Schmidt, U., Lieberknecht, A., Boekens, H., & Griesser, H.(1983). Total synthesis of zizyphine A. Synthesis of peptide alkaloids. 8. Amino acids and peptides. 40. The Journal of Organic Chemistry, 48(16), 2680-2685. doi:10.1021/jo00164a010

Schmidt, Ulrich, Albrecht Lieberknecht, Hilmar Boekens, and Helmut Griesser. "Total Synthesis of Zizyphine A. Synthesis of Peptide Alkaloids. 8. Amino Acids and Peptides. 40". The Journal of Organic Chemistry, 48.16 ( 1983 ): 2680-2685.