The alkyne pathway to keramadine from the marine sponge Agelas sp.

Abstract

Abstract A novel synthesis of the pyrrole-imidazole alkaloid keramadine ( 1 ) from the marine sponge Agelas sp. is described. Regiocontrol is reached by the Pd-catalyzed alkynylation of 1-benzenesulfonyl-4-iodoimidazole, followed by N-methylation employing trimethyloxonium tetrafluoroborate. Key step is the double hydrogenation of a 5-alkynyl-2-azidoimidazole which simultanously generates the ( Z )-double bond and the amino function of 1 .