Synthesis, characterization and molecular modelling of a novel dipyridamole supramolecule – X-ray structure, quantum mechanics and molecular dynamics study to comprehend the hydrogen bond structure–activity relationship

Co-amorphous formulation of dipyridamole with p-hydroxybenzoic acid: Underlying molecular mechanisms, physical stability, dissolution behavior and pharmacokinetic study

Coamorphization has been proven to be an effective approach to improve bioavailability of poorly soluble active pharmaceutical ingredients (APIs) by virtue of solubilization, and also contributes to overcome limitation of physical stability associated with amorphous drug alone. In current work, a co-amorphous formulation of dipyridamole (DPM), a poor solubility drug, with p-hydroxybenzoic acid (HBA) was prepared and investigated. At a molar ratio of 1:2, DPM and HBA were melted result in the formation of a binary co-amorphous system. The DPM-HBA co-amorphous was structurally characterized by powder X-ray diffraction (PXRD), temperature modulated differential scanning calorimetry (mDSC), high performance liquid chromatography (HPLC) and solution state ¹H nuclear magnetic resonance (¹H NMR). The molecular mechanisms in the co-amorphous were further analysed via Fourier-transform infrared (FTIR) and Raman spectroscopies, as well as density functional theory (DFT) calculation. All the results consistently revealed the presence of hydrogen bonding interactions between -OH of DPM and -COOH on HBA. Accelerated test and glass transition kinetics showed excellent physical stability of DPM-HBA co-amorphous compared with amorphous DPM along with glass transition temperatures (T_g). The phase-solubility study indicated that complexation occurred between DPM and HBA in solution, which contributed to the solubility and dissolution enhancement of DPM in co-amorphous system. Pharmacokinetic study of co-amorphous DPM-HBA in mouse plasma revealed that the DPM exhibited 1.78-fold and 2.64-fold improvement in AUC_0‑∞ value compared with crystalline and amorphous DPM, respectively. This current study revealed coamorphization is an effective approach for DPM to improve the solubility and biopharmaceutical performance.

A Short Review on Structural Concepts of Metal Complexes of Proton Transfer Salts of Pyridine-2-Carboxylic Acid

In this study, a brief review of the proton transfer salts synthesized from the reaction of piperazine with pyridine-2-carboxylic acid and their metal complexes since 2009 was made. The metals in the studied compounds are mostly d-block metals. In complexes, the anionic component of the salt is coordinated to the metal, while the cationic component is present only as a complementary ion in a complex.

Hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) Simulation: A Tool for Structure-based Drug Design and Discovery

Quantum mechanics (QM) is physics based theory which explains the physical properties of nature at the level of atoms and sub-atoms. Molecular mechanics (MM) construct molecular systems through the use of classical mechanics. So, hybrid quantum mechanics and molecular mechanics (QM/MM) when combined together can act as computer-based methods which can be used to calculate structure and property data of molecular structures. Hybrid QM/MM combines the strengths of QM with accuracy and MM with speed. QM/MM simulation can also be applied for the study of chemical process in solutions as well as in the proteins, and has a great scope in structure-based drug design (CADD) and discovery. Hybrid QM/MM also applied to HTS, to derive QSAR models and due to availability of many protein crystal structures; it has a great role in computational chemistry, especially in structure- and fragment-based drug design. Fused QM/MM simulations have been developed as a widespread method to explore chemical reactions in condensed phases. In QM/MM simulations, the quantum chemistry theory is used to treat the space in which the chemical reactions occur; however the rest is defined through molecular mechanics force field (MMFF). In this review, we have extensively reviewed recent literature pertaining to the use and applications of hybrid QM/MM simulations for ligand and structure-based computational methods for the design and discovery of therapeutic agents.

Synthesis and crystal structure of 2,4,6,8-tetrakis(3,5-di-tert-butylphenoxy)pyrimido[5,4-d]pyrimidine: expansion of the Piedfort concept

The title host compound, designed to self-assemble to form a new type of extended core Piedfort unit reminiscent of an eight-legged spider host, forms a number of crystalline inclusion compounds favouring oxygen-containing guest mol­ecules. We have established the presence of this unit in the unsolvated mol­ecular crystal at 100 K, which is monoclinic, space group P2₁/n, with Z = 8. The new Piedfort unit is chiral and its core structure closely approximates to D₂ symmetry, with both enanti­omers present in the crystal. Rather than being superposed with a staggered arrangement of nitro­gen atoms, the rings are rotated by an angle of approximately 45° with respect to each other.

The title host compound, C₆₂H₈₄N₄O₄, designed to self-assemble to form a new type of extended core Piedfort unit reminiscent of an eight-legged spider host, forms a number of crystalline inclusion compounds favouring oxygen-containing guest mol­ecules. We have established the presence of this unit in the unsolvated mol­ecular crystal at 100 K, which is monoclinic, space group P2₁/n, with Z = 8. The new Piedfort unit is chiral and its core structure closely approximates to D₂ symmetry, with both enanti­omers present in the crystal. Rather than being superposed with a staggered arrangement of nitro­gen atoms, the rings are rotated by an angle of approximately 45° with respect to each other, and the shortest contact between them is 3.181 (2) Å. The compound’s significant inclusion properties may be taken to suggest the participation of an extended Piedfort unit in the microcrystalline adducts formed. The presence of such a dimeric host unit in the clathrates has, however, not yet been established because of the current lack of suitable single crystals for X-ray analysis.

Enhancing anti-thrombogenicity of biodegradable polyurethanes through drug molecule incorporation

Sufficient and sustained anti-thrombogenicity is essential for blood-contacting materials, because blood coagulation and thrombosis caused by platelet adhesion and activation on material surfaces may lead to functional failure and even fatal outcomes. Covalently conjugating antithrombogenic moieties into polymer, instead of surface modifying or blending, can maintain the anti-thrombogenicity of polymer at a high level over a time range. In this study, series of randomly crosslinked, elastic, biodegradable polyurethanes (PU-DPA) were synthesized through a one-pot and one-step method from polycaprolactone (PCL) diol, hexamethylene diisocyanate (HDI) and anti-thrombogenic drug, dipyridamole (DPA). The mechanical properties, hydrophilicity, in vitro degradation, and anti-thrombogenicity of the resultant PU-DPA polymers can be tuned by altering the incorporated DPA amount. The surface and bulk hydrophilicity of the polyurethanes decreased with increasing hydrophobic DPA amount. All PU-DPA polymers exhibited strong mechanical properties and good elasticity. The degradation rates of the PU-DPAs decreased with increasing DPA content in both PBS and lipase/PBS solutions. Covalently incorporating DPA into the polyurethane significantly reduced the platelet adhesion and activation compared to the polyurethane without DPA, and also can achieve sustained anti-thrombogenicity. The PU-DPA films also supported the growth of human umbilical vein endothelial cells. The attractive mechanical properties, blood compatibility, and cell compatibility of this anti-thrombogenic biodegradable polyurethane indicate that it has a great potential to be utilized for blood-contacting devices, and cardiovascular tissue repair and regeneration.

Brain grants permission of access to Zika virus but denies entry to drugs: a molecular modeling perspective to infiltrate the boundary

Thein silicodesign of targeted Zika virus inhibitors.