The present invention provides the improved methods for preparing romidepsin. Its preparation process be under the conditions of production, purifying or storage romidepsin, prevent to be formed unwanted adduct with this. It has been found that being below about 6. in purification apparent pH0 (, for example, in apparent pH 4.0 and 6.0), it has been found that the reduction of the disulfide bond prevented has been found that and subsequent dimerization, formation that is oligomeric or polymerizeing adduct. Dimerization, oligomeric or polymerization adduct are left the present invention also provides the monomer romidepsin of composition.
