Synthesis and Stereochemistry of Axinastatin 4

Axinastatin 4 from a marine sponge was synthesized by high-dilution BOP-Cl cyclization of Trp-Val-Pro-Leu-Thr-Pro-Leu in 94% yield (only 2.5% at normal dilution), showing the configurations of the last three amino acids to be S. Synthetic axinastatin 4 was devoid of cytostatic activity.