Skipped diene synthesis essay - TyTix, LLC
A stereodivergent strategy for the synthesis of skipped dienes is developed. The method consists of hydroboration of allenes and Migita–Kosugi–Stille coupling, which allows for access to all four possible stereoisomers of the skipped dienes. The hydroboration is especially useful for providing both -allylic and -allylic alcohols from the same allene by simply changing the organoborane reagent. The strategy was successfully applied to a unified total synthesis of the madangamine alkaloids via a common ABCE-tetracyclic intermediate with a (,)-skipped diene. The late-stage variation of the D-ring enabled the supply of synthetic madangamines A, C, and E for the first time.
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Skipped polyenes (i.e. 1,4-dienes and higher homologues) are stereodefined components of a vast array of biologically important natural products, including polyunsaturated fatty acids. While widespread in nature, these architectures are generally considered to represent significant barriers to efficient chemical synthesis. While partial reduction of skipped poly-ynes provides a pathway to a subset of such structures, general chemical methods for the preparation of skipped polyenes that contain varied stereochemistries and substitution patterns are lacking. Here, we describe a metal-promoted reductive cross-coupling reaction between vinylcyclopropanes and alkynes (or vinylsilanes) that provides stereoselective access to a diverse array of skipped polyenes through a process that establishes one C–C bond, generates up to three stereodefined alkenes, and can be used to introduce stereogenic centers at the central positions of the skipped polyene motif. We also demonstrate the significance of the present bond construction by preparing substituted and stereodefined polyunsaturated synthetic fatty acids.
Fatty acids are a subset of small molecules that are essential for life, playing not only central roles in compartmentalization and membrane function but also impacting cellular pathways that regulate blood pressure, clotting and lipid levels as well as the immune response and inflammation.(–) Polyunsaturated fatty acids (i.e. arachidonic acid, α-linoleic acid, γ-linoleic acid and eicosapentaenoic acid) are a subset of this large class of biomolecules that are present in all higher organisms and play critical roles in human health ().(,) These ubiquitous biomolecules share a common structural motif that imparts their unique properties – methylene interrupted polyenes (highlighted in blue). This central architectural feature is a stereodefined motif that is encountered throughout nature, with examples including structurally complex bioactive natural products from polyketide, terpene and alkaloid biosynthetic pathways. These more architecturally intricate molecules, identified as potent antibiotic, antifungal and cytotoxic agents, house skipped polyenes that contain stereochemically diverse di- and tri-substituted alkenes (i.e. ripostatin A, madangamine A).(–) Notably, more complex examples include secondary metabolites that house 1,4-dienes with stereogenic sp3 carbons at the central position of the isolated non-conjugated diene (i.e. jerangolid D and phorbasin C).(–)