A Concise Microwave-Assisted Synthesis of 2-Aminoimidazole Marine Sponge Alkaloids of the Isonaamines Series

Abstract: A short and efficient route to 1,4-substituted 2-aminoim-idazole alkaloids starting from the easily accessible 2-alkylami-nopyrimidines and a-bromo aldehydes is reported. The formation of the intermediate imidazo[1,2-a]pyrimidinium salts and subsequent cleavage were facilitated by microwave irradiation. Marine sponge alkaloids preclathridines A, C and isonaamines A, C, D were ob-tained in high yields using the optimized one-pot two-step proce-dure. Key words: natural products, ring opening, cleavage, imidazo[1,2-a]pyrimidin-1-ium salts, 2-aminoimidazoles Marine sponges have been proven to be a source of bio-logically active alkaloids and their metabolites. Among the calcareous sponges, the genera Leucetta and Clathrina are a rich source of imidazole alkaloids. Since the first dis-covery of 2-aminoimidazole alkaloids in marine sponge