Reference Standard
| CAS Number | Not assigned |
| Formula | C₄₄H₆₇NO₁₃ |
| Molecular Weight | ~819.99 g/mol |
| Purity | As per USP reference standard specifications |
| Storage | Store at −20 °C to 2–8 °C; protect from light |
A carboxylic acid degradation impurity of tacrolimus formed by oxidation at the C-21 position.
Used as a USP impurity reference standard for quality control and regulatory compliance of tacrolimus API and formulations.
Qualified by HPLC impurity profiling, LC-MS, and NMR per USP monograph.
