(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.