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Dale L Boger - One of the best experts on this subject based on the ideXlab platform.

Joanne Stubbe - One of the best experts on this subject based on the ideXlab platform.

  • definition of the effect and role of the Bleomycin A2 valerate substituents preorganization of a rigid compact conformation implicated in sequence selective dna cleavage
    Journal of the American Chemical Society, 1998
    Co-Authors: Dale L Boger, Timothy M Ramsey, Silvia T Hoehn, Joanne Stubbe
    Abstract:

    The synthesis and a comparative study of deglycoBleomycin A2 analogues containing key modifications in the valerate subunit are described in efforts that define the role of the linker length and it...

  • a systematic evaluation of the Bleomycin A2 l threonine side chain its role in preorganization of a compact conformation implicated in sequence selective dna cleavage
    Journal of the American Chemical Society, 1998
    Co-Authors: Dale L Boger, Timothy M Ramsey, Silvia T Hoehn, Hui Cai, Joanne Stubbe
    Abstract:

    The preparation and examination of 3−7 are detailed and constitute analogues of deglycoBleomycin A2 (2) containing systematic modifications in the l-threonine side chain. The studies revealed a sub...

  • assessment of the role of the Bleomycin A2 pyrimidoblamic acid c4 amino group
    Journal of the American Chemical Society, 1998
    Co-Authors: Dale L Boger, Timothy M Ramsey, Silvia T Hoehn, Hui Cai, John W Kozarich, Joanne Stubbe
    Abstract:

    The preparation and examination of 3 and 4 and their unnatural epimers 6 and 7 by following a new and alternative synthesis of 2 was conducted to assess the role of the pyrimidine C4 amine of Bleomycin A2 (1) and deglycoBleomycin A2 (2). The agent 3 bearing a pyrimidine C4 dimethylamino substituent exhibited a substantially diminished DNA cleavage efficiency (10−15×) relative to 2 and the loss of the characteristic 5‘-GC/5‘-GT cleavage selectivity. The agent 4 in which the pyrimidine C4 amino group was removed exhibited an even greater diminished DNA cleavage efficiency (30×) relative to that for 2. For this agent, the characteristic cleavage selectivity is either slightly or significantly reduced depending on the assay conditions. Even in the instances where it was not substantially altered, the ability to detect it required a temperature of 4 versus 25−37 °C. This information and temperature dependence suggest a reduced binding interaction and are consistent with the participation of the pyrimidine C4 a...

  • structural characterization of co Bleomycin A2 brown free and bound to d ccaggcctgg
    Journal of the American Chemical Society, 1997
    Co-Authors: Siu Man Lui, John W Kozarich, Dana E Vanderwall, Christopher J Turner, Xuejun Tang, Joanne Stubbe
    Abstract:

    A model for the structure of the aquated form of cobalt Bleomycin (H2O-CoBLM or CoBLM A2 brown), free and bound to d(CCAGGCCTGG)2 (1) is reported based on molecular modeling using the constraints obtained from 2D NMR studies. CoBLM A2 brown has a chiral organization of its ligands, including the axial primary amine of β-aminoalanine, identical to the hydroperoxide form of cobalt BLM (HOO-CoBLM or CoBLM A2 green). H2O-CoBLM forms a 1:1 complex with 1 with a Kd of 2 × 10-6 M which is in slow exchange on the NMR time scale. The complex exhibits 44 intermolecular NOEs and 56 intramolecular NOEs within H2O-CoBLM itself. Molecular modeling reveals that H2O-CoBLM's mode of binding, basis for sequence specificity, and chemical specificity are almost identical to that previously reported for HOO-CoBLM (Wu, W.; Vanderwall, D. E.; Turner, C. J.; Kozarich, J. W.; Stubbe, J. J. Am. Chem. Soc. 1996, 118, 1281−1294). The bithiazole tail is inserted from the minor groove 3‘ to C6 and the terminal thiazolium ring is well ...

  • solution structure of co Bleomycin A2 green complexed with d ccaggcctgg
    Journal of the American Chemical Society, 1996
    Co-Authors: Dana E Vanderwall, Christopher J Turner, John Kozarich W And, Joanne Stubbe
    Abstract:

    The solution structure of Co·Bleomycin (CoBLM) A2 green (the hydroperoxide form of CoBLM) complexed with the self-complementary oligonucleotide d(CCAGGCCTGG) with a cleavage site at C6 has been determined by 2D NMR spectroscopic methods and molecular dynamics calculations. Intermolecular NOEs (60 between CoBLM A2 green and DNA) and intramolecular NOEs (61 within CoBLM A2 green) have defined the position and orientation of CoBLM A2 green with respect to its single binding site in the duplex. CoBLM A2 green is a stable analog of the activated BLM, the Fe3+ hydroperoxide (Sam, J. W.; Tang, X.-J.; Peisach, J. J. Am. Chem. Soc. 1994, 116, 5250−5256). These studies have provided the first structural insight into the mode of binding of the bithiazole tail of CoBLM A2 green to DNA, the basis for specificity of its cleavage at pyrimidines (Py) in d(G-Py) sequences, and the orientation of its terminal oxygen of the hydroperoxide relative to the 4‘ carbon hydrogen bond being cleaved in the DNA. The bithiazole tail i...

Timothy M Ramsey - One of the best experts on this subject based on the ideXlab platform.

  • definition of the effect and role of the Bleomycin A2 valerate substituents preorganization of a rigid compact conformation implicated in sequence selective dna cleavage
    Journal of the American Chemical Society, 1998
    Co-Authors: Dale L Boger, Timothy M Ramsey, Silvia T Hoehn, Joanne Stubbe
    Abstract:

    The synthesis and a comparative study of deglycoBleomycin A2 analogues containing key modifications in the valerate subunit are described in efforts that define the role of the linker length and it...

  • a systematic evaluation of the Bleomycin A2 l threonine side chain its role in preorganization of a compact conformation implicated in sequence selective dna cleavage
    Journal of the American Chemical Society, 1998
    Co-Authors: Dale L Boger, Timothy M Ramsey, Silvia T Hoehn, Hui Cai, Joanne Stubbe
    Abstract:

    The preparation and examination of 3−7 are detailed and constitute analogues of deglycoBleomycin A2 (2) containing systematic modifications in the l-threonine side chain. The studies revealed a sub...

  • assessment of the role of the Bleomycin A2 pyrimidoblamic acid c4 amino group
    Journal of the American Chemical Society, 1998
    Co-Authors: Dale L Boger, Timothy M Ramsey, Silvia T Hoehn, Hui Cai, John W Kozarich, Joanne Stubbe
    Abstract:

    The preparation and examination of 3 and 4 and their unnatural epimers 6 and 7 by following a new and alternative synthesis of 2 was conducted to assess the role of the pyrimidine C4 amine of Bleomycin A2 (1) and deglycoBleomycin A2 (2). The agent 3 bearing a pyrimidine C4 dimethylamino substituent exhibited a substantially diminished DNA cleavage efficiency (10−15×) relative to 2 and the loss of the characteristic 5‘-GC/5‘-GT cleavage selectivity. The agent 4 in which the pyrimidine C4 amino group was removed exhibited an even greater diminished DNA cleavage efficiency (30×) relative to that for 2. For this agent, the characteristic cleavage selectivity is either slightly or significantly reduced depending on the assay conditions. Even in the instances where it was not substantially altered, the ability to detect it required a temperature of 4 versus 25−37 °C. This information and temperature dependence suggest a reduced binding interaction and are consistent with the participation of the pyrimidine C4 a...

  • synthesis and evaluation of potential nπ and nσ metal chelation sites within the β hydroxy l histidine subunit of Bleomycin A2 functional characterization of imidazole nπ metal complexation
    Bioorganic & Medicinal Chemistry, 1996
    Co-Authors: Dale L Boger, Timothy M Ramsey, Hui Cai
    Abstract:

    The synthesis and evaluation of 4 and 5, fully functionalized deglycoBleomycin A2 (2) analogues incorporating an oxazole and a pyrrole in place of the beta-hydroxy-L-histidine imidazole, are detailed. The oxazole agent is only capable of Npi metal complexation through a form related to the N1-H imidazole tautomer of Bleomycin A2 (1) while the pyrrole agent may potentially mimic the Nsigma metal complexation capabilities of the imidazole N3-H tautomer. Metal complexes (Fe-II, Fe-III) of 4 and 5 were found to cleave duplex DNA in the presence of O2 (Fe-II) or H2O2 (Fe-III). The oxazole agent 4 which is incapable of Nsigma metal chelation was found to behave analogous to, albeit slightly less effectively than, deglycoBleomycin A2 resulting in the characteristic 5'-GC/5'-GT sequence selective cleavage of duplex DNA directly confirming that imidazole/oxazole Npi metal chelation is sufficient for functional reactivity. Importantly, the effective substitution of the oxazole O-1 for the histidine N-1 further illustrates that this group does not require deprotonation upon metal complexation, oxygen activation, or the ensuing oxidation reactions, that the functional Bleomycin A2 tautomer is the imidazole N'-H tautomer, and that the imidazole N'-H functionality is not contributing to the polynucleotide recognition through H-bonding to the phosphate backbone or nucleotide bases. In contrast, the pyrrole agent 5 which is incapable of Npi metal chelation, but possesses the capabilities of functioning as a Nsigma metal donor was also found to cleave duplex DNA, but does so in a nonsequence selective fashion with a significantly reduced efficiency and a diminished double to single strand cleavage ratio both only slightly above that of background iron itself. These observations are analogous to those made with 3 which lacks the imidazole altogether and further support the observations that Nsigma coordination, not Npi coordination, of the imidazole is required for the functional activity of Bleomycin A2.

  • synthesis of key analogs of Bleomycin A2 that permit a systematic evaluation of the linker region identification of an exceptionally prominent role for the l threonine substituent
    Bioorganic & Medicinal Chemistry, 1995
    Co-Authors: Dale L Boger, Timothy M Ramsey, Steven L Colletti, Shuji Teramoto, Jiacheng Zhou
    Abstract:

    The synthesis of a full series of analogs 2b-k of deglycoBleomycin A2 (2a) containing systematic variations in the linker domain of Bleomycin A2 (1) is described. The agents 2b-k, which are not accessible through structural modification of 1 or 2a, constitute key substructure analogs incorporating deep-seated structural modifications in the linker domain capable of delineating the contribution of the individual backbone substituents to the DNA cleavage efficiency, characteristic DNA cleavage selectivity, and double strand to single strand DNA cleavage ratio. The comparative examination of the DNA cleavage properties of the Fe(II) and Fe(III) complexes of 2a-k upon activation by O2-thiol or H2O2, respectively, revealed several characteristic features and trends. First, none of the substituents affect the characteristic 5'-GC, 5'-GT > 5'-GA DNA cleavage selectivity of Bleomycin A2. In contrast, an exceptionally prominent role for the L-threonine substituent and an important role for the C4-methyl substituent of the (2S,3S,4R)-4-amino-3-hydroxy-2-methylpentanoic acid subunit were observed on the DNA cleavage efficiency of the agents. Similarly, the L-threonine substituent was found to substantially increase the ratio of double strand to single strand DNA cleavage events (2-3 times). In a w794 DNA cleavage assay, shortening the linker region by two carbons resulted in an exceptionally large reduction in DNA cleavage efficiency (125 times) and provided an agent that was only 1.3 times more effective than Fe(III) indicating that this deep-seated modification essentially destroys the DNA cleavage capabilities of the agent. The L-threonine substituent contributes in an exceptional manner, and its removal resulted in a 25 times reduction in DNA cleavage efficiency. A substantial contribution was observed for the C4-methyl group on the 4-aminobutanoic acid subunit and its removal resulted in a 7 times reduction in DNA cleavage efficiency. Little effect for the C3-hydroxyl and C2-methyl substituents on the 4- aminobutanoic acid subunit was observed (0-2.5 times) and even their inversion of stereochemistry had little impact on DNA cleavage efficiency or selectivity. Notably, the magnitude of the previously unappreciated L-threonine substituent contribution to the DNA cleavage efficiency and on the ratio of double to single strand DNA cleavage events is the largest effect observed to date including the well recognized disaccharide potentiation (6 times) of the DNA cleavage properties. Consequently, the past role and relative importance of the L-threonine subunit and substituent has been underestimated. Moreover, the cumulative effect of the two important linker chain substituents clearly illustrate that the functional role of this domain is much more important than its simply serving as a linker.

Nikos Katsaros - One of the best experts on this subject based on the ideXlab platform.

  • preparation structure determination and cytotoxicity of the pd ii Bleomycin A2 complex
    European Journal of Inorganic Chemistry, 2004
    Co-Authors: Athanasios Papakyriakou, Ioannis Bratsos, Maria E Katsarou, Nikos Katsaros
    Abstract:

    The solution structure of the PdII·Bleomycin A2 complex was resolved by NMR spectroscopy in combination with molecular modelling. The preparation of the complex in 1.0 M NaCl aqueous solutions leads to the formation of a major compound, which is very stable at ambient temperature. Our NMR spectroscopic data demonstrate that Bleomycin is coordinated through the β-aminoalanine secondary amine, the pyrimidine ring N1, the deprotonated histidyl amide and the imidazole N1, in contrast to an earlier study that proposed coordination of the valerate amide. 2D NMR spectroscopic data were used as distance constraints in simulated annealing molecular-dynamics calculations and the first solution structure of a square-planar metallo-Bleomycin is reported. In order to assess the toxicity of PdII·Bleomycin, cytotoxicity measurements were performed in U937 and K562 leukemia cell lines using two methods. In both cell lines the free drug and the complex exhibit similar toxicity as a function of time. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

  • nmr and molecular modelling studies on the solution structure of the iniii Bleomycin A2 complex
    European Journal of Inorganic Chemistry, 2003
    Co-Authors: Athanasios Papakyriakou, Nikos Katsaros
    Abstract:

    The solution structure of the InIII−Bleomycin A2 complex (InBLM) has been determined by NMR studies in combination with molecular modelling. Our data indicate that BLM is coordinated to InIII through five nitrogen ligands in a distorted tetragonal pyramid configuration. The stability and homogeneity of InBLM has allowed us to obtain a well-defined model of the complex formed at low pH, which is a very potent tumour-imaging agent. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

  • the solution structure of the ga iii Bleomycin A2 complex resolved by nmr and molecular modeling interaction with d ccaggcctgg
    Journal of Biological Inorganic Chemistry, 2003
    Co-Authors: Athanasios Papakyriakou, Barbara Mouzopoulou, Nikos Katsaros
    Abstract:

    The solution structure of the Ga(III)-Bleomycin A2 complex (GaBLM) has been determined using 2D NMR methods in combination with molecular dynamics calculations. Complete assignment of the amide and amine protons, observation of 80 NOEs and measurement of 15 (3)JH(-H) coupling constants provided us with a well-defined structure using a restrained simulated annealing protocol. On the basis of distance and dihedral angle constraints agreement, along with potential energy considerations, the favored model is a five-coordinate complex with the primary amine of beta-aminoalanine holding the axial position of a distorted tetragonal pyramid. The disaccharide moiety of GaBLM is not a ligand, sharing the same side of the equatorial plane with the axial amine ligand. Titration of the self-complementary oligonucleotide d(CCAGGCCTGG) with GaBLM results in the formation of only one 1:1 complex in slow exchange on the NMR time scale. Our data indicate that the bithiazole moiety intercalates between the C6*G15 and C7*G14 base pairs, in a similar mode to that reported by earlier studies. Structural implications and comparisons to other metallo-Bleomycins are discussed.

Sidney M. Hecht - One of the best experts on this subject based on the ideXlab platform.

  • Total synthesis of deamido Bleomycin A2, the major catabolite of the antitumor agent Bleomycin
    Journal of the American Chemical Society, 2002
    Co-Authors: Ying Zou, Nour Eddine Fahmi, Corine Vialas, Guy M. Miller, Sidney M. Hecht
    Abstract:

    Metabolic inactivation of the antitumor antibiotic Bleomycin is believed to be mediated exclusively via the action of Bleomycin hydrolase, a cysteine proteinase that is widely distributed in nature. While the spectrum of antitumor activity exhibited by the Bleomycins is believed to reflect the anatomical distribution of Bleomycin hydrolase within the host, little has been done to characterize the product of the putative inactivation at a chemical or biochemical level. The present report describes the synthesis of deamidoBleomycin demethyl A2 (3) and deamido Bleomycin A2 (4), as well as the respective aglycones. These compounds were all accessible via the key intermediate Nα-Boc-Nβ-[1-amino-3(S)-(4-amino-6-carboxy-5-methylpyrimidin-2-yl)propion-3-yl]-(S)-β-aminoalanine tert-butyl ester (16). Synthetic deamido Bleomycin A2 was shown to be identical to the product formed by treatment of Bleomycin A2 with human Bleomycin hydrolase, as judged by reversed-phase HPLC analysis and 1H NMR spectroscopy. Deamido ble...

  • chemical and structural characterization of the interaction of Bleomycin A2 with d cgcgaattcgcg 2 efficient double strand dna cleavage accessible without structural reorganization
    Journal of the American Chemical Society, 2001
    Co-Authors: Michael V Keck, Richard A Manderville, Sidney M. Hecht
    Abstract:

    A detailed description of the interaction between Fe(II)·Bleomycin A2 and the Dickerson-Drew dodecamer d(CGCGAATTCGCG)2 is presented. The reaction between Bleomycin and this substrate leads to DNA cleavage at two major sites, adenosine5 and cytidine11, and two minor sites, cytidine3 and thymidine8. The pattern and relative intensities of cleavage at these sites was not entirely consistent with what would be predicted based on the preference of the drug for cleavage at the pyrimidines of 5‘-GC-3‘ and 5‘-GT-3‘ sites. Insight into the origins of the apparent alteration of selectivity was provided by examination of the structure of the duplex which had been determined by X-ray crystallography. This indicated that the C4‘ hydrogens of the two nucleotides located at the strongest cleavage sites, C11 on one strand and A5 on the other, were oriented toward each other in the minor groove. Two-dimensional NMR measurements and molecular dynamics modeling indicated that a metalloBLM could bind to the duplex in an ori...

  • total synthesis of Bleomycin group antibiotics total syntheses of Bleomycin demethyl A2 Bleomycin A2 and decarbamoyl Bleomycin demethyl A2
    ChemInform, 1999
    Co-Authors: Kiyoaki Katano, Yoshiaki Aoyagi, Mark Overhand, Steven J Sucheck, William C Stevens, Cynthia D Hess, Xiang Zhou, Sidney M. Hecht
    Abstract:

    The total syntheses of Bleomycin A2 (1) by two routes are described. The final step in the synthesis of Bleomycin A2 involves methylation of Bleomycin demethyl A2 (2). This Bleomycin derivative is of interest mechanistically, and can also provide access to other Bleomycins via its known chemical conversion to Bleomycinic acid. Accordingly, the synthetic strategy presented represents a particularly versatile approach for the elaboration of a wide variety of BLM congeners. Bleomycin was constructed from five key intermediates, the syntheses of which are described. 1,6-Di-O-acetyl-3,4-di-O-benzyl-2-O-[2,4,6-tri-O-acetyl-3-O-(N-acetylcarbamoyl)-α-d-mannopyranosyl]-β-l-gulopyranose (3) was converted quantitatively to its disaccharide chloride (4), the latter of which was condensed with Nα,Nim-bis(t-Boc)-(S)-erythro-β-hydroxyhistidine (7) to provide α-O-glycosidated product 16. The subsequent couplings with benzyl valerate 8, threonylbithiazole 9, and Nα-t-Boc-pyrimidoblamic acid (10) afforded access to bleomyc...