Some sulfonylureas are an important class of environmental benign, ultra-low dosage herbicides. X-ray diffraction spectra of bio-active sulfonylureas were carefully examined and an intra-molecular hydrogen bond was first reported here. By theoretical calculation, three essential structural requirements for the bio-activity were concluded as follows: (a) all intramolecular hydrogen bonds cause a coplanar conjugated system between the heterocycle and urea moiety; (b) carbomyl oxygen, sulfonyl oxygen and heterocyclic nitrogen form three negative centers; (c) between sulfonylamido and phenyl ortho substituent, there is a cavity. A Caliper model thus deduced reasonably explains the structure/activity relationship of bioactive sulfonylureas. A 3-D contour map of a pseudo-ALS model was set up with which could lead to further design of novel ALS inhibitors, including some possible non-sulfonylureas leads.

Key words: SULFONYLUREA, MOLECULAR DESIGN, INTRAMOLECULARLY, HYDROGEN BONDS, STRUCTURE ACTIVITY RELATIONSHIP, BIOLOGICAL ACTIVITY, HERBICIDES