4-Mercaptomethyl Dipicolinic Acid Dimethyl Ester is an intermediate used in the synthesis of 4-Mercaptomethyl Dipicolinic Acid (M225380), which is a Dipicolinic acid tag for rigid lanthanide tagging of proteins and paramagnetic NMR Spectroscopy. The tag, 4-mercaptomethyl-dipicolinic acid, binds lanthanide ions with nanomolar affinity, is readily attached to proteins via a disulfide bond, and avoids the problems of diastereomer formation associated with most of the conventional lanthanide tags.