On the Rearrangements of Biologically-Relevant Vinyl Allene Oxides to cis-Cyclopentenones, Ketols, Cyclopropylcarbinols and Favorskii-type Carboxylic Acids

In addition to stereodefined cis-cyclopentenones, the rearrangement of naturally-occurring vinyl allene oxides can provide ketols, cyclopropylcarbinols, and Favorskii-type bis-(Z)-but-2-en-1-yl acetic acids. These processes have been studied by DFT computations using...

Rearrangement of vinyl allene oxide geometric isomers to cyclopentenones. Further computational insights with biologically relevant model systems

A computational study of the rearrangement of vinyl allene oxides of biological relevance, which include alkyl (methyl, propyl) or unsaturated groups (allyl, crotyl) attached to the Csp3 atom has revealed interesting insights into the formation of naturally occurring cyclopentenones.

A unifying mechanism for the rearrangement of vinyl allene oxide geometric isomers to cyclopentenones

Z-Vinyl allene oxides are predicted to rearrange with high fidelity to stereodefined cyclopentenones through intermediate cyclopropanones.

Isolation and Characterization of Two Geometric Allene Oxide Isomers Synthesized from 9S-Hydroperoxylinoleic Acid by Cytochrome P450 CYP74C3

Specialized cytochromes P450 or catalase-related hemoproteins transform fatty acid hydroperoxides to allene oxides, highly reactive epoxides leading to cyclopentenones and other products. The stereochemistry of the natural allene oxides is incompletely defined, as are the structural features required for their cyclization. We investigated the transformation of 9S-hydroperoxylinoleic acid with the allene oxide synthase CYP74C3, a reported reaction that unexpectedly produces an allene oxide-derived cyclopentenone. Using biphasic reaction conditions at 0 °C, we isolated the initial products and separated two allene oxide isomers by HPLC at −15 °C. One matched previously described allene oxides in its UV spectrum (λmax 236 nm) and NMR spectrum (defining a 9,10-epoxy-octadec-10,12Z-dienoate). The second was a novel stereoisomer (UV λmax 239 nm) with distinctive NMR chemical shifts. Comparison of NOE interactions of the epoxy proton at C9 in the two allene oxides (and the equivalent NOE experiment in 12,13-epoxy allene oxides) allowed assignment at the isomeric C10 epoxy-ene carbon as Z in the new isomer and the E configuration in all previously characterized allene oxides. The novel 10Z isomer spontaneously formed a cis-cyclopentenone at room temperature in hexane. These results explain the origin of the cyclopentenone, provide insights into the mechanisms of allene oxide cyclization, and define the double bond geometry in naturally occurring allene oxides.