R₁ is H, halo, nitro, cyano, amino, C_1-6 alkyl, C_1-6 alkoxy, C_3-10 cycloalkyl, C_1-10 heterocycloalkyl, aryl, or heteroaryl;

W₁ is C_1-10 heterocycloalkyl or NH—CH₂—Ar1-(CH₂)_m-A1;

one of W₂ and W₃ is NR_aR_b; and

the other of W₂ and W₃ is NH—CH₂—Ar2-(CH₂)_n-A2,

each of Ar1 and Ar2, independently, is five-membered heteroaryl;

each of A1 and A2, independently, is H, OH, SH, CO₂R_c, PO₃R_cR_d, NH₂, benzylamino, isopropylamino, ethanolamino, carbamido, guanidinyl, C_1-6 alkoxy, C_3-10 cycloalkyl, C_3-10 cycloalkyloxy, C_1-10 heterocycloalkyl, C_1-10 heterocycloalkyloxy, aryl, aryloxy, heteroaryl, heteroaryloxy, or NCOR_c;

each of R_a and R_b, independently, is H, C_1-6 alkyl, C_3-10 cycloalkyl, C_1-10 hetero-cycloalkyl, or R_a and R_b, together with the nitrogen atom to which they are bonded, are C_1-10 heterocycloalkyl;

each of R_c and R_d, independently, is H, C_1-6 alkyl, C_3-10 cycloalkyl, C_1-10 hetero-cycloalkyl, aryl, or heteroaryl;

each of C_1-6 alkyl, C_1-6 alkoxy, C_3-10 cycloalkyl, C_3-10 cycloalkyloxy, C_1-10 hetero-cycloalkyl, C_1-10 heterocycloalkyloxy, aryl, heteroaryl, aryloxy, heteroaryloxy, ethanolamino, benzylamino, and carbamido, is optionally substituted with hydroxyl, halo, nitro, cyano, amino, C_1-6 alkyl, arylalkyl, C_1-6 alkoxyl, C_1-6 carboxyalkyl, aryl, heteroaryl, PO₃R_eR_f, NCOR_e, NC(O)OR_e, C(O)OR_e, COR_e, (CH₂)_x—PO₃R_eR_f, (CH₂)_x—NCOR_e, or (CH₂)_x—C(O)OR_e;

each of R_e and R_f, independently, is H, C_1-6 alkyl, C_3-10 cycloalkyl, C_1-10 hetero-cycloalkyl, aryl, or heteroaryl;

each of m and n, independently, is 0, 1, 2, 3, 4, or 5; and

x is 1, 2, 3, or 4.