Marine organisms produce numerous secondary metabolites that exhibit a
wide range of biological activities, which have applications in pharmaceutical research.
Numerous secondary metabolites have been discovered from various marine organisms
and studied for their chemical and biological properties. Among the secondary
metabolites of marine organisms, alkaloids constitute a versatile group of bioactive
natural products with promising bio-activities. Several alkaloids, such as
pyridoacridines, pyrroles, bisindole, isoquinolines, quinolizidines and bromotyrosines,
etc., to name a few, have been isolated from marine organisms. The chemical diversity
and bio-activities of marine alkaloids are reported in several research and review
articles. Quinolizidine alkaloids (QAs) are a group of compounds that possess either a
quinolizidine ring or its derivatives. They are isolated from terrestrial plants, animals
and also from numerous marine organisms, such as sponges, tunicates, fungus, etc.
Biological activities exhibited by QAs include ichthyotoxicity, chemical defense, antimicrobial,
antiviral, and inhibition of nicotinic acetylcholine receptors. In the past
years, a few scattered reviews appeared on the isolation of QAs from natural sources,
mostly from terrestrial sources, but the reports skipped several QAs of marine origin.
This chapter presents a comprehensive review of various quinolizidine and
bis-1-oxaquinolizidine alkaloids isolated from marine organisms, detailing their
chemical structures and reported biological properties. Further, the chapter highlighted
synthesis of some marine-derived QAs, namely, petrosins, xestospongins,
clavepictines, pictamine, citrinadins A and B.
Keywords: 1-Oxa-Bisquinolizidine, Marine Organisms, Pictamine Alkaloid,
Quinolizidine Alkaloids, Sonogoshira Coupling, Sponges, Synthesis, Tunicates.
