New (RS)-benzoxazepin-purines with antitumour activity: The chiral switch from (RS)-2,6-dichloro-9-[1-(p-nitrobenzenesulfonyl)-1,2,3,5-tetrahydro-4,1-benzoxazepin-3-yl]-9H-purine

► (RS)-14 presents an IC50 = 0.166 mM against the human cancerous cell line MDA-MB-231. ► (R)-14 and (S)-14 are equally potent, but more potent than the corresponding (RS)-14. ► (R)-14 induces apoptosis against MCF-7 up to 52.50 % of cell population after 48 h. ► (RS)-14 induces no acute toxicity in mice after two weeks of treatment.