Solid-Phase-Based Total Synthesis and Stereochemical Assignment of the Cryptic Natural Product Aurantizolicin

The total synthesis and stereochemical assignment of the polyazole cyclopeptide aurantizolicin was achieved by connecting the solution synthesis of building blocks with solid-phase peptide synthesis. Macrothiolactonization and an <i>aza</i>-Wittig reaction provided the natural product macrocycle in high yield as well as key stereoisomers. NMR comparison as well as isolation of the natural product from the producer organism Streptomyces aurantiacus confirmed the presence and sequence of one l-Ile and one d-<i>allo</i>-Ile residue in aurantizolicin.