized artificial membrane structure containing free fatty acid, cholesterol, and synthetic ceramide analog compounds to mimic the stratum corneum barrier function. Transdermal preparations containing 2.64% of different sucrose esters and/or Transcutol and a constant (5%) of ibuprofen were investigated to determine the effects of these penetration enhancers. The study demonstrated the good correlation of the permeability data obtained through use of human skin membrane and the in vitro Skin PAMPA system. The Skin PAMPA artificial membrane serves as quick and relatively deep tool in the early stages of transdermal delivery systems, through which the enhancing efficacy of excipients can be screened so as to facilitate the choice of effective penetration components.

The fundamental physico-chemical parameters of sertraline, a potent selective serotonin reuptake inhibitor and reference compound in the development of new antidepressive agents, were determined. The thermodynamic solubility of the hydrochloride salt (S = 4.24 +/- 0.02 mg/ml) and the free base form (S = 0.002 mg/ml) was measured by the saturation shake-flask method. The co-solvent technique in methanol/water mixtures and the Yasuda-Shedlovsky extrapolation were applied for the determination of the dissociation constant (pKa = 9.16 +/- 0.02). The partition of sertraline was studied in octanol/water and alkane/water systems determining the logPoct and logPch)values by potentiometric and shake-flask methods, respectively. These experimental data were used to interpret the excellent pharmacokinetic properties of the molecule. The high lipophilicity value (logPoct = 4.30 +/- 0.01) of the nonionised form confirms the good absorption and distribution in the body. However, the good brain penetration can better be explained with the lack of polar interactions evidenced here by the zero DeltalogP (logPoct-logPch) value of sertraline.

A novel potentiometric procedure has recently been described for rapid measurement of equilibrium aqueous solubility values of organic acids, bases, and ampholytes that form supersaturated solutions. In this procedure, the equilibrium solubility is actively sought by changing the concentration of the neutral form by adding HCl or KOH titrants and monitoring the rate of change of pH due to precipitation or dissolution in a process called Chasing Equilibrium. In this article, we seek to validate the procedure against a shake-flask protocol for solubility determination. A set of 16 small organic compounds, covering a wide range of solubilities was chosen for the study. Interestingly, while 10 compounds in the study were found to chase equilibrium, the others did not. Kinetic solubility data was also collected. It was noted that kinetic solubility was consistently higher than equilibrium solubility for chasers, but correlated well with equilibrium solubility for nonchasers. The ratio of kinetic to equilibrium solubility indicated a compound's ability to form supersaturated solutions.

log P values of 29 biologically active chalcone (1) and cyclic chalcone analogues E -2-(X-benzylidene)-1-indanones (2) and E -2-(X-benzylidene)-1-tetralones (3) have been determined by an optimized and validated RP-TLC method. RP-TLC was performed on silanized silica gel 60F 254 as stationary phase with methanol-water, 60 + 40 ( v/v ) as mobile phase. The RP-TLC method was validated by analysis of three drugs, diazepam, progesterone, and PGE 1 ethyl ester, with known log P SF (shake-flask) values. The experimentally determined log P TLC values were compared with the log P values predicted by use of the CLOGP program. On the basis of the log P TLC values of the investigated chalcones (1), the cyclic chalcone analogues (2, 3), and previously investigated, related, E -2-(X-benzylidene)-1-benzosuberones (4) the effect on lipophilicity of ring size and the nature and position of substituents were studied. It was found that the open-chain chalcones (1) and the five-membered ring E -2-(X-benzylidene)-1-indanones...

Some cyclic chalcone analogues [E-2-(X-benzylidene)-1-indanones, -tetralones, and -benzosuberones], on-plate UV light-catalyzed formation of new chromatographic spots, can be observed during thin-layer chromatography (TLC). Gas chromatographic (GC) analysis of selected derivatives indicates the formation of one new substance in each case. GC coupled with mass spectrometry and 1 H NMR analysis of the samples reveals that the compounds formed are the respective Z-2-(X-benzylidene)-1-indanones, -tetralones, and -benzosuberones. Two-dimensional TLC shows that the E/Z isomerization is a reversible process. By means of the RP-TLC, the logarithm of n-octanol-water partition coefficient (log P) values of E- and Z-isomeric pairs of selected 2-(X-benzylidene)-1-benzosuberones is determined. The Z-isomers are less lipophilic than the E-isomers.

The protonation macro- and microconstants have been measured for tyramine at three temperatures using potentiometry combined with UV spectroscopy. The experimentally determined zwitterion/neutral tautomerization equilibrium constant for tyramine in aqueous solution decreases with increasing temperature from log kz = 1.03 at T = 287 K to log k z = 0.39 at T = 310 K. Using the van't Hoff isochore, the tautomerization enthalpy was calculated as −9.3 to −13.4 kcal mol−1 in the indicated temperature range. Theoretical calculations on the solvent effects have been performed using the PCM polarizable continuum dielectric solvent approach at the B3LYP/6-31G* level, and by performing Monte Carlo simulations utilizing the free energy perturbation method. The applied PCM approach, including B3LYP/6-311++G** and MP2/6-31G* single point calculations, as well, consistently favours the neutral form in aqueous solution both for tyramine and dopamine. In contrast, Monte Carlo simulations predict solvent effects that are ...

A new method of the European Pharmacopoeia (Ph. Eur.)—alkalimetry in alcohol–water mixture with potentiometric end-point detection—for the assay of halide salts of alkaloids and other organic N-bases has been investigated using 13 substances. The results were compared to those obtained by nonaqueous direct acidimetry. In general, our measurements show that the Ph. Eur. method may be regarded as an environment-friendly, precise, reproducible approach, with average S.D. ±0.33. However, in six cases out of 13, the method did not work. In these cases, the first inflexion point, which should appear due to the neutralization of a defined, small volume of HCl added to the solution of the sample before the titration, was missing on the potentiometric titration curves. This was observed for papaverine chloride, pilocarpine chloride, pyridoxine chloride, thiamine chloride, histamine dichloride and noscapine chloride; this missing inflexion point hampered the exact measurement of the alkaloid content. This study shows that the method, in the present official form, can be applied only for compounds with pKa values of seven or higher. For the salts of weaker bases, a modified approach (titration in 70% ethanol, without addition of HCl) is proposed.

Protonation macro- and microconstants have been determined experimentally for the 4-aminophenol molecule and five hydroxy-substituted 2-phenylethylamines: tyramine, octopamine, dopamine, norepinephrine and epinephrine. In aqueous solution, 4-aminophenol is in the form of the neutral zero-net-charge tautomer, whereas (hydroxyphenyl)ethylamines exhibit tautomeric and conformational equilibria between the zwitterionic (zw) and the neutral (n) forms. The zw/n ratio was measured in the range of 0.09–7.43. No evident correlation has been found between the structural changes and changes in the zw/n values for this set of compounds. Polarizable continuum solvent calculations in the SCIPCM and PCM approximations and explicit solvent Monte Carlo simulations have been performed for theoretical investigation of tautomeric/conformational equilibria for the 4-aminophenol, tyramine and dopamine. Gas-phase and in-solution geometry optimizations were carried out mostly at the DFT/B3LYP/6-31G* level followed by B3LYP/6-311++G** single point calculations. All calculations found the neutral form as the stable one for the 4-aminophenol molecule in aqueous solution with an aniline-type amino group. Continuum solvent calculations underestimate the stability of the zwitterion relative to the neutral form for glycine and tyramine with an aliphatic amine group in the molecule. The calculated values are subject to a large basis set effect for tyramine. For explicit solvent calculations, an atomic charge set has been proposed where the charges were fitted to the molecular electrostatic potential calculated by using the self-consistent in-solution wave function. Using PCM/B3LYP/6-31G*-based atomic charges in Monte Carlo simulations, the preference of the zwitterionic tyramine was demonstrated. For reaching a better accord with the experimental free energy difference, corrections including intermolecular solute–solvent vibrational entropies are to be considered. Theoretical studies for the trans dopamine zwitterion predict the preference of the 4-OH form over the 3-OH isomer.

Muscarinic agonists might be useful in the treatment of neurological disorders, including Alzheimer's disease, schizophrenia, chronic pain, and drug abuse. Previous studies identified a series of bis-1,2,5-thiadiazole derivatives of 1,2,5,6-tetrahydropyridine with high activity and selectivity for muscarinic receptors. To develop compounds with improved central nervous system penetration, several new derivatives were synthesized and characterized for muscarinic receptor binding and activity. One ligand (11) exhibited agonist activity at M(1), M(2), and M(4) receptors, a selectivity profile suggesting potential utility in the treatment of schizophrenia.

Ten pairs of pyridazinone regioisomers were prepared, and their lipophilicity was described by the logarithm of the octanol/water partition coefficient (log P) determined experimentally and calculated with prediction methods. The 4- and 5-(substituted amino)-3(2H)-pyridazinone regioisomers were synthesized by nucleophilic substitution of one of the chloro atoms of 4,5-dichloro-2-methyl-3(2H)-pyridazinone or its 6-nitro derivative. Structures of new compounds were proven by spectroscopic methods. The experimental log P values were obtained by a shake flask method in octanol and a Sörensen buffer (pH 7.4) solvent system. A consequent difference was found in the lipophilicity of regioisomers. For each isomer pair, the log P value of the 4-isomer was significantly (average by 0.75 log unit) higher than that of the 5-isomer. Some quantum chemical calculations as well as X-ray analysis of two pairs of regioisomers were also carried out to gain insight into the structural differences of regioisomers. The log P values were calculated by the fragmental approach KOWWIN and a QSPR analysis (3DNET). The a priori KOWWIN gave poor agreement, but with the programs KOWWIN with EVA (experimental value adjusted) and 3DNET, the results were generally in agreement with experiment.

Correct QSAR analysis requires reliable measured or calculated logP values, being logP the most frequently utilized and most important physico-chemical parameter in such studies. Since the publication of theoretical fundamentals of logP prediction, many commercial software solutions are available. These programs are all based on experimental data of huge databases therefore the predicted logP values are mostly acceptable - especially for known structures and their derivatives. In this study we critically reviewed the published methods and compared the predictive power of commercial softwares (CLOGP, KOWWIN, SciLogP/ULTRA) to each other and to our recently developed automatic QS(P)AR program. We have selected a very diverse set of 625 known drugs (98%) and drug-like molecules with experimentally validated logP values. We have collected 78 reported "outliers" as well, which could not be predicted by the "traditional" methods. We used these data in the model building and validation. Finally, we used an external validation set of compounds missing from public databases. We emphasized the importance of data quality, descriptor calculation and selection, and presented a general, reliable descriptor selection and validation technique for such kind of studies. Our method is based on the strictest mathematical and statistical rules, fully automatic and after the initial settings there is no option for user intervention. Three approaches were applied: multiple linear regression, partial least squares analysis and artificial neural network. LogP predictions with a multiple linear regression model showed acceptable accuracy for new compounds therefore it can be used for "in-silico-screening" and/or planning virtual/combinatorial libraries.

Having measured the log P value of γ-hydroxybutyric acid (GHB) in chloroform/water and dichloromethane/water systems at T = 25 and 37 °C, the relative log P value for the structural analogue γ-aminobutyric acid (GABA), log P (GABA) − log P (GHB), has been determined theoretically. A combined ab initio/Monte Carlo method for obtaining the internal free energy and the relative solvation free energy, respectively, has been applied for studying the conformational/tautomeric equilibria of GABA in the three solvents. Free energy changes for the partition processes have been calculated within thermodynamic cycles. There is no significant difference in the log P values for the neutral GABA and GHB of −1.22 ± 0.12 at 37 °C, as measured in the chloroform/water system. Using the more polar dichloromethane solvent as the organic phase, the GABA log P increases compared to its log P in chloroform. Because GABA almost entirely takes the zwitterionic form in aqueous solution, it is a key question whether this tautomeric...

In line with the postulate that the physiological functions of bile acids, in particular their contribution to the regulation of the fat metabolism, may be related to their ion-pairing ability, this paper provides data on the chromatographic aspects related to their ion-pairing ability. The paper provides data about the chromatographic aspects of this subject. The ion-pairing (i.e. HPLC-retention-increasing) effects of the therapeutically applied deoxycholic acid epimers (7-deoxycholic acid, DOC; chenodeoxycholic acid, ChDOC; and ursodeoxycholic acid, UDOC) were studied in a reversed-phase HPLC system. As cationic partner substances, nine quaternary ammonium drug compounds were used as cationic partners The ion-pairing activities of the deoxycholic acids were found to be very strong, and much better than those of anionic ion-pairing agents such as pentanesulfonic acid and caproic acid. The natures of the binding of the DOC epimers by the C18 surface were also determined. While DOC and ChDOC formed double ...

The p K a values of 25 structurally diverse drug compounds including mono-, di- and tri-protic molecules were determined by a recently developed multi-wavelength spectrophotometric technique, called dip-probe absorption spectroscopy (D-PAS), and the traditional spectrophotometric titration. All experiments were performed at 25.0±0.5°C in an ionic strength of 0.15 M KCl in two laboratories (Semmelweis and Sirius), to evaluate the reproducibility and reliability of the spectrophotometric techniques for p K a determination. It was found that the p K a values determined by the D-PAS technique are in excellent agreement with values measured by the traditional spectrophotometric method (average deviation=0.08 units) and are consistent with the literature data where available. We have demonstrated that the D-PAS approach is a simple, precise and easy-to-use method for p K a determination of drug molecules with ionisable group(s) in proximity to chromophore(s). The advantages and limitations of spectrophotometric p K a determination are discussed

The acid-base equilibria of several diprotic amphoteric drugs, namely, niflumic acid, norfloxacin, piroxicam, pyridoxine and 2-methyl-4-oxo-3H-quinazoline-3-acetic acid have been characterized in terms of microconstants and tautomeric ratios. A multiwavelength spectrophotometric (WApH) titration method for determination of acid dissociation constants (pKa values) of ionizable compounds developed previously was applied for this purpose. Microspeciation was investigated by three approaches: (1) selective monitoring of ionizable group by spectrophotometry, (2) deductive method and (3) kz method for determination of tautomeric ratio from co-solvent mixtures. The formulation for (3) has been derived and found to invoke fewer assumptions than a reported procedure (K. Takacs-Novak, A. Avdeef, K.J Box, B. Podanyi, G. Szasz, J. Pharm. Biomed. Anal., 12 (1994) 1369–1377). It has been shown that the WApH technique, for such types of ampholytes, is able to deduce the microconstants and tautomeric ratios which are in good agreement with literature data.

The lipophilicity of 17 newly synthesized potential NMDA and cholecystokinin antagonist 2-methyl-4-oxo-3H-quinazoline-3-alkyl-carboxylic acid derivatives has been investigated. The apparent partition coefficients of two amphoteric compounds of overlapping protonation (Q1 and Q2) were determined by shake-flask method and converted into true log P values using the protonation microconstants. The difference between their lipophilicity expressed with the true partition coefficients was less, than it could be expected from the 2D structures and was explained with conformational preferences and formation of intramolecular interactions. Out of the other 15 monoprotic quinazolone compounds the lipophilicity of ten molecules (Q8–Q17, experimental set) was determined by TLC method with the help of a calibration set consisting of 12 standard molecules, five quinazolones (Q3–Q7) and seven pyrido[1,2-a]pyrimidines (PP1–PP7). In order to justify the suitability of pyrido-pyrimidines as standards for the chromatographic log P determination of quinazolones, first Q3–Q7 were examined by TLC and HPLC using PP1–PP7 for calibration. Data showed good agreement of results obtained by shake-flask and two different chromatographic methods indicating the similar chromatographic behavior of the two bicyclic systems and the relevance of PP1–PP7 to extend the calibration set of quinazolones. The obtained log P values proved mostly the expected structure–activity relationships. Some findings, however, have revealed specific partition behavior of the compounds providing useful information in the estimation of their pharmacokinetics, and these are discussed in the paper.

Purpose. Acid dissociation constants (pKa values) denote the extent of ionization of drug molecules at different pH values, which is important in understanding their penetration through biological membranes and their interaction with the receptors. However, many drug molecules are sparingly soluble in water or contain ionization centres with overlapping pKa values, making precise pKa determination difficult using conventional spectrophotometric titration. In this work, we investigate a multiwavelength spectrophotometric titration (WApH) method for the determination of pKa values.

Purpose. The ion-pair partition of quaternary ammonium (QA) pharmacons with organic counter ions of different lipophilicity, size, shape and flexibility was studied to elucidate relationships between ion-pair formation and chemical structure.

A series of imidazo[1,2- c ]quinazolines of different lipophilic character was prepared. According to their antioxidant (cyclic voltammetry) properties they all should be potent inhibitors of lipid peroxidation. Under the given circumstances (NADPH-induced lipid peroxidation in rat brain microsomes and Fe 2+ -induced lipid peroxidation in rat brain homogenate), however, their lipid peroxidation inhibitory activity was strongly dependent on their lipophilicity.

Transdermal drug delivery has been growing extensively in the past decades, therefore new, reliable and cost-effective in vitro models were demanded to support the research and development on this field. Model membrane of PAMPA mimicking skin penetration was first described in 2006, but the need for more bio-mimetic system has been arisen by new industrial tendencies and a bio-relevant system was published in 2012. Since its first publication Skin PAMPA has already been applied by several universities and industrial groups successfully and the first articles, podium and poster presentations have been appeared. The original Skin PAMPA model has been further developed in order to extend its application for formulations. Examples of liquid or semi-solid formulation projects and transdermal patch studies are available beside standard solution applications. The present review demonstrates the different approaches needed for various type of samples, provides examples of applications and practical conclusions for further improvement.

The solubilities in water and 1-octanol of 22 nitrogen-bridgehead quinazolone derivatives were investigated. The data were determined with a conventional method, with the typical confidence intervals at 95% probability level about ±5% and the precision good enough to evaluate the influence of structural modifications and to compare data with the lipophilicity of molecules. Solubilities in water spanned five orders of magnitude depending on the substituents attached to the ring-system. The solubility in octanol was generally somewhat higher and the range was only three magnitudes. Aqueous solubilities were more sensitive to structural changes than those in octanol. Solubility ratios were computed and fitted to the predictive relationship with two independent variables proposed by Yalkowsky. The equation with solubility ratios gave better results than the one calculated with experimental log P (partition coefficient) values. That corresponds to the known difference of solubility ratios (log SR) and log P values, caused mainly by the mutual solubility of two phases in log P measurements. The solubility ratio and the partition coefficient have the same trend but the values differ significantly. Thus the partition coefficient and the solubility ratio are not recommended for estimation of aqueous solubility (log Sw) data of these compounds.