Manzamine alkaloids can be isolated from marine sponges. They often contain ft-carboline. This group has a diverse range of bioactivities. It also has its own way of establishing its structures. An intramolecular Diels-Adler reaction for manzamines has been proposed. The a is bisdihydropyridine (derived probably from amonia), and the ft is intramolecular cycloaddition in a pentacyclic
structure57. The ^ is a tetracyclic intermedia, and the A is manzamine A and manzamine B and manzamine C (Figure 72).
The best-known manzamines are ent-8-hydroxymanzamine A, manzamines B-M and X, keramamine, kauluamine and xestomanzamines A and B.
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