(3aS,4S,6aR)-Hexahydro-α-methyl-2-oxo-1H-thieno[3,4-d]imidazole-4-pentanoic Acid Methyl Ester is an intermediate in the synthesis of 9-Methyl Biotin (mixture of diastereomers) (M294075), which is an impurity of Biotin (B389040). Biotin EP Impurity D.