Structural and energy insights on solid-state complexes with trimethoprim: a combined theoretical and experimental investigation.

We present here a new structure of a 1:1 salt of trimethoprim with hemifumarate, highlighted by single-crystal X-ray diffraction and computational conformational studies. This salt was formed during cocrystallization assays conducted to combine trimethoprim and other APIs whose combination exhibits interesting properties. Theoretical in vacuo investigations have been performed on the organic salt through a DFT two-dimensional conformational scan of torsion angles between the two aromatic moieties of trimethoprim. The evaluation of relative energies for hydrogen-bond interactions in the structure has also been performed. Comparison with conformational data from structures implying trimethoprim retrieved from the Cambridge Structural Database (CSD) shows good agreement with theoretical results, proving the validity of vacuum ab initio calculations in describing the energetic landscape of the molecule and thereby gain initial insight into the prediction process for possible new conformations and therefore potential new polymorphs.

How does binding of imidazole-based inhibitors to heme oxygenase-1 influence their conformation? Insights combining crystal structures and molecular modelling.

Heme oxygenase-1 (HO-1) inhibition is associated with antitumor activity. Imidazole-based analogues show effective and selective inhibitory potency of HO-1. In this work, five single-crystal structures of four imidazole-based compounds are presented, with an in-depth structural analysis. In order to study the influence of the conformation of the ligands on binding to protein, conformational data from crystallography are compared with quantum mechanics analysis and molecular docking studies. Molecular docking of imidazole-based analogues in the active site of HO-1 is in good agreement with the experimental structures. Inhibitors interact with the heme cofactor and a hydrophobic pocket (Met34, Phe37, Val50, Leu147 and Phe214) in the HO-1 binding site. An alternate binding mode can be hypothesized for some inhibitors in the series.

Crystal structure of 2,2'-oxybis(4-methylquinoline).

The title compound, C20H16N2O, (I), has been unwittingly obtained from the slow evaporation of a saturated solution of commercial benserazide hydro-chloride [benserazide, (II), being one of the principal therapeutic compounds used for the management of Parkinson's disease, mostly used in combination with levodopa]. The mol-ecule of (I) is composed of two planar 4-methyl-quinoline aromatic moieties [maximum deviations of 0.0104 (18) and 0.016 (2) Å], almost perpendicular to each other [dihedral angle = 89.5 (2)°], bridged by an O atom. The supra-molecular organization consists of a π-bonded chain, resulting from the stacking of mol-ecules related by inversion centres located along direction [111].

Pharmaceutical salts and cocrystals involving amino acids: a brief structural overview of the state-of-art.

Salification of new drug substances in order to improve physico-chemical or solid-state properties (e.g. dissolution rate or solubility, appropriate workup process, storage for further industrial and marketing development) is a well-accepted procedure. Amino acids, like aspartic acid, lysine or arginine take a great part in this process and are implicated in several different formulations of therapeutic agent families, including antibiotics (amoxicillin from beta lactam class or cephalexin from cephalosporin class), NSAIDs (ketoprofen, ibuprofen and naproxen from profen family, acetylsalicylic acid) or antiarrhythmic agents (e.g. ajmaline). Even if more than a half of known pharmaceutical molecules possess a salifiable moiety, what can be done for new potential drug entity that cannot be improved by transformation into a salt? In this context, after a brief review of pharmaceutical salts on the market and the implication of amino acids in these formulations, we focus on the advantage of using amino acids even when the target compound is not salifiable by exploiting their zwitterionic potentialities for cocrystal edification. We summarize here a series of new examples coming from literature to support the advantages of broadening the application of amino acids in formulation for new drug substances improvement research for non-salifiable molecules.

Solid-state-trapped reactive ammonium carbamate self-derivative salts of prolinamide.

Single crystals for two polymorphs of the ammonium carbamate self-derivative salt of prolinamide have been successfully obtained and characterized. Decarbonation of the carbamate salts was monitored by calorimetry, confirming stabilization of the reactive carbonated adducts in the solid state. Sublimation of the salts afforded crystals of prolinamide, leading to the first crystal structure of this otherwise common molecule. Reactivity of the ammonium carbamate self-derivative salt is further illustrated by the observation of a series of derived products, including dehydroprolinamide, a methylene-bridged prolinamide, and a bicyclic derivative. Crystal structures of these products display distinct amidic and/or non-amidic hydrogen bonding. This study emphasizes the reactivity of carbonated amines stabilized in the solid and opens perspectives for a systematic study of (solid-state) reactions involving these trapped reactive species.

4-Nitro-N-phthalyl-l-tryptophan.

THE CRYSTAL STRUCTURE OF THE TITLE COMPOUND [SYSTEMATIC NAME: (2R)-3-(1H-indol-3-yl)-2-(4-nitro-1,3-dioxoisoindolin-2-yl)propanoic acid], C(19)H(13)N(3)O(6), an analogue of epigenetic modulator RG108, is constrained by strong hydrogen bonds between the indole N-H group and a carbonyl O atom of the phthalimide ring of a symmetry-related mol-ecule, and between the protonated O atom of the carboxyl group and a carbonyl O atom of the phthalimide ring. π-π stacking inter-actions with centroid-centroid distances of 3.638 (1) and 3.610 (1) Šare also observed between indole and phthalimide rings.

Structural study of piracetam polymorphs and cocrystals: crystallography redetermination and quantum mechanics calculations.

Pharmaceutical compounds are mostly developed as solid dosage forms containing a single-crystal form. It means that the selection of a particular crystal state for a given molecule is an important step for further clinical outlooks. In this context, piracetam, a pharmaceutical molecule known since the sixties for its nootropic properties, is considered in the present work. This molecule is analyzed using several experimental and theoretical approaches. First, the conformational space of the molecule has been systematically explored by performing a quantum mechanics scan of the two most relevant dihedral angles of the lateral chain. The predicted stable conformations have been compared to all the reported experimental geometries retrieved from the Cambridge Structural Database (CSD) covering polymorphs and cocrystals structures. In parallel, different batches of powders have been recrystallized. Under specific conditions, single crystals of polymorph (III) of piracetam have been obtained, an outcome confirmed by crystallographic analysis.

Advantages of cocrystallization in the field of solid-state pharmaceutical chemistry: L-Proline and MnCl(2).

Cocrystallization (formation of a "cocrystal") is an emerging method to optimize physico-chemical properties of pharmaceutically active compounds. One elegant technique used to obtain such cocrystals is grinding the components together, either alone or in the presence of a small amount of solvent (so called solvent-drop grinding). Dry grinding has been used here to obtain cocrystals (actually a hydrated salt) of L-Proline and MnCl(2). In that context, a new crystalline structure of a multicomponent molecular complex composed of L-Proline and MnCl(2) is here reported. The complex was characterized by powder and single-crystal X-ray diffraction and differential scanning calorimetry. This study underlines the interest of grinding as a method to synthesize original solid-state complexes. It also emphasizes the advantage of combining calorimetric and X-ray diffraction to characterize the newly formed solids. Finally, our work provides structural basis for the role that L-Proline can play within multicomponent solid-state molecular complexes, in particular as a potential cocrystal former acting by both ionic and H-bond interactions when combined to molecules of pharmaceutical interest.

The dicyclo-hexyl-amine salt of RG108 (N-phthalyl-l-tryptophan), a potential epigenetic modulator.

The dicyclo-hexyl-amine salt of RG108 (N-phthalyl-l-tryptophan) co-crystallizes with a water mol-ecule and a disordered mol-ecule of dimethyl-formamide (DMF), viz. dicyclo-hexyl-aminium (S)-2-(1,3-dioxoisoindolin-2-yl)-3-(1H-indol-3-yl)propanoate dimethyl-formamide solvate monohydrate, C(12)H(24)N(+)·C(19)H(13)N(2)O(4) (-)·C(3)H(7)NO·H(2)O. The conformation of the deprotonated compound is constrained by charge-assisted strong hydrogen bonds with the dicyclo-hexyl-aminium ion and a dense hydrogen-bond network involving co-crystallized solvent mol-ecules. The dihedral angle between the fused ring systems in the anion is 58.35 (4)°.