Synthesis and Fungitoxicity of New Peptidyl 1,3,4-Oxadiazolo[3,2-a]pyrimidin-5-ones

Michael addition of nitrogen nucleophiles 2-amino-5-aryl-1,3,4-oxadiazoles IIa, b to 4-arylidene-5-oxazolones Ia, b followed by ring transformation of the resultant Michael adducts IIIa − d yielded 6-acetamido-2,7-diaryl-6,7-dihydro-5 H -1,3,4-oxadiazolo[3,2- a ]pyrimidin-5-ones IVa − d in a one-pot procedure. The compounds IVa − d on deacetylation furnished their 6-amino analogues Va − d, which were converted into their 6-peptidyl (Gly-Gly and Gly- l -Phe) amino derivatives VIIa − h . The compounds III − V and VII were evaluated in vitro for their fungitoxicities against Aspergillus niger and Fusarium oxysporum . Some of the compounds displayed activities comparable with that of the commercial fungicide Dithane M-45. Structure−activity relationships for the screened compounds are discussed.