Christian B W Stark

University of Hamburg, Hamburg, Hamburg, Germany

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Publications (7)31.1 Total impact

  • Jens Schmidt, Zeinab Khalil, Robert J Capon, Christian B W Stark
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    ABSTRACT: The heronapyrroles A-C have first been isolated from a marine-derived Streptomyces sp. (CMB-0423) in 2010. Structurally, these natural products feature an unusual nitropyrrole system to which a partially oxidized farnesyl chain is attached. The varying degree of oxidation of the sesquiterpenyl subunit in heronapyrroles A-C provoked the hypothesis that there might exist other hitherto unidentified metabolites. On biosynthetic grounds a mono-tetrahydrofuran-diol named heronapyrrole D appeared a possible candidate. We here describe a short asymmetric synthesis of heronapyrrole D, its detection in cultivations of CMB-0423 and finally the evaluation of its antibacterial activity. We thus demonstrate that biosynthetic considerations and the joint effort of synthetic and natural product chemists can result in the identification of new members of a rare class of natural products.
    Beilstein Journal of Organic Chemistry 01/2014; 10:1228-32. · 2.80 Impact Factor
  • Jens Schmidt, Christian B W Stark
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    ABSTRACT: The synthesis of 2-nitro-4-oligoprenyl substituted pyrrole derivatives relevant to the heronapyrroles and related natural products was investigated. Among numerous approaches nitration of a 3-farnesyl-substituted unprotected pyrrole using AcONO2 gave best results, albeit still with unsatisfactory yield and regioselectivity. Therefore, the synthesis of (-)-heronapyrrole C acid, an analogue of the naturally occurring antibiotic heronapyrrole C, carrying a bioisosteric carboxylate in place of the nitro group was examined. In lieu of the unsatisfactory nitration a regioselective acylation with Cl3CCOCl was carried out (> 8:1 regioselectivity; in contrast to the 1:1.3 ratio for the nitration). The trichloromethyl ketone was converted to the desired acid in a haloform reaction at the final stage of the synthesis. Further key steps of the analogue synthesis involved a position- and stereoselective Corey-Noe-Lin-dihydroxylation and an organocatalytic double Shi-epoxidation. A biomimetic polyepoxide cyclization cascade established the bis-THF backbone. Thus, (-)-heronapyrrole C acid was synthesized in 8 steps (14.5% overall yield) from commercially available starting materials.
    The Journal of Organic Chemistry 12/2013; · 4.56 Impact Factor
  • Jens Schmidt, Christian B W Stark
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    ABSTRACT: The first synthesis of (-)-heronapyrrole C, the enantiomer of a unique farnesylated 2-nitropyrrole natural product is described. With none of the chiral centers of heronapyrrole C originally assigned, we proposed the most likely natural configuration on the basis of a putative biosynthetic pathway. The key step of the synthesis is a biomimetic polyepoxide cyclization cascade to establish the bis-THF moiety. Thus, (-)-heronapyrrole C is synthesized in eight steps from commercially available starting materials.
    Organic Letters 07/2012; 14(16):4042-5. · 6.14 Impact Factor
  • Andrea-Katharina C Schmidt, Christian B W Stark
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    ABSTRACT: A new method to accomplish glycol cleavage to carboxylic (di)acids in one step using catalytic amounts of tetrapropylammonium perruthenate (TPAP) together with N-methylmorpholine N-Oxide (NMO) as the stoichiometric oxidant is presented. In addition to regenerating the active catalyst, the N-oxide stabilizes intermediary carbonyl hydrates and thereby shifts a crucial equilibrium. The mild oxidation protocol is applicable to a broad range of substrates providing the respective acids, diacids, or keto acids in high yields.
    Organic Letters 11/2011; 13(21):5788-91. · 6.14 Impact Factor
  • Daniel Aicher, Susanna Gräfe, Christian B W Stark, Arno Wiehe
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    ABSTRACT: The synthesis of novel β-functionalized derivatives of the clinically used photosensitizer Temoporfin has been achieved by nucleophilic addition reactions to a corresponding diketo chlorin. The β-substituted dihydroxychlorin products exhibit a strong absorption in the red spectral region, a high singlet oxygen quantum yield, and were found to be highly effective in in vitro assays against HT-29 tumor cells.
    Bioorganic & medicinal chemistry letters 10/2011; 21(19):5808-11. · 2.65 Impact Factor
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    Andrea-Katharina C Schmidt, Christian B W Stark
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    ABSTRACT: We present a simple, mild, and highly effective method for the direct conversion of primary alcohols to carboxylic acids. TPAP serves as the catalyst, and NMO·H(2)O plays a dual role, acting as the co-oxidant and as a reagent for aldehyde hydrate stabilization. This previously unknown stabilizing effect of geminal diols by N-oxides is the key for the efficiency of the overall transformation.
    Organic Letters 08/2011; 13(16):4164-7. · 6.14 Impact Factor
  • Daniel Aicher, Arno Wiehe, Christian Stark
    Synlett 01/2010; 2010(03):395-398. · 2.66 Impact Factor