Biocatalyzed Synthesis of Benzoyl and Cinnamoylamides Inspired by Rice Phytoalexins

Worldwide, phytopathogenic fungi, bacteria, and viruses are responsible for huge crop losses each year, threatening agricultural progress and food security and causing massive economic damages. Pyricularia oryzae represents one of the most dangerous fungal phytopathogens being the cause of rice blast, a highly destructive disease widely distributed across the world. In this critical context, good agricultural practices necessarily need to be supported using novel, effective, and sustainable agrochemicals. It is known that plants naturally counteract exogenous infections by synthesizing defense secondary metabolites, known as phytoalexins. Inspired by N-benzoyltryptamine and N-cinnamoyltryptamine, two phytoalexins found in Oryza sativa, we designed a collection of tryptamine-based derivatives. The compounds were synthesized exploiting an enzymatic approach, using Candida antarctica Lipase B (CaL-B) as a biocatalyst and tert-amyl alcohol (t-AA) as an unconventional green solvent. The activity was evaluated against a panel of different phytopathogenic fungi as well as selected Gram-negative and Gram-positive bacteria. The obtained results pave the way for novel nature-inspired products as a valuable alternative to currently available pesticides.