Luigi G. Marzilli

Organocobalt B12 models: axial ligand effects on the structural and coordination chemistry of cobaloximes

Article de synthese presentant les structures cristallines et moleculaires de molecules contenant la moitie Co(DH) 2 , ou DH est le monoanion de la dimethylglyoxime. Les structures RX sont comparees aux structures en solution. Discussion des implications pour la biochimie de la vitamine B 12

Inactivation of Human Immunodeficiency Virus Type 1 by Porphyrins

ABSTRACT We have evaluated the anti-human immunodeficiency virus (HIV) activity of a series of natural and synthetic porphyrins to identify compounds that could potentially be used as microbicides to provide a defense against infection by sexually transmitted virus. For assays we used an epithelial HeLa-CD4 cell line with an integrated long terminal repeat-β-galactosidase gene. For structure-activity analysis, we divided the porphyrins tested into three classes: (i) natural porphyrins, (ii) metallo-tetraphenylporphyrin tetrasulfonate (metallo-TPPS4) derivatives, and (iii) sulfonated tetra-arylporphyrin derivatives. None of the natural porphyrins studied reduced infection by more than 80% at a concentration of 5 μg/ml in these assays. Some metal chelates of TPPS4 were more active, and a number of sulfonated tetra-aryl derivatives showed significantly higher activity. Some of the most active compounds were the sulfonated tetranaphthyl porphyrin (TNapPS), sulfonated tetra-anthracenyl porphyrin (TAnthPS), and sulfonated 2,6-difluoro-meso-tetraphenylporphine [TPP(2,6-F2)S] and its copper chelate [TPP(2,6-F2)S,Cu], which reduced infection by 99, 96, 94, and 96%, respectively. Our observations indicate that at least some of these compounds are virucidal, i.e., that they render the virus noninfectious. The active compounds were found to inhibit binding of the HIV type 1 gp120 to CD4 and also to completely inhibit the ability of Env proteins expressed from recombinant vectors to induce cell fusion with receptor-bearing target cells. These results support the conclusion that modified porphyrins exhibit substantial activity against HIV and that their target is the HIV Env protein.

31P NMR and viscometric studies of the interaction of meso-tetra(4-N-methyl-pyridyl)porphine and its Ni(II) and Zn(II) derivatives with DNA

The interactions of meso-tetra(4-N-methylpyridyl) porphine (TMPyP) and its Zn(II) and Ni(II) derivatives with DNA have been investigated by 31P NMR and viscometric titrations. TMPyP and its Ni derivative increase the viscosity of linear DNA, cause unwinding and reverse coiling of superhelical DNA, and induce a separate downfield peak in the 31P NMR spectrum of DNA. The Zn derivative slightly decreases the viscosity of linear DNA, does not unwind superhelical DNA, and does not give a downfield NMR peak. The main DNA 31P NMR signal is shifted slightly upfield on either the addition of TMPyP or the Ni compound. These results indicate that TMPyP and the Ni(II), but not the Zn(II), derivative bind to DNA by intercalation.

Effect of N-alkyl substituents on the DNA binding properties of meso-tetrakis (4-N-alkylpyridinium-4-yl)porphyrins and their nickel derivatives

Resonance Raman, NMR, and visible spectroscopies, as well as viscosity and equilibrium dialysis studies were used to assess the effect of the N-alkyl substituent of meso-tetrakis(4-N-alkylpyridinium-4-yl)porphyrin cations on DNA binding. The DNAs studied include the native DNA, calf thymus DNA (CT DNA), the synthetic polynucleotides [poly(dGdC)]2 and [poly(dAdT)]2, and the oligonucleotide d(TATACGTATA)2. Both the porphyrins and the metalloporphyrins containing Ni(II) were examined with the N-alkyl = propyl (TPrpyP(4) and NiTPrpyP(4)) and 2-hydroxyethyl (TEtOHpyP(4) and NiTEtOHpyP(4)). The results were compared to those from the parent porphyrins with the N-methyl substituent (TMpyP(4) and NiTMpyP(4)). For almost all the comparisons made, the new porphyrin cations gave results very similar to those for the TMpyP(4) species. The resonance Raman study indicated that for the three DNA polymers all the Ni species were in the four-coordinate form when bound to all three polymers. It is suggested that both TPrpyP(4) and TEtOHpyP(4) bind to GC regions of DNA in the same intercalative manner as TMpyP(4) with the N-alkyl substituent extended into the solvent. For AT regions of DNA, the binding of TPrpyP(4) and TEtOHpyP(4) is nonintercalative, as found previously for TMpyP(4). The NiPrpy(4) and NiTEtOHpyP(4) cations bind to these polymers in a similar manner to the apo-porphyrins. The similar Raman spectral changes for the three Ni porphyrins upon addition of [poly(dAdT)]2 suggest that partial intercalation is not occurring because models indicate that it would be difficult to accommodate the bulkier N-alkyl substituents.

Interactions of DNA with a new electron-deficient tentacle porphyrin: meso-Tetrakis[2,3,5,6-tetrafluoro-4-(2-trimethylammoniumethylamine)phenyl]porphyrin

A new electron-deficient tentacle porphyrin meso-tetrakis[2,3,5,6-tetrafluoro-4-(2-trimethylammoniumethylamine )phenyl]porphyrin (TthetaF4TAP) has been synthesized. The binding interactions of TthetaF4TAP with DNA polymers were studied for comparison to those of an electron-deficient tentacle porphyrin and an electron-rich tentacle porphyrin; these previously studied porphyrins bind to DNA primarily by intercalative and outside-binding modes, respectively. The three tentacle porphyrins have similar size and shape. The basicity of TthetaF4TAP indicated that it has electronic characteristics similar to those of the intercalating electron-deficient tentacle porphyrin. However, TthetaF4TAP binds to calf thymus DNA, [poly(dA-dT)]2, and [poly(dG-dC)]2 in a self-stacking, outside-binding manner under all conditions. Evidence for this binding mode included a significant hypochromicity of the Soret band, a conservative induced CD spectrum, and the absence of an increase in DNA solution viscosity. As found previously for the electron-rich porphyrin, the results suggest that combinations of closely related self-stacked forms coexist. The mix of forms depended on the DNA and the solution conditions. There are probably differences in the detailed features of the self-stacking adducts for the two types of tentacle porphyrins, especially at high R (ratio of porphyrin to DNA). At low R values, the induced CD signal of TthetaF4TAP/CT DNA resembled that of TthetaF4TAP/[poly(dA-dT)]2, suggesting that TthetaF4TAP binds preferentially at AT regions. Competitive binding experiments gave evidence that TthetaF4TAP binds preferentially to [poly(dA-dT)]2 over [poly (dG-dC)]2. Thus, despite the long, positively charged, flexible substituents on the porphyrin, the binding of TthetaF4TAP is significantly affected by base-pair composition. Similar characteristics were found previously for the electron-rich tentacle porphyrin. Thus, significant changes in electron richness have relatively minor effects on this outside binding selectivity for AT regions. TthetaF4TAP is the first porphyrin with electron deficiency and shape similar to intercalating porphyrins that does not appear to intercalate. All porphyrins reported to intercalate have had pyridinium substituents. Thus, the electronic distribution in the porphyrin ring, not just the overall electron richness, may play a role in facilitating intercalation.

99mTc(CO)3-Nitrilotriacetic Acid : A New Renal Radiopharmaceutical Showing Pharmacokinetic Properties in Rats Comparable to Those of 131I-OIH

To develop a 99mTc renal tracer with a capacity to measure effective renal plasma flow comparable to that of the clinical gold standard 131I-o-iodohippurate (131I-OIH) and superior to that of 99mTcO-mercaptoacetyltriglycine, which has a clearance only 50%−60% that of 131I-OIH, we investigated 99mTc-tricarbonyl nitrilotriacetic acid (Na2[99mTc(CO)3(NTA)]). This radiopharmaceutical, which is based on an aminopolycarboxylate ligand, is formed as a single species and has a dangling carboxylate group favoring tubular transport. Methods: Na2[99mTc(CO)3(NTA)] was prepared by using commercially available NTA and an IsoLink kit and isolated by high-performance liquid chromatography. The stability of Na2[99mTc(CO)3(NTA)] in isotonic saline was assessed for 24 h and was further evaluated by incubation in 0.1 M cysteine and histidine for 4 h at 37°C. The biodistribution of Na2[99mTc(CO)3(NTA)], coinjected with 131I-OIH as an internal control, was evaluated in 5 normal Sprague–Dawley rats at 10 min, 5 normal Sprague–Dawley rats at 60 min (group A), and 6 rats with renal pedicle ligation at 60 min (group B) after injection. Clearance and extraction fraction studies were conducted in 2 normal Sprague–Dawley rats, and urine and plasma from 2 additional normal rats each were analyzed for metabolites by high-performance liquid chromatography. Results: The radiochemical purity of Na2[99mTc(CO)3(NTA)] was greater than 99%, the complex was stable for 24 h at physiologic pH, and the challenge experiments showed no degradation. In normal rats, the percentage dose in the urine at 10 and 60 min was 108% ± 9% and 101% ± 5%, respectively, that of 131I-OIH; minimal hepatic or gastrointestinal activity was demonstrated. In group B rats, Na2[99mTc(CO)3(NTA)] was better retained in the blood and had less excretion into the bowel than did 131I-OIH (P < 0.01). The plasma clearances of Na2[99mTc(CO)3(NTA)] and 131I-OIH were comparable, but the extraction fraction of Na2[99mTc(CO)3(NTA)] was 93.5% ± 3.8%, compared with 67.9% ± 6.1% for 131I-OIH. Plasma protein binding of Na2[99mTc(CO)3(NTA)] averaged 67% ± 7%, and red cell uptake was 7% ± 2%. Conclusion: Na2[99mTc(CO)3(NTA)] is stable, exists as a single species, and has pharmacodynamic properties in rats comparable to those of 131I-OIH.

The CoCH3 bond in Shiff base B12 models: influence of the trans and equatorial ligands as assessed by Fourier transform Raman spectroscopy

Properties of the CoC bond in organocobalt methyl Schiff base B12 model compounds in CHCl3 solution were probed using near-IR Fourier transform Raman spectroscopy. The influence of the trans ligand (L) on the CoCH3 stretching (νCoCH3) frequency was investigated by varying the trans ligand of [LCo(salen)(CH3)]. The influence of L is related to the ground state CoC bond strength and correlates empirically with the CoC bond length in closely related models. The νCoCH3, frequency decreased from 518 to 500 cm− with L in the order methanol 1-methylimidazole>4-dimethylaminopyridine ≽ pyridine ≽ piperidine > quinuclidine > triethylphosphine. This decrease reflects the greater electron in the 2eg orbital which results from the expected increase in the electron-donating character of L. The νCoCH3, frequency of the L = 2-methylpyridine (2-Mepy) derivative was detected at 518 cm−1, higher than the value of 512 cm−1 for the L = py derivative. This result is attributed to repulsion between the 2-Me group and the equatorial ligand, steric interactions making the coordination of the trans 2-Mepy ligand weaker. The νCoCH3 frequency for the putative five-coordinate [Co(salen)(CH3)] compound was detected at 513 cm−1 (491cm−1 for the CD3 analog), close to frequencies found for the six coordinate salen complexes studied. The νCoCH3 frequency of pyridine derivatives of several well known B12 model compounds was found to increase with changing equatorial ligands in the order (DO)(DOH)pn < (DH)2 < saloph < salen2. This trend suggests the ground state CoC bond experiences an apparent strengthening that could be attributed to a decrease in electron occupation of the anti-bonding 2eg orbital. We hypothesize that this orbital increases in energy across the series.

MOLECULAR ORBITAL STUDY OF COMPLEXES OF ZINC(II) WITH IMIDAZOLE AND WATER MOLECULES

Geometry optimizations and energy calculations have been performed at the density functional B3LYP level on imidazole (HL), imidazolate (L−), imidazolium (H2L+), 3-methylimidazole, 4-methylimidazole, 5-methylimidazole, [Zn(HL)]2+, [Zn(3-MeL)]2+, [Zn4-Me(HL)]2+, [Zn5-Me(HL)]2+, [Zn(OH)]+, [Zn(H2O)]2+, [Zn(H2O)6]2+, [Zn(H2O)(HL)]2+, [Zn(HL)2]2+, [Zn(HL)3]2+, [Zn(OH)(HL)3]+ and [Zn(H2O)(HL)3]2+. Coordination of zinc(II) at N(1) of imidazole causes nearly the same changes in bond distances and base inner angles in the imidazole framework as protonation does. The ZnO and ZnN distances in [Zn(H2O)m(HL)n]2 complexes become longer as the number of coordinating ligands increases. Calculated bond dissociation energies show that HL is more strongly bound than H2O to Zn(II) and its complexes. The population analysis indicates that the imidazole ligand transfers charge to Zn(II) and is a much more efficient charge neutralizer than H2O. The analysis further indicates that imidazole is very strongly polarized by Zn(II). Intermolecular ZnN stretching and ZnNC bending bands in [Zn(HL)]2+ are weak in intensity; the former is red-shifted upon coordination of H2O. The OH stretching frequencies are blue-shifted when imidazole is coordinated to [Zn(H2O)]2+.

Amino- and hydroxytetraphenylporphyrins with activity against the human immunodeficiency virus

A series of amino- and hydroxytetraphenylporphyrin derivatives was found to have activity against the human immunodeficiency virus type 1 (HIV-1) in human peripheral blood mononuclear cells. Activity tends to be associated with increased hydrophilicity of the porphyrins for the porphyrins with one substituent on each phenyl ring but there is no clear pattern for the porphyrins with two substituents on each phenyl ring. The antiviral activity of certain porphyrins has been demonstrated in the absence of light, suggesting a non-photochemical process. Whereas only some of the porphyrins that inhibit HIV-1 in culture inhibit HIV-1 reverse transcriptase in a cell-free system, none of those tested inhibit DNA polymerase α.

Coordinating properties of alkylated 6-aminopurines. Electrostatic potential distributions for 3-methyladenine and 9-methyladenine and preparation and structure of cis-diamminebis(3-methyladenine)platinum(II) nitrate trihydrate

Electrostatic potential maps have been computed for 3-methyladenine and 9-methyladenine under the INDO molecular orbital approximation. These maps clearly indicate a shift in the attractive electrophilic site from N ( 1) of the six-membered pyrimidine ring to N(7) of the five-membered imidazole ring and a marked increase in molecular dipole moment on going from the 9-substituted to the 3-substituted purine. These features help to rationalize the increased ligating power of 3-alkylated 6-aminopurines over 9-alkylated 6-aminopurines. The synthesis, solution ‘H NMR spectrum, and solid-state molecular and crystal structure of cis-diamminebis(3-methyladenine)platinum(II) nitrate trihydrate, ~ is [ (NH~)~Pt(3-MeA) ,1(N03)2.3H20, are also reported. The compound crystallizes in the triclinic system, space group P1, with a = 10.877 (4) A, b = 15.395 (5) A, c = 7.604 (2) A, CY = 103.33 ( 2 ) O , p = 102.90 (2)O, y = 99.94 (2)O, V = 1173.6 A3, Z = 2 (based on a molecular weight of 705.52 for [Pt(NH3)2(C,N,H,)2](N03)2.3H20), Dmcasd = 1.99 (1) g ~ m ~ , and Dmld = 1.99 g ~ m ~ . The crystal structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares techniques to an R value of 0.044. The C ~ S [ ( N H , ) ~ R ( ~ M ~ A ) ~ ] ~ + cation is essentially square planar with the two independent 3-MeA ligands showing N(7)-Pt bonding and is arranged in a head-to-tail fashion such that the complex cation possesses approximate C2 molecular symmetry. Principal geometrical parameters are as follows: Pt-N(ammine) = 2.039 (6) A, 2.031 (6) A; Pt-N(7)(3-MeA) = 2.010 (4) A, 2.004 (4) A; N(ammine)-Pt-N(ammine) = 90.6 (2)O; N(7)-Pt-N(7) = 89.5 (2)’; interbase dihedral angle = 90.6O; base/PtN, coordination plane dihedral angle = 98.9, 11 1.8’. The extended crystal structure exhibits two different types of base-stacking interactions and two different kinds of base pairing through hydrogen bonds. There is also an extensive network of hydrogen bonds. Further stabilization is afforded by base/nitrate anion stacking. The IH N M R spectrum of the platinated 3-MeA ligand is compared to that of the free base and to the spectra of several Co(III)-3-alkylated 6-aminopurine complexes. The present complex affords a model for an N(7)J,.AMP-Pt-N(7)Y-AMP type cross-linking mode that is perhaps applicable to the binding of Pt(I1) antitumor drugs to DNA. It is suggested that such a cross-link would demand about the same degree of local denaturation of a polynucleotide as one of the type N(7),,.GMp-Pt-N(7),t.GMP.