Design, Preparation, Characterization and Evaluation of Five Cocrystal Hydrates of Fluconazole with Hydroxybenzoic Acids

To modulate the physicochemical properties of fluconazole (FLZ), a multifunctional antifungal drug, the crystal engineering technique was employed. In this paper, five novel cocrystal hydrates of FLZ with a range of phenolic acids from the GRAS list, namely, 2,4-dihydroxybenzoic acid (24DHB), 3,4-dihydroxybenzoic acid (34DHB, form I and form II), 3,5-dihydroxybenzoic acid (35DHB), and 3,4,5-trihydroxybenzoic acid (345THB) were disclosed and reported for the first time. Crystals of these five hydrates were all obtained for single-crystal X-ray diffraction (SCXRD) analysis. Robust (hydroxyl/carboxyl) O-H. . . N_arom hydrogen bonds between acids and FLZ triazolyl moiety were observed to be dominant in guiding these crystal forms. The water molecule plays the role of supramolecular "linkage" in the strengthening and stabilization of these hydrates by interacting with FLZ and acids through O-H. . . O hydrogen bonds. In particular, the formation of FLZ-34DHB-H₂O (1:1:1) significantly reduces hygroscopicity and hence improves the stability of FLZ, the latter of which is unstable and easily transforms into its monohydrate form. Increased initial dissolution rates were observed in the obtained cocrystal forms, and an enhanced intrinsic dissolution rate was obtained in FLZ-35DHB-H₂O (1:1:1) in comparison with commercialized FLZ form II.

Synthon hierarchy in theobromine cocrystals with hydroxybenzoic acids as coformers

Cocrystals, solids composed of molecular and/or ionic compounds connected by noncovalent interactions, are objects of interest in crystal engineering. Theobromine, as an active pharmaceutical ingredient, was used in cocrystallization with dihydroxybenzoic acids.

Theobromine cocrystals with monohydroxybenzoic acids – synthesis, X-ray structural analysis, solubility and thermal properties

Theobromine, a compound from the purine alkaloid group, is much less soluble in polar solvents than its analogues, i.e. caffeine and theophylline, that is why it was used as an active pharmaceutical ingredient (API) model in cocrystal preparation.

Towards medicinal mechanochemistry: evolution of milling from pharmaceutical solid form screening to the synthesis of active pharmaceutical ingredients (APIs)

This overview highlights the emergent area of mechanochemical reactions for making active pharmaceutical ingredients (APIs), and covers the latest advances in the recently established area of mechanochemical screening and synthesis of pharmaceutical solid forms, specifically polymorphs, cocrystals, salts and salt cocrystals. We also provide an overview of the most recent developments in pharmaceutical uses of mechanochemistry, including real-time reaction monitoring, techniques for polymorph control and approaches for continuous manufacture using twin screw extrusion, and more. Most importantly, we show how the overlap of previously unrelated areas of mechanochemical screening for API solid forms, organic synthesis by milling, and mechanochemical screening for molecular recognition, enables the emergence of a new research discipline in which different aspects of pharmaceutical and medicinal chemistry are addressed through mechanochemistry rather than through conventional solution-based routes. The emergence of such medicinal mechanochemistry is likely to have a strong impact on future pharmaceutical and medicinal chemistry, as it offers not only access to materials and reactivity that are sometimes difficult or even impossible to access from solution, but can also provide a general answer to the demands of the pharmaceutical industry for cleaner, safer and efficient synthetic solutions.

Quantitative determination of activation energies in mechanochemical reactions

Mechanochemical reactions often result in 100% yields of single products, making purifying procedures obsolete. Mechanochemistry is also a sustainable and eco-friendly method. The ever increasing interest in this method is contrasted by a lack in mechanistic understanding of the mechanochemical reactivity and selectivity. Recent in situ investigations provided direct insight into formation pathways. However, the currently available theories do not predict temperature T as an influential factor. Here, we report the first determination of an apparent activation energy for a mechanochemical reaction. In a temperature-dependent in situ study the cocrystallisation of ibuprofen and nicotinamide was investigated as a model system. These experiments provide a pivotal step towards a comprehensive understanding of milling reaction mechanisms.

Supramolecular architectures in two 1:1 cocrystals of 5-fluorouracil with 5-bromothiophene-2-carboxylic acid and thiophene-2-carboxylic acid

In solid-state engineering, cocrystallization is a strategy actively pursued for pharmaceuticals. Two 1:1 cocrystals of 5-fluorouracil (5FU; systematic name: 5-fluoro-1,3-dihydropyrimidine-2,4-dione), namely 5-fluorouracil–5-bromothiophene-2-carboxylic acid (1/1), C5H3BrO2S·C4H3FN2O2, (I), and 5-fluorouracil–thiophene-2-carboxylic acid (1/1), C4H3FN2O2·C5H4O2S, (II), have been synthesized and characterized by single-crystal X-ray diffraction studies. In both cocrystals, carboxylic acid molecules are linked through an acid–acid R 2 2(8) homosynthon (O—H...O) to form a carboxylic acid dimer and 5FU molecules are connected through two types of base pairs [homosynthon, R 2 2(8) motif] via a pair of N—H...O hydrogen bonds. The crystal structures are further stabilized by C—H...O interactions in (II) and C—Br...O interactions in (I). In both crystal structures, π–π stacking and C—F...π interactions are also observed.

Supramolecular hydrogen-bonding patterns in 1:1 cocrystals of 5-fluorouracil with 4-methylbenzoic acid and 3-nitrobenzoic acid

The design of a pharmaceutical cocrystal is based on the identification of specific hydrogen-bond donor and acceptor groups in active pharmaceutical ingredients (APIs) in order to choose a `complementary interacting' molecule that can act as an efficient coformer. 5-Fluorouracil (5FU) is a pyrimidine derivative with two N—H donors and C=O acceptors and shows a diversity of hydrogen-bonding motifs. Two 1:1 cocrystals of 5-fluorouracil (5FU), namely 5-fluorouracil–4-methylbenzoic acid (5FU–MBA), C4H3FN2O2·C8H8O2, (I), and 5-fluorouracil–3-nitrobenzoic acid (5FU–NBA), C4H3FN2O2·C7H5NO4, (II), have been prepared and characterized by single-crystal X-ray diffraction. In (I), the MBA molecules form carboxylic acid dimers [R 2 2(8) homosynthon]. Similarly, the 5FU molecules form two types of base pair via a pair of N—H...O hydrogen bonds [R 2 2(8) homosynthon]. In (II), 5FU interacts with the carboxylic acid group of NBA via N—H...O and O—H...O hydrogen bonds, generating an R 2 2(8) ring motif (heterosynthon). Furthermore, the 5FU molecules form base pairs [R 2 2(8) homosynthon] via N—H...O hydrogen bonds. Both of the crystal structures are stabilized by C—H...F interactions.

Polymorphs, hydrates and solvates of a co-crystal of caffeine with anthranilic acid

A polymorph screen on a new 1:1 co-crystal of caffeine, C8H10N4O2, with anthranilic acid, C7H7NO2, has revealed a rich diversity of crystal forms (two polymorphs, two hydrates and seven solvates, including two sets of isostructural solvates). These forms were prepared by liquid-assisted grinding and solution crystallization, and the crystal structures of nine of these forms have been solved using either single-crystal or powder X-ray data. The structures contain O-H...N and N-H...O hydrogen bonds through which caffeine and anthranilic acid molecules assemble to form zigzag-type chains. These chains can interact in an anti-parallel and offset manner to form cage- or channel-type skeletons within which solvent molecules can be located, giving rise to the diversity of forms observed for this co-crystal. In contrast, an equivalent series of liquid-assisted grinding and solution crystallization experiments with the closely related system of theobromine, C7H8N4O2, and anthranilic acid resulted in the formation of only one 1:1 co-crystal form.

Evaluation of the formation pathways of cocrystal polymorphs in liquid-assisted syntheses

Small but important: the kind of solvent added in liquid-assisted grinding syntheses of cocrystals influences the final product and the reaction rate.

Synthon polymorphs of 1 : 1 co-crystal of 5-fluorouracil and 4-hydroxybenzoic acid: their relative stability and solvent polarity dependence of grinding outcomes

Two synthon polymorphs of 1 : 1 co-crystals of 5-fluorouracil and 4-hydroxybenzoic acid were synthesized, and the crystal structures were determined.