In this article it is described the synthesis route towards an enantiomerically pure compound of pharmacological interest (pyrrolobenzodiazepine dilactam). The relevant contribution here is the use for the first time of the Self-Disproportionation of Enantiomers (SDE) effect to enrich an intermediate of the synthesis. This effect may occur when a mixture of enantiomers is sublimated: either the sublimated product or the residual become enriched in one of the quiral species. This case is even more outstanding because the SDE effect is even observed using non-chiral chromatography.