Synthesis, insecticidal activity and inhibition on topoisomerase I of 20(S)-t-Boc-amino acid derivatives of camptothecin.

Camptothecin (CPT), a quinolone alkaloid extracted from Camptotheca acuminata Decne, exhibits potential insecticidal activities against various insect species. Our previous studies have showed that CPT induced apoptosis in Spodoptera exigua Hübner cell line and inhibited the relaxation activity of topoisomerase I (Topo I). In this study, total seven 20(S)-t-butoxy carbonyl-amino acid derivatives of CPT were synthesized and evaluated for insecticidal activities, cytotoxicity and Topo I inhibitory activities. Results showed that introduction of t-Boc amino acids to 20-position on CPT improves contact assay and cytotoxicity of most derivatives toward S. exigua but reduces inhibitory effect on relaxation activity of S. exigua Topo I. Furthermore, compounds 1d and 1g demonstrated higher level of contact activities and cytotoxicity than CPT and hydroxyl-camptothecin (HCPT), which are potential to be developed as potential insecticides targeted at more than Topo I.