With the emergence of highly pathogenic avian influenza (HPAI) H7N9 and H5N1 strains, there is a pressing need to develop direct-acting antivirals (DAAs) to combat such deadly viruses. The M2-S31N proton channel of the influenza A virus (A/M2) is one of the validated and most conserved proteins encoded by the current circulating influenza A viruses; thus, it represents a high-profile drug target for therapeutic intervention. We recently discovered a series of S31N inhibitors with the general structure of adamantyl-1-NH2(+)CH2-aryl, but they generally had poor physical properties and some showed toxicity in vitro. In this study, we sought to optimize both the adamantyl as well as the aryl/heteroaryl group. Several compounds from this study exhibited submicromolar EC50 values against S31N-containing A/WSN/33 influenza viruses in antiviral plaque reduction assays with a selectivity index greater than 100, indicating that these compounds are promising candidates for in-depth preclinical pharmacology.