A new saikosaponin was isolated from Bupleurum chinense DC., and its structure was identified as 3β,16α,23,28,30_pentahydroxy_olean_11,13(18)_dien_3_O_β_D_glucopyranosyl(1→6)_[α_L_rhamnopyranosyl (1→4)]_β_D_glucopyranoside on the basis of chemical and spectral evidence, named as saikosaponin q_1. In addition, two known saikosaponins, 3″_O_acetyl_saikosaponin d and 3″_O_acetyl_saikosaponin b 2, were also isolated and identified from this plant for the first time.
A series of O6-benzylguanine （O6-BG） derivatives was synthesized, and their in vitro AGT （O^6-Alkylguanine DNA alkyltransferase） inhibitory ability was evaluated by MTT method to investigate the possibility to be promising precursors of PET tracers. O^6--BG and its derivatives, HMBG, MOBG, MOMBG, BABP and PEG, were synthesized from guanine respectively. The AGT inhibitory ability of the compounds were tested by evaluating their effects on increasing sensitivity of HeLa cancer cells to 1,3-bis （2-chloroethyl）-l-nitrosourea （BCNU） with MTT method. Their order of AGT inhibitory activities follows HMBG ≥ O^6-BG ≥ MOBG ≥ MOMBG, whereas the BABP and PEG showed no AGT inhibition activity. HMBG, MOBG and MOMBG would be promising as precursor candidates of PET tracers for tumor imaging.
