New γ-pyrone propionates from the Indian Ocean sacoglossan Placobranchus ocellatus

Mining the Tetraene Manifold: Total Synthesis of Complex Pyrones from Placobranchus ocellatus

“…Two unnamed natural products, bicyclo[4.2.0]octadiene 5 and endoperoxide 7, were found in Placobranchus ocellatus which we propose to call ocellapyrones A and B, respectively. [3] Although structure 6 was originally proposed for the bicylco[4.2.0]octadiene natural product (ocellapyrone A), our results (see below) and a recent report by Baldwin and co-workers [4] lead to the reassignment of its structure as 5. Furthermore, two pyrones with a bicyclo[4.2.0]octane skeleton, elysiapyrones A (8) and B (9), were isolated from Elysia diomedea.…”

“…[15] The detailed structures of 5 and 6 were elucidated by extensive NOE interaction studies and the conversion of 6 into ocellapyrone B (7), whose relative configuration has been unequivocally assigned. [3,16] A more rational synthesis of 5 and 6 is shown in Scheme 4. Olefination of the known aldehyde 17 [17] followed by iodine-tin exchange, as before, gave vinyl stannane 18.…”

“…The synthetic material was identical in all respects ( 1 H and 13 C NMR, IR, MS) to the natural product. [3] Finally, ruthenium-catalyzed isomerization [19] of ocellapyrone B (7) gave bisepoxide 20, which is a homologue of elysiapyrone A. Although this compound has not been isolated from natural sources so far, it seems entirely possible that it could be found, as endoperoxides can be readily converted into bisepoxides both under thermal and photochemical conditions.…”

Peroxy natural products

“…153 Several years later, tridachiahydropyrones B and C were proved to be the same compound characterized as 278. 154 The same species, P. ocellatus, provided the possibly artefactual peroxy derivative 279, 155 whose relative configuration was confirmed at the same year. 156 A Panamanian collection of the sacoglossan mollusc Elysia diomedea yielded the endoperoxide 280, structurally closely related to 279.…”

Shaping the Polypropionate Biosynthesis in the Solar‐Powered Mollusc Elysia viridis

“…[7] Similar skeleton rearrangements are rather common, and in the last years several additional A C H T U N G T R E N N U N G examples have been described in the sacoglossan chemistry. [10,17,18] To test the photochemical stability of Elysia propionates, elysione (6; 2.1 mg) and epoxyelysione (7; 0.3 mg) were Table 1. NMR spectroscopic data of major polypropionates of Elysia viridis and 13 C-incorporation of elysione (6) after feeding experiments with sodium…”