Nonprotecting Group Synthesis of a Phospholipase C Activatable Probe with an Azo-Free Quencher

The near-infrared fluorescent activatable smart probe Pyro-phosphatidylethanolamine (PtdEtn)-QSY was synthesized and observed to selectively fluoresce in the presence of phosphatidylcholine-specific phospholipase C (PC-PLC). PC-PLC is an important biological target as it is known to be upregulated in a variety of cancers, including triple negative breast cancer. Pyro-PtdEtn-QSY features a QSY21 quenching moiety instead of the Black Hole Quencher-3 (BHQ-3) used previously because the latter contains an azo bond, which could lead to biological instability