Flavone Cocrystals: A Comprehensive Approach Integrating Experimental and Virtual Methods

The dapsone/flavone cocrystal system served as a benchmark for both experimental and virtual screening methods. Expanding beyond this, two additional active pharmaceutical ingredients (APIs), sulfanilamide and sulfaguanidine, structurally related to dapsone were chosen to investigate the impact of substituents on cocrystal formation. The experimental screening involved mechanochemical methods, slurry experiments, hot-melt extrusion, and the contact preparation method. The virtual screening focused on crystal structure prediction (CSP), molecular complementarity, hydrogen-bond propensity, and molecular electrostatic potentials. The CSP studies not only indicated that each of the three APIs should form cocrystals with flavone but also reproduced the known single- and multicomponent phases. Experimentally, dapsone/flavone cocrystals ACC, BCC, CCC, and DCC were reproduced, CCC was identified as a nonstoichiometric hydrate, and a fifth cocrystal (ECC), a t-butanol solvate, was discovered. The cocrystal polymorphs ACC and BCC are enantiotripically related, and DCC, exhibiting a different stoichiometric ratio, is enthalpically stabilized over the other cocrystals. For the sulfaguanidine/flavone system, two novel, enantiotripically related cocrystals were identified. The crystal structures of two cocrystals and a flavone polymorph were solved from powder X-ray diffraction data, and the stability of all cocrystals was assessed through differential scanning calorimetry and lattice energy calculations. Despite computational indications, a diverse array of cocrystallization techniques did not result in a sulfanilamide/flavone cocrystal. The driving force behind dapsone's tendency to cocrystallize with flavone can be attributed to the overall strength of flavone interactions in the cocrystals. For sulfaguanidine, the potential to form strong API···API and API···coformer interactions in the cocrystal is a contributing factor. Furthermore, flavone was found to be trimorphic.

Exploring the Supramolecular Interactions and Thermal Stability of Dapsone:Bipyridine Cocrystals by Combining Computational Chemistry with Experimentation

The application of computational screening methodologies based on H-bond propensity scores, molecular complementarity, molecular electrostatic potentials, and crystal structure prediction has guided the discovery of novel cocrystals of dapsone and bipyridine (DDS:BIPY). The experimental screen, which included mechanochemical and slurry experiments as well as the contact preparation, resulted in four cocrystals, including the previously known DDS:4,4'-BIPY (2:1, CC₄₄-B) cocrystal. To understand the factors governing the formation of the DDS:2,2'-BIPY polymorphs (1:1, CC₂₂-A and CC₂₂-B) and the two DDS:4,4'-BIPY cocrystal stoichiometries (1:1 and 2:1), different experimental conditions (such as the influence of solvent, grinding/stirring time, etc.) were tested and compared with the virtual screening results. The computationally generated (1:1) crystal energy landscapes had the experimental cocrystals as the lowest energy structures, although distinct cocrystal packings were observed for the similar coformers. H-bonding scores and molecular electrostatic potential maps correctly indicated cocrystallization of DDS and the BIPY isomers, with a higher likelihood for 4,4'-BIPY. The molecular conformation influenced the molecular complementarity results, predicting no cocrystallization for 2,2'-BIPY with DDS. The crystal structures of CC₂₂-A and CC₄₄-A were solved from powder X-ray diffraction data. All four cocrystals were fully characterized by a range of analytical techniques, including powder X-ray diffraction, infrared spectroscopy, hot-stage microscopy, thermogravimetric analysis, and differential scanning calorimetry. The two DDS:2,2'-BIPY polymorphs are enantiotropically related, with form B being the stable polymorph at room temperature (RT) and form A being the higher temperature form. Form B is metastable but kinetically stable at RT. The two DDS:4,4'-BIPY cocrystals are stable at room conditions; however, at higher temperatures, CC₄₄-A transforms to CC₄₄-B. The cocrystal formation enthalpy order, derived from the lattice energies, was calculated as follows: CC₄₄-B > CC₄₄-A > CC₂₂-A.

Mechanochemistry in Portugal-A Step towards Sustainable Chemical Synthesis

In Portugal, publications with mechanochemical methods date back to 2009, with the report on mechanochemical strategies for the synthesis of metallopharmaceuticals. Since then, mechanochemical applications have grown in Portugal, spanning several fields, mainly crystal engineering and supramolecular chemistry, catalysis, and organic and inorganic chemistry. The area with the most increased development is the synthesis of multicomponent crystal forms, with several groups synthesizing solvates, salts, and cocrystals in which the main objective was to improve physical properties of the active pharmaceutical ingredients. Recently, non-crystalline materials, such as ionic liquids and amorphous solid dispersions, have also been studied using mechanochemical methods. An area that is in expansion is the use of mechanochemical synthesis of bioinspired metal-organic frameworks with an emphasis in antibiotic coordination frameworks. The use of mechanochemistry for catalysis and organic and inorganic synthesis has also grown due to the synthetic advantages, ease of synthesis, scalability, sustainability, and, in the majority of cases, the superior properties of the synthesized materials. It can be easily concluded that mechanochemistry is expanding in Portugal in diverse research areas.

Expanding the Solid Form Landscape of Bipyridines

Two bipyridine isomers (2,2'- and 4,4'-), used as coformers and ligands in coordination chemistry, were subjected to solid form screening and crystal structure prediction. One anhydrate and a formic acid disolvate were crystallized for 2,2'-bipyridine, whereas multiple solid-state forms, anhydrate, dihydrate, and eight solvates with carboxylic acids, including a polymorphic acetic acid disolvate, were found for the 4,4'-isomer. Seven of the solvates are reported for the first time, and structural information is provided for six of the new solvates. All twelve solid-state forms were investigated comprehensively using experimental [thermal analysis, isothermal calorimetry, X-ray diffraction, gravimetric moisture (de)sorption, and IR spectroscopy] and computational approaches. Lattice and interaction energy calculations confirmed the thermodynamic driving force for disolvate formation, mediated by the absence of H-bond donor groups of the host molecules. The exposed location of the N atoms in 4,4'-bipyridine facilitates the accommodation of bigger carboxylic acids and leads to higher conformational flexibility compared to 2,2'-bipyridine. For the 4,4'-bipyridine anhydrate ↔ hydrate interconversion hardly any hysteresis and a fast transformation kinetics are observed, with the critical relative humidity being at 35% at room temperature. The computed anhydrate crystal energy landscapes have the 2,2'-bipyridine as the lowest energy structure and the 4,4'-bipyridine among the low-energy structures and suggest a different crystallization behavior of the two compounds.

New insight into improving the solubility of poorly soluble drugs by preventing the formation of their hydrogen-bonds: a case of dapsone salts with camphorsulfonic and 5-sulfosalicylic acid

The improved solubility of two salts of dapsone (DAP) was investigated from the view point of structures and hydrogen bonding.

Preparation and solid-state characterization of dapsone pharmaceutical cocrystals through the supramolecular synthon strategy

Based on the design concept of supramolecular synthons, “–NH2⋯Npyridine” was used to prepare cocrystals of DAP: (1 : 1) and (2 : 1) DAP-PYR, which could be transformed into each other by mechanochemistry.

The Lisbon Supramolecular Green Story: Mechanochemistry towards New Forms of Pharmaceuticals

This short review presents and highlights the work performed by the Lisbon Group on the mechanochemical synthesis of active pharmaceutical ingredients (APIs) multicomponent compounds. Here, we show some of our most relevant contributions on the synthesis of supramolecular derivatives of well-known commercial used drugs and the corresponding improvement on their physicochemical properties. The study reflects, not only our pursuit of using crystal engineering principles for the search of supramolecular entities, but also our aim to correlate them with the desired properties. The work also covers our results on polymorphic screening and describes our proposed alternatives to induce and maintain specific polymorphic forms, and our approach to avoid polymorphism using APIs as ionic liquids. We want to stress that all the work was performed using mechanochemistry, a green advantageous synthetic technique.

Eutectics and Salt of Dapsone With Hydroxybenzoic Acids: Binary Phase Diagrams, Characterization and Evaluation

Poor solubility and low dissolution rate of pharmaceuticals in many cases largely limit their bioavailability and efficacy. One of the promising approaches to improve dissolution behavior is to develop new multicomponent solid forms. Herein we use this strategy to synthesize new multicomponent solids of dapsone (DAP), which belongs to BCS class IV, with a series of hydroxybenzoic acid coformers. A new salt of DAP with 2,6-dihydroxybenzoic acid (26DHBA) and 4 eutectics with other hydroxybenzoic acids were reported through comprehensive characterizations using powder X-ray diffraction DSC, and vibrational spectroscopy techniques. The salt formation was evidenced by the presence of ionic interactions detected using FT-IR and Raman spectroscopy, and the stoichiometric ratio was determined to be 1:1. Binary phase diagrams were established to determine the composition of eutectics. The cause for salt and eutectic selection was further understood by computing molecular electrostatic potential (MEP) surface where 26DHBA shows the greatest acidity. Moreover, the powder dissolution study and microenvironment pH measurement reveal that both salt and eutectics of DAP display improvements on the dissolution rate and equilibrium concentration in which the acidity of coformers plays a dominant role. Our findings provide a direction for future coformer screening of multicomponent solids with improved pharmaceutical properties.

Development and Characterization of Dapsone Cocrystal Prepared by Scalable Production Methods

In this study, the formation of caffeine/dapsone (CAF/DAP) cocrystals by scalable production methods, such as liquid-assisted grinding (LAG) and spray drying, was investigated in the context of the potential use of processed cocrystal powder for pulmonary delivery. A CAF/DAP cocrystal (1:1 M ratio) was successfully prepared by slow evaporation from both acetone and ethyl acetate. Acetone, ethyl acetate, and ethanol were all successfully used to prepare cocrystals by LAG and spray drying. The powders obtained were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), thermogravimetry (TGA), and Fourier transform infrared spectroscopy (FTIR). Laser diffraction analysis indicated a median particle size (D₅₀) for spray-dried powders prepared from acetone, ethanol, and ethyl acetate of 5.4 ± 0.7, 5.2 ± 0.1, and 5.1 ± 0.0 μm respectively, which are appropriate sizes for pulmonary delivery by means of a dry powder inhaler. The solubility of the CAF/DAP cocrystal in phosphate buffer pH 7.4, prepared by spray drying using acetone, was 506.5 ± 31.5 μg/mL, while pure crystalline DAP had a measured solubility of 217.1 ± 7.8 μg/mL. In vitro cytotoxicity studies using Calu-3 cells indicated that the cocrystals were not toxic at concentrations of 0.1 and of 1 mM of DAP, while an in vitro permeability study suggested caffeine may contribute to the permeation of DAP by hindering the efflux effect. The results obtained indicate that the CAF/DAP cocrystal, particularly when prepared by the spray drying method, represents a possible suitable approach for inhalation formulations with applications in pulmonary pathologies.

Molecular Level Understanding of the Reversible Phase Transformation between Forms III and II of Dapsone

The reversible solid-state phase transformation between the neat forms II and III of dapsone (DDS) was studied using thermal analytical methods, variable temperature X-ray diffraction and solid-state modeling at the electronic level. The first order III ↔ II phase transformation occurs at 78 ± 4 °C with a heat of transition of 2 kJ mol^-1 and a small hysteresis. The two isosymmetric polymorphs (both P2₁2₁2₁) differ only in movement of layers of molecules and show a small variation in conformation. The combination of variable-temperature single-crystal structure determinations and pair-wise intermolecular energy calculations allowed us to unravel the single-to-single crystal transformation at a molecular level, to estimate the molecular contributions to the heat of transformation and to rationalize why the room and low temperature form III is the less dense polymorphic form, which is a rare phenomenon in enantiotropically related pairs of polymorphs in molecular crystals.

MechanoAPI-ILs: Pharmaceutical Ionic Liquids Obtained through Mechanochemical Synthesis

An alternative, efficient, and green synthetic strategy for the preparation of pharmaceutical ionic liquids using mechanochemistry (MechanoAPI-ILs) is reported. Six new API-ILs based on gabapentin and l-glutamic acid were successfully synthesized and characterized, demonstrating that mechanochemistry is a very promising synthetic strategy. Results compare both the new and the classical approach and clearly show the advantages of the new method. This new technique is faster, solvent free, reproducible, selective, and leads to higher yields.

Possibility of a magnetic [BN fullerene:B6 cluster]− nanocomposite as a vehicle for the delivery of dapsone

The dapsone interacting weakly with BNF (a) and functionalized BNF (b). Magnetism is induced in the molecule (c) by the BNF.

Sulfonate salts of the therapeutic agent dapsone: 4-[(4-aminophenyl)sulfonyl]anilinium benzenesulfonate monohydrate and 4-[(4-aminophenyl)sulfonyl]anilinium methanesulfonate monohydrate

Dapsone, formerly used to treat leprosy, now has wider therapeutic applications. As is the case for many therapeutic agents, low aqueous solubility and high toxicity are the main problems associated with its use. Derivatization of its amino groups has been widely explored but shows no significant therapeutic improvements. Cocrystals have been prepared to understand not only its structural properties, but also its solubility and dissolution rate. Few salts of dapsone have been described. The title salts, C12H13N2O2S(+)·C6H5O3S(-)·H2O and C12H13N2O2S(+)·CH3SO3(-)·H2O, crystallize as hydrates and both compounds exhibit the same space group (monoclinic, P21/n). The asymmetric unit of each salt consists of a 4-[(4-aminophenyl)sulfonyl]anilinium monocation, the corresponding sulfonate anion and a water molecule. The cation, anion and water molecule form hydrogen-bonded networks through N-H...O=S, N-H...Owater and Owater-H...O=S hydrogen bonds. For both salts, the water molecules interact with one sulfonate anion and two anilinium cations. The benzenesulfonate salt forms a two-dimensional network, while the hydrogen bonding within the methanesulfonate salt results in a three-dimensional network.