Isocyclosporin A is an isomer of the well-known immunosuppressive drug Cyclosporin A, resulting from the isomerization of the unique MeBmt amino acid residue. Unlike Cyclosporin A, it lacks significant immunosuppressive activity due to poor binding to cyclophilin and subsequent failure to inhibit calcineurin. This compound is primarily utilized in pharmaceutical research and quality control as:

• A negative control in immunological and cellular assays.
• An analytical reference standard for detecting Cyclosporin A impurities via HPLC, LC-MS, or other methods.
• A tool in studies of drug stability, metabolism, pharmacokinetics, and formulation degradation.

Its role highlights the importance of monitoring isomer formation in Cyclosporin A therapeutics.