Rebeccamycin biosynthesis

Independently, in 1998, the Cordell (290,379,380) and Pearce (381) groups published some preliminary biosynthetic results on staurosporine and rebeccamycin, typical representative members of the indolo[2,3-fl]pyrrolo[3,4-c]carbazole alkaloids. Cordell s biosynthetic studies on staurosporine were based on feeding experiments with L-tryptophan. These studies showed that two units of L-tryptophan, with the two carbon side-chains intact, were responsible for the biosynthesis of staurosporine aglycone. Further experimental studies are necessary to establish the nature of the intermediate in the biotransformation of L-tryptophan to staurosporine. Although these studies are not complete, they gave for the first time insight into the biosynthesis of staurosporine (379,380). 

Fig. 4.2 A ribbon diagram of tryptophan 7-halogenase, an enzyme important in the biosynthesis of pyrrolnitrin and rebeccamycin. (Photo K.-H. van Pee and J. H. Naismith)...

Yeh E, Gameau S, Walsh CT (2005) Robust in vitro Activity of RebF and RebH, a Two-Component Reductase/Halogenase, Generating 7-Chlorotryptophan During Rebeccamycin Biosynthesis. Proc Natl Acad Sci USA 102 3960... 

The biosynthesis of 1 follows a pattern seen for all bisindoles that have been biosynthetically investigated thus far [17, 163, 164] two molecules of L-tryptophan (123) are oxidized and then dimerized to give an initial bisindole skeleton (Fig. 24). Historically, the biosynthesis of staurosporine (121) has been investigated in parallel with that of rebeccamycin (124), a related bisindole. Both molecules are thought to be biosynthesized through nearly identical routes to give the aglycone... 

That chlorination occurs early in the biosynthesis of rebeccamycin is shown by the identification of two genes in the biosynthetic duster and their ability to chlorinate tryptophan at C-7 as shown in Scheme 19.5 [117]. 

Fig. 20.1 Gene clusters for biosynthesis of rebeccamycin, staurosporine, and AT2433.

Rebeccamycin is a natural product that inhibits DNA topoisomerase I and has been studied as a potential anticancer agent because of the importance of DNA topoisomerase I in cell growth and proliferation. Rebeccamycin analogues are being used in clinical trials for the treatment of neoplastic tumors,renal cell cancer, and leukemia, " rehO is one of the 11 genes in the rebeccamycin biosynthetic cluster. The protein product, RebO, is an L-amino acid oxidase that contains a noncovalently bound FAD. RebO catalyzes the oxidation of 7-chloro-L-tryptophan in an early step in rebeccamycin biosynthesis (Equation (4)). 

In recent years, the enzymes responsible for the introduction of halogen in biological systems have been identified. One group of vanadium bromoperoxidases is found in marine algae [69-71]. 7-Chlorination of tryptophan is involved in the biosynthesis of materials such as pyrrolnitrin and rebeccamycin. The enzyme is a flavin-dependent monooxygenase that generates hypochlorite ion. The structure of the enzyme is such that the OCl ion is conducted to the indole binding site over a distance of about 10 A [72, 73]. 

Figure 549 Schematic representation of the organization of the gene cluster responsible for rebeccamycin biosynthesis in Sacchawthrix aerocolonigenes ATCC39243.

CYP245A1 (StaP) from Streptomyces sp. TR-A0274 catalyzes the aryl-aryl coupling of chro-mopyrrolic acid in staurosporine biosynthesis [154, 253, 254], Staurosporine and the structurally related compounds rebeccamycin (Fig. 6.14)... 

Howard-JonesAR, Walsh CT (2007)Nonenzymatic oxidative steps accompanying action of the cytochrome P450 enzymes StaP and RebP in the biosynthesis of staurosporine and rebeccamycin. J Am Chem Soc 129 11016-11017... 

Yeh E, Garneau S, Walsh CT. Robust in vitro activity of RebF and RebH, a two-component reductase/halogenase, generating 7-chlorotryptophan during rebeccamycin biosynthesis. Proc. Nat. Acad. Sci. USA 2005 102 3960-3965. 

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