Melflufen: A Journey from Discovery to Multi-Kilogram Production

Ethyl (2S)-2-[(2S)-2-amino-3-[bis-(2-chloroethyl)amino]phenyl]propaneamido]-3-(4-fluorophenyl)propanoate hydrochloride, (melphalan flufenamide or Melflufen), is an alkylating agent intended for the treatment of multiple myeloma. Initially only milligram quantities were synthesized, following a route starting from pharmaceutical-grade melphalan. Along with the pharmaceutical development, adjustments were made to the original medicinal chemistry route. This resulted in material for early clinical trials, but it became obvious that further development was necessary. Development resulted in a route in which two phenyl alanine derivatives were coupled to give a dipeptide. This intermediate was further manipulated to give an aniline which could be converted into the desired compound melflufen. The aniline derivative was converted to the corresponding N,N-bis-chloroethylaniline using chloroacetic acid and borane. Deprotection and conversion to the hydrochloride gave melflufen in good yield and excellent purity. Production was performed without chromatography at multi-kilogram scale to supply the API for Phase III studies and commercial validation batches.