Trans-3,4-diacetoxypiperidine as a model for novel pH-triggered conformational switches

An acid-induced conformational flip of trans-3,4-diacetoxy-1-benzylpiperidine has been determined by 1H NMR. It occurs while the apparent pH (pD) of the d4-methanol solution decreases from 6 to 3. Due to an intramolecular hydrogen bond, the conformer with axial position of both acetoxy groups becomes strongly predominant. The separation of the acetoxy groups increases drastically. Thus, in similar structures an incorporated trans-3,4-disubstituted piperidine moiety can serve as a conformational pH-trigger when equipped with substituents designed to perform certain geometry-dependent functions, for example, as cation chelators or as lipid tails. The power of this trigger was estimated as ∼10 kJ/mol.