Programs and Methods for Calculation of log P-values

Molecular lipophilicity calculations of chemically heterogeneous chemicals and drugs on the basis of structural similarity and physicochemical parameters

QSARs based on molecular polarizability (alpha) and H-bond acceptor factors (sigma Ca) as independent variables provided good predictability of octanol/water partition coefficients (P) for chemicals and drugs. However, for some molecules containing few functional groups, the calculated values deviated significantly from those observed. This approach gave good results when applied to a set of 138 chemicals and drugs previously studied by Mannhold and Dross who compared other methods to calculate log P values. At the same time, three variations on a molecular similarity approach were pursued. In this study, a large training set with experimentally determined octanol/water partition coefficients (P) was searched for structures closely related to the compound-of-interest. The most successful of these variations took the mean log P value of few most closely related compounds after each was adjusted for differences between their and the compound-of-interest's polarizabilities (alpha) and H-bond acceptor capacities (sigma Ca).

Synthesis and correlations between experimental and calculated lipophilic indices of new 1,2-benzisothiazole derivatives with potential antimicrobial activity

Five series of new hydrazones (1a-m, 2a-m, 3a-m, 4a-m, 5a-m) with potential antimicrobial activity were synthesized from cyclic (1 and 4) or acyclic (2, 3 and 5) 1,2-benzisothiazolylhydrazides and characterized. Condensation of the appropriate hydrazide with aldehydes afforded the designed compounds. Aldehydes carrying different hydrophobic substituents were used and the five series were designed so that the hydrophobicity also varied among congeners. Retention parameters were measured by HPLC employing a deactivated alkyl-bonded silica column and different eluent systems (methanol-aqueous buffer, acetonitrile-water). The hydrophobicity chromatographic parameters (log k') were compared with those provided by measurement of partitioning of solutes between n-octanol and water (log P), and with theoretical partition coefficients, calculated by a fragmental method and scaled according to the experimental values. Correlations between different hydrophobicity indices are reported and discussed.

Virtual screening of intestinal drug permeability

Lead compounds generated in high throughput drug discovery programmes often have unfavorable biopharmaceutical properties, resulting in a low success rate of such drug candidates in clinical development. Drug companies and researchers would thus like to have methods of predicting biopharmaceutical properties accurately. The intestinal permeability to a lead compound is one such property which is particularly important. Therefore, access to methods to accurately predict biopharmaceutical properties, such as the intestinal permeability of a large series of compounds, is of particular importance. This review deals with new theoretical methods used to predict intestinal drug permeability. There are several possible transport routes across the intestine, but theoretical methods generally deal with only one of them, the passive transcellular route. Therefore, this review will also discuss the relative importance of passive and active drug transport and efflux routes using recent data generated in cell cultures, animal models and human subjects.

The n-octanol and n-hexane/water partition coefficient of environmentally relevant chemicals predicted from the mobile order and disorder (MOD) thermodynamics

The quantitative thermodynamic development of the mobile order and disorder theory in H-bonded liquids is extended in order to predict the partition coefficient. With respect to the classical predictive methods, the great advantage of the present approach resides in the possibility of predicting partition coefficient not only in the reference n-octanol/water partitioning system, but also in any mutually saturated two-phase system made up of two largely immiscible solvents. Constructed from the various free energy contributions encoded in the distribution process, the model furthermore provides a useful tool to understand both the origin and the factors, like the solute molar volume, that determine the partitioning of non-electrolytes between two immiscible liquid phases. From the comparison of the relative magnitude of the terms which contribute to the overall log P value, much information can also be gained concerning the variation of the partition coefficients of the same substances in different distribution systems. For example, the model has successfully been applied to the log P prediction of a number of environmentally important chemicals of varying structure, size and chemical nature in the n-octanol/water and n-hexane/water systems. Whatever the complexing or non-complexing substances studied, the hydrophobic effect always represent the driving force that rules distribution processes in the aqueous environments. As the dominant contribution to the partition coefficient in any organic/aqueous binary system, it is evidenced why hydrophobicity is usually considered to be a good measure of lipophilicity.

Absorption prediction from physicochemical parameters

Modern drug design not only focuses on the pharmacological activity of a compound but also considers its ability to be absorbed and to reach its site of action. The prediction of in vivo barrier permeabilities, particularly intestinal absorption and blood-brain barrier passage, are substantial concerns in the development of new drug compounds. For several decades, n-octanol-water partition coefficients dominated absorption prediction. In recent years, the basic physicochemical parameters describing both membrane permeability and lipophilicity have been established. This review provides an outline of some selected absorption-prediction models with emphasis on intestinal absorption.

The solubility of gases and vapours in ethanol - the connection between gaseous solubility and water-solvent partition

Ostwald solubility coefficients, as log L, for solutes in water and ethanol have been combined to give log PEtOH for partition between the two pure solvents. Sixty-four such values have been correlated through our solvation equation, the coefficients of which lead to the conclusion that ethanol and water solvents are equally strong hydrogen-bond bases, but that ethanol is much weaker as a hydrogen-bond acid. A slightly different solvation equation has been used to correlate 68 values of log LEtOH; the coefficients in this equation yield the same conclusions as to the hydrogen-bond acidity and basicity of bulk ethanol. In addition, an analysis of the various terms in the log LEtOH correlation equation allows the elucidation of the various chemical factors that govern the solubility of gaseous solutes in ethanol solvent at 298 K.Key words: solubility, partition, hydrogen-bonding, ethanol, water.