Abstract
Pinacol esters of boronic acids are widely used as starting materials in organic synthesis for Suzuki-Miyaura chemistry. The accurate analysis of these esters is complicated by competing hydrolysis to the corresponding boronic acids under typical RP-HPLC testing conditions. To address this challenge, we evaluated conditions to minimize on-column hydrolysis during RP-HPLC analysis. The effects of several HPLC parameters on hydrolysis were explored through the design of experiment (DoE) studies. Three columns bearing different silanol activities were selected to analyze boronate esters: Agilent Zorbax Eclipse XDB C18, Phenomenex Onyx Monolithic, and Waters XTerra MS C18. It was determined that the stationary phase has a significant influence on the rate of on-column hydrolysis, as did formic acid concentration in mobile phase. Column temperature had a minor effect. The optimized method, using an XTerra MS C18 column and mobile phase with no pH modifier, was applied to various boronate esters and minimal to no on-column hydrolysis was observed.
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