Biosynthesis of Pellucidin A in Peperomia pellucida (L.) HBK

Peperomia pellucida (L.) HBK (Piperaceae) ("jabuti herb") is an herbaceous plant that is widespread in the tropics and has several ethnomedicinal uses. The phytochemical study of leaf extracts resulted in the isolation of 2,4,5-trimethoxycinnamic acid, 5,6,7-trimethoxyflavone, 2,4,5-trimethoxystyrene, 2,4,5-trimethoxybenzaldehyde, dillapiol, and sesamin in addition to pellucidin A. The co-occurrence of styrene and cyclobutane dimers suggested the formation of pellucidin A by a photochemical [2+2] cycloaddition of two molecules of 2,4,5-trimethoxystyrene. To investigate this biogenesis, analysis of plant leaves throughout ontogeny and treatments such as drought, herbivory and, exposure to jasmonic acid and UV₃₆₅ light were carried out. Significant increases in the content of dillapiol (up to 86.0%) were found when P. pellucida plants were treated with jasmonic acid, whereas treatment under UV₃₆₅ light increase the pellucidin A content (193.2%). The biosynthetic hypothesis was examined by feeding various ¹³C-labeled precursors, followed by analysis with GC-MS, which showed incorporation of L-(2-¹³C)-phenylalanine (0.72%), (8-¹³C)-cinnamic acid (1.32%), (8-¹³C)-ferulic acid (0.51%), (8-¹³C)-2,4,5-trimethoxycinnamic acid (7.5%), and (8-¹³C)-2,4,5-trimethoxystyrene (12.8%) into pellucidin A. The enzymatic conversion assays indicated decarboxylation of 2,4,5-trimethoxycinnamic acid into 2,4,5-trimethoxystyrene, which was subsequently dimerized into pellucidin A under UV light. Taken together, the biosynthesis of pellucidin A in P. pellucida involves a sequence of reactions starting with L-phenylalanine, cinnamic acid, ferulic acid, 2,4,5-trimethoxycinnamic acid, which then decarboxylates to form 2,4,5-trimethoxystyrene and then is photochemically dimerized to produce pellucidin A.