A-770041 is a selective and orally active Src-family Lck inhibitor. A-770041 inhibits Lck with an IC50 value of 147 nM with the presence of 1 mM ATP. A-770041 shows 300-fold selective to Lck over Fyn, the other Src family kinase involved in T-cell signaling. A-770041 can be used for the research of acute rejection.