Co-crystals, Salts or Mixtures of Both? The Case of Tenofovir Alafenamide Fumarates

Glasdegib Dimaleate: Synthesis, Characterization and Comparison of Its Properties with Monomaleate Analogue

Glasdegib is a recently approved drug for the treatment of acute myeloid leukemia. It is formulated and marketed in monomaleate salt form. In our investigation, we were able to prepare a glasdegib dimaleate form, which could, in theory, exist in double-salt form or as a mixture of salt and co-crystal species. Therefore, the obtained crystals of glasdegib dimaleate were characterized via 15N ssNMR and single-crystal X-ray diffraction, which revealed that the obtained glasdegib dimaleate exists in double-salt form. This is a surprising finding based on the pKa values for glasdegib and maleic acid. Furthermore, we fully characterized the new dimaleate form using thermal analyses (DSC and TGA) and spectroscopy (IR and Raman). Finally, the physicochemical properties, such as solubility and chemical stability, of both forms were determined and compared.

On the Single-Crystal Structure of Tenofovir Alafenamide Mono-Fumarate: A Metastable Phase Featuring a Mixture of Co-Crystal and Salt

Tenofovir alafenamide (TAF) is a prodrug of tenofovir as a potent nucleotide reverse transcriptase inhibitor. It serves as the key component of Genvoya^® for the first-line treatment of human immunodeficiency virus infection (HIV) and is the active component of Vemlidy^® for the treatment of chronic hepatitis B. Vemlidy^® is also a monotherapeutic regimen formulated as TAF hemifumarate (1; TAF:fumarate = 2:1). In this work, we report for the first time the single-crystal structure of TAF fumarate hemihydrate (2, TAF:fumarate:H₂O = 2:2:1). Compound 2 is initially documented as a salt in which one proton of the fumaric acid migrates to the amine group of the adenine moiety in TAF. It was recently proposed that ca. 20–30% proton is transferred to the N atom on the aromatic adenine backbone. We herein provide definitive single-crystal X-ray diffraction results to confirm that 2, though phase pure, is formed as a mixture of co-crystal (75%) and salt (25%). It features two pairs of TAF fumarates, wherein one of the four H atoms on the fumaric acid is transferred to the N atom of the adjacent adenine moiety while the other three carboxylates remain in their intrinsic acid form. Compound 2 is a metastable phase during the preparation of 1 and can be isolated by halting the reaction during the refluxing of TAF and fumaric acid in acetonitrile (MeCN). Our report complements the previous characterizations of TAF monofumarate, and its elusive structural patterns are finally deciphered.

Supramolecular Diversity of Oxabicyclo[2.2.2]octenes Formed between Substituted 2H-Pyran-2-ones and Vinyl-Moiety-Containing Dienophiles

In Diels–Alder reactions, 2H-pyran-2-ones as dienes can yield a large variety of cycloadducts with up to four contiguous carbon stereogenic centers. Some of the potentially most useful, however difficult to prepare due to their low thermal stability, are the primary CO2-containing oxabicyclo[2.2.2]octenes, which could be formed as eight distinctive isomers (two sets of regioisomers, each of these composed of four different stereoisomers). A high-pressure synthesis of such products was recently described in a few cases where vinyl-moiety-containing dienophiles were used as synthetic equivalents of acetylene. However, structures of the primary products have been so far only rarely investigated in detail. Herein, we present seven novel single-crystal X-ray diffraction structures of such cycloadducts of both stereoisomeric forms, i.e., endo and exo. Additionally, we present a single-crystal structure of a rare case of a cyclohexadiene system stable at room temperature, obtained as a secondary product upon the retro-hetero-Diels–Alder elimination of CO2 under thermal conditions (microwave irradiation), during this elimination the symmetry is increased and out of eight initially possible isomers of the reactant, this number in the product is decreased to four. In oxabicyclo[2.2.2]octene compounds, centrosymmetric hydrogen bonding was found to be the predominant motif and diverse supramolecular patterns were observed due to rich variety of C–H⋯O and C–H⋯π interactions.