Oligodeoxyribonucleotides with Conjugated Dihydropyrroloindole Oligopeptides: Preparation and Hybridization Properties

Synthesis of a new class of conjugates between oligodeoxyribonucleotides (ODNs) and minor groove binders (MGBs) is described. The MGBs are analogs of the potent antibiotic CC-1065 and consist of repeating 1,2-dihydro-3H-pyrrolo[3,2-e]indole-7-carboxylate (DPI) subunits with N-3 carbamoyl or tert-butyloxycarbonyl groups (CDPI or BocDPI subunits, respectively). The ODN-MGB conjugates were obtained by postsynthetic modification of 5'- or 3'-amino-tailed ODNs with the 2,3,5,6-tetrafluorophenyl (TFP) esters of CDPI1-3 or BocDPI1-2 or by ODN synthesis using a CDPI3-modified controlled pore glass (CPG) support. The hybridization properties of MGB-tailed octathymidylates were determined; they varied with respect to the site of conjugation (3' or 5'), the nature of the linker, the length of the DPI oligopeptide, and the type of N-3 substitution. Optical melting studies showed that the linkage of CDPI1-3 residues to (dTp)8 significantly increased the stability of hybrids formed by the latter with poly(dA). The extent of stabilization increased with the length of the peptide. When CDPI3 was conjugated to either end of (dTp)8, the melting temperature (Tm) of the hybrid formed with poly(dA) was increased by 43-44 degrees C. Free CDPI3 stabilized the (dTp)8-poly(dA) hybrid by only 2 degrees C, thus demonstrating the importance of conjugation. (dTp)8-CDPI1-3 conjugates also formed stabilized duplexes with poly(rA). The extent of stabilization was half that observed with poly(dA).