Design and synthesis of new mass tags for matrix-free laser desorption ionization mass spectrometry (LDI-MS) based on 6,11-dihydrothiochromeno[4,3-b]indole

Abstract

We have rationally designed and synthesized new mass tags that are heterolytically cleavable upon UV-irradiation; these tags are based on a 6,11-dihydrothiochromeno[4,3-b]indole skeleton. Unless exposed to UV light, the dithioacetal group maintained its stability under normal conditions. After chemical conjugation of the mass tags with biomolecules of interest, such as proteins, the resulting conjugates efficiently and selectively generated the corresponding mass-tag fragment ions without the aid of a matrix under laser desorption/ionization (LDI) conditions. We envision that these new dithioacetal-based tags would provide a new platform of the so-called matrix-free laser desorption ionization mass spectrometry (LDI-MS), that would allow multiple detection of biomarkers with high sensitivity and selectivity. The limit of detection (LOD) of these tags was measured to be 5 fmol in the case of non-conjugated mass tag themselves and 2.8 fmol in the case of mass-tag-conjugated myoglobin.