Lee D. Jennings

Cyclobutane carboxamide inhibitors of fungal melanin: biosynthesis and their evaluation as fungicides.

A new fungicide lead has been identified by enzyme screening of a focused combinatorial library. The lead compound 4, a potent inhibitor of scytalone dehydratase (SD), exhibits fungicidal activity upon foliar application but does not show systemic activity. The X-ray crystal structure of the enzyme-inhibitor complex and an appreciation for the relationship between physical properties and systemic activity enabled us to rapidly improve upon this initial lead. The geminal halogen-methyl group combination was found to be optimal for interaction with the bounding serine and asparagine side-chain residues. Replacement of CF3 with methyl was a key discovery, giving inhibitors with slightly diminished enzyme inhibition potency while significantly increasing systemic activity. Amides prepared from amines with 2,4-dichloro substitution on the phenyl ring gave the most potent enzyme inhibitors. Two compounds from this series showed systemic activity comparable to the commercial standard and were selected for outdoor testing in flooded plots which simulate rice paddies.

A new potent inhibitor of fungal melanin biosynthesis identified through combinatorial chemistry

A new fungicide lead has been identified by in vitro screening of a focused combinatorial library. Amides (768) were synthesized in pools of four and assayed as inhibitors of scytalone dehydratase. Deconvolution of one of the most active pools led to the discovery of a potent inhibitor of the enzyme 3b (K(i) = 26 pM), which has fungicidal properties.