Ca2+-regulated photoproteins of ctenophores lose bioluminescence activity when exposed to visible light. Little is known about the chemical nature of chromophore photoinactivation. Using a total synthesis strategy, we have established the structures of two unusual coelenterazine products, isolated from recombinant berovin of the ctenophore Beroe abyssicola, which are Z/E isomers. We propose that during light irradiation, these derivatives are formed from 2-hydroperoxycoelenterazine via the intermediate 8a-peroxide by a mechanism reminiscent of that previously described for the auto-oxidation of green-fluorescent-protein-like chromophores.