Laetirobin from the parasitic growth of Laetiporus sulphureus on Robinia pseudoacacia.

(+/-)-Laetirobin (1) was isolated as a cytostatic lead from Laetiporus sulphureus growing parasitically on the black locust tree, Robinia pseudoacacia, by virtue of a reverse-immunoaffinity system. Using an LC/MS procedure, milligram quantities of (+/-)-laetirobin (1) were obtained, and the structure of 1 was elucidated by X-ray crystallography and confirmed by NMR spectroscopy. Preliminary cellular studies indicated that (+/-)-laetirobin (1) rapidly enters in tumor cells, blocks cell division at a late stage of mitosis, and invokes apoptosis.