The lipophilic behaviour of organic compounds:2. The development of an aliphatic hydrocarbon/water fragmental system via interconnection with octanol-water partitioning data

Anisotropic solvent model of the lipid bilayer. 1. Parameterization of long-range electrostatics and first solvation shell effects

A new implicit solvation model was developed for calculating free energies of transfer of molecules from water to any solvent with defined bulk properties. The transfer energy was calculated as a sum of the first solvation shell energy and the long-range electrostatic contribution. The first term was proportional to solvent accessible surface area and solvation parameters (σ(i)) for different atom types. The electrostatic term was computed as a product of group dipole moments and dipolar solvation parameter (η) for neutral molecules or using a modified Born equation for ions. The regression coefficients in linear dependencies of solvation parameters σ(i) and η on dielectric constant, solvatochromic polarizability parameter π*, and hydrogen-bonding donor and acceptor capacities of solvents were optimized using 1269 experimental transfer energies from 19 organic solvents to water. The root-mean-square errors for neutral compounds and ions were 0.82 and 1.61 kcal/mol, respectively. Quantification of energy components demonstrates the dominant roles of hydrophobic effect for nonpolar atoms and of hydrogen-bonding for polar atoms. The estimated first solvation shell energy outweighs the long-range electrostatics for most compounds including ions. The simplicity and computational efficiency of the model allows its application for modeling of macromolecules in anisotropic environments, such as biological membranes.

Application of Hansch's model to capsaicinoids and capsinoids: a study using the quantitative structure-activity relationship. A novel method for the synthesis of capsinoids

We describe a synthetic approach for two families of compounds, the capsaicinoids and capsinoids, as part of a study of the quantitative relationship between structure and activity. A total of 14 capsaicinoids of increasing lateral chain lengths, from 2 to 16 carbon atoms, were synthesized. In addition, 14 capsinoids with identical lateral chains, as well as capsiate and dihydrocapsiate, have been synthesized, and a new method for the synthesis of these compounds has been developed. The yields range from 48.35 to 98.98%. It has been found that the synthetic capsaicinoids and capsinoids present a lipophilia similar to those of the natural compounds and present similar biological activity. The bioactivity of the synthetic capsaicinoids and capsinoids decreases proportionally to the degree of difference in lipophilia (higher or lower) compared to the natural compounds. Biological activity was determined using the etiolated wheat (Triticum aestivum L.) coleoptiles bioassay and by comparing results of the synthesis with those presented by their counterpart natural compounds. The bioactivities found correlated directly to the lipophilic properties of the synthesized compounds.

Modified benzoxazinones in the system Oryza sativa-Echinochloa crus-galli: an approach to the development of biorational herbicide models

The utility of benzoxazinones and some of their synthetic derivatives in the search for new leads for herbicide model development has been explored. The work described focuses on obtaining derivatives that present selectivity in the system Oryza sativa- Echinochloa crus-galli. To achieve this goal the influence of lipophilicity in this system has been studied by preparing 14 ester derivatives at the N-4 position of D-DIBOA along with other compounds with different functionalization and chain lengths at position C-2. These compounds have been tested in the aforementioned system, and the dose-response profiles have been compared. The most active compound was 2-ethyl-4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one, which presented higher selectivity than the specific herbicide Cotanil-35. These results confirm the potential of D-DIBOA as a lead herbicide for the control of Echinochloa spp. in rice crops.

Application of Hansch's model to guaianolide ester derivatives: a quantitative structure-activity relationship study

A quantitative structure-activity study to evaluate the effect of lipophilia/aqueous solubility on etiolated wheat coleoptiles elongation has been carried out with 34 guaianolides having different numbers of hydroxyl groups and ester side chains of variable length and structure: linear, branched, aromatic, and unsaturated. Compounds have been tested in a range of concentrations between 10 and 1000 microM. Data show a strong influence of lipophilia, expressed as logP values. Specially, data from alkylic side chain ester derivatives adjust to the mathematical model based on Hansch's transport theory; hence, a quantitative structure-activity relationships (QSAR) correlation with a high degree of reliance is provided. Moreover, all active compounds fit the Lipinski's rule of five. Also, the presence of additional hydroxyl groups and their derivatives in the basic skeleton does not affect the mode of action but greatly influences the activity, as they modify the transport through membranes and aqueous phases. Finally, a second hydroxyl group enhances differences of activity between alkylic side chain derivatives by increasing differences in van der Waals interactions.