Design of Bifunctional Nucleic Acid Ligands. In: Pullman B, Jortner J, editors. Molecular Basis of Specificity in Nucleic Acid-Drug Interactions. Dordrecht: Springer Netherlands; 1990. pp. 275-90. [DOI: 10.1007/978-94-011-3728-7_19]

Synthesis of oligonucleotides with a 2'-cap at the 3'-terminus via reversed phosphoramidites

[reaction: see text] A method is presented for the synthesis of single compounds or small combinatorial libraries of oligonucleotides with 2'-acylamido-2'-deoxyuridine residues at the 3'-terminus. Selection experiments identified the residue of anthraquinone-2-carboxylic acid as a "molecular cap" that increases the UV melting point of the duplex (5'-ACGCGU-3')(2) by up to 28 degrees C compared to the unmodified control duplex.

Direct photocleavage of HIV-DNA by quinacridine derivatives triggered by triplex formation

Amino-p-quinacridine compounds (PQs) have been shown to stabilize strongly and specifically triple-helical DNA. Moreover, these derivatives display photoactive properties that make them efficient DNA cleavage agents. We exploited these two properties (triplex-specific binding and photoactivity) to selectively cleave a double-stranded (ds)DNA sequence present in the HIV-1 genome. Cleavage was first carried out on a linearized plasmid (3300 bp) containing the HIV polypurine tract (PPT) that allowed targeting by a triplex-forming oligonucleotide (TFO). PQ(3)(), the most active compound of the series, efficiently cleaved double-stranded DNA in the vicinity of the PPT when this sequence had formed a triplex with a 16-mer TFO. Investigation of the cleavage at the molecular level was addressed on a short DNA fragment (56 bp); the photoinduced cleavage by PQ(3)() occurred only in the presence of the triple helix. Nevertheless, unusual cleavage patterns were observed: damage was observed at guanines located 6-9 bp away from the end of the triple helical site. This cleavage is very efficient (up to 60%), does not require alkaline treatment, and is observed on both strands. A quinacridine-TFO conjugate produced the same cleavage pattern. This observation, along with others, excludes the hypothesis of a triplex-induced allosteric binding site of PQ(3 )()adjacent to the damaged sequence and indicates that PQ(3 )()preferentially binds in the vicinity of the 5'-triplex junction. Irradiation in the presence of TFO-conjugates with acridine (an intercalative agent) and with the tripeptide lys-tryp-lys led to a complete inhibition of the photocleavage reaction. These results are interpreted in terms of competitive binding and of electron-transfer quenching. Together with the findings of simple mechanistic investigations, they led to the conclusion that the photoinduced damage proceeds through a direct electron transfer between the quinacridine and the guanines. This study addresses the chemical mechanism leading to strand breakage and characterizes the particular photosensitivity of the HIV-DNA target sequence which could be an oxidative hot spot for addressed photoinduced strand scission by photosensitizers.

DNA recognition by intercalators and hybrid molecules

Experiments are described which probe the role of the 2-amino group of guanine as a critical determinant of the recognition of nucleotide sequences in DNA by specific ligands. Homologous samples of tyrT DNA substituted with inosine or 2,6-diaminopurine residues in place of guanosine or adenine respectively yield characteristically modified footprinting patterns when challenged with sequence-selective antibiotics such as echinomycin, actinomycin or netropsin. The capacity of small molecules to recognise particular DNA sequences is exploited in the 'combilexin' strategy to target small molecules to defined sites in DNA. A composite molecule containing a distamycin moiety linked to an intercalating ellipticine derivative has been synthesised and shown to bind tightly to DNA but without much sequence-selectivity. Refinement of this molecule based on predictions from molecular modelling has led to the synthesis of a second generation derivative bearing an additional positive charge: this new hybrid molecule is strongly selective for binding to AT-rich tracts in DNA.