Potentiometric and NMR complexation studies of phenylboronic acid PBA and its aminophosphonate analog with selected catecholamines

Boronic acids are a class of intensively explored compounds, which according to their specific properties have been intensively explored in last decades. Among them phenylboronic acids and their derivatives are most frequently examined as receptors for diverse carbohydrates. In turn, there is a large gap in basic research concerning complexation of catecholamines by these compounds. Therefore, we decided to undertake studies on interaction of chosen catecholamines, namely: noradrenaline (norephinephrine), dopamine, L-DOPA, DOPA-P (phosphonic analog of L-DOPA) and catechol, with simple phenyl boronic acid PBA by means of potentiometry and NMR spectroscopy. For comparison, the binding properties of recently synthesized phenylboronic receptor 1 bearing aminophosphonate function in meta-position were investigated and showed promising ability to bind catecholamines. The protonation and stability constants of PBA and receptor 1 complexes were examined by potentiometry. The obtained results demonstrated that PBA binds the catecholamines with the following affinity order: noradrenaline ⩾ dopamine ≈ L-DOPA > catechol > DOPA-P, while its modified analog 1 reveals slightly different preferences: dopamine > noradrenaline > catechol > L-DOPA > DOPA-P.

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► Binding abilities of PBA and receptor 1 with chosen catechol group containing molecules were investigated.
► Potentiometric and NMR studies were performed.
► Protonation constants for catecholamines and two boronic receptors PBA and 1 were calculated.
► Stability constants of complexes PBA and 1 with catecholamines were determined. At high pH values the complexes breakdown was observed.
► The stepwise binding constants log Ktet for formed complexes were calculated.