Iodinated indole alkaloids from Plakortis simplex - New plakohypaphorines and an evaluation of their antihistamine activity.

Three new iodinated tryptophan derivatives, plakohypaphorines D-F (4-6), have been isolated from the Caribbean sponge Plakortis simplex. Their structures have been determined by application of spectroscopic methods and microwave-assisted selective dehalogenation. Compound 5 is the first naturally occurrung triiodinated indole, while compound 6 is a unique metabolite in possessing both chlorine and iodine atoms on the indole nucleus. Anti-histamine activity for the whole series of plakohypaphorines A-F has been evaluated and only the diiodinated analogues proved to be active, showing a specific antagonism of the non-competitive type.