(74f) Optimization of Whole Broth Extraction: a Case Study of Secondary Metabolite Isolation

The isolation of fermentation secondary metabolites is required for the synthesis of many semi-synthetic anti-infective drugs. Early in development, the purification of these compounds is often difficult due to low broth titers, poorly defined impurities, unusual solubility characteristics and the presence of closely related analogs. Direct extraction of these pharmaceutically active intermediates from the whole broth is usually the primary step of the isolation process. In many cases, early isolation processes involve extraction of the broth with a miscible solvent such as methanol or acetone, followed by removal of the cell solids, and subsequently requires chromatography for concentration and purification. However this generates low purity extracts due to the extraction of water soluble impurities and results in a chromatography step with low productivity. This paper will present a case study on the switch to the use of an immiscible solvent for whole broth extraction to increase extract purity and concentration, while also increasing overall productivity. Chemical and physical parameters, such as solvent/co-solvent composition, phase ratio, temperature and pH, were investigated, resulting in an initial extraction step which increased the whole broth extract purity over that of the miscible solvent case by thirty-fold. Development and optimization of a subsequent extractive sequence increased the stream purity sufficiently to eliminate the need for chromatography prior to crystallization. The importance of tailoring the solvent composition to match the polarity of the product will be demonstrated.