Diagnostic absolute configuration determination of clavulanate potassium: A comprehensive investigation of chiroptical spectroscopies and theoretical calculations.

•Convenient methods were demonstrated to determine the absolute configuration of CP.•DFT calculation was applied to simulate and elucidate the spectroscopies observation.•Two characteristic cotton effects were found in ECD consisted with simulation.•Four diagnostic peaks of VCD were found to distinguish CP from its stereoisomers.•Conformational and vibrational properties of CP were revealed by theoretical method.