Natural Products for Drug Discovery: Discovery of Gramines as Novel Agents against a Plant Virus.

Plant viral diseases seriously affect crop yield and quality. The natural product gramine (1) and its simple structural analogues 2-35 were synthesized from indoles, amines, and aldehydes in one step. The antiviral effects of these alkaloids were evaluated systematically. Most of these compounds were found to have higher antiviral effects than commercial ribavirin for the first time. Especially compounds 22, 30, and 31 exhibited significantly higher effects than ningnanmycin, thereby emerging as novel antiviral leads for further optimization. The preliminary implementation indicated that these compounds likely inhibit the assembly of tobacco mosaic virus (TMV) by cross-linking TMV capsid protein. Gramine analogues were also found to have broad-spectrum fungicidal effects. Although gramine has been reported to have influence on germination and development of Erysiphe graminis, these compounds displayed no fungicidal effects against Blumeria graminis f. sp. tritici on wheat in our test. Some of these compounds also exhibited certain insecticidal activities.