Theoretical design of a bis-orthopepetide derivative of a tetracationic porphyrin targeted toward a six-base pair sequence of DNA

Major versus minor groove DNA binding of a bisarginylporphyrin hybrid molecule: a molecular mechanics investigation

On the basis of theoretical computations, we have recently synthesised [Perrée-Fauvet, M. and Gresh, N., Tetrahedron Lett., 36 (1995) 4227] a bisarginyl conjugate of a tricationic porphyrin (BAP), designed to target, in the major groove of DNA, the d(GGC GCC)2 sequence which is part of the primary binding site of the HIV-1 retrovirus site [Wain-Hobson, S. et al., Cell, 40 (1985) 9]. In the theoretical model, the chromophore intercalates at the central d(CpG)2 step and each of the arginyl arms targets O6/N7 belonging to guanine bases flanking the intercalation site. Recent IR and UV-visible spectroscopic studies have confirmed the essential features of these theoretical predictions [Mohammadi, S. et al., Biochemistry, 37 (1998) 6165]. In the present study, we compare the energies of competing intercalation modes of BAP to several double-stranded oligonucleotides, according to whether one, two or three N-methylpyridinium rings project into the major groove. Correspondingly, three minor groove binding modes were considered, the arginyl arms now targeting N3, O2 sites belonging to the purine or pyrimidine bases flanking the intercalation site. This investigation has shown that: (i) in both the major and minor grooves, the best-bound complexes have the three N-methylpyridinium rings in the groove opposite to that of the phenyl group bearing the arginyl arms; (ii) major groove binding is preferred over minor groove binding by a significant energy (29 kcal/mol); and (iii) the best-bound sequence in the major groove is d(GGC GCC)2 with two successive guanines upstream from the intercalation. On the other hand, due to the flexibility of the arginyl arms, other GC-rich sequences have close binding energies, two of them being less stable than it by less than 8 kcal/mol. These results serve as the basis for the design of derivatives of BAP with enhanced sequence selectivities in the major groove.

Dimerization of tetracationic porphyrins: ionic strength dependence

Cationic porphyrins are under study in a number of contexts including their interaction with biological targets, as possible therapeutic agents and as building blocks for molecular devices such as molecular photodiodes and solar cells. Many cationic porphyrins dimerize readily in aqueous solution. Dimerization in turn can control the properties of the porphyrin as well as its binding to its target. The propensity of a porphyrin to dimerize in aqueous solution can be estimated by recording the optical spectrum of the solution as a function of the concentration of added salt. Analysis of the data in terms of the Debye-Hückel formalism gives an estimate of the extent of dimerization as a function of ionic strength. Data for TMPyP4 [meso-tetrakis(4-N-methylpyridinium)porphyrin] and its butyl and octyl homologs; TMAP [meso-tetrakis(4-N,N,N-trimethylanilinium)porphyrin]; T theta PP [meso-tetrakis[4-N-[(3-(trimethyl-ammonio)propyl)oxy]phenyl]porphyrin] and the ferrocenyl porphyrin P3Fc are discussed. Dimerization may affect binding of the cationic porphyrins to their targets, e.g., DNA.

Structure and energetics in the complexes of a double-stranded B-DNA dodecamer with netropsin derivatives of a tricationic water-soluble porphyrin: a theoretical investigation

The structural and energetical characteristics of the complexes formed between two auto-complementary DNA dodecamers, d(CGCGAATTCGCG)2, and d(GCGCAATTGCGC)2, and two novel netropsin (I) and glycine-netropsin (II) conjugates of a tricationic water-soluble porphyrin are investigated in detail by means of theoretical computations. This study was prompted by the successful chemical synthesis of II, which was recently reported (Anneheim-Herbelin, G., Perrée-Fauvet, M., Gaudemer, A., Hélissey, P., Giorgi-Renault, S. and Gresh, N., Tetrahedron Lett. 34, 7263 (1993)). The results indicate that: a) Intercalative binding of II does not entail significant distortions of the DNA backbone, and the Net moiety can bind tightly to the core of the minor groove. b) Intercalative binding of I is computed to energetically weaker than that of II. This is a consequence of the reduced length of the oligopeptide arm, such that the terminal propionamidinium group interacts less favorably with the fourth A-T base-pair than is the case with II. c) Nonintercalative binding of II produces considerable conformational distortions of the DNA. These results in a break of the DNA axis in between the fourth and the fifth base-pairs, namely, at the level where the long axis of the chromophore and of the oligopeptide intersect.