Ascidians (class Ascidiacea) belong to the subphylum Urochordata (Tunicata) and are generally called as tunicates because the body is covered by tunic,a sack-like case,or sea squirts since they spurt water when disturbed.Nitrogenous secondary metabolites form more than 80% of new natural products obtained from ascidians and showed a wide variety of bioactivities.This review describes the structures and bioactivities of major classes of unique nitrogenous ascidian metabolites:cyclic peptides,in which aplidine is in the Phase II clinical trials,pyridoacridine alkaloids,(3-carboline alkaloids,lamellarins and related pyrrole alkaloids,ecteinascidins (ETs,ET 743 completed the Phase III clinical trials),diterpene and steroidal alkaloids,and polysulfur alkaloids.
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