Structures and stereochemistry of three novel unique Polyaxibetaines from the marine source

Betaines and similar zwitterionic compounds are widely distributed in terrestrial plants and algae, as well as in marine invertebrates. In biological systems, these highly soluble dipolar molecules serve as organic osmolytes (osmoprotectants). Example of betaines isolated from marine invertebrates are homarine, nor- and aminozooanemonin, pyridinebetaines A and B. Most of these compounds are amphoteric low-molecular weight quaternary ammonium compounds deriving from proteinogenic or non- proteinogenic amino acids in which the nitrogen atom is fully methylated. Within a recent investigation of alkaloids from Axinella sponges, we have examined specimens of Axinella polypoides collected along Sardinian coasts and we have isolated three novel unique compounds, polyaxibetaines A-C (1-3), whose structure elucidations are the subjects of this paper.