TLR9 antagonist 1 diformate is a selective hTLR9 antagonist with an IC50 of 0.1 nM against hTLR9. TLR9 antagonist 1 diformate exhibits favorable pharmacokinetic and pharmacodynamic properties. TLR9 antagonist 1 diformate can be used in the research of systemic lupus erythematosus[1].