Christian B. W. Stark

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Organization: Universit?t Hamburg , Germany

Department: Institut für Organische Chemie

Title: (PhD)

TOPICS

Organic Chemistry

Chemicals
References

Synthesis of (+)-Greek Tobacco Lactone via a Diastereoablative Epoxidation and a Selenium-Catalyzed Oxidative Cyclization

Co-reporter:Stefan Leisering, Iker Riaño, Christian Depken, Leona J. Gross, Manuela Weber, Dieter Lentz, Reinhold Zimmer, Christian B. W. Stark, Alexander Breder, and Mathias Christmann

Organic Letters March 17, 2017 Volume 19(Issue 6) pp:

Publication Date(Web):March 3, 2017

DOI:10.1021/acs.orglett.7b00484

An asymmetric synthesis of the C11-homoterpenoid (+)-Greek tobacco lactone is developed starting from readily available (R)-linalool. The synthesis is comprised of four operations and features a diastereoablative epoxidation and an oxidative tetrahydropyran formation using vanadium-, palladium-, and selenium-catalyzed cyclizations.

Large-Scale Synthesis of Symmetric Tetramine Ligands by Using a Modular Double Reductive Amination Approach

Co-reporter:Maik Tretbar

European Journal of Organic Chemistry 2017 Volume 2017(Issue 46) pp:6942-6946

Publication Date(Web):2017/12/15

DOI:10.1002/ejoc.201700772

Tetramine ligands play an important role in a broad range of transition metal catalyzed transformations. We here present a flexible and modular approach to this class of ligands using a double reductive amination strategy. Thus, the target molecules were prepared in a highly efficient manner in only three steps, from commercially available starting materials. Excellent overall yields, of up to 96 % were reached. Notably, chiral C2-symmetric ligands are available using this procedure. All reactions are easily scalable and the tetramine ligands were obtained in excellent purity, while only a single chromatographic purification is required at the end of the three step sequence.

Total Synthesis of Cytospolide D and Its Biomimetic Conversion to Cytospolides M, O, and Q

Co-reporter:Gunnar Ehrlich and Christian B. W. Stark

Organic Letters 2016 Volume 18(Issue 19) pp:4802-4805

Publication Date(Web):September 16, 2016

DOI:10.1021/acs.orglett.6b02193

A total synthesis of cytospolide D, starting from l-glutamic acid, is described. The critical macrolactonization to the 10-membered lactone containing an (E)-configured double bond was successfully achieved by Shiina esterification. Conversion of cytospolide D to its bicyclic derivatives M, O, and Q was accomplished under mild conditions, lending support to the proposed biosynthetic hypothesis.

Diastereodivergente inverse Prenylierung von Indol- und Tryptophan-Derivaten: Totalsynthese von Amauromin, Novoamauromin und epi-Amauromin

Co-reporter:Dipl.-Chem. Jonas M. Müller ;Dr. Christian B. W. Stark

Angewandte Chemie 2016 Volume 128( Issue 15) pp:4877-4881

Publication Date(Web):

DOI:10.1002/ange.201509468

Abstract

Eine regio- und stereoselektive inverse Prenylierung von Indol- und Tryptophan-Derivaten wird präsentiert. Alle vier möglichen Stereoisomere sind durch diese Iridium-katalysierte Reaktion zugänglich. Die Stereoselektivität wird durch eine Kombination aus chiralem Phosphoramidit-Liganden mit einem achiralen Boran-Additiv gesteuert und kann abhängig von der Art des Borans vollständig umgekehrt werden. Es genügt somit nur ein Enantiomer des Liganden, um alle denkbaren Stereoisomere herzustellen. Das synthetische Potential der Methode wurde in einer kurzen Synthese von Amauromin und seinen zwei natürlichen Diastereomeren demonstriert.

Diastereodivergent Reverse Prenylation of Indole and Tryptophan Derivatives: Total Synthesis of Amauromine, Novoamauromine, and epi-Amauromine

Co-reporter:Dipl.-Chem. Jonas M. Müller ;Dr. Christian B. W. Stark

Angewandte Chemie International Edition 2016 Volume 55( Issue 15) pp:4798-4802

Publication Date(Web):

DOI:10.1002/anie.201509468

Abstract

A regio- and stereoselective reverse prenylation of indole and tryptophan derivatives is presented. All four possible stereoisomers are accessible through this iridium-catalyzed reaction. The stereoselectivity is controlled by a chiral phosphoramidite ligand in combination with an achiral borane additive and can be switched by changing the nature of the borane. One enantiomer of the ligand is thus sufficient to prepare all possible isomers. The synthetic potential of this method was demonstrated by a short total synthesis of amauromine and its two natural diastereomers.

An Aged Precatalyst Solution Leads to High Catalytic Activity: Oxidative Cyclization of 1,5-Dienes Using ppm Amounts of Ruthenium

Co-reporter:Juliane Adrian;Stefanie Roth; Christian B. W. Stark

ChemCatChem 2016 Volume 8( Issue 9) pp:1679-1684

Publication Date(Web):

DOI:10.1002/cctc.201600179

Abstract

The ruthenium tetroxide catalyzed direct oxidative cyclization is a powerful synthetic method for the diastereoselective preparation of THF diols from simple achiral 1,5-diene starting materials with significant relevance to target-oriented and natural product synthesis. We here report that an aged precatalyst solution exhibits an extraordinarily high reactivity. Thus, even at 50 ppm catalyst loading, impressive results were achieved with good to high yields and excellent diastereoselectivities for the four stereogenic centers that were established in this single-step transformation. Turnover numbers of up to 15 000 and turnover frequencies of up to 3660 h⁻¹ were obtained. The ageing effect was analyzed spectroscopically and a preliminary hypothesis to explain the reactivity is given. Finally, the generality of this effect in oxidative cyclization chemistry was demonstrated by using a set of substrates with different substitution patterns and different geometries of the reacting double bonds.

Modular and Stereodivergent Approach to Unbranched 1,5,9,n-Polyenes: Total Synthesis of Chatenaytrienin-4

Co-reporter:Juliane Adrian and Christian B. W. Stark

The Journal of Organic Chemistry 2016 Volume 81(Issue 18) pp:8175-8186

Publication Date(Web):August 26, 2016

DOI:10.1021/acs.joc.6b01051

An iterative strategy for the stereodivergent synthesis of unbranched 1,5,9,n-polyenes (and -polyynes) was investigated. Starting from a terminal alkyne the iteration cycle consists of a C3 extension (allylation), a chemoselective hydroboration, an alkyne reduction, and an oxidation of the associated alcohol with subsequent C1 homologation. Double bond geometry is controlled using stereoselective alkyne reductions, employing either the Lindlar hydrogenation protocol or an aluminum hydride reduction. In a model sequence it was demonstrated that the strategy is applicable to the synthesis of 1,5,9,n-polyenes with any possible double bond configuration accessible in equally high efficiency and selectivity. It is worth noting that our approach does not require any protecting group chemistry. Furthermore, using the same strategy, the first total synthesis of chatenaytrienin-4, the proposed unsaturated biosynthetic precursor of the bis-THF acetogenin membranacin, was examined. Thus, the all-cis 1,5,9-triene natural product was prepared in 15 steps from commercially available starting materials in 6% overall yield.

Mimicking the active site of aldehyde dehydrogenases: stabilization of carbonyl hydrates through hydrogen bonds

Co-reporter:A. J. K. Roth, M. Tretbar and C. B. W. Stark

Chemical Communications 2015 vol. 51(Issue 75) pp:14175-14178

Publication Date(Web):09 Jun 2015

DOI:10.1039/C5CC02831K

Aldehyde hydrates are important but highly unstable, transient intermediates in biological and synthetic oxidations to carboxylic acids. We here report N-oxides as the first class of chemical reagents capable of stabilizing such water adducts. This stabilizing effect (studied in solution and in the solid state) seems to be based on the formation of hydrogen bonds.

Total Synthesis of Muricadienin, the Putative Key Precursor in the Solamin Biosynthesis

Co-reporter:Juliane Adrian and Christian B. W. Stark

Organic Letters 2014 Volume 16(Issue 22) pp:5886-5889

Publication Date(Web):November 7, 2014

DOI:10.1021/ol502849y

The first total synthesis of muricadienin, the unsaturated putative precursor in the biosynthesis of trans- and cis-solamin is described. Key steps in the synthesis are a chemoselective hydroboration, a Z-selective Wittig reaction, and a Fries rearrangement for introducing the terminal α-substituted butenolide. Thus, muricadienin can be synthesized in 11 steps from commercially available starting materials in 42% overall yield.

Synthetic Endeavors toward 2-Nitro-4-Alkylpyrroles in the Context of the Total Synthesis of Heronapyrrole C and Preparation of a Carboxylate Natural Product Analogue

Co-reporter:Jens Schmidt and Christian B. W. Stark

The Journal of Organic Chemistry 2014 Volume 79(Issue 5) pp:1920-1928

Publication Date(Web):December 4, 2013

DOI:10.1021/jo402240g

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 the 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 eight steps (14.5% overall yield) from commercially available starting materials.

Total synthesis of (±)-paracaseolide A and initial attempts at a Lewis acid mediated dimerization of its putative biosynthetic precursor

Co-reporter:David S. Giera and Christian B. W. Stark

RSC Advances 2013 vol. 3(Issue 44) pp:21280-21284

Publication Date(Web):09 Sep 2013

DOI:10.1039/C3RA44590A

A short (5 steps) and highly efficient (25% overall yield) synthesis of paracaseolide A is described. Crucial steps are an α-iodination of a butenolide, a Suzuki coupling and a thermal Diels–Alder reaction. In attempts at Lewis acid catalyzed [4 + 2]-cycloadditions a set of novel dimerization products of the proposed biosynthetic paracaseolide A precursor were produced.

Biomimetic Synthesis and Proposal of Relative and Absolute Stereochemistry of Heronapyrrole C

Co-reporter:Jens Schmidt and Christian B. W. Stark

Organic Letters 2012 Volume 14(Issue 16) pp:4042-4045

Publication Date(Web):July 20, 2012

DOI:10.1021/ol300954s

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.

Synthesis of β-functionalized Temoporfin derivatives for an application in photodynamic therapy

Co-reporter:Daniel Aicher, Susanna Gräfe, Christian B.W. Stark, Arno Wiehe

Bioorganic & Medicinal Chemistry Letters 2011 21(19) pp: 5808-5811

Publication Date(Web):

DOI:10.1016/j.bmcl.2011.07.113

Mimicking the active site of aldehyde dehydrogenases: stabilization of carbonyl hydrates through hydrogen bonds

Co-reporter:A. J. K. Roth, M. Tretbar and C. B. W. Stark

Chemical Communications 2015 - vol. 51(Issue 75) pp:NaN14178-14178

Publication Date(Web):2015/06/09

DOI:10.1039/C5CC02831K