Reference Standard
| CAS Number | Not assigned |
| Formula | C₄₄H₆₇NO₁₁ |
| Molecular Weight | ~786 g/mol |
| Purity | ≥95% |
| Storage | Store at −20 °C; protect from moisture |
A lactone-rearranged impurity of tacrolimus formed by intramolecular esterification under stress conditions.
Used as an impurity reference in stability studies and regulatory submissions.
Characterized using HPLC, LC-MS, NMR, and forced degradation comparison studies.
