Revealing the Structure of 6-Aminopenillanic Acid: The Active Nucleus of Penicillins

6-Aminopenicillanic acid is a penicillanic acid compound and is the active nucleus common to all penicillins. Using laser ablation techniques, we transformed the solid into the gas phase and characterized its conformational panorama by combining supersonic expansions and Fourier transform microwave techniques. Five conformers were determined, adopting different spatial configurations. Among them, the axial and equatorial forms, which are biologically relevant, have been observed. The structural similarity to d-Ala-d-Ala and the detection of both axial and equatorial forms could explain its potential as a penicillin core and its capability as an antibiotic.