Abstract: AimTo improve the biological activity of A-ring modified analogues of camptothecin. MethodsA-ring modified camptothecins were synthesized from 10-hydroxycamptothecin or 7-ethyl-10-hydroxycamptothecin (SN-38) in three or four steps. Their cytotoxicity was evaluated using MTT assay, and their in vivo antitumor activity against mouse liver cancer H₂₂ was tested. ResultsFive hexacyclic camptothecins (6a, 6b, 6c, 7a and 7b) are target compounds, and ten camptothecin derivatives are new compounds. ConclusionThe modification of a 1,4-oxazine-2-one ring fused with positions 9 and 10 of A-ring will reduce the antitumor activity of camptothecins.