A novel pyruvate kinase M2 (PKM2)-specific activator, [11C]DASA-23 and derivatives thereof, and methods for their rapid synthesis are provided. The probes are particularly useful in methods for the non-invasive positron emission tomography (PET) detection and imaging of PKM2 expression in subcutaneous and orthotopic tumors. [11C]DASA-23 cell uptake correlates with PKM2 protein expression in cultured tumor cells and orthotopic tumors are delineated from the surrounding normal brain tissue in vivo.