Actinomycine, XIX. Antibiotica aus Actinomyceten, XL. Konstitution und Synthese des Actinomycin-Chromophors

Isolation, chemistry, and biology of pyrrolo[1,4]benzodiazepine natural products

The isolation of the antitumor antibiotic anthramycin in the 1960s prompted extensive research into pyrrolo[1,4]benzodiazepines (PBD) as potential therapeutics for the treatment of cancers. Since then, nearly 60 PBD natural products have been isolated and evaluated with regard to their biological activity. Synthetic studies and total syntheses have enabled access to PBD analogues, culminating in the development of highly potent anticancer agents. This review provides a summary of the occurrence and biological activity of PBD natural products and covers the strategies employed for their total syntheses.

In vitro antibacterial activity of Phx-3 against Helicobacter pylori

Phx-3, one of the phenoxazine derivatives, is reported to have inhibitory effect on Mycobacterium species and Chlamydia pneumoniae but not Escherichia coli, Salmonella Typhimurium, Pseudomonas aeruginosa, Staphylococcus aureus, Listeria monocytogenes. The bactericidal activities of Phx-3 against Helicobacter pylori strains have not been assessed. Then, we measured minimum inhibitory concentration of Phx-3 for Helicobacter strains and assessed the morphological and biochemical effects of Phx-3 on H. pylori. In present study, it has shown that H. pylori strains including clarithromycin resistant strain and Helicobacter musterae were killed effectively by the treatment with Phx-3. Furthermore, severe morphological changes such as membrane blebbing and formation of hollows in H. pylori were detected. In addition, induction of heat shock protein 60 was observed. Taken together, Phx-3 has antibacterial activity against Helicobacter pylori.

The actinomycin biosynthetic gene cluster of Streptomyces chrysomallus: a genetic hall of mirrors for synthesis of a molecule with mirror symmetry

A gene cluster was identified which contains genes involved in the biosynthesis of actinomycin encompassing 50 kb of contiguous DNA on the chromosome of Streptomyces chrysomallus. It contains 28 genes with biosynthetic functions and is bordered on both sides by IS elements. Unprecedentedly, the cluster consists of two large inverted repeats of 11 and 13 genes, respectively, with four nonribosomal peptide synthetase genes in the middle. Nine genes in each repeat have counterparts in the other, in the same arrangement but in the opposite orientation, suggesting an inverse duplication of one of the arms during the evolution of the gene cluster. All of the genes appear to be organized into operons, each corresponding to a functional section of actinomycin biosynthesis, such as peptide assembly, regulation, resistance, and biosynthesis of the precursor of the actinomycin chromophore 4-methyl-3-hydroxyanthranilic acid (4-MHA). For 4-MHA synthesis, functional analysis revealed genes that encode pathway-specific isoforms of tryptophan dioxygenase, kynurenine formamidase, and hydroxykynureninase, which are distinct from the corresponding enzyme activities of cellular tryptophan catabolism in their regulation and in part in their substrate specificity. Phylogenetic analysis indicates that the pathway-specific tryptophan metabolism in Streptomyces most probably evolved divergently from the normal pathway of tryptophan catabolism to provide an extra or independent supply of building blocks for the synthesis of tryptophan-derived secondary metabolites.

Purification and characterization of tryptophan dioxygenase from Streptomyces parvulus

Tryptophan dioxygenase, derived from Streptomyces parvulus, was purified to near homogeneity and shown to have a native Mr of 88,000. Kinetic parameters of the enzyme were determined and evidence suggesting that it is a hemoprotein was obtained. Tryptophan dioxygenase has a high specificity toward L-tryptophan with an apparent Km of 0.3 mM. L-3-Hydroxykynurenine was a competitive inhibitor with respect to L-tryptophan with a Ki of 0.16 mM. In vitro, the enzyme displayed little activity in the absence of a reducing agent; ascorbate, at 50 mM, was the preferred reductant providing almost a 50-fold increase in enzyme activity. The regulation of tryptophan dioxygenase synthesis and activity is described. The expression of the enzyme is correlated with the biosynthesis of actinomycin D in S. parvulus. These results support the hypothesis that tryptophan dioxygenase functions as the first enzyme in the sequence converting L-tryptophan to the chromophore of this antibiotic.

Biosynthesis of the actinomycin chromophore: incorporation of 3-hydroxy-4-methylanthranilic acid into actinomycins by Streptomyces antibioticus

Actinomycin synthesis by washed mycelia of Streptomyces antibioticus has been conducted in the presence of 3-hydroxy-4-methylanthranilate-(carboxyl-(14)C). Incorporation of this compound into actinomycins has been observed, which constitutes further evidence that 3-hydroxy-4-methylanthranilate is an intermediate in actinomycin biosynthesis. The position of the incorporated label has been determined to be within the actinomycin chromophore, and the label appears to be equally distributed between both halves of the chromophore. Incidental to these findings was the observation that the (14)C-labeled actinomycins were subject to rapid reabsorption by the organism with actinomycin V taken up preferentially to actinomycin IV.