Halogenated pyrrolo[2,3- <i>d</i> ]pyrimidine nucleosides from marine organisms

4-Amino-5-bromopyrrolo[2,3-d]pyrimidine has been isolated from a sponge ( Echinodictyum sp.). The pharmacologically active constituent of the red alga Hypnea valendiae has been identified as 4-amino-7-(5'-deoxyribos-1'ß-yl)-5-iodopyrrolo[2,3-d]pyrimidine (7). A second nucleoside, tentatively assigned as the 1'a isomer of (7), has also been isolated.