Process for the isolation of pseudomonic acid a from pseudomonic acid complex-containing culture broth

A process for the isolation of the pseudomonic acid A antibiotic of pharmaceutical quality from the culture broth of one of the pseudomonic acid A-producing species of the Pseudomonas bacterium genus comprising the extraction of the biosynthesized pseudomonic acid A from the culture broth at acidic pH with a chlorinated aliphatic hydrocarbon or isobutyl acetate, followed by purification, is disclosed. The invention includes processes for purification of the isolated pseudomonic acid A, including (a) by the distribution of the evaporated extract residue between the aqueous-alcohol and some aliphatic or aromatic hydrocarbon, and then the extraction of the increased water-containing aqueous-alcoholic phase with methylene chloride, ethyl acetate, or isobutyl acetate; (b) by the extraction of the extract with aqueous ammonium hydrogen carbonate, alkali metal hydroxide or ammonium hydroxide solution and the acidification of the resulting alkaline aqueous extract, then reextraction again with a chlorinated aliphatic hydrocarbon or isobutyl acetate; and (c) by the concentration of the extract and the recrystallization of the crystalline pseudomonic acid A in a mixture of isobutyl acetate and petroleum ether, or acetonitrile, or aqueous acetonitrile.