The Diels-Alder cyclization reaction one of most important ring-forming This versatile reaction and all of hetematom variants have been extensively utilized the chemical syntheses of a large variety that no documented the enzyme-catalyzed Diels-Alder reaction ate in literature, despite and Wright the isolation from culture extracts of fungus Penicillium brevicompactum. These compounds, present very small amounts the extracts, were A-E. Based primarily and biogenetic considerations, the was proposed for brevianamide This structure was later its S-bromo derivative. 5 X-ray structure established the and absolute configuration of 1. In addition also found in both and P. ochraceum led to discovery new member this class, brevianamide F (3). Moreover, brevianamides and D were from irradiation nor D is present and worked-up the dark, and are therefore considered artifacts. The brevianamides belong to a class of mycotoxins that has joined the paraherquamides (1, paraherquamide and marcfortines (8, marcfortine A). While has been and insecticidal effects lo, the paraherquamide family have very potent antiparasitic The most distinctive feature the structures and 8 is presence core bicyclo[2.2.2] ring system which has been invoked to formally arise from a [4+2] cycloaddition. After Porter and Sammes published a suggestion on how the formation of the polycyclic system in these compounds takes place,lb Birch and associates carried out some preliminary studies on the biosynthesis of these compounds.12h They found that [153H,8-r'T]brevianamide F ([153H, 8-14(31]-3), [%'hryptophan, and [3H]proline are biosynthetically incorporated into brevianamide A (1) in cultures of P. brevicompactum. From these observations, they proposed 12h a biosynthetic pathway that involved prenylation of 3 to yield the indole 5 (deoxybrevianamide E) 13 as a fit step. Formation of the bicycle [2.2.2] dioxopiperazine nucleus would arise via oxidation of the tryptophanyl moiety, followed by a unique intramolecular [4+2] cycloaddition reaction to furnish the hexacyclic indole 4. Well-precedented t4 oxidative spiro-rearrangement of 4 would afford the spiroindoxyl system to give 1 and 2. During the course of our studies on the synthesis of the brevianamides 15 we observed that the structure of 2 is not the one proposed by Birch, but that of its enuntiomer. Birch's original proposal was modified by us t6 to accommodate the fact that totally synthetic and semi-synthetic brevianamide B (2, obtained from brevianamide A (1) by a redox protocol) is, in fact, the enantiomer of the natural brevianamide B (2). Since the hypothetical biogenetic intermediate 4 was a key substance in our revised proposal on the biogenesis of the brevianamides, we decided to synthesize this substance in labeled, racemic form for biosynthetic feeding experiments and examine its incorporation in brevianamides A (1) and B (2). This would also allow us to ascertain the possible presence of this substance in cultures of P. brevicompactum, using the synthetic material as a reference. Although deoxybrevianamide E (5) has been included in all proposals for the biosynthesis of the brevianamides thus far, no previous experiments have validated this hypothesis. We have undertaken the synthesis of a radio-labeled derivative of this substance, thus allowing us to perform feeding experiments in order to validate its intermediacy in this biosynthetic process. Herein we report our latest results on our work on the biosynthesis of the brevianamides; part of these studies have recently been published as a communication.17