Is phototridachiahydropyrone a true natural product?

The occurrence of (-)-phototridachiahydropyrone (5) in nature has been proven. This compound has been now identified as minor component of the extract of marine sacoglossan mollusk Elysia crispata from which the main (-)-tridachiahydropyrone (4) was previously described. Synthetic (±)-5 was for-merly obtained by Moses' group by biomimetic photochemical conversion of (±)-tridachiahydropyrone(4). The same authors suggested that compound 5 had to be a natural product derived from precursor 4 "yet to be discovered". Comparison of CD profiles of natural (-)-4 and (-)-5 indicated the same absolute configuration for both compounds. This evidence is in agreement with the concerted mechanism proposed for the photochemical conversion.