Concise Synthesis of (−)-GA<sub>18</sub> Methyl Ester
Lei Li, Weida Liang, Mario E. Rivera, Yecheng Wang, Mingji Dai
Abstract
Gibberellins (GAs) are important plant hormones, but some of their family members are in extremely limited natural supply including GA18. Herein, we report a concise synthesis of (−)-GA18 methyl ester, a member of the C20 gibberellins, from commercially available and cheap andrographolide. Our synthesis features an intramolecular ene reaction to form the C ring, an oxidative cleavage followed by aldol condensation to realize a ring contraction and form the challenging trans-hydrindane (AB ring), and a photochemical [2+2] cycloaddition accompanied by a subsequent SmI2-mediated skeletal rearrangement to construct the methylenebicyclo[3.2.1]octanol moiety (CD ring).
Topics & Concepts
ChemistryMoietyIntramolecular forceStereochemistryCycloadditionGibberellinRing (chemistry)Aldol condensationAldol reactionTropaneOrganic chemistryCatalysisGeneticsBiologyGinseng Biological Effects and ApplicationsBiological and pharmacological studies of plantsBiological Activity of Diterpenoids and Biflavonoids