Crystallization and physicochemical investigation of melevodopa hydrochloride, a commercially available antiparkinsonian active substance

Abstract

In this work, the levodopa methyl ester was crystallized from different solvents and its physicochemical proper- ties were explored. This active pharmaceutical ingredient (API) is commercially available as an effervescent tablet in Italy. The crystallization methods were solvent evaporation from different solvents (water, ethanol, methanol) and crystalliza- tion by adding an antisolvent. These methods led to the same product which had the same different X­ray powder dif-fractogram that was different from the diffractogram of raw LDME. According to the hot­stage microscopy and differential scanning calorimetry (DSC), the melting point was remarkably decreased, however, above the melting point, the melt tended to recrystallize to the raw LDME which was shown by an exothermic peak on the DSC curve. This was verified by an additional test during which the API was heated to 145 °C, thereafter the diffractogram matched perfectly with theraw LDME. These results indicate the presumable formation of a new polymorph. During the crystallization, the LDME did not degrade according to the high-performance liquid chromatography. Besides the recrystallization kinetics of the amorphous form was also followed, the activation energy of recrystallization was 85.3 kJ/mol, the diffractogram of recrys- tallization was the same as in the case of the crystallized products.