Article

Halogenation of unactivated carbon centers in natural product biosynthesis: trichlorination of leucine during barbamide biosynthesis.

Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Journal of the American Chemical Society (Impact Factor: 11.44). 04/2006; 128(12):3900-1. DOI: 10.1021/ja060151n
Source: PubMed

ABSTRACT The in vitro reconstitution of leucine halogenation during barbamide biosynthesis has been accomplished. It has been demonstrated that the triple chlorination of the unactivated pro-R methyl group of the peptidyl carrier protein-tethered l-Leu substrate is carried out by the tandem action of two nonheme iron(II)-dependent halogenases, BarB1 and BarB2. Investigation of the substrate specificities of each of the halogenating enzymes revealed their complementary roles in the generation of trichloroleucine.

0 Followers
 · 
95 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Five lipopeptides of the lyngbyabellin structure class, four cyclic (1-3, and 5) and one linear (4), were isolated from the extracts of two collections of filamentous marine cyanobacteria obtained from Palmyra Atoll in the Central Pacific Ocean. Their planar structures and absolute configurations were elucidated by combined spectroscopic and chromatographic analyses as well as chemical synthesis of fragments. In addition to structural features typical of the lyngbyabellins, such as two thiazole rings and a chlorinated 2-methyloctanoate residue, these new compounds possess several unique aspects. Of note, metabolites 2 and 3 possessed rare mono-chlorination on the 3-acyloxy-2-methyloctanoate residue while lyngbyabellin N (5) had an unusual N,N-dimethylvaline terminus. Lyngbyabellin N also possessed a leucine statine residue, and showed strong cytotoxic activity against HCT116 colon cancer cell line (IC50 = 40.9 ± 3.3 nM).
    European Journal of Organic Chemistry 09/2012; 2012(27):5141-5150. DOI:10.1002/ejoc.201200691 · 3.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mononuclear nonheme Fe(II) (MNH) and alpha-ketoglutarate (α-KG) dependent halogenases activate O2 to perform oxidative halogenations of activated and non-activated carbon centers. While the mechanism of halide incorporation into substrate has been investigated, the mechanism by which halogenases prevent oxidations in the absence of chloride is still obscure. Here, we characterize the impact of chloride on the metal center coordination and reactivity of the fatty acyl-halogenase HctB. Stopped-flow kinetic studies show that the oxidative transformation of the Fe(II)-α-KG-enzyme complex is > 200-fold accelerated by saturating concentrations of chloride in both the absence and presence of covalently bound substrate. By contrast, the presence of substrate, which generally brings about O2 activation at enzymatic MNH centers, only has a ~ 10 fold effect in the absence of chloride. Circular dichroism (CD) and magnetic CD studies demonstrate that chloride binding triggers changes in the metal center ligation: chloride binding induces the proper binding of substrate as shown by variable-temperature, variable-field (VTVH) MCD studies of non-α-KG-containing forms and the conversion from 6 coordinate (6C) to 5C/6C mixtures when α-KG is bound. In the presence of substrate, a site with square pyramidal 5-coordinate geometry is observed, which is required for O2 activation at enzymatic MNH centers. In the absence of substrate an unusual trigonal bipyramidal site is formed, which accounts for observed slow, uncoupled reactivity. Molecular dynamics simulations suggest that the binding of chloride to the metal center of HctB leads to a conformational change in the enzyme that makes the active site more accessible to substrate and thus facilitates the formation of the catalytically competent enzyme-substrate complex. Results are discussed in relation to other MNH dependent halogenases.
    Journal of the American Chemical Society 05/2014; 136(26). DOI:10.1021/ja503179m · 11.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An iron-catalyzed carbodi- and trichloromethylation of activated alkenes with readily available dichloro- and tetrachloromethane has been developed. A diaryliodonium salt is used as an efficient oxidant in this transformation. This reaction tolerates a variety of functional groups and allows for a highly efficient synthesis of various chloro-containing oxindoles.
    Organic Letters 09/2014; 46(11). DOI:10.1021/ol502411c · 6.32 Impact Factor