Enantiomeric N-acetyldopamine trimers from Cicadae Periostracum and their absolute configurations

Six previously undescribed N-acetyldopamine (NADA) trimmer racemates, percicamides A−F (1−6), were isolated from a 70% ethanol extract of Cicadae Periostracum. Subsequent chiral-phase separation afforded six pairs of enantiomers, (+)- and (−)-percicamides A−F (1a/1b−6a/6b). Their structures including absolute configurations were elucidated by combined extensive spectroscopic data and quantum chemical calculations. Compounds 1−6 represent the first examples of NADA trimmers with a cis-relationship of H-7′/H-8′ or H-7′′/H-8′′. Bioassays verified that all isolated compounds showed weak inhibitory effects on nitric oxide production in RAW 264.7 cells.