For 1a and 1b, one of the chlorine atoms in the tail is a halogen bond donor to the backbone carbonyl oxygen of His241 (Fig. ), and for 1e, it is a halogen bond acceptor from the side chain of Lys244 (Fig. ). For these compounds, with 4-atom-long linkers, the phenyl tail is also involved in parallel stacking interactions with the imidazole ring of His241.