Thiazolyl peptide antibacterial nocathiacin I (1)was converted to nocathiacin IV (4) in high yield usingiodomethane and hydriodic acid in THF at 45 °C. Severalsimplified dehydroalanine-containing systems undergo dehydroalanine cleavage under the same conditions, althoughin these cases iodomethane is not needed for efficientconversion. The mild reaction conditions are in contrast withother methods described in the literature.