Total syntheses of cyclopeptides of plant origin and investigations of orthogonal protection

Cyclopeptide alkaloids are a group of closely related macrocyclic polyamide bases of plant origin. The term cyclopeptide describes their cyclic structures (13, 14, and 15 membered ring sizes) which contain amide bonds. They are alkaloids because they originate from plants and exhibit slight basicity, resulting from the methylated amino functions present on one of the amino acid residues. Cyclopeptide alkaloids are reported to have some antibiotic properties and to be weakly active against lower fungi and gram-positive bacteria. We have developed strategies and methodologies for the synthesis of these natural products. The isolation of three antitumor cyclic pentapeptides, astins A, B, and C, from the medicinal plant A. tataricus (Compositae), known in Chinese medicine, has prompted us to find suitable syntheses for the nonessential amino acids present in these natural products. The approaches towards the total synthesis of these compounds are discussed in Chapter 2. The selective transformations of N-Fmoc groups to N-Boc groups and N-Cbz groups have been accomplished. These reactions are very practical and useful in peptide synthesis, and are discussed in Chapter 3