Molecular recognition between oligopeptides and nucleic acids: DNA binding selectivity of a series of 1,2,4-triazole-containing lexitropsins.

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The synthesis of a series of 1,2,4-triazole-containing oligopeptide lexitropsins related to the natural antitumor antibiotic distamycin is described. The binding properties of these new agents to both native DNAs and synthetic polydeoxyribonucleotides were determined by UV absorption and circular dichroism studies. The DNA binding and sequence selectivity of these agents have been determined by complementary strand MPE footprinting on two restriction fragments of pBR322 DNA. The lexitropsins bearing one 1,2,4-triazole moiety bind to AT sequences like distamycin but also tolerate GC sites. However, 3, which contains two contiguous 1,2,4-triazole moieties, appears not to recognize AT stretches and demands two consecutive GC bases in the middle of a four-base recognition site. The triazole lexitropsins avoid ATTT (4264-4267) and AAAA (4273-4276) to which distamycin binds strongly to the EcoRI/Hind III fragment. Determination of pKa values indicates the 1,2,4-triazole units are protonated under physiological conditions. The avoidance of AT stretches and the recognition of GC base sites by 3 suggest molecular recognition in these cases is determined, not by electrostatic effects, but rather by invoking a hydrogen bond between the triazole 4-nitrogen and G-2NH2 in the minor groove.