Characterization of eptifibatide during drug formulation stability assays

The objective of the study was to determine the identity of a new impurity detected in HPLC chromatograms of research samples of eptifibatide manufactured by a new process and formulated into drug product. The identification of the unknown impurity was required in order to understand the mechanism of its formation. The analysis was performed by using tandem mass spectrometers coupled with a reversed-phase gradient HPLC system. The unknown compound was then structurally elucidated by matrix-assisted laser desorption ionization (MALDI) tandem mass spectrometry. The mass spectrometric results showed that the protonated molecular ion of the unknown compound was m/z 862.3347 with molecular formula: C(36)H(52)N(11)O(10)S(2). The unknown compound was a linear peptide and was related to Asp-clipped eptifibatide. It was formed from Asp-clipped eptifibatide by the reaction of the amino group of tryptophan moiety with formaldehyde followed by electrophilic attack on the nitrogen of indole.