Synthesis of Impurities of Pramipexole Dihydrochloride

Structure Identification and Risk Assurance of Unknown Impurities in Pramipexole Oral Drug Formulation

Impurities compounds in any pharmaceutical product or drug substance are inevitable from a chemistry point of view. The quality and safety of a pharmaceutical product are also significantly affected by these impurities content; therefore, impurities need to be identified and characterized through the use of appropriate analytical methods. Pramipexole is a nonergot dopamine agonist used to treat various Parkinson's disease symptoms. Two unknown impurities were detected from a pramipexole dihydrochloride solid dosage form. These impurities were identified and characterized using ultra-performance liquid chromatography coupled with high-resolution mass spectroscopy (UPLC-HRMS). These impurities were found to be enriched when mannitol existed in the formulation. The structure and mechanism involved in the existence of the impurities were proposed. Furthermore, observation of the binding affinity potential risk of these impurities to the pramipexole receptor has also been demonstrated through molecular docking and molecular dynamics simulation study. The binding energy result showed that pramipexole interaction with dopamine receptors D2 and D3 was higher than pramipexole mannose adduct and pramipexole ribose adduct.

Synthesis, Isolation, Identification and Characterization of a Drug-Excipient Interaction Degradation Impurity in Pramipexole by HPLC, LC/MS and NMR

A drug-excipient interaction impurity associated with the degradation process of pramipexole was isolated. The impurity was detected during the stability study of pramipexole extended-release tablets. It was found at a relative retention time of 0.88 with respect to pramipexole, using the pramipexole gradient HPLC-UV detection method described in the USP. The structure of the impurity was identified and fully characterized using high resolution mass spectrometry, IR and NMR techniques, as presented herein. The degradation impurity was identified as (S)-N2-(methoxymethyl)-N6-propyl-4,5,6,7-tetrahydro-1,3-benzothiazole-2,6-diamine. The drug-excipient interaction mechanism of its formation was proposed. An efficient and straightforward synthetic approach was developed to prepare the degradation impurity to confirm its proposed degradation pathway and structure.