The present invention provides a group of novel compounds that inhibit the proteolytic activity of 3C proteases which are found in picornaviruses, particularly rhinoviruses. In picornaviruses the RNA genome is translated into a single large viral polyprotein precursor. The precursor demonstrates auto-proteolytic activity, cleaving itself into mature viral gene products. Therefore, compounds of the current invention are particularly useful in treating picornaviral infections by interrupting the processing of the viral gene products into mature and infectious viral particles. The current invention also provides a novel process the preparation of compounds of the current invention. The process entails the selective reduction of an imide intermediate representing a marked improvement over processes known in the art for making peptidyl-aldehydes.