Acidity,lipophilicity, solubility,absorption, and polar surface area of some ACE inhibitors

Computational chemical methods have been used to correlate the molecular properties of the 10 ACE inhibitors (captopril, enalapril, perindopril, lisinopril, ramipril, trandolapril, quinapril, fosinopril, benazepril, and cilazapril) and some of their active metabolites (enalaprilat, perindoprilat, ramiprilat, trandolaprilat, quinaprilat, fosinoprilat, benazeprilat, and cilazaprilat). The computed pK _a values correlate well with the available experimental values. In the dicarboxylic ACE inhibitors, the carboxyalkyl carboxylate group of the ACE inhibitors studied is more acidic than the C-terminal carboxylate. However, at physiological pH = 7.4 both carboxyl groups of ACE inhibitors are completely ionized and the dicarboxyl-containing ACE inhibitors behave as strong acids. The available experimental partition coefficients of these ACE inhibitors investigated are well reproduced by the neural network-based ALOGPs and the fragment-based KoWWiN methods. All parent drugs (and prodrugs), with the exception of fosinopril, are compounds with low lipophilicity. Calculated pK _a, lipophilicity, solubility, absorption, and polar surface area of the most effective ACE inhibitors for the prevention of myocardial infarction, perindopril and ramipril, were found similar. Therefore, it is probable that the experimentally observed differences in the survival benefits in the first year after acute myocardial infarction in patients 65 years of age or older correlate closely to the physicochemical and pharmacokinetic characteristics of the specific ACE inhibitor that is used.     

Avoiding gas-phase calculations in theoretical p<Emphasis Type=Italic>K</Emphasis><Subscript>a</Subscript> predictions

CBS-QB3, two simplified and less computationally demanding versions of CBS-QB3, DFT-B3LYP, and HF quantum chemistry methods have been used in conjunction with the CPCM continuum solvent model to calculate the free energies of proton exchange reactions in water solution following an isodesmic reaction approach. According to our results, the precision of the predicted pK _a values when compared to experiment is equivalent to that of the thermodynamic cycles that combine gas-phase and solution-phase calculations. However, in the aqueous isodesmic reaction schema, the accuracy of the results is less sensitive to the presence of explicit water molecules and to the global charges of the involved species since the free energies of solvation are not required. In addition, this procedure makes easier the prediction of pK _a values for molecules that undergo large conformational changes in solvation process and makes possible the pK _a prediction of unstable species in gas-phase such as some zwitterionic tautomers. The successive pK _a values of few amino acids corresponding to the ionization of the α-carboxylic acid and α-amine groups, which is one of the problematic cases for thermodynamic cycles, were successfully calculated by employing the aqueous isodesmic reaction yielding mean absolute deviations of 0.22 and 0.19 pK _a units for the first and second ionization processes, respectively.     

Catalytic hydrogenation of persubstituted <Emphasis Type=Italic>p</Emphasis>-nitrosophenols

Catalytic hydrogenation of dialkyl 2-hydroxy-4,6-dimethyl-5-nitrosobenzene-1,3-dicarboxylates over Pd/C gave the corresponding previously unknown dialkyl 5-amino-2-hydroxy-4,6-dimethylbenzene-1,3-dicarboxylates. The first-order rate constants for the hydrogenation process were found to be linearly related to steric constants of the alkyl groups.     

X-ray crystal structures of <Emphasis Type=Italic>p</Emphasis>-halogenated 6,6-diphenylfulvenes

Crystal structures of a series of p-halogenated 6,6-diphenylfulvenes 2–5 are reported and comparatively discussed including the known structure of the non-halogenate parent compound 1. The molecular structures show twisted conformations of the plane aryl and fulvene subunits against each other, rather unaffected by the different halogen substituents. The packing structures exclusively involve C–H···X (X = F, Cl, π) contacts while Hal···Hal and π-stacking interactions do not occur.     

Synthesis and some transformations of <Emphasis Type=Italic>N</Emphasis>,2,2-trimethyltetrahydro-2<Emphasis Type=Italic>H</Emphasis>-pyran-4-amine

Reaction of 2,2-dimethyltetrahydro-2H-pyran-4-one with aqueous methanamine, followed by reduction of the Schiff base thus obtained with sodium tetrahydridoborate gave N,2,2-trimethyltetrahydro-2H-pyran-4-amine which was subjected to cyanoethylation with acrylonitrile. The resulting 3-(2,2-dimethyltetrahydro-2H-pyran-4-ylmethylamino)propanenitrile was reduced with lithium tetrahydridoaluminate to N-(2,2-dimethyltetrahydro-2H-pyran-4-yl)-N-methylpropane-1,3-diamine, and some chemical transformations of the latter were studied.     

Reaction of methylpheophorbides <Emphasis Type=Italic>d</Emphasis> and <Emphasis Type=Italic>b</Emphasis> with amines

A series of formyl analogs of chlorin e₆ 13-amides were synthesized in high yields by reaction under mild conditions of primary and secondary amines with methylpheophorides b and d. In contrast with the secondary 13-amides, tertiary 13-amides were found as two isomers differing in the orientation of the amide plane relative to the plane of the chlorin ring. Methylpheophorbides b and d were more reactive toward the amines than methylpheophorbide a.     

<Emphasis Type=Italic>bis</Emphasis>-Cardenolides

Twelve new bis-cardenolides were synthesized by reaction of natural cardenolides with diamines to form imines and ammonium salts. Anomalous physicochemical properties consisting of resistance to hydrolysis and increased polarity were observed for the bis-ketoimines.     

Comparative characteristics of water-soluble proteins from <Emphasis Type=Italic>Larix sibirica</Emphasis>, <Emphasis Type=Italic>Picea obovata</Emphasis>, and <Emphasis Type=Italic>Abies sibirica</Emphasis> bud meristem

The amount of water-soluble proteins in bud meristem of Larix sibirica L., Picea obovata L., and Abies sibirica L. was shown to increase by 2-3 times in autumn during development of low-temperature resistance. The fractional composition of water-soluble proteins of the studied species and the amino-acid composition of groups of water-soluble proteins with different molecular weight (MW) were similar. Nitrogen accumulated as aspartic acid, glycine, and alanine in high- and medium-molecular-weight proteins. The peptides (MW < 5 kDa) typically had a high content of hydrophobic proline and hydrophilic tyrosine.