In our previous phytochemical studies on Scutellaria barbata D. DON, we reported the isolation of ten neo-clerodane diterpenoid alkaloids, which showed significant cytotoxic activities.1-3) As a continuous search for more novel neo-clerodane diterpenoids, we have further investigated the aerial parts of this species and isolated four new neo-clerodane diterpenoid alkaloids, named scutebarbatines I-L (1-4). By means of detailed spectroscopic methods, the structures of four new compounds, 1-4, were elucidated. In addition, the four new compounds were screened for cytotoxity against three tumor cell lines (HONE-1 nasopharyngeal, KB oral epidermoid carcinoma, and HT29 colorectal carcinoma cells), with IC 50 values being in the range 3.2-8.3 mM. Herein we report on the isolation, structure elucidation, as well as evaluation of the cytotoxic effects of these four new compounds. Results and DiscussionCompound 1 was isolated as white needles, and showed a positive response to many alkaloid reagents. The molecular formula was established as C 30 H 41 NO 8 by HR-FAB mass spectrum, which gave a quasi-molecular ion at m/z 544.2919 [MϩH] ϩ . The IR spectrum displayed absorption bands at 1726, 1710, 1590, 1478, 1440, 1251, 888 4,5) Based on the above data and comprehensive 2D NMR experiments ( 1 H-1 H COSY, HMQC, HMBC), the structure of 1 was established as shown in Fig. 1. The relative stereochemistry of the chiral centers in 1 was resolved by 2D ROESY data. In the ROESY experiment (Fig. 1), the cross peaks were observed from H-10 to H 2 -18 and H-6, and from H 3 -20 to H-11, H 3 -17 and H 2 -19. Thus, H 3 -17, H 2 -19, H 3 -20 and H-11 were on the same molecular plane (a-configuration) while H-6, H-10 and H 2 -18 were on the opposite side of the molecular plane (b-configuration). Four new neo-clerodane diterpenoid alkaloids, named scutebarbatines I-L (1-4), were isolated from the whole plant of Scutellaria barbata D. DON. Their structures were established on the basis of detailed spectral analyses. In vitro, the four new compounds showed significant cytotoxic activities against three human cancer lines (HONE-1 nasopharyngeal, KB oral epidermoid carcinoma, and HT29 colorectal carcinoma cells), and gave IC 50 values in the range 3.2-8.3 m mM.

New neo-Clerodane Diterpenoid Alkaloids from Scutellaria barbata with Cytotoxic Activities. -Scutebarbatines I -L (I) and (II) are isolated from the whole plant. They show significant cytotoxic activities against 3 human cancer cell lines. -(DAI*, S.-J.; LIANG, D.-D.; REN, Y.; LIU, K.; SHEN, L.; Chem.