Pepstatins are a group of naturally occurring cyclic peptides that inhibit aspartic proteases, a type of enzyme that breaks down proteins. They are isolated from various actinomycete species of Streptomyces and Actinosynnema. Pepstatins are often used in laboratory research to study the function of aspartic proteases and as tools to probe the mechanism of action of these enzymes. In addition, pepstatins have been explored for their potential therapeutic use in various diseases, including cancer, viral infections, and cardiovascular disease. However, they have not yet been approved for clinical use.