A NEW KIND OF FASCIOLICIDE - MOLECULAR AND ELECTRONIC-STRUCTURES OF SOME O-HYDROXYBENZENESULFONANILIDES

The molecular and electronic structures of some fasciolicidal o-hydrox ybenzenesulfonanilides (HBSA) have been studied using X-ray diffractio n and semiempirical MO calculation. In these compounds, the phenolic h ydroxyl forms a strong intramolecular hydrogen bond with an adjacent s ulfonyl oxygen atom and the strength of the d-p dative S<--N bond, whi ch may control the electron delocalization throughout the entire molec ule, is affected by substituents on the phenyl rings on both sides. Ow ing to the poor delocalization, the contribution of the keto-form of t he resonance structure is larger for some phenolate anions of HBSA in solution, and this may be a key factor determining the potency of fasc iolicidal activity of HBSA.