Synthesis of All Four Stereoisomers of 3-(tert-Butoxycarbonyl)-3-azabicyclo[3.1.0]hexane-2-carboxylic Acid

• Bettina Bakonyi^†
• Markus Furegati^*‡
• Christian Kramer^§
• Luigi La Vecchia^‡
• Flavio Ossola^‡

• ^† Doetsch Grether AG, Falkensteinerstrasse 37, 4132 Muttenz, Switzerland
• ^‡ Preparations Laboratories, Global Discovery Chemistry, Novartis Institutes for Biomedical Research, Klybeckstrasse 141, 4057 Basel,Switzerland
• ^§ Institute of General, Inorganic and Theoretical Chemistry and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria

A synthesis of all four stereoisomers of 3-(tert-butoxycarbonyl)-3-azabicyclo[3.1.0]hexane-2-carboxylic acid has been developed, thereby significantly shortening the known literature procedures for the syntheses of these unnatural amino acids. With a simple adjustment of the reaction conditions, we were able to obtain either pure cis or trans acid. Optical resolution was accomplished via diastereomeric salt formation or alternatively via chromatography on a chiral stationary phase. Finally, ab initio calculations gave an explanation for the observed cis selectivity in the initial step.

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