Pharmaceutical and analytical characterisation of (2R)-(3-amino-2-fluoropropyl)sulphinic acid, a GABAB receptor agonist

(2R)-(3-Amino-2-fluoropropyl)sulphinic acid (AFPSiA) is a potent GABAB agonist, which makes it a possible alternative in future GERD treatment. The degradation of AFPSiA was investigated to support the drug-development effort. The compound is too polar to be compatible with regular reversed-phase LC. Moreover, the compound and the degradation products cannot be detected by UV due to low absorption. Instead, the degradation of AFPSiA was followed by two different capillary electrophoresis methods with indirect UV detection and 1H NMR and 19F NMR. AFPSiA was very unstable in basic conditions and at temperatures above room temperature. The corresponding sulphonic acid and allylamine are formed via two separate degradation routes. Both these degradation products may cause unwanted side-effects in vivo. Aqueous solutions of AFPSiA were found to be more stable at pH between 1 and 3. It was suggested that AFPSiA should be stored frozen, preferably at −70 °C. In solid state, the compound can be stored at ambient conditions in closed vials with low relative humidity. A solid oral dosage form should be kept in a blister package.