Separation of structurally similar nocathiacin analogues by reversed phase chromatography.

The complete separation of structurally similar compounds has been a challenge due mainly to their similarity on physical and chemical properties. In the present study, a simple and effective chromatographic method to separate and purify nocathiacin acid from its structural analogue nocathiacin I was developed. After evaluating mobile phase compositions on the retention characteristics by reversed phase high-performance liquid chromatography (HPLC), the elution order of nocathiacin I and nocathiacin acid was completely reversed, and the resolution value between the two analogues was improved, by varying pH value and ionic strength, to greater than 10 from merged peaks under initial conditions. In addition, a preparative isolation of nocathiacin acid was performed by reversed phase column chromatography under the guidance of the HPLC study. This chromatographic method resulted in an efficient process to obtain pure nocathiacin acid with a recovery rate of 83%. The present approach offers a new methodology for the separation of structurally closely related secondary metabolites.