Isotopic labelling with chlorine-37

摘要

Mometasone furoate1 is a potent corticosteroid marketed by Schering and a stable isotope labelled version 1 with eight extra atomic mass units (amu) was required as an internal standard. Mass labelling of mometasone furoate with only deuterium and carbon-13 would be a significant challenge without manipulation of the steroid skeleton. The use of chlorine-37 as an isotopic labelling tool is rarely considered, since the sole commercial source of chlorine-37 label is sodium [37Cl]chloride, available with 95% incorporation. However, its use in a synthesis of 1 was considered feasible, leaving only four amu to be incorporated into the furoic acid moiety, a straightforward task. A chlorine-37 isotopic abundance of not less than 75% was needed for sufficient sensitivity of the mass spectrometric assay.