An efficient and convenient methodology for the synthesis of the 3-(trans-2-aminocyclopropyl) alanine and 3-(trans-2-nitrocyclopropyl) alanine moieties found in the core of belactosin A and hormaomycin, respectively, is reported. By using an enantioenriched substituted alpha-nitro diazoester in a diastereoselective intramolecular cyclopropanation reaction, the trans-nitrocyclopropyl alanine moiety can be obtained efficiently in five steps from the initial alpha-nitrocyclopropyl lactone unit, thus achieving the synthesis of the cyclopropane core of the two natural products.