Terahertz and Raman Spectroscopic Investigation of Anti-tuberculosis Drug-Drug Cocrystallization Involving 4-aminosalicylic Acid and Pyrazinamide

The supramolecular synthon behavior within cocrystals of pyrazinamide and alkyl dicarboxylic acids: A perspective from terahertz spectroscopy and quantum chemical calculation

Pyrazinamide (PZA) is a widely-used anti-tuberculosis pharmaceutical, but its poor solubility prompts us to optimize pharmaceutical performance. Cocrystallization is a promising technique to improve physiochemical properties of active pharmaceutical ingredient (API) by connecting it with cocrystal former (CCF) via intermolecular interactions. Even though a series of alkyl dicarboxylic acids are employed to form cocrystal structures, systematic understanding on the role of intermolecular interactions is still missing. Therefore, terahertz (THz) spectroscopy and quantum chemical calculation are combined to elucidate the behavior of ubiquitous supramolecular synthons, such as hetero-synthons of acid-pyrazine, acid-amide and homo-synthon of amide-amide, from energy's view. Potential energy is calculated to differentiate the stability within polymorphs of PZA-MA cocrystal and free energy is evaluated to compare the solubility of PZA-CCF cocrystals respectively. With regard to vibrational energy, THz spectral fingerprints are theoretically assigned to specific vibrations and attributed to the flexibility deformation of supramolecular synthons based on oscillation theory, where stretching and twisting modes dominate the collective vibrational behavior. It provides a promising tool to evaluate cocrystal performance from its driving force and insightful guidance to discover new pharmaceutical cocrystals.

Vibrational spectroscopic detection and analysis of isoniazid-nicotinamide-succinic acid ternary cocrystal

In this paper, binary and ternary cocrystals in the ternary cocrystal system of isoniazid-nicotinamide-succinic acid were prepared by solvent evaporation and grinding methods. All of them were characterized by terahertz time-domain spectroscopy (THz-TDS), confirming that the cocrystals could be obtained by the above two methods. In addition, to investigate the formation of hydrogen bonds and their influence in cocrystal, several possible forms of hydrogen bond in cocrystal were simulated by density functional theory (DFT). The simulated result was in good agreement with the experimental result, indicating that the hydrogen bonds in cocrystal were the carboxyl groups on both side of succinic acid forming a pyridine N-carboxylic acid heterosynthon with pyridine N of isoniazid or nicotinamide respectively. Meanwhile, the vibrational modes of the cocrystal were analyzed to investigate the effect of hydrogen bond to the molecules. To further understand the formation process of ternary cocrystal in this system, Raman spectroscopy was used to analyze the cocrystal samples with different time of grinding. Process information of cocrystal formation were obtained by analyzing the changes of the characteristic peaks in the corresponding Raman spectra. These results provide a wealth of information and a unique approach to the analysis of both structures and intermolecular interactions shown within ternary cocrystal.

New cocrystals of heterocyclic drugs: structural, antileishmanial, larvicidal and urease inhibition studies

Many heterocycles have been developed as drugs due to their capacity to interact productively with biological systems. The present study aimed to synthesize cocrystals of the heterocyclic antitubercular agent pyrazinamide (PYZ, 1, BCS III) and the commercially available anticonvulsant drug carbamazepine (CBZ, 2, BCS class II) to study the effect of cocrystallization on the stability and biological activities of these drugs. Two new cocrystals, namely, pyrazinamide-homophthalic acid (1/1) (PYZ:HMA, 3) and carbamazepine-5-chlorosalicylic acid (1/1) (CBZ:5-SA, 4), were synthesized. The single-crystal X-ray diffraction-based structure of carbamazepine-trans-cinnamic acid (1/1) (CBZ:TCA, 5) was also studied for the first time, along with the known cocrystal carbamazepine-nicotinamide (1/1) (CBZ:NA, 6). From a combination drug perspective, these are interesting pharmaceutical cocrystals to overcome the known side effects of PYZ (1) therapy, and the poor biopharmaceutical properties of CBZ (2). The purity and homogeneity of all the synthesized cocrystals were confirmed by single-crystal X-ray diffraction, powder X-ray diffraction and FT-IR analysis, followed by thermal stability studies based on differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Detailed intermolecular interactions and the role of hydrogen bonding towards crystal stability were evaluated quantitatively via Hirshfeld surface analysis. The solubility of CBZ at pH 6.8 and 7.4 in 0.1 N HCl and H2O were compared with the values of cocrystal CBZ:5-SA (4). The solubility of CBZ:5-SA was found to be significantly improved at pH 6.8 and 7.4 in H2O. All the synthesized cocrystals 3-6 exhibited a potent urease inhibition (IC50 values range from 17.32 ± 0.89 to 12.3 ± 0.8 µM), several times more potent than standard acetohydroxamic acid (IC50 = 20.34 ± 0.43 µM). PYZ:HMA (3) also exhibited potent larvicidal activity against Aedes aegypti. Among the synthesized cocrystals, PYZ:HMA (3) and CBZ:TCA (5) were found to possess antileishmanial activity against the miltefosine-induced resistant strain of Leishmania major, with IC50 values of 111.98 ± 0.99 and 111.90 ± 1.44 µM, respectively, in comparison with miltefosine (IC50 = 169.55 ± 0.20 µM).

Mechanical Activation by Ball Milling as a Strategy to Prepare Highly Soluble Pharmaceutical Formulations in the Form of Co-Amorphous, Co-Crystals, or Polymorphs

Almost half of orally administered active pharmaceutical ingredients (APIs) have low solubility, which affects their bioavailability. In the last two decades, several alternatives have been proposed to modify the crystalline structure of APIs to improve their solubility; these strategies consist of inducing supramolecular structural changes in the active pharmaceutical ingredients, such as the amorphization and preparation of co-crystals or polymorphs. Since many APIs are thermosensitive, non-thermal emerging alternative techniques, such as mechanical activation by milling, have become increasingly common as a preparation method for drug formulations. This review summarizes the recent research in preparing pharmaceutical formulations (co-amorphous, co-crystals, and polymorphs) through ball milling to enhance the physicochemical properties of active pharmaceutical ingredients. This report includes detailed experimental milling conditions (instrumentation, temperature, time, solvent, etc.), as well as solubility, bioavailability, structural, and thermal stability data. The results and description of characterization techniques to determine the structural modifications resulting from transforming a pure crystalline API into a co-crystal, polymorph, or co-amorphous system are presented. Additionally, the characterization methodologies and results of intermolecular interactions induced by mechanical activation are discussed to explain the properties of the pharmaceutical formulations obtained after the ball milling process.

Cocrystals of tuberculosis antibiotics: Challenges and missed opportunities

Cocrystals have been extensively used to improve the physicochemical properties and bioavailability of active pharmaceutical ingredients. Cocrystals of anti-tuberculosis medications are among those commonly reported. This review provides a summary of the tuberculosis antibiotic cocrystals reported in the literature, providing the main results on current tuberculosis medications utilized in cocrystals. Moreover, anti-tuberculosis cocrystals limitations and advantages are described, including evidence for enhanced solubility, stability and effect. Opportunities to enhance anti-tuberculosis medications and fixed dose combinations using cocrystals are given. Several cocrystal pairs are suggested to enhance the effectiveness of anti-tuberculosis drugs.

The fingerprints of nifedipine/isonicotinamide cocrystal polymorph studied by terahertz time-domain spectroscopy

Cocrystal is constructed to improve physicochemical properties of active pharmaceutical ingredient and prevent polymorphism via intermolecular interactions. However, recent examples on cocrystal polymorphs display significantly different properties. Even though some analytical techniques have been used to characterize the cocrystal polymorphic system, it remains unclear how intermolecular interactions drive and stabilize the structure. In this work, we study the cocrystal polymorphs of nifedipine (NFD) and isonicotinamide (INA) using terahertz (THz) spectroscopy. Form I and form II of NFD-INA cocrystals show spectral fingerprints in THz region. Temperature-dependent THz spectra display distinguished frequency shifts of each fingerprint. Combined with solid-state density functional theory (DFT) calculations, the experimental fingerprints and their distinct responses to temperature are elucidated by specific collective vibrational modes. The vibrations of hydrogen bonding between dihydropyridine ring of NFD and INA are generally distributed below 1.5 THz, which play important roles in stabilizing cocrystal and preventing the oxidation of NFD. The rotations of methyl group in NFD are widely distributed in the range of 1.5-4.0 THz, which helps the steric recognition. The results demonstrate that THz spectroscopy is a sensitive tool to discriminate cocrystal polymorphs. It has the potential to be used as a non-invasive technique for pharmaceutical screening.

The necessity of periodic boundary conditions for the accurate calculation of crystalline terahertz spectra

Terahertz vibrational spectroscopy has emerged as a powerful spectroscopic technique, providing valuable information regarding long-range interactions - and associated collective dynamics - occurring in solids. However, the terahertz sciences are relatively nascent, and there have been significant advances over the last several decades that have profoundly influenced the interpretation and assignment of experimental terahertz spectra. Specifically, because there do not exist any functional group or material-specific terahertz transitions, it is not possible to interpret experimental spectra without additional analysis, specifically, computational simulations. Over the years simulations utilizing periodic boundary conditions have proven to be most successful for reproducing experimental terahertz dynamics, due to the ability of the calculations to accurately take long-range forces into account. On the other hand, there are numerous reports in the literature that utilize gas phase cluster geometries, to varying levels of apparent success. This perspective will provide a concise introduction into the terahertz sciences, specifically terahertz spectroscopy, followed by an evaluation of gas phase and periodic simulations for the assignment of crystalline terahertz spectra, highlighting potential pitfalls and good practice for future endeavors.

Terahertz and Raman Spectroscopic Investigation of Monohydrate Cocrystal of Antitubercular Isoniazid with Protocatechuic Acid

Pharmaceutical cocrystal provides an alternative modification strategy for the formulation development of drugs owning to their potential ability to improve the physicochemical properties of active pharmaceutical ingredients (APIs) efficiently by changing inter-molecular interactions between raw materials. Isoniazid (INH) is an indispensable main drug for the treatment of tuberculosis, but its tablet formulation is unstable and prone to degradation. In the present study, the monohydrate cocrystal of INH and protocatechuic acid (PA) was prepared by solvent evaporation using PA as cocrystal former to optimize the properties of INH. The parent materials and corresponding 1:1 molar ratio INH-PA monohydrate cocrystal have been characterized by the terahertz time-domain (THz-TDS) and Raman spectroscopy. The THz absorption spectra displayed that there were obvious differences between the peaks of experimental cocrystal and the parent materials, and the same situation was found in Raman vibrational spectra. In addition, density functional theory (DFT) was applied to simulating and optimizing the structure of INH-PA monohydrate cocrystal and supplied corresponding vibrational modes. Our results provided a unique method to characterize the formation of INH-PA monohydrate cocrystal at the molecular-level and a lot of information about cocrystal structure and intra-molecular and/or inter-molecular hydrogen bond interactions in the emerging pharmaceutical cocrystal fields.