Identification and structural elucidation of an oxidation product generated during stability studies of Cabergoline drug product

Cabergoline is a dopamine agonist with applications as anti-Parkinson drug and prolactin inhibitor. The cabergoline drug product Laktostop® 50 µg/mL is used in veterinary medicine for lactation suppression in cats and dogs e.g. during false pregnancy. Recently, during ongoing HPLC stability testing of Laktostop® 50 µg/mL a new oxidation product of Cabergoline was identified. A synthesis starting from Cabergoline was developed, followed by full characterization of the unknown impurity. Preliminary HPLC and LC-MS analyses indicated the unknown impurity as mono-oxygenated product of Cabergoline (Cabergoline N-oxide) that is presumably formed with oxygen by a radical mechanism. Thus, Cabergoline was treated with oxidizing agents such as m-chloroperoxybenzoic acid to afford the desired Cabergoline-N-oxide as a byproduct. After isolation by column chromatography, NMR and LC-MS-MS studies provided evidence that oxidation occurred at the N-allyl nitrogen of Cabergoline to form Cabergoline-N-oxide. © 1905 Elsevier Science. All rights reserved [Display omitted] •Synthesis and isolation of an oxidation product starting from cabergoline.•Identity was demonstrated by HPLC experiments and high-resolution mass spectrometry.•Structure elucidation by MS-MS fragmentation experiments and 1D/2D NMR analysis.•Radical induced formation mechanism is proposed.