Application of tert-Butyl Disulfide-Protected Amino Acids for the Fmoc Solid-Phase Synthesis of Lactam Cyclic Peptides under Mild Metal-Free Conditions.

Lactam cyclic peptides are a class of interesting and pharmaceutically active molecules, but their previous syntheses have required the use of heavy metals and/or forcing conditions. Here, we describe the efficient application of the previously reported tert-butyl disulfide-protected amino acids and their use in the efficient, solid-phase synthesis of a series of lactam cyclic peptides under mild, metal-free conditions.