The crystal structure of pukeleimide C, a novel pyrrolic compound from a shallow-water variety of the marine blue-green alga Lyngbya majuscula, is reported. The nitrogenous moiety of malyngamide A (I), an unusual chlorine-containing 7@)-methoxytetradec-4(E)-enamide from a toxic, shallow-water variety of the blue-green alga Lyngbya majuscula, 1 consists of a 4-methoxy-A 3 -pyrrolin-2-one attached via an imide linkage to a sever carbon amino acid having the same carbon skeleton as the sponge metabolite dysidin2 and the fungal metabolite penicillic acid. 3 Minor amounts of several related compounds that lack the fatty acid unit are present in this strain of L. majuscula. We report here the structure of one of these novel compounds, pukeleimide C (4). 4