Potential of immobilized artificial membrane chromatography for lipophilicity determination of arylpropionic acid non-steroidal anti-inflammatory drugs

Molecular lipophilicity can be expressed by logP or more conveniently by logk, i.e. determined by the traditional shake-flask technique or by liquid chromatography. The logk of 11 arylpropionic non-steroidal anti-inflammatory drugs (NSAIDs) was determined at pH 7.4 of the eluent using two stationary phases i.e. octadecylsilane phase and an immobilized artificial membrane (IAM.PC.MG) packing. The chromatographic retention factors extrapolated to 100% aqueous phase (logk(wODS) and logk(wIAM)) were correlated with n-octanol/water lipophilicity parameters (logP) and with n-octanol/water partition coefficients corrected for ionization at pH 7.4 (logD7.4). In this series of compounds, significant linear correlations (r>0.94) between the chromatographic parameters (logk(wIAM)) and the reference lipophilicity data (logP and logD7.4) were described. Moreover, regression analysis between the lipophilicity parameters and some pharmacokinetic data for the drugs under study were performed. The logk(wIAM) parameter over n-octanol/water partition data seems to provide a good model to obtain lipophilicity parameters of arylpropionic acid NSAIDs for quantitative structure-activity relationships studies.     

Retention of quinolones on human serum albumin and alpha1-acid glycoprotein HPLC columns: relationships with different scales of lipophilicity.

The retention of 10 quinolone antibacterial agents on HPLC stationary phases supporting human serum albumin (HSA) or alpha(1)-acid glycoprotein (AGP) was investigated. Among ofloxacine and flumequine, the two chiral compounds in the selected set, only the latter showed a split chromatographic peak and only on HSA but not on AGP, indicating that enantioselective specific sites play only a minor role in the retention. The retention of quinolones, which included four acidic and six zwitterionic congeners, was correlated with various lipophilicity scales: (i) theoretically calculated values, clogP, (ii) values measured at pH 7.4 by the shake-flask method, logD(7.4), and (iii) values extrapolated by retention data measured by ion-pair reversed-phase high performance liquid chromatography (RP-HPLC). We assumed that the latter values, logP(i.p.), were close to the lipophilicity of the neutral forms, logP(N), for both acidic and zwitterionic congeners. No relationship was found between retention on serum proteins and clogP values, whereas a reasonable relationship was found with logD(7.4) values, but only when the two subclasses, acidic and zwitterionic congeners, were considered separately. The relationship between retention data on serum proteins and logP(i.p.) values indicated that the affinity for serum proteins depends on the lipophilicity of the neutral forms only for logP values up to 1.5. Above this value, protein retention does not further increase, becoming almost constant. Based on both the observations above reported and the small values of the slopes of regression equations, we conclude that the interaction of the more lipophilic quinolones, mainly the zwitterions, with serum proteins is not governed uniquely by lipophilicity but also by other mechanisms, probably of electrostatic nature.     

Prediction of distribution coefficients from structure. Comparison of calculated and experimental data for various drugs.

The efficiency of the program PrologD to predict distribution coefficients (D) at any pH and pairing ion concentration has been tested using experimental logD values for various drugs measured under standard conditions of buffers and ionic strength. Clonidine derivatives, fluoroquinolones and beta-blockers were included as particular pharmacological classes within the testing data set. Calculations were performed using the three logP estimation options implemented in the program. PrologD proved to be very efficient and can be of great advantage in drug research. Prediction patterns and correlations between experimental and calculated data indicate acceptable results for more than 80% of the data. In addition, comparable studies using the different options permitted suggestions for the more suitable logP estimation method in respect of the particular classes of compounds.     

Getting physical in drug discovery II: the impact of chromatographic hydrophobicity measurements and aromaticity

Here, we review the performance of chromatographic hydrophobicity measurements in a data set of 100,000 GlaxoSmithKline compounds, demonstrating the advantages of the method over octanol-water partitioning and highlighting new insights for drug discovery. The value of chromatographic measurements, versus other hydrophobicity estimates, was supported by improved relationships with solubility, permeation, cytochrome P450s, intrinsic clearance, hERG binding and promiscuity. We also observed marked differentiation of the relative influence of intrinsic and effective hydrophobicity. The summing of hydrophobicity values plus aromatic ring count [logD(pH7.4) (or logP)+#Ar], indicated a wide relevance for simplistic 'property forecast indices' in developability assays, clearly enhanced by chromatographic values; therefore establishing new foundations for enriching property-based drug design.     

药物理化参数与乳糜微粒结合率的模型建立及其在预测药物淋巴转运中的应用

药物与乳糜微粒的结合率可表示药物淋巴转运倾向。测定了5种模型药物(卤泛群、灰黄霉素、桂利嗪、辛伐他汀和洛伐他汀)与乳糜微粒的结合率及其在长链甘油三酯中的溶解度。以偏最小二乘回归(PLS)分析建立了乳糜微粒结合率与药物分子理化参数的线性关系。得到各理化参数对药物与乳糜微粒结合的影响大小依次为:极性表面积(PSA)>氢键受体数(HBA)>氢键供体数(HBD)>长链甘油三酯中溶解度(SLCT)>熔点(mp)>表观油水分配系数(logP)>pH 7.4时表观油水分配系数(logD)>自由旋转键(FRB)>分子体积(MV)>分子量(MW)>密度,其中SLCT、logP、logD和密度起正向变化作用,其他理化性质起负向变化作用。药物分子各理化参数中,PSA、HBA、HBD及SLCT对预测药物的淋巴转运可能起较大作用。     

On quantitative relationships between drug-like compound lipophilicity and plasma free fraction in monkey and human

Drug interactions with plasma proteins influence their pharmacokinetics and pharmacodynamics. We aimed to test whether a strong quantitative relationship exists between plasma free fraction (f(P) ) and lipophilicity for low molecular weight nonacidic drug-like compounds. We measured the n-octanol-buffer distribution coefficients at pH 7.4 ((m) logD) of 18 diverse radiotracers (<470 Da) used for brain imaging with positron emission tomography in vivo. Lipophilicities were also computed as (c) logD with two software packages. The f(P) values for monkeys and humans were determined by ultrafiltration and transformed into m logD(pr/pl) values representing the log(10) of the within phase partition of the radiotracers between plasma proteins and remaining plasma. (m) logD(pr/pl) correlated strongly with (m) logD for human ((m) logD(pr/pl) = 0.733(m) logD-0.780, r(2) = 0.74) and monkey ((m) logD(pr/pl) = 0.780(m) logD-1.15, r(2) = 0.83), but less strongly with (c) logD. These relationships were significantly different between species (P = 0.006). Removal of eight fluorinated compounds from the datasets raised r(2) to 0.81 and 0.91 for humans and monkeys, respectively. For the tested compounds, we conclude that n-octanol-buffer (pH 7.4) distribution strongly models that between plasma proteins and remaining plasma and moreover that (m) logD accounts for over 74% of compound (m) logD(pr/pl) and is a strong determinant of f(P).     

Determination of lipophilicity of novel potential antituberculotic agents using HPLC on monolithic stationary phase and theoretical calculations

The HPLC analyses on the monolithic stationary phase were employed for rapid determination of lipophilicity of the two sets of newly synthesized potential antituberculotic agents. The analyses utilized the mixture of methanol and phosphate buffer (pH 7.4) as a mobile phase and a flow rate of 4mL/min. Monolithic stationary phase enabled to significantly reduce the time of analyses, achieve appropriate peak shapes for all tested compounds as well as the separation of positional isomers. Furthermore, the theoretical lipophilic parameters (logP) for all compounds were calculated employing the chemical programs (e.g., ACD/logP, HyperChem, miLogP, AlogP, KOWWIN and COSMOFrag, etc.). The experimental data (logk) and calculated logP values were compared by linear regression analysis. The highest correlation for both series was obtained for KOWWIN and miLogP programs. However, capability of particular chemical software to precisely predict lipophilicity of a compound is structurally dependent. Thus the predictive power of the selected program should be verified using experimental method. The results of this study documented that experimental determination of lipophilicity using HPLC on monolithic stationary phase is practical and reasonable for this purpose.     

Prediction of volume of distribution values in humans for neutral and basic drugs using physicochemical measurements and plasma protein binding data

We present a method for the prediction of volume of distribution in humans, for neutral and basic compounds. It is based on two experimentally determined physicochemical parameters, ElogD(7.4) and f(i(7.4)), the latter being the fraction of compound ionized at pH 7.4 and on the fraction of free drug in plasma (f(u)). The fraction unbound in tissues (f(ut)), determined via a regression analysis from 64 compounds using the parameters described, is then used to predict VD(ss) via the Oie-Tozer equation. Accuracy of this method was determined using a test set of 14 compounds, and it was demonstrated that human VD(ss) values could be predicted, on average, within or very close to 2-fold of the actual value. The present method is as accurate as reported methods based on animal pharmacokinetic data, using a similar set of compounds, and ranges between 1.62 and 2.20 as mean-fold error. This method has the advantage of being amenable to automation, and therefore fast throughput, it is compound and resources sparing, and it offers a rationale for the reduction of the use of animals in pharmacokinetic studies. A discussion of the potential errors that may be encountered, including errors in the determination of f(u), is offered, and the caveats about the use of computed vs experimentally determined logD and pK(a) values are addressed.     

Determination of n-octanol/water partition and membrane binding of cationic porphyrins

Porphyrin and their derivatives are being systematically studied as photosensitizers for photodynamic therapy. The ability to predict their membrane partition properties is of key importance to unveil their in vivo activity and applications. Several n-octanol/water partition coefficients (logP(OW)) of porphyrin derivatives have been reported in the literature but large discrepancies have been observed. Reproducible and reliable logP(OW) data for a series of 20 cationic meso-phenyl(pyridyl)porphyrin derivatives were determined by correlating logP(OW) with the partition coefficients measured in a more adequate n-butanol/water system. Linear correlations as a function of the number of positively charged groups bound to the periphery of the porphyrin rings were found within each series. A significant effect of the stereochemistry and nature of the positively charged substituents was also observed, but diminished steadily converging to a similar value in the mono-substituted derivatives. Binding constants to liposomes were shown to be proportional to logP(OW), except for the cis-isomers of doubly charged porphyrins. The cis-isomer presented smaller logP(OW) and higher membrane affinity. The effect was explained based on the amphiphilic nature of the cis-porphyrin.     

ElogD(oct): a tool for lipophilicity determination in drug discovery. 2. Basic and neutral compounds.

We present an RP-HPLC method for the determination of the octanol-water distribution coefficients at pH 7.4, as log values, for neutral and basic drugs, which combines ease of operation with high accuracy. The method is shown to work for a training set of 90 molecules comprised largely of drugs, and it was also applied to a test set of 10 proprietary compounds. This work expands the applicability of the method presented in our earlier report, for the determination of logP(oct) for neutral compounds (J. Med. Chem. 2000, 43, 2922-2928), and it offers the same general features but widens the scope. Generally, the method (i) is compound sparing (< or =1 mL of a 50-100 microg/mL solution needed), (ii) is insensitive to concentration and phase ratio effects observed in some shake-flask determinations, (iii) is amenable to rapid determinations (< or = 20 min on average), (iv) is insensitive to impurities, (v) possesses a wide lipophilicity range (>7 log units), and (vi) offers a good accuracy, (vii) an excellent reproducibility, (viii) and an excellent potential for automation. To the best of our knowledge, a similar performance, on a set of noncongeneric drugs, has not been previously reported. We refer to the value generated via this method as ElogD(oct).     

Piperazinylalkyl prodrugs of naproxen improve in vitro skin permeation.

Novel morpholinyl (4a) and piperazinylalkyl (4b-e) esters were synthesized and evaluated in vitro for their properties as bioreversible topically administered dermal prodrugs of naproxen. These ionizable prodrugs exhibited various aqueous solubilities and lipophilicities, depending on the pH of medium. As indicated by octanol-buffer partition coefficients (logP(app)) at pH 7.4, all of the prodrugs were significantly more lipophilic (logP(app)=0.7-3.9) than naproxen (logP(app)=0.3). Furthermore, the most aqueous of the soluble prodrugs (4b-d) were only 2-3-fold less soluble in an aqueous buffer of pH 7.4 ( approximately 30-50 mM) than was naproxen ( approximately 100 mM). At a pH of 5.0, prodrugs showed a generally higher aqueous solubility and similar logP(app) values, compared to naproxen. The chemical and enzymatic hydrolysis of prodrugs at 37 degrees C was investigated in aqueous buffer solutions (pH 5.0 and 7.4) and in 80% human serum (pH 7.4), respectively. The prodrugs showed moderate chemical stability (t(1/2)=15-150 days at pH 5.0), and they were hydrolyzed enzymatically to naproxen, with half-lives ranging from 0.4 to 77 min. In permeation studies using post-mortem human skin in vitro, the flux of naproxen was 6.5 and 1.6 nmol/cm(2). h in a saturated aqueous buffer vehicle of pH 7.4 and 5.0, respectively. Among the prodrugs, two piperazinyl derivatives (4c and 4d) resulted in a 9- and 4-fold enhancement of permeation, respectively, when compared to naproxen itself at pH 7.4. 4c also resulted in a significantly (4-fold) better permeation than naproxen at pH 5.0. In conclusion, piperazinyl esters improved skin permeation of naproxen and are promising prodrugs of naproxen for topical drug delivery.     

Drug permeability across a phospholipid vesicle based barrier: a novel approach for studying passive diffusion.

The aim of this study was to develop a novel predictive medium-throughput screening method for drug permeability, with use of a tight barrier of liposomes on a filter support. To our knowledge no one has succeeded in depositing membrane barriers without the use of an inert solvent such as hexadecane. The first part of the study involved development of a protocol for preparation of these barriers, which were made of liposomes from egg phosphatidylcholin in phosphate buffer pH 7.4 with 10 % (v/v) ethanol. The liposomes were deposited into the pores and onto the surface of a filter support (mixed cellulose ester) by use of centrifugation. Solvent evaporation and freeze-thaw cycling were then used to promote fusion of liposomes. A tight barrier could thus be obtained as shown with calcein permeability and electrical resistance. In the second part of the study the model was validated using 21 drug compounds, which cover a wide range of physicochemical properties and absorption (F(a)) in humans (13-100%). The drug permeation studies were carried out at room temperature with phosphate buffer (pH 7.4) in both acceptor and donor chambers. The apparent permeability coefficients obtained from the phospholipid vesicle based model correlated well with literature data on human absorption in vivo, which suggests that its performance is adequate and that the method is suitable for rapid screening of passive transport of new chemical entities. The results obtained from our model were compared with polar surface area (PSA) and experimental logD and with results obtained by established permeability screening methods such as immobilized liposome chromatography (ILC), the PAMPA models and the Caco-2 model. Our approach seems to model the in vivo absorption better than PSA, experimental logD, the ILC and PAMPA models, when similar conditions are used as in our assay, and equally well as the Caco-2 model and the Double Sink PAMPA (DS-PAMPA) model.     

The impact of in vitro binding on in vitro-in vivo extrapolations, projections of metabolic clearance and clinical drug-drug interactions

This review provides a vista of the current opportunities and remaining challenges in the area of in vitro-in vivo extrapolation, with particular emphasis on drug binding terms in predictive models, which has been the source of much controversy. Although the importance of fu(inc) (fraction unbound in in vitro incubations) has been acknowledged for decades, it is not always applied in practice. This is somewhat disappointing, since although it may be onerous to measure this term for large numbers of compounds, algorithms to estimate the term from logD(7.4) or logP have been detailed in the literature. These are sufficiently robust to negate routine measurement in early drug discovery. Several groups have recently established convincing relationships between unbound in vivo and in vitro metabolic intrinsic clearance (CL(int)). In the authors' laboratory, correlations of this type have been constructed for rat, dog and Man. The use and interpretation of these models within a drug discovery setting is discussed. The quantitative prediction of drug-drug interactions from in vitro cytochrome P450 (CYP) inhibition data remains a challenge. Although extensive literature databases are at last emerging, apparent ad hoc use of terms for in vivo inhibitor concentrations and only occasional consideration of fu(inc) may only have confused matters. The effect of accounting for drug binding on the accuracy of predictions is reviewed. Other themes including the impact of fu(inc) on relative activity factors (RAFs) and how in vitro data quality and inter-laboratory differences can confound quantitative human pharmacokinetic predictions are also developed.     

pH值对吡罗昔康理化性质及其经皮渗透性能的影响

目的:研究pH值对吡罗昔康理化性质及经皮渗透性能的影响,为其经皮给药制剂的研究提供实验依据。方法:用HPLC法测定药物在水、不同pH缓冲液(PBS)中的溶解度;采用双波长分光光度法测定药物的解离常数(pKa);摇瓶法测定药物的表观油水分配系数(logP);利用透皮扩散池以稳态渗透速率常数(Js)和通透系数(Ps)为评价指标研究药物的透皮效果。结果:吡罗昔康的pKa为6.33。32℃时,吡罗昔康在pH 7.4的缓冲液中logP为0.17,且溶解度和Js均达到最大,分别为(420.445)μg.mL-1和(64.612±0.011)μg.cm-2.h-1;Ps为(0.154±0.014)cm.h-1。结论:调节药物pH值,使药物维持较高的溶解度和分子型药物比例,可望获得理想的皮肤通透性。     

CBUA-NO平衡溶解度和表观油水分配系数的测定

目的：测定2-（4-氯苄叉基）-3-羰基熊果酸-（2-硝氧乙基）酯（CBUA-NO）的平衡溶解度和表观油水分配系数。方法：HPLC法测定CBUA-NO在不同表面活性剂中的溶解度及其在不同pH磷酸盐缓冲液介质中的油水分配系数。结果：不同表面活性剂对CBUA-NO的增溶作用有差异,CBUA-NO在1 mg·L^-1聚山梨酯80中溶解度最大;正辛醇-水体系中,CBUA-NO油水分配系数随油/水比例的升高而增大,pH=7.6,O/W=1时,CBUA-NO的油水分配系数最大,lgP=2.02。结论：建立的方法准确、可靠,可快速测定CBUA-NO的平衡溶解度和表观油水分配系数,为其体内动态的进一步研究提供依据。     

Insights into structure-activity relationships from lipophilicity profiles of pyridin-2(1H)-one analogs of the cardiotonic agent milrinone.

The pH-dependent distribution profiles of a series of pyridin-2(1H)-one analogs of the inotropic/vasodilator agent milrinone, determined in 1-octanol/water (and for a number of them also in chloroform-water) using a pH-metric technique, showed that partition coefficients of the neutral forms (logP(N)) significantly encode for 2-pyridone/2-hydroxypyridine tautomerism. A comparison between experimental and calculated logP (CLOG P) values indicated that electron-withdrawing substituents, at the C(6) position, and to a lesser extent at the C(3) and C(5) positions, push up logPs toward the values of the more lipophilic 2-hydroxypyridine tautomers. RP-HPLC parameters (log k'omega) carry for large part similar information related to tautomerism-dependent lipophilicity, but they were also found to reasonably correlate with the solute molar volumes (r2 = 0.75). Investigating the implications of ionization and partition properties in modulating the in vitro cardiotonic activity of the examined compounds revealed that a high fraction of the neutral species at physiological pH, predominantly in the more polar pyridone (OX) tautomer, increases the positive inotropic potency.     

Determining the Effect of pH on the Partitioning of Neutral,Cationic and Anionic Chemicals to Artificial Sebum: New Physicochemical Insight and QSPR Model

Purpose

Sebum is an important shunt pathway for transdermal permeation and targeted delivery, but there have been limited studies on its permeation properties. Here we report a measurement and modelling study of solute partition to artificial sebum.

Methods

Equilibrium experiments were carried out for the sebum-water partition coefficients of 23 neutral, cationic and anionic compounds at different pH.

Results

Sebum-water partition coefficients not only depend on the hydrophobicity of the chemical but also on pH. As pH increases from 4.2 to 7.4, the partition of cationic chemicals to sebum increased rapidly. This appears to be due to increased electrostatic attraction between the cationic chemical and the fatty acids in sebum. Whereas for anionic chemicals, their sebum partition coefficients are negligibly small, which might result from their electrostatic repulsion to fatty acids. Increase in pH also resulted in a slight decrease of sebum partition of neutral chemicals.

Conclusions

Based on the observed pH impact on the sebum-water partition of neutral, cationic and anionic compounds, a new quantitative structure-property relationship (QSPR) model has been proposed. This mathematical model considers the hydrophobic interaction and electrostatic interaction as the main mechanisms for the partition of neutral, cationic and anionic chemicals to sebum.

     

Physicochemical characterization of five glyburide powders: A BCS based approach to predict oral absorption.

The purpose of this study was to investigate the suitability of physicochemical parameters of Active Pharmaceutical Ingredients (APIs) as input functions for the Advanced Compartmental Absorption and Transit Model (ACAT) to predict the oral absorption of drug products. Five different glyburide APIs were characterized using X-ray powder diffraction (XRPD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Raman spectroscopy, particle size and particle size distribution, specific surface area and true density measurements, as well as dissociation constant (pK(a)), partition coefficient (logP) and distribution coefficient (logD). The computer simulations were performed using GastroPlustrade mark. The results of XPRD, DSC and Raman spectroscopy indicated that no significant differences in crystal form were present in the five APIs. However, significant differences in particle size and particle size distribution were observed. A basic in vitro/in vivo relationship between the APIs' particle size and clinically observed plasma time profiles was established. The study demonstrates that in silico methods can assist the formulation scientist to set meaningful API specifications. Computer simulations could shorten the drug development process since appropriate bioawaivers, based on data from simulation studies, may be justified.