A convergent approach to midpacamide and dispacamide pyrrole-imidazole marine alkaloids

A two-step synthesis of the N-acylated α-azido-ω-aminovalerate, a common intermediate for the synthesis of midpacamide and dispacamide, is described. This intermediate undergoes cyclization through the corresponding α-ureido ester derivative to give the 3-methylhydantoin ring present in midpacamide, whereas the reaction with triphenylphosphine, tosyl isocyanate and ammonia followed by cyclization of the resulting guanidine derivative provides the 2-aminoimidazole ring present in dispacamide.