30517-65-8Relevant articles and documents
Silyl triflate-mediated ring-closure and rearrangement in the synthesis of potential bisfuran-containing intermediates of aflatoxin biosynthesis
Graybill, Todd L.,Casillas, Eduard G.,Pal, Kollol,Townsend, Craig A.
, p. 7729 - 7746 (2007/10/03)
The biosynthetic pathway to the potent mycotoxin aflatoxin B1 is unusually long and complex, proceeding from anthraquinone to xanthone to coumarin nuclear types bearing fused tetrahydro- and bisdihydrofuran rings. A synthetic strategy is described involving two silyl triflate-mediated cyclization and rearrangement processes that have enabled both furofuran oxidation states to be readily achieved and undesired but thermodynamically favorable side reactions to be avoided in the preparation of these ring systems. In the first an o-methoxymethyl phenylacetaldehyde is cyclized directly to the five-membered, differentially protected hemiacetal, while in the second this group, appropriately substituted, can be rearranged to a 4- trialkylsilyloxy-2,5-methano-1,3-benzodioxepane. The latter masked dialdehyde is sufficiently stable to strong base, mild acid, and oxidants to allow all needed aryl ring systems to be constructed. Using these methods, total syntheses of (±)-versicolorin B, (±)-versicolorin A, its hemiacetal, and its 6-deoxy derivative, (±)-6-deoxyversicolorin A, have been achieved, and these are reported herein, as well as preparation of the methyl ester of a putative o-carboxybenzophenone biosynthetic intermediate. In work described elsewhere, incorporation experiments with 13C-labeled forms of these compounds have made possible the complete elucidation of bisfuran biosynthesis characteristic of the first major phase of aflatoxin formation in vivo.
