A series of 1-thia-4-azaspiro[4.5]decan-3-ones bearing an amide group at C-4 and various substitutions at C-2 and C-8 were synthesized and evaluated against human coronavirus and influenza virus. Compounds 7m, 7n, 8k, 8l, 8m, 8n, and 8p were found to inhibit human coronavirus 229E replication. The most active compound was N-(2-methyl-8-tert-butyl-3-oxo-1-thia-4-azaspiro[4.5]decan-4-yl)-3-phenylpropanamide (8n), with an EC50 value of 5.5 mu M, comparable to the known coronavirus inhibitor, (Z)-N-[3-[4-(4-bromophenyl)-4-hydroxypiperidin-1-yl]-3-oxo-1-phenylprop-1-en-2-yl]benzamide (K22). Compound 8n and structural analogs were devoid of anti-influenza virus activity, although their scaffold is shared with a previously discovered class of H3 hemagglutinin-specific influenza virus fusion inhibitors. These findings point to the 1-thia-4-azaspiro[4.5]decan-3-one scaffold as a versatile chemical structure with high relevance for antiviral drug development.