Conformational preferences in model antiviral compounds: A spectroscopic and computational study of phenylurea and 1,3-diphenylurea

The conformational preferences of two model anti-viral pharmaceuticals, phenylurea and 1,3-diphenylurea, isolated in the gas phase, have been explored using a combination of ultra-violet and infra-red ion-dip spectroscopy and quantum chemical computation. Two conformers have been assigned for each species associated with cis and trans configurations of the amide groups and stabilised by weak intramolecular hydrogen bonding between the amide group and the aromatic ring, NH --> pi (cis) or CH --> O=C (trails). In 1,3-diphenyl urea, the folded (global minimum) trans-cis and the extended trans trans conformers were both populated but the highly folded cis-cis structure, located at considerably higher energy, could not be detected.