Deglycobleomycin A2 Research Articles

Definition of the Effect and Role of the Bleomycin A2 Valerate Substituents: Preorganization of a Rigid, Compact Conformation Implicated in Sequence-Selective DNA Cleavage

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 its substituents. In addition to demonstrating that the C3-hydroxy group exhibits only a modest effect (1−2×) that may be attributed to an intermolecular H-bond with DNA and that the length of the linker is important (C4 > C5 > C3 > C2), the studies illustrate that the substantial impact of the C4-methyl group is linked to the presence of the C2-methyl group, while the modest impact of the C2-methyl group itself (ca. 2×) is not coupled to the presence of the C4-methyl group. These effects may be explained by the conformational properties of the agents resulting from the substitutions and beautifully fit the models of DNA-bound Co(III)OOH bleomycin A2 and deglycobleomycin A2. The magnitude of the effects suggests that an important functional role of the linker region is to facilitate adoption of a rigid, compact conformation productive for DNA cleavage. The studies also identify a second potential site that may adopt two nearly equivalent conformations which may constitute a swivel point that permits access to a class of related bound structures adaptable to the conformational characteristics of the multiple cleavage sites or access to both strands of DNA from a common intercalation site important for both primary (single strand) and secondary (double strand) cleavage.

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

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...

NMR Studies of Co·Deglycobleomycin A2 Green and Its Complex with d(CCAGGCCTGG)

NMR studies of the hydroperoxide form of cobalt deglycoBleomycin A2 (HOO−CodGBLM) and its complex with oligonucleotide d(CCAGGCCTGG) (1, C is the site of cleavage) are presented in an effort to establish deglycoBLM as a prototype for studies with BLM analogues, synthesized without the sugar moieties (Boger et al. Bioorg. Med. Chem. 1995, 3, 1281−1295). The structure determination of free HOO−CodGBLM has been hampered by the lack of NOE or ROE information. By direct comparison of the chemical shifts and coupling constants of HOO−CodGBLM with its glycosylated parent HOO−CoBLM, the former is shown to share many global structural features with the latter, including the nature of axial ligands (a point recently disputed by Caceres-Cortes et al. Eur. J. Biochem. 1997, 244, 818−828), the screw sense of metal-coordinating ligands, and the folding of the peptide linker region. The structure of HOO−CodGBLM bound to 1 is reported based on molecular modeling using NMR constraints (39 intermolecular and 44 intramolecu...

Assessment of the Role of the Bleomycin A2 Pyrimidoblamic Acid C4 Amino Group

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...

DNA Strand Scission by Bleomycin Group Antibiotics

Certain properties of the bleomycin analogs deglycobleomycin A2 and decarbamoylbleomycin A2 have been characterized. In common with bleomycin A2, both deglycobleomycin A2 and decarbamoylbleomycin A2 were found to mediate DNA degradation in the presence of Fe(II) + O2. Both analogs were found to have essentially the same sequence selectivity for DNA strand scission as bleomycin A2 when a 5'-[23P]-end-labeled linear duplex DNA derived from SV40 DNA was employed as a substrate. Product analysis for the three analogs was carried out by assay for malondialdehyde (precursors) after digestion of calf thymus DNA, and also by hplc analysis of the digestion products formed from the dodecanucleotide d(CGCTTTAAAGCG). All three Fe(II) X bleomycin A2 analogs produced the same products, albeit not in the same relative amounts.

Deglyco-bleomycin. Degradation of DNA and formation of a structurally unique Fe(II) . CO complex.

In analogy with bleomycin, deglyco-bleomycin B2 has been found to form a stable, diamagnetic complex with Fe(II) and CO. Although the stoichiometry of this complex appeared to be the same as that formed with bleomycin, the geometry of the deglyco-bleomycin complex was fundamentally different, especially as regards orientation of the beta-aminoalanine moiety. In the presence of Fe(II) and O2, deglyco-bleomycin A2 and deglyco-bleomycin B2 were found to release [3H]thymine from radiolabeled PM-2 DNA; when employed at limiting concentrations, deglyco-bleomycin A2 and B2 gave about half as much [3H]thymine release as the respective bleomycins. In view of the spectral evidence (Burger, R. M., Horwitz, S. B., Peisach, J., and Wittenberg, J. B. (1979) J. Biol. Chem. 254, 12299-12302) that Fe(II) . bleomycin . CO has the same geometry as the complex formed by initial association of bleomycin, Fe(II), and O2, the accumulated data suggest strongly that all metal complexes of bleomycin (derivatives) capable of DNA degradation need not have the same geometry.

A new synthesis of deglyco-bleomycin A2 aiming at the total synthesis of bleomycin

An improved route to synthesize deglyco-bleomycin A2, the aglycon of bleomycin A2, aiming at the total synthesis of bleomycin is described. The new route is characterized by the stepwise elongation of the amino acid constituents and the use of a thiol ester obtained by aldol condensation.

Total synthesis of deglyco-bleomycin A2

Deglyco-bleomycin A2, the aglycon of bleomycin A2, has been synthesized for the first time.