A series of 9-(alkylthiomethyl)-10-hydroxycamptothecins and pyrano-fused camptothecin derivatives were synthesized via the reaction of topotecan hydrochloride with various thiols and alkyl vinyl ethers respectively. In the reactions, topotecan hydrochloride was utilized as ortho-quinonemethide (o-QM) precursor. The configuration of 19 was determined by 1H NMR and NOESY spectra as syn-isomers, suggesting that the cycloaddition of topotecan with alkyl vinyl ethers could undergo a hetero Diels–Alder reaction. All the synthesized compounds were screened on cancer cell lines HepG2, KB, HCT-8 and SGC7901. Some compounds were selected to assess their inhibitory activity against Topo I via Topo I mediated DNA cleavage assays. The results showed that among those tested 9-(alkylthiomethyl)-10-hydroxycamptothecins, the compounds with bulkier hydrophobic side chains at 9-position have better bioactivities. As well as all pyrano-fused camptothecins possess antiproliferative activity against the tested cancer cell lines. Docking studies suggested that there are more interactions between the novel analogues and the binding site of Topo I.Most of new derivatives exhibited comparable activity to 10-hydroxycamptothecin and topotecan in cell-level and enzyme-level assays.

Six derivatives of 10-hydroxycamptothecin were prepared via solvolysis of topotecan in corresponding alcohols and acetic anhydride. We attributed the specific reactivity of topotecan to the internal hydrogen-bonding between 10-hydroxy and the nitrogen atom in position 9. As a result the reaction underwent through an intermediate ortho-quionomethlide species to reach equilibrium. Bioactivity screening data showed all products could potentially inhibit the proliferation of several cancer cell lines in vitro and a bigger size group in 9-position would be favorable for the anti-tumor activities observably.Six derivatives of 10-hydroxycamptothecin were prepared via solvolysis of topotecan in corresponding alcohols and acetic anhydride and evaluated in vitro as anti-tumor agents.