Charged cyclic hexapeptides: Updating molecular descriptors for permeability purposes.

Three polar cyclic hexapeptides differently charged at physiological pH (1 = neutral, 2 = anionic, 3 = cationic) were synthesized and their cell permeability measured. Lipophilicity in octanol/water didn't account for the higher permeability of the cationic derivative but three chromatographic indexes (log KwIAM, log k' HILIC and log k' c-HILIC) were more efficient to this respect. NMR amide chemical shift temperature coefficients (ΔδNH/ΔT) were used to explore the IMHB network of the backbone. MD simulations in different environments (water, chloroform and DMPC lipid bilayer) highlighted that the charged amino group of the lysine moiety of 3 is not involved in the formation of any IMHB in water whereas a different behavior is registered in chloroform and DMPC lipid bilayer. Overall this paper highlights how a combination of experimental and computational approaches could help in comparing permeability and physicochemical properties of neutral and charged cyclic peptides.

Lipophilicity of amyloid ß-peptide 12-28 and 25-35 to unravel their ability to promote hydrophobic and electrostatic interactions.

The growing interest for peptide therapeutics calls for new strategies to determine the physico-chemical properties responsible for the interactions of peptides with the environment. This study reports about the lipophilicity of two fragments of the amyloid ß-peptide, Aß 25-35 and Aß 12-28. Firstly, computational studies showed the limits of log D(7.4)oct in describing the lipophilicity of medium-sized peptides. Chromatographic lipophilicity indexes (expressed as log k', the logarithm of the retention factor) were then measured in three different systems to highlight the different skills of Aß 25-35 and Aß 12-28 in giving interactions with polar and apolar environments. CD studies were also performed to validate chromatographic experimental conditions. Results show that Aß 12-28 has a larger skill in promoting hydrophobic and electrostatic interactions than Aß 25-35. This finding proposes a strategy to determine the lipophilicity of peptides for drug discovery purposes but also gives insights in unraveling the debate about the aminoacidic region of Aß responsible for its neurotoxicity.

Efficient microwave-assisted synthetic protocols and in silico behaviour prediction of per-substituted ß-cyclodextrins.

Selective per-substituted cyclodextrin design enables the carrier's physicochemical and binding properties to be tailored and can even modify some biological native structure effects. We herein report a number of highly efficient microwave-assisted synthetic protocols for the preparation of several amino, ureido and thioureido per-substituted ß-cyclodextrin derivatives. A rapid parallel synthetic approach has given a set of 14 different CD derivatives. Our strategy is supported by computational analyses which were used to estimate the physicochemical behaviour of per-substituted derivatives and to tailor suitable substituents.

Molecular interaction fields based descriptors to interpret and compare chromatographic indexes.

Molecular Interaction Fields (MIFs) based descriptors can be conveniently used to characterize and compare chromatographic scales. In this study, Quantitative Structure-Retention Relationships (QSRR) for eight different chromatographic systems were obtained with VolSurf+ descriptors and Partial Least Squares (PLS). A new and purpose-designed analysis tool highlights the different balance of intermolecular interactions governing solute retention, and estimates the similarity between chromatographic systems.

Development of molecular hydrogen-bonding potentials (MHBPs) and their application to structure-permeation relations.

Hydrogen bonds are major forces of recognition in biochemistry and molecular pharmacology; they are an essential component of intermolecular interactions and determine to a significant extent the 3D-structure of bio-macromolecules. To explore three-dimensional H-bonding properties, a new tool called Molecular Hydrogen-Bonding Potentials (MHBPs) was created. The development of this tool is based on a stepwise procedure similar to the one used successfully to generate the Molecular Lipophilicity Potential (MLP). First, a H-bonding fragmental system was developed starting from published solvatochromic parameters. An atomic H-bonding donor fragmental value (alpha) is associated to each hydrogen atom in a polar moiety. Similarly, an atomic H-bonding acceptor fragmental value (beta) is associated to each polar atom. A distance function and an angle function were defined to take into account variations of the MHBPs in space. The fragmental system and the geometric functions were then combined to generate the MHBPs. These are calculated at each point of an adequate molecular surface or on a three-dimensional grid. The MHBPs were compared with GRID interactions energies and correlated with success to oral drug absorption data. Available examples demonstrate that the MHBPs are a promising computational tool in drug design. Their combination with CoMFA and VolSurf is being studied.

Lipophilicity behaviour of the Zwitterionic antihistamine cetirizine in phosphatidylcholine liposomes/water systems.

PURPOSE: The partitioning of cetirizine in a phosphatidylcholine liposomes/water system was compared with that of hydroxyzine and acrivastine to gain insight into the mechanisms of interaction of its various electrical species with membranes. METHODS: The lipophilicity profiles of the compounds were obtained from equilibrium dialysis and potentiometry, and compared with changes in NMR relaxation rates. RESULTS: The neutral form of hydroxyzine interacted mainly via hydrophobic interactions with the bilayer lipid core of the membrane, whereas for the cationic form both hydrophobic and electrostatic interactions were involved. Zwitterionic and anionic cetirizine were less lipophilic than its cation, which behaved like the corresponding species of hydroxyzine. Zwitterionic cetirizine interacted more by weak electrostatic interactions with the polar headgroups of phospholipids than by hydrophobic interactions with the membrane interior. The lipophilicity of its anion reflected the balance of repulsive electrostatic interactions between the carboxylate and phosphate groups and the hydrophobic interactions with the lipid core. CONCLUSION: The study confirms that various mechanisms influence the interaction of solutes with liposomes. Combining experimental techniques and using suitable reference compounds proves useful.

Pyrazole analogues of prazosin.

A series of analogues of prazosin, in which 1-methyl or 1-phenylpyrazole moieties were substituted for the furan ring, were synthesized and studied for their alpha 1-adrenoceptor antagonist activity. The role of the five member heterocyclic substructures in determining the affinity for the alpha 1-receptor is briefly discussed.

Mechanisms of liposomes/water partitioning of (p-methylbenzyl)alkylamines.

PURPOSE: The objective of this study was to compare and interpret the variations in lipophilicity of homologous (p-methylbenzyl)alkylamines (MBAAs) in isotropic (octanol/water) and anisotropic (zwitterionic liposomes/water) system. METHODS: Two experimental approaches were used, namely the pH-metric method to measure lipophilicity parameters in octanol/water and liposomes/water systems, and changes in NMR relaxation rates to validate the former method and to gain additional insights into the mechanisms of liposomes/water partitioning. RESULTS: For long-chain homologues (N-butyl to N-heptyl), the octanol/water and liposomes/water systems mostly expressed hydrophobicity. In contrast, the lipophilicity of the shorter homologues (N-methyl to N-propyl) in the two systems expressed various electrostatic and polar interactions. CONCLUSIONS: The study sheds light on the molecular interactions between zwitterionic liposomes and amphiphilic solutes in neutral and cationic form.

New 1,4-dihydropyridines conjugated to furoxanyl moieties, endowed with both nitric oxide-like and calcium channel antagonist vasodilator activities.

A series of 4-phenyl-1,4-dihydropyridines substituted at the ortho and meta positions of the phenyl ring with NO-donating furoxan moieties and their non-NO-releasing furazan analogues were synthesized and pharmacologically characterized. The vasodilator activities of these compounds were evaluated on rat aorta and expressed as EC50 values or as EC50iGC values when obtained in the presence of inhibitors of guanylate cyclase methylene blue (MB) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Affinities to 1, 4-DHP receptors on Ca2+ channels, expressed as IC50 values, were determined through displacement experiments of [3H]nitrendipine on rat cortex homogenates. A linear correlation between IC50 and EC50 values was found for compounds unable to release NO. EC50calcd values for derivatives containing NO-donor moieties, expression of the Ca2+-blocking component of their vasodilator activity, were interpolated on this linear regression. They showed a good correspondence with EC50iGC values determined in the presence of soluble guanylate cyclase inhibitors. Analysis of EC50iGC/EC50 ratios provided a useful tool to distinguish well-balanced hybrids from derivatives biased toward Ca2+-blocking or NO-dependent vasodilator activity. A detrimental effect on affinity to the 1, 4-DHP receptor, due to substitution at the ortho and meta positions of the 4-phenyl ring, was observed. SAR to explain this effect is proposed.

Insight into the lipophilicity of the aromatic N-oxide moiety.

PURPOSE: A systematic study to assess the influence of N-oxygenation on the lipophilicity of aromatic weak bases was performed. METHODS: The methods used were experimental (CPC and shake-flask techniques) and computational (AMI semi-empirical method). RESULTS: The intrinsic increment in the log P(oct) system for an oxygen atom added to form an aromatic N-oxide, designated as diff(log PN(O) -N), was -1.91, but the presence of para-substituents markedly affected this value. The good linear relationship (r2 = 0.92) between diff(log PN(O) - N), and the electronic density on the oxygen atom suggests that H-bond acceptor basicity is the main structural factor responsible for the variations in lipophilicity of aromatic N-oxides. Partition coefficients of aromatic N-oxides in dodecane/buffer and chloroform/buffer systems also support this hypothesis. CONCLUSIONS: The solvent-dependent polarity of the N-oxide moiety is mainly due to its marked H-bond acceptor basicity.

Furoxans as nitric oxide donors. 4-Phenyl-3-furoxancarbonitrile: thiol-mediated nitric oxide release and biological evaluation.

4-Phenyl-3-furoxancarbonitrile (2) affords nitric oxide under the action of thiol cofactors. Two principal products were isolated in the reaction with thiophenol: the phenylcyanoglyoxime (6) and 5-amino-3-phenyl-4-(phenylthio)isoxazole (7). Mechanisms which could account for the formation of these two products are discussed. Compound 2 is an efficient activator of the rat lung soluble guanylate cyclase, displays high vasodilatory activity on strips of rat thoracic aorta precontracted with noradrenaline, and is a potent inhibitor of platelet aggregation.

Paramagnetic water proton relaxation enhancement: from contrast agents in MRI to reagents for quantitative "in vitro" assays.

The use of stable complexes of paramagnetic metal ions as probes in analytical applications of the NMR technique is discussed. Two examples are given that involve the determination of the total Fe3+ content of human serum transferrin (Tf) and the extent of glycation of human serum albumin (HSA). The method is based on the measurement of the longitudinal water proton relaxation times, conveniently altered following a selective chemical interaction between the substrate and the paramagnetic probe.