(A) Halogen bonding interaction between 4 and an analogue of 5 (20) and Met105 on BRD4 D1. Conserved water molecules are shown in red (PDB 7RXR, 7RXS). (B) Backbone overlay of BRD4 D1 bound to H4 K5ac,K8ac (PBD 3UVW, violet) and bound to 20 (PDB 7RXS, gray). ΔCαN (the backbone Cα–Cα difference at Asn140 of BRD4 D1 with H4 K5ac,K8ac and with inhibitors) and ΔCαK (the backbone Cα–Cα difference at Lys141 of BRD4 D1 with H4 K5ac,K8ac and with inhibitors) were measured. The side chain of Lys141 was removed for clarity. The structure of 20 can be found in Table 4.