Predicting crystal form stability under real-world conditions

The physicochemical properties of molecular crystals, such as solubility, stability, compactability, melting behaviour and bioavailability, depend on their crystal form1. In silico crystal form selection has recently come much closer to realization because of the development of accurate and affordable free-energy calculations2-4. Here we redefine the state of the art, primarily by improving the accuracy of free-energy calculations, constructing a reliable experimental benchmark for solid-solid free-energy differences, quantifying statistical errors for the computed free energies and placing both hydrate crystal structures of different stoichiometries and anhydrate crystal structures on the same energy landscape, with defined error bars, as a function of temperature and relative humidity. The calculated free energies have standard errors of 1-2 kJ mol-1 for industrially relevant compounds, and the method to place crystal structures with different hydrate stoichiometries on the same energy landscape can be extended to other multi-component systems, including solvates. These contributions reduce the gap between the needs of the experimentalist and the capabilities of modern computational tools, transforming crystal structure prediction into a more reliable and actionable procedure that can be used in combination with experimental evidence to direct crystal form selection and establish control5.

A Mild Synthesis of Aryl Triflates Enabling the Late-Stage Modification of Drug Analogs and Complex Peptides

We report the discovery of a novel strategy to convert phenols into the corresponding aryl triflates using 1-methyl-3-((trifluoromethyl)sulfonyl)-1,3-dihydro-2H-benzo[d]imidazol-2-one in the presence of a fluoride source. This novel reagent can be handled without any precautions to exclude air or moisture making this method highly convenient. The reactions generally show very clean conversions within only a few minutes at room temperature. The mild conditions allow the so far unprecedented O-triflation of tyrosine in peptides bearing challenging side chains present for example in arginine and histidine including the late-stage triflation of complex bioactive peptides. We show how aryl triflates - an interesting but so far underutilized group - can be used to optimize physicochemical and in vitro properties of compound series in medicinal chemistry. We believe that this method is highly attractive for applications in peptide functionalization as well as automated and medicinal chemistry.

Experimental and simulated distribution and interaction of water in cellulose esters with alkyl chain substitutions

This study investigated the effect of the average length of substituted side chains in different cellulose esters on water sorption and the water association mechanism. For this purpose, a set of esters with a similar total degree of substitution was selected: cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate. Dynamic vapor sorption was used to determine the effect of the side chain length on sorption, desorption, and the occurrence of water clustering. Since water association in the structure was of interest, molecular dynamics simulations were performed on cellulose acetate and cellulose acetate propionate. This study showed that cellulose acetate appears to be water-sensitive and experiences hysteresis upon water sorption, which was attributed to structural changes. The simulations also showed that water is screened out by the side chains and forms intermolecular hydrogen bonds, primarily to the carbonyl oxygen rather than the residual hydroxyl groups.

Designing Selective Drug-like Molecular Glues for the Glucocorticoid Receptor/14-3-3 Protein-Protein Interaction

The ubiquitously expressed glucocorticoid receptor (GR) is a nuclear receptor that controls a broad range of biological processes and is activated by steroidal glucocorticoids such as hydrocortisone or dexamethasone. Glucocorticoids are used to treat a wide variety of conditions, from inflammation to cancer but suffer from a range of side effects that motivate the search for safer GR modulators. GR is also regulated outside the steroid-binding site through protein-protein interactions (PPIs) with 14-3-3 adapter proteins. Manipulation of these PPIs will provide insights into noncanonical GR signaling as well as a new level of control over GR activity. We report the first molecular glues that selectively stabilize the 14-3-3/GR PPI using the related nuclear receptor estrogen receptor α (ERα) as a selectivity target to drive design. These 14-3-3/GR PPI stabilizers can be used to dissect noncanonical GR signaling and enable the development of novel atypical GR modulators.

A peculiar dehydration and solid–solid phase transition of the active pharmaceutical ingredient AZD9898 based on in situ single crystal-to-single crystal transformations

Isostructural dehydration from form A hydrate to form B, and solid–solid phase transition from form B to C of AZD9898 were revealed by in situ single crystal-to-single crystal transformations.

Structural origin of physicochemical properties differences upon dehydration and polymorphic transformation of ciprofloxacin hydrochloride revealed by structure determination from powder X-ray diffraction data

Crystallochemical study of three phases of ciprofloxacin hydrochloride reveals the mechanisms of dehydration, polymorphic transformation, and differences in physicochemical properties.

Capturing a new hydrate polymorph of amodiaquine dihydrochloride dihydrate via heterogeneous crystallisation

A new polymorph of amodiaquine dihydrochloride dihydrate was obtained via heterogenous crystallization. This new polymorph showed difference in two-dimensional sheet structure compare to previously known polymorph.

A new solvate of epalerstat, a drug for diabetic neuropathy

Epalerstat {systematic name: (5Z)-5-[(2E)-2-methyl-3-phenyl-prop-2-en-1-yl-idene]-4-oxo-2-sulfanyl-idene-1,3-thia-zolidine-3-acetic acid} crystallized as an acetone monosolvate, C15H13NO3S2·C3H6O. In the epalerstat mol-ecule, the methyl-propyl-enediene moiety is inclined to the phenyl ring and the five-membered rhodamine ring by 21.4 (4) and 4.7 (4)°, respectively. In addition, the acetic acid moiety is found to be almost normal to the rhodamine ring, making a dihedral angle of 85.1 (2)°. In the crystal, a pair of O-H⋯O hydrogen bonds between the carb-oxy-lic acid groups of epalerstat mol-ecules form inversion dimers with an R22(8) loop. The dimers are linked by pairs of C-H⋯O hydrogen bonds, enclosing R22(20) loops, forming chains propagating along the [101] direction. In addition, the acetone mol-ecules are linked to the chain by a C-H⋯O hydrogen bond. Epalerstat acetone monosolvate was found to be isotypic with epalerstat tertra-hydro-furan solvate [Umeda et al. (2017 ▸). Acta Cryst. E73, 941-944].

Epalrestat tetra-hydro-furan monosolvate: crystal structure and phase transition

Epalrestat, an important drug for diabetic neuropathy, has been reported to exist in polymphic, solvated and co-crystal forms. Herein, we report on the crystal structure of epalerstat tetra­hydro­furan solvate which crystallizes in the triclinic space group P. On desolvation, epalerstat Form II (monoclinic, C2/c) is obtained.

The title compound, epalrestat {systematic name: (5Z)-5-[(2E)-2-methyl-3-phenyl­prop-2-en-1-yl­idene]-4-oxo-2-sulfanyl­idene-1,3-thia­zolidine-3-acetic acid}, crystallized as a tetra­hydro­furan monosolvate, C₁₅H₁₃NO₃S₂·C₄H₈O. Epalrestat, an important drug for diabetic neuropathy, has been reported to exist in polymphic, solvated and co-crystal forms. In the mol­ecule reported here, the phenyl ring is inclined to the rhodamine ring by 22.31 (9)°, and the acetic acid group is almost normal to the rhodamine ring, making a dihedral angle of 88.66 (11)°. In the crystal, pairs of O—H⋯O hydrogen bonds are observed between the carb­oxy­lic acid groups of epalerstat mol­ecules, forming inversion dimers with an R₂²(8) loop. The dimers are linked by pairs of C—H⋯O hydrogen bonds, forming chains along [101]. The solvate mol­ecules are linked to the chain by a C—H⋯O(tetra­hydro­furan) hydrogen bond. A combination of thermal analysis and powder X-ray diffraction revealed that title compound desolvated into epalerstat Form II. One C atom of the tetra­hydro­furan solvate mol­ecule is positionally disordered and has a refined occupancy ratio of 0.527 (18):0.473 (18).

Crystal structure of olivetolic acid: a natural product from Cetrelia sanguinea (Schaer.)

The packing in olivetolic acid is similar to that in resorcinolic acid.

The title compound, C₁₂H₁₆O₄ (systematic name: 2,4-dihy­droxy-6-pentyl­benzoic acid) is a natural product isolated from C. sanguinea (Schaer.) and is reported to have various pharmacological activities. The mol­ecule is approximately planar (r.m.s. deviation for the non-H atoms = 0.096 Å) and features an intra­molecular O—H⋯O hydrogen bond. In the crystal, each olivetolic acid mol­ecule is connected to three neighbours via O—H⋯O hydrogen bonds, generating (10-1) sheets. This crystal is essentially isostructural with a related resorcinolic acid with a longer alkyl chain.