TTBK1-IN-2 (compound 29) is a potent Tau-Tubulin kinase (TTBK1) inhibitor with IC50s of 0.24 and 4.22 μM, respectively. TTBK1-IN-2 reveals good brain penetration in vivo and is able to reduce TDP-43 phosphorylation not only in cell cultures but also in the spinal cord of transgenic TDP-43 mice.