Two previous undescribed cyclic pentapeptide-type compounds (1–2), with two known ones (3–4), were first isolated and purified from Clerodendrum japonicum (Thunb.) Sweet. Their structures were elucidated by extensive spectroscopic data (1D and 2D NMR) analysis. The absolute configurations of the two compounds were assigned using a combination of Marfey’s method and HPLC-MS analysis. All four compounds showed weak cytotoxicity against four human cancer cells lines (T24, A549, HepG2, MGC-803), with IC50 values ranging from 23.8 to 39.6 μM.
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