Synthesis and biological evaluation of novel homocamptothecins conjugating with dihydropyrimidine derivatives as potent topoisomerase I inhibitors.

Homocamptothecin (hCPT) is a camptothecin (CPT) homologue with the insertion of a methylene (CH₂) spacer between the alcohol moiety and carbonyl group of the classical six-membered α-hydroxylactone ring. This modification provides higher lactone stability and did not impair its activity against topoisomerase I (Topo I), but rather appears to improve it compared to CPT. In an attempt to improve the antitumor activity of homocamptothecins, a series of novel hCPT derivatives conjugating with dihydropyrimidine (DHPM) derivatives was designed and synthesized based on a synthetic route which couples 7-formylhomocamptothecin with different dihydropyrimidine derivates. Most of the synthesized compounds exhibited good antiproliferative activity on tumor cell lines A549, MDA-MB-435 and HCT116. Furthermore, this class of compounds showed superior Topo I inhibition activity comparable to or higher than CPT.