The isolation of fermentation derived secondary metabolites is required for the synthesis of many anti-infective drugs. High purity (> 90 wt%) metabolites are required to support subsequent synthesis steps for conversion to the API. Purification of these compounds via crystallization is difficult due to the low purity of the initial product coupled with the production of various product analogs. A chromatography step is typically implemented to upgrade the product purity prior to performing crystallization. Since chromatography can negatively impact the process productivity and economics, the goal was to develop a crystallization utilizing a partially purified feed stream.

An investigation into the feasibility of crystallization from a crude, partially-purified product stream without using chromatography in the isolation process is presented. The motivation behind the development of a temperature cycling crystallization to produce high purity crystals (> 90 wt%) from crude extract will be described. Details of this crystallization process are presented, which include solubility curves, crystallization kinetics, and particle size distribution. The effect of system parameters, such as cooling rates, water content, and agitation, on yield and purity is also presented. The optimization of this preferential crystallization increased the product purity by 30-35 wt% with an increase in yield of 15-20% while also producing easily filterable crystals. This process was implemented on a 25 kg scale to produce material to support clinical development.