Two new isomers of domoic acid from a red alga, Chondria armata.

Isodomoic acids G and H, two new isomers of the neurotoxin domoic acid, along with isodomoic acids A, B, E and F, were isolated from a red alga, Chondria armata, collected at the southern tip of Kyushu Island. The structures of two of these were deduced to be (E, E) and (Z, E) isomers of 2-carboxy-4-(5-carboxy-l-methyl-2-hexenylidene)-3-pyrro- lidineacetic acid, based on electrospray ionization mass and [1H]nuclear magnetic resonance spectral analyses including [1H-1H]correlation spectroscopy and nuclear Overhauser effect correlation spectroscopy.