Elisabethin A (1) was first isolated in 1998 from the Carribean sea whip Pseudopterogorgia Elisabethae by A. D. Rodríguez together with<br/>several other highly bioactive secondary terpenoid metabolites.1 For example, some pseudopterosins possess high anti-inflammatory and analgesic properties.2 The unique structure and biological activity from of some these natural products motivated synthetic research groups to establish synthetic approaches resulting in many reported total syntheses of Pseudopterogorgia Elisabethae diterpenes.3<br/>A still unsolved challenge is the total synthesis of Elisabethin A. Several attempts of synthetic research groups were reported but none of them were able to establish a total synthesis of this complex molecule.4 Although Mulzer et al. reported in 2003 a total synthesis, there is strong evidence for wrong stereochemical assignment. 5<br/>Elisabethin A contains a cis, trans- annulated 5,6,6-ring system bearing 6 contiguous stereocenters with one quaternary carbon center. It also features a highly substituted quinone derivative with an electron-rich dienone system. Special attention has been drawn to the stereochemistry in position 7. This alpha acidic proton cannot be epimerized under standard conditions since it suffers from conformational constrains.<br/>Our idea for the total synthesis of Elisabethin A relies upon a late stage Sakurai allylation followed by Dienone-Phenol rearrangement to introduce the quaternary stereocenter and to build up the trans-decalin system. Starting from literature known building blocks 2 and 3 the total synthesis will be achieved in 16 steps. Further keys steps are an intramolecular Diels Alder reaction and a Grob−Eschenmoser fragmentation like process.

Studies towards the total synthesis of Elisabethin A

253rd National Meeting (2017)

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