Synthesis of the octahydroindole core of aeruginosins: A new bicyclic alpha-amino acid

The first synthesis of 6-hydroxyoctahydroindole-2-carboxylic acid derivatives with a cis fusion in the azabicyclic nucleus is described. The synthesis involves a Birch reduction of O-methyl-L-tyrosine followed by an aminocyclization in acid medium to give a mixture of 6-oxo-octahydroindole-2-carboxylic acids 3 and 4, which could be separated after dibenzylation. Transesterification, hydrogenolysis in the presence of acetic anhydride and reduction of the amido ketones 9 and 10 provides the four stereoisomeric alcohols from which alcohol 14 showed nmr data very close to the aeruginosin 298-A core. Copyright (C) 1996 Elsevier Science Ltd