Semisynthestic Pyrrolizidine Alkaloid N-Oxide Antitumor Agents. Esters of Heliotridine

Article abstract of DOI:10.1021/jm00403a008

The C-9 and C-7 monoesters and C-7,C-9 diesters of heliotridine with (S)-(+)- and (R)-(-)-2-hydroxy-2-phenylbutiric acid were prepared, converted into their N-oxides, and compared with the corresponding C9 monoesters of retronecine in the in vivo P388 lymphcytic leukemia screen.Relative in vitro cytotoxicities of some of the free bases and their corresponding N.oxides were also measured against the A204 rhabdomyosarcoma cell line by using the soft agar colony forming assay.Stereochemistry at C-7 of the necine and at C-2' of the necic acid appears to have a significant effect on the antitumor activity in this system.In the heliotridine series, the configuration of the necic acid has a pronounced effect on the selectivity (C-7 vs C-9) in esterification with carbodiimidazole.An explanation for this site selectivity is offered.