11032-05-6

Details of the synthesis method of the tumor promoters teleocidin B-3 (3), teleocidin B-4 (4) and dihydroteleocidin B-4 (9) (=dihydroteleocidin B) from (S)- and (R)-methyl N-methyl-N-[7-(3,6,7-trimethyl-1,6-octadien-3-yl)-4-indolyl]-L-valinates (20b and 20a) are presented.

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A unified and modular approach to the teleocidin B family of natural products is presented that proceeds in 11 steps and features an array of interesting strategies and methods. Indolactam V, the known biosynthetic precursor to this family, was accessed through electrochemical amination, Cu-mediated aziridine opening, and a remarkable base-induced macrolactamization. Guided by a desire to minimize concession steps, the tactical combination of C-H borylation and a Sigman-Heck transform enabled the convergent, stereocontrolled synthesis of the teleocidins.

TleD is a SAM (S-Adenosyl-L-methionine)-dependent methyltransferase and acts as one of the key enzymes in the teleocidin B biosynthesis pathway. Besides methyl transferring, TleD also rearranges the geranyl and indole moieties of the precursor to form a six-membered ring. Moreover, it does not show homologies with any known terpenoid cyclases. In order to elucidate how such a remarkable reaction could be achieved, we determined the complex crystal structures of TleD and the cofactor analogue S-Adenosyl-L-homocysteine with or without the substrate teleocidin A1. A domain-swapped pattern via an additional N-Terminal α-helix is observed in TleD hexamers. Structural comparison and alignment shows that this additional N-Terminal α-helix is the common feature of SAM methyltransferase-like cyclases TleD and SpnF. The residue Tyr21 anchors the additional N-Terminal α-helix to a 'core SAM-MT fold' and is a key residue for catalytic activity. Molecular dynamics simulation results suggest that the dihedral angle C23-C24-C25- C26 of teleocidin A1 is preferred to 60-90° in the TleD and substrate complex structure, which tend to adopt a Re-face stereocenter at C25 position after reaction and is according to in vitro enzyme reaction experiments. Our results also demonstrate that methyl transfer can be a new chemical strategy for carbocation formation in the terpene cyclization, which is the key initial step.

Teleocidin B is an indole terpenoid isolated from Streptomyces. Due to its unique chemical structure and ability to activate protein kinase C, it has attracted interest in the areas of organic chemistry and cell biology. Here, we report the identification of genes encoding enzymes for teleocidin B biosynthesis, including nonribosomal peptide synthetase (tleA), P-450 monooxygenase (tleB), prenyltransferase (tleC), and methyltransferase (tleD). The tleD gene, which is located outside of the tleABC cluster on the chromosome, was identified by transcriptional analysis and heterologous expression. Remarkably, TleD not only installs a methyl group on the geranyl moiety of the precursor but also facilitates the nucleophilic attack from the electron-rich indole to the resultant cation, to form the indole-fused six-membered ring. This is the first demonstration of a cation, generated from methylation, triggering successive terpenoid ring closure.

The potent tumor promoters, optically active teleocidins B-3 (3) and B-4 (4), were totally synthesized mostly using our synthetic pathway for the teleocidin A series.The key reaction, the BF3*Et2O-catalyzed intramolecular Friedel-Crafts cyclization, was applied at the final stage of the synthesis to the acetates (18a and 18b) to form the teleocidin B framework. KEYWORDS teleocidin B-3; teleocidin B-4; tumor promoter; total synthesis; BF3*Et2O-catalyzed reaction; intramolecular Friedel-Crafts reaction

First total syntheses of (+/-)-Teleocidin B-3(1c) and B-4(1d) were achieved by several functionalizing reactions starting from indole.

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The known metabolites, indole-3-aldehyde, indole-3-carboxylic acid, cyclo-Leu-Val, cyclo-Pro-Leu and phenyl acetamide were isolated from Streptoverticillium olivoreticuli together with pimprinin derivatives.Four more complex natural products having strong vesicatory toxicity, olivoretin A, B, C and D, were also isolated and based on the chemical correlation with D, A was proved to be O-methyl olivoretin D.By X-ray analysis the structure of olivoretin D, having strong epigenetic activities, was found to have exactly the same structure as teleocidin B.Keywords - Streptoverticillium olivoreticuli; olivoretin A; olivoretin B; olivoretin C; teleocidin B; isolation; 13C-NMR; X-ray analysis