Using glucaminium-based ionic liquids for improving the separation of 2-aminopyrimidine-5-ylboronic acid and its pinacol ester by high performance liquid chromatography

A reversed-phase high performance liquid chromatography (HPLC) method is described for the determination of boronic acids that are commonly present as impurities in pinacolboronate ester reagents. Boronic acids and their pinacolboronate esters are key reagents in the Suzuki–Miyaura coupling reaction. The retention of hydrophilic boronic acids in reversed-phase chromatography is often a challenge, especially in very high pH mobile phases, which are needed to mitigate the on-column degradation of pinacolboronate esters. In this study, a hydrophilic boronic acid, 2-aminopyrimidine-5-ylboronic acid, was complexed with specifically functionalized glucaminium-based ionic liquids that were added to the diluent. The two glucaminium-based ILs possess cis-diol moieties that are capable of forming complexes with boronic acids. In addition, aromatic functional groups within the glucaminium cation allow strong π–π interactions with the polymeric stationary phase. Using this approach, the limit of detection for 2-aminopyrimidine-5-ylboronic acid was found to be 3–4 μM. The quantification of 2-aminopyrimidine-5-ylboronic acid within a 2-aminopyrimidine-5-pinacolboronate ester sample was successfully achieved using this method.