Table 20

We have previously synthesized a 2,5-diphenylfuranamidine dication (4) and presented evidence that this compound binds to AT sequences in DNA by a minor-groove interaction mode but binds to GC sequences by intercalation (1,2). To probe these sequence-dependent binding modes in more detail, and particularly to obtain additional evidence for the binding mode in GC rich sequences, we have synthesized and studied the DNA complexes of 1-3 which have the furan ring of 4 replaced by 2,6-substituted pyridine (1), pyrimidine (2), or triazine (3) ring systems. The three compounds with a six-membered central ring system bind to AT DNA sequences more weakly than the furan compound, but retain the minor-groove binding mode. The pyridine and pyrimidine derivatives bind to GC sequences of DNA more strongly than the furan, but the triazine derivative binds more weakly. The aromatic proton signals of 1-3, as previously observed with 4 shift upfield by approximately 0.5 ppm or greater on complex formation with polyd(G-C)2. This and other spectroscopic as well as viscosity and kinetics results indicate that 1-4 bind to GC sites in DNA by intercalation. A nonclassical intercalation model, with the twisted-unfused, aromatic ring system intercalated into an intercalation site of matching structure can explain all of our and the literature results for the GC binding mode of these unfused, aromatic compounds.

Section: Introductionmentioning

confidence: 99%

Different Binding Mode in AT and GC Sequences for Unfused-Aromatic Dications

Tanious

Spychala

Kumar

et al. 1994

“…The recently published crystal structure of distamycin-DNA complex (24) exhibits a remarkable similarity with that reported for netropsin-DNA complex. Previous studies have shown that the preferred binding sites for netropsin (or distamycin A) on DNA contain stretches of four or more AT base pairs (17)(18)(19)(20)(21)(22). From binding of a series of homologous distamycin A analogs to DNA it is found that each analog exhibits a 6-fold lower affinity if one of the critical AT base pairs in an AT -cluster is replaced by a GC pair (20,43).…”

Section: Discussionmentioning

confidence: 99%

“…From literature data it is known that sibiromycin forms a covalent adduct with a guanine base in the minor DNA groove (14)(15)(16), whereas distamycin A and netropsin bind in the minor groove noncovalently to runs of four or more AT base pairs (17)(18)(19)(20)(21)(22). They avoid DNA regions containing guanine bases in the two polynucleotide strands .…”

Section: Introductionmentioning

confidence: 99%

Interaction of Lambda cro Repressor with Synthetic Operator 0_R3 Studied by Competition Binding with Minor Groove Binders

Gursky

Surovaya

Kurochkin

et al. 1992

In the present work, we employ a combination of CD spectroscopy and gel retardation technique to characterize thermodynamically the binding of lambda phage cro repressor to a 17 base pair operator OR3. We have found that three minor groove-binding antibiotics, distamycin A, netropsin and sibiromycin, compete effectively with the cro for binding to the operator OR3. Among these antibiotics, sibiromycin binds covalently to DNA in the minor groove at the NH2 of guanine, whereas distamycin A and netropsin interact preferentially with runs of AT base pairs and avoid DNA regions containing guanine bases in the two polynucleotide strands. Only subtle DNA conformation changes are known to take place upon binding of these antibiotics. Both the CD spectral profiles and the results of the gel retardation experiments indicate that distamycin A and netropsin can displace cro repressor from the operator OR3. The binding of cro repressor to the OR3 is accompanied by considerable changes in CD in the far-UV region which appear to be attributed to a DNA-dependent structural transition in the protein. Spectral changes are also induced in the wavelength region of 270-290 nm. The CD spectral profile of the cro-OR3 mixture in the presence of distamycin A can be represented as a sum of the CD spectrum of the repressor-operator complex and spectrum of distamycin-DNA complex at the appropriate molar ratio of the bound antibiotic to the operator DNA (r). When r tends to the saturation level of binding the CD spectrum in the region of 270-360 nm approaches a CD pattern typical of complexes of the antibiotic with the free DNA oligomer. This suggests that simultaneous binding of cro repressor and distamycin A to the same DNA oligomer is not possible and that distamycin A and netropsin can be used to determine the equilibrium affinity constant of cro repressor to the synthetic operator from competition-type experiments. The binding constant of cro repressor to the OR3 is found to be (6 +/- 1).10(6)M-1 at 20 degrees C in 10 mM sodium cacodylate buffer (pH 7.0) in the presence of 0.1 M NH4F.

“…Particular interest attaches to trying to understand those factors that determine sequence selectivity (1) since there are now several instances recognized in the case of chemotherapeutic agents where biological potency is related to such sequence preferences (6)(7)(8)(9)(10).…”

Section: Introductionmentioning

confidence: 99%

“…This group includes kikumycin 1 (11), anthelvencin 2 (12), distamycin 3 (13), netropsin 4 (14), amidinomycin 5 (15), and noformycin 6 (16) (Scheme 1). Evidence from biochemical pharmacology indicates that these oligopeptide antibiotics act to block the template function of DNA by binding primarily to (AT)n sequences in the minor groove (6,17). While these natural products 1-6 exhibit only moderate antiviral and anticancer activity, lexitropsins to which they gave rise are capable of recognizing longer and alternative sequences (18)(19)(20) and exhibit considerably enhanced potency as anticancer and antiviral (including HIV-1) agents (21,22).…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical and Molecular Mechanics Studies on the Binding of Stereoisomers of the Oligopeptide Antibiotics Amidinomycin and Noformycin to the Minor Groove of B-DNA

Sapse

Feng

Fugler-Domenico

et al. 1993

Ab initio calculations (Hartree-Fock) using the 6-31G basis set have been performed on two chiral oligopeptide antitumor antibiotics amidinomycin 5 and noformycin 6. The latter are DNA minor groove binding agents related to the A.T recognizing netropsin 4 and distamycin 3 but, unlike the latter, bear stereocenters (two for 5 and one for 6) that may be expected to affect binding to the B-DNA receptor. Geometry optimized conformations, energies and distribution of electrostatic charges within the molecules were derived. The rotational barrier for bond C3-C6 in 6 was calculated to be ca. 6 kcal.mole-1 and the dipole moment for 6 was 7.69D and for 5 was 5.58D. The ab initio derived parameters of the geometry optimized conformations of the different possible stereoisomeric forms of 5 and 6 were used to interpret their different interactions with the minor groove of DNA at both A.T and G.C sequences and the results were compared with molecular mechanics calculations. The order of binding of the four stereoisomers of 5 at the preferred (A.T)n sequences by both ab initio and molecular mechanics calculations is 1S,3R > RR > RS > SS. The predicted energy differences for complexation with DNA of the other stereoisomers from that of 1S,3R are: RR (4.2%); RS (6.7%) and SS (21.5%). In the case of noformycin the 4R structure binds more effectively than the enantiomer. Considerations of phasing in the computed distances between hydrogen bond donating sites in the DNA-bound antibiotics provide further insight into the binding processes. In the complexes of noformycin 6 the N-N1-N4 and N1-N5 distances (9.05 and 9.15 A respectively for 4R-6 and 9.23 and 9.26 A respectively for 4S-6) are close to the optimum value of 9.1 A for effective binding. In the case of amidinomycin 5 the best agreement with the optimum value occurs with the strongest binding diastereomer 1S,3R (N1-N3 = 8.91, N1-N4 = 9.41 A). The unexpected result, consistent in both ab initio and molecular mechanics treatments, is that, in contrast to the cases of kikumycin 1 and anthelvencin 2, the natural 3S configuration of 5 and 4S of 6 do not confer maximal binding efficiency. This suggests that biogenetic factors in the generation of the oligopeptide antibiotics lead to maximum DNA binding in the cases of kikumycin and anthelvencin but not in the cases of amidinomycin and noformycin.