T-3364366 is a reversible, slow-binding, thienopyrimidinone delta-5 desaturase (D5D) inhibitor with IC50s of 1.9 nM and 2.1 nM in HepG2 and RLN-10 cells, respectively. T-3364366 exhibits potent D5D (IC500=19 nM) inhibitory activity and excellent selectivity away from delta-6 desaturase (D6D, IC50=6200 nM) and delta-9 desaturase (stearoyl-CoA desaturase, SCD,50 >10000 nM) in the enzymatic activity assay.