Specific Activity of Synthesized Analogs of Germination Self-inhibitors from Urediniospores of the Oat Rust Fungus.

Abstract

In order to investigate the structure-activity relationships of cinnamate-type self-inhibitors, we synthesized some dimethyl benzalmalonates which had an additional methoxy carbonyl group at the α-position of the cinnamates. Two compounds, dimethyl 3, 4-dimethoxybenzalmalonate (DDB) and dimethyl 4-hydroxy-3-methoxybenzalmalonate (DHMB) showed great activity against germination of rust urediniospores approximately equal to the genuine self-inhibitors, methyl cis-3, 4-dimethoxycinnamate (MDC) and methyl cis-ferulate (MF). DDB showed higher activity against Puccinia coronata f. sp. avenae than Puccinia graminis f. sp. tritici. DHMB showed the reverse result. This means that DDB and DHMB have the same specificity as the genuine self-inhibitors. Among dimethyl benzalmalonates synthesized, compounds having a methoxy group at the meta position on the benzene ring inhibited germination of rust urediniospores. However the activity of dimethyl 3-methoxybenzalmalonate (D3MB) having only one methoxy group was about 100, 000 times less than that of DDB. Germination of urediniospores inhibited by treatment of DDB was reversed by washing with water, while germination inhibition by treatment of D3MB was not reversed by washing with water. DDB did not inhibit spore germination of other fungi equal to the genuine self-inhibitors, MDC and MF. In contrast D3MB inhibited spore germination of many fungi. This result shows that methoxy groups at both meta and para positions on the benzene ring are important for the specific activity of the self-inhibitor of P. coronata f. sp. avenae.