ring system which was transformed in 4 steps into 3-aminonocardicinic acid. A protected side chain of nocardicin D was synthesized from d-asparagine in 6 steps. Coupling of these units and further conversion to nocardicins A, B and D followed published procedures. Using l-asparagine for the synthesis of the side chain led to unnatural isonocardicin A. Biological activities of the products are compared