The alpha-amino-5-oxo-7-oxabicyclo[4.1.0]heptane-2-propanoic acid framework of anticapsin and related compounds is generated by base-catalysed fragmentation of 2-amino-5,6-epoxy-1-hydroxybicyclo[2.2.2]octane-2-carboxylic acid derivatives in a retro-aldol-like reaction.