In one embodiment, the invention relates to compounds wherein, when Xz is CZ and Z is ???(CR1R1???)n???NR2???(CR3R3???)m???B and T is a bond, then R6 is H and Xb and Xd are both CH. In one embodiment, the invention relates to compounds wherein, when X, is CZ and Z is ???(CR1R1???)n???NR2???C(O)???(CR3R3???)m???B and T is a bond, then n is not 0.