(±)-Aspongamide A, an <i>N</i>-Acetyldopamine Trimer Isolated from the Insect <i>Aspongopus chinensis,</i> Is an Inhibitor of p-Smad3

(±)-Aspongamide A (1), an unusual trimer of N-acetyldopamine (NADA) bearing a novel tetrahydrobenzo[a]dibenzo[b,e][1,4]dioxine structure, and a pair of NADA dimeric enantiomers (2) were isolated from Aspongopus chinensis. The structures of compounds 1 and 2 were assigned using spectroscopic methods. Compound 1 was found to be an inhibitor of Smad3 phosphorylation in transforming growth factor-β1 (TGF-β1) induced rat renal proximal tubular cells and suppressed extracellular matrix expression in mesangial cells under diabetic conditions.