The three-dimensional atomic-level structure of an amorphous glucagon-like peptide-1 receptor agonist

Amorphous formulations are increasingly used in the pharmaceutical industry due to their increased solubility, but their structural characterization at atomic-level resolution remains extremely challenging. Here, we characterize the complete atomic-level structure of an amorphous glucagon-like peptide-1 receptor (GLP-1R) agonist using chemical shift driven NMR crystallography. The structure is determined from measured chemical shift distributions for 17 of the 32 carbon atoms and 16 of the 31 hydrogen atoms in the molecule. The chemical shifts are able to provide a detailed picture of the atomic-level conformations and interactions, and we identify the structural motifs that play a major role in stabilization of the amorphous form. In particular, hydrogen bonding of the carboxylic acid proton is strongly promoted although no carboxylic acid dimer is formed. Two orientations of the benzodioxole ring are promoted in the NMR structure, corresponding to a significant stabilization mechanism. Our observation that inclusion of water leads to stabilization of the carboxylic acid group might be used as a strategy in future formulations where hydrogen bonding between neighboring molecules may otherwise be hindered by sterics.

无定形制剂（amorphous formulations）因溶解度提升而愈发广泛地应用于制药工业，但其原子级分辨率下的结构表征仍极具挑战性。本研究借助化学位移驱动的核磁共振晶体学（chemical shift driven NMR crystallography），完成了某无定形胰高血糖素样肽-1受体（glucagon-like peptide-1 receptor, GLP-1R）激动剂的全原子级结构表征。该结构基于分子内32个碳原子中的17个、31个氢原子中的16个的实测化学位移分布（chemical shift distributions）解析得到。化学位移可清晰呈现该分子的原子级构象与相互作用特征，本研究还明确了对无定形形式稳定化起到关键作用的结构基元。具体而言，尽管未形成羧酸二聚体，羧酸质子（carboxylic acid proton）的氢键作用得到了显著强化。在该核磁共振结构中，苯并二氧环（benzodioxole ring）的两种取向得到了稳定，这对应着一种重要的稳定化机制。本研究观察到，水分子的掺入可稳定羧酸基团，这一发现可为未来的制剂开发提供策略：当相邻分子间的氢键作用因空间位阻受阻时，即可采用该方案。