Total Synthesis of the Proposed Structure for Protoaculeine B, a Polycationic Marine Sponge Metabolite, with a Homogeneous Long-Chain Polyamine.

By establishing the procedures for sequential deprotections, reaction monitoring, purification, and handling, for the first time, we achieved the total synthesis of the proposed structure for protoaculeine B (2), which is a highly hydrophilic and polycationic amino acid. The NMR and mass spectra and chemical reactivity of the synthetic sample differed from those of natural protoaculeine B, which indicates the necessity for revision of the originally reported structure.