New antimitotic bicyclic peptides, celogentins D–H, and J, from the seeds of Celosia argentea

Six new bicyclic peptides, celogentins D–H () and J () have been isolated from the seeds of Celosia argentea, and the structures including its absolute stereochemistry were determined by using extensive NMR methods and chemical means. Celogentins E–H () and J () showed potent inhibition of tubulin polymerization, while the inhibitory activity of celogentin D () was modest. Structure–activity relationship study indicates that ring size of the bicyclic ring system including unusual βs-Leu, Trp, and His residues would be important for their biological activity.