6KEK 6KEK 6kek Crystal structure of BRD4 bromodomain 1 (BD1) in complex with 6-hydroxy-16-methoxy-11-methyl-2-oxa-11-azatetracyclo[8.6.1.03,8.013,17]heptadeca-1(16),3,5,7,9,13(17),14-heptaen-12-one 6KEK-noatom