A cell-permeable quinone epoxide that selectively inhibits BTK catalytic activity (BTK; IC50s = 10 and 3 μM for basal and activation levels, respectively); binds to BTK-PH and blocks the interaction between BTK-PH and PKC (IC50 = 100 μM in human mast cell lysates) without affecting PKC activity; minimal effect on Lyn, Syk, PKA, casein kinase I, ERK1, ERK2, and p38 kinase activities,