Abstract The total syntheses of two alkaloids isolated from a marine sponge of the Leucetta sp. have been accomplished in 6 and 7 steps starting from a 4,5-diiodoimidazole derivative. Grignard mediated halogen–metal exchange was used to install the benzyl side chain. C2 substitution was accomplished via lithiation followed by quenching with trisyl azide which provided isonaamine C after hydrogenation. Isonaamidine E was then prepared from isonaamine C via introduction of the hydantoin ring by reaction with an activated parabanic acid derivative.