- Tridentate Nickel(II)-Catalyzed Chemodivergent C-H Functionalization and Cyclopropanation: Regioselective and Diastereoselective Access to Substituted Aromatic Heterocycles
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A Schiff-base nickel(II)-phosphene-catalyzed chemodivergent C-H functionalization and cyclopropanation of aromatic heterocycles is reported in moderate to excellent yields and very good regioselectivity and diastereoselectivity. The weak, noncovalent interaction between the phosphene ligand and Ni center facilitates the ligand dissociation, generating the electronically and coordinatively unsaturated active catalyst. The proposed mechanisms for the reported reactions are in good accord with the experimental results and theoretical calculations, providing a suitable model of stereocontrol for the cyclopropanation reaction.
- Nag, Ekta,Gorantla, Sai Manoj N. V. T.,Arumugam, Selvakumar,Kulkarni, Aditya,Mondal, Kartik Chandra,Roy, Sudipta
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supporting information
p. 6313 - 6318
(2020/09/02)
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- Identification of Novel Unspecific Peroxygenase Chimeras and Unusual YfeX Axial Heme Ligand by a Versatile High-Throughput GC-MS Approach
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Catalyst discovery and development requires the screening of large reaction sets necessitating analytic methods with the potential for high-throughput screening. These techniques often suffer from substrate dependency or the requirement of expert knowledge. Chromatographic techniques (GC/LC) can overcome these limitations but are generally hampered by long analysis time or the need for special equipment. The herein developed multiple injections in a single experimental run (MISER) GC-MS technique allows a substrate independent 96-well microtiter plate analysis within 60 min. This method can be applied to any laboratory equipped with a standard GC-MS. With this concept novel, unspecific peroxygenase (UPO) chimeras, could be identified, consisting of subdomains from three different fungal UPO genes. The GC-technique was additionally applied to evaluate an YfeX library in an E. coli whole-cell system for the carbene-transfer reaction on indole, which revealed the thus far unknown axial heme ligand tryptophan.
- Knorrscheidt, Anja,Püllmann, Pascal,Schell, Eugen,Homann, Dominik,Freier, Erik,Weissenborn, Martin J.
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p. 4788 - 4795
(2020/07/21)
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- Directed Evolution of a Cytochrome P450 Carbene Transferase for Selective Functionalization of Cyclic Compounds
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Transfers of carbene moieties to heterocycles or cyclic alkenes to obtain C(sp2)-H alkylation or cyclopropane products are valuable transformations for synthesis of pharmacophores and chemical building blocks. Through their readily tunable active-site geometries, hemoprotein "carbene transferases" could provide an alternative to traditional transition metal catalysts by enabling heterocycle functionalizations with high chemo-, regio-, and stereocontrol. However, carbene transferases accepting heterocyclic substrates are scarce; the few enzymes capable of heterocycle or cyclic internal alkene functionalization described to date are characterized by low turnovers or depend on artificially introduced, costly iridium-porphyrin cofactors. We addressed this challenge by evolving a cytochrome P450 for highly efficient carbene transfer to indoles, pyrroles, and cyclic alkenes. We first developed a spectrophotometric high-throughput screening assay based on 1-methylindole C3-alkylation that enabled rapid analysis of thousands of P450 variants and comprehensive directed evolution via random and targeted mutagenesis. This effort yielded a P450 variant with 11 amino acid substitutions and a large deletion of the non-catalytic P450 reductase domain, which chemoselectively C3-alkylates indoles with up to 470 turnovers per minute and 18000 total turnovers. We subsequently used this optimized alkylation variant for parallel evolution toward more challenging heterocycle carbene functionalizations, including C2/C3 regioselective pyrrole alkylation, enantioselective indole alkylation with ethyl 2-diazopropanoate, and cyclic internal alkene cyclopropanation. The resulting set of efficient biocatalysts showcases the tunability of hemoproteins for highly selective functionalization of cyclic targets and the power of directed evolution to enhance the scope of new-to-nature enzyme catalysts.
- Brandenberg, Oliver F.,Chen, Kai,Arnold, Frances H.
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supporting information
p. 8989 - 8995
(2019/06/13)
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- Tryptamine Synthesis by Iron Porphyrin Catalyzed C?H Functionalization of Indoles with Diazoacetonitrile
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The functionalization of C?H bonds with non-precious metal catalysts is an important research area for the development of efficient and sustainable processes. Herein, we describe the development of iron porphyrin catalyzed reactions of diazoacetonitrile with N-heterocycles yielding important precursors of tryptamines, along with experimental mechanistic studies and proof-of-concept studies of an enzymatic process with YfeX enzyme. By using readily available FeTPPCl, we achieved the highly efficient C?H functionalization of indole and indazole heterocycles. These transformations feature mild reaction conditions, excellent yields with broad functional group tolerance, can be conducted on gram scale, and thus provide a unique streamlined access to tryptamines.
- Hock, Katharina J.,Knorrscheidt, Anja,Hommelsheim, Renè,Ho, Junming,Weissenborn, Martin J.,Koenigs, Rene M.
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supporting information
p. 3630 - 3634
(2019/02/13)
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- Biocatalytic Strategy for Highly Diastereo- and Enantioselective Synthesis of 2,3-Dihydrobenzofuran-Based Tricyclic Scaffolds
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2,3-Dihydrobenzofurans are key pharmacophores in many natural and synthetic bioactive molecules. A biocatalytic strategy is reported here for the highly diastereo- and enantioselective construction of stereochemically rich 2,3-dihydrobenzofurans in high enantiopurity (>99.9% de and ee), high yields, and on a preparative scale via benzofuran cyclopropanation with engineered myoglobins. Computational and structure-reactivity studies provide insights into the mechanism of this reaction, enabling the elaboration of a stereochemical model that can rationalize the high stereoselectivity of the biocatalyst. This information was leveraged to implement a highly stereoselective route to a drug molecule and a tricyclic scaffold featuring five stereogenic centers via a single-enzyme transformation. This work expands the biocatalytic toolbox for asymmetric C–C bond transformations and should prove useful for further development of metalloprotein catalysts for abiotic carbene transfer reactions.
- Vargas, David A.,Khade, Rahul L.,Zhang, Yong,Fasan, Rudi
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supporting information
p. 10148 - 10152
(2019/07/04)
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- Myoglobin-Catalyzed C?H Functionalization of Unprotected Indoles
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Functionalized indoles are recurrent motifs in bioactive natural products and pharmaceuticals. While transition metal-catalyzed carbene transfer has provided an attractive route to afford C3-functionalized indoles, these protocols are viable only in the presence of N-protected indoles, owing to competition from the more facile N?H insertion reaction. Herein, a biocatalytic strategy for enabling the direct C?H functionalization of unprotected indoles is reported. Engineered variants of myoglobin provide efficient biocatalysts for this reaction, which has no precedents in the biological world, enabling the transformation of a broad range of indoles in the presence of ethyl α-diazoacetate to give the corresponding C3-functionalized derivatives in high conversion yields and excellent chemoselectivity. This strategy could be exploited to develop a concise chemoenzymatic route to afford the nonsteroidal anti-inflammatory drug indomethacin.
- Vargas, David A.,Tinoco, Antonio,Tyagi, Vikas,Fasan, Rudi
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supporting information
p. 9911 - 9915
(2018/07/31)
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- HFIP-promoted Bischler indole synthesis under microwave irradiation
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1,1,1,3,3,3-Hexafluoropropan-2-ol (HFIP) was found to be effective for the Bischler indole synthesis under microwave irradiation in the absence of a metal catalyst. Under the catalysis of HFIP, a wide range of α-amino arylacetones were successfully transf
- Yao, Guangkai,Zhang, Zhi-Xiang,Zhang, Cheng-Bei,Xu, Han-Hong,Tang, Ri-Yuan
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- Dearomative Indole (3 + 2) Reactions with Azaoxyallyl Cations - New Method for the Synthesis of Pyrroloindolines
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Herein, we report the first examples of the synthesis of pyrroloindolines by means of (3 + 2) dearomative annulation reactions between 3-substituted indoles and highly reactive azaoxyallyl cations. Computational studies using density functional theory (DFT) (B3LYP-D3/6-311G++) support a stepwise reaction pathway in which initial C-C bond formation takes place at C3 of indole, followed by ring closure to give the observed products. Insights gleaned from these calculations indicate that the solvent, either TFE or HFIP, can stabilize the transition state through H-bonding interactions with oxygen of the azaoxyallyl cation and other relevant intermediates, thereby increasing the rates of these reactions.
- DiPoto, Maria C.,Hughes, Russell P.,Wu, Jimmy
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supporting information
p. 14861 - 14864
(2015/12/08)
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- N -aminopyridinium salts as precursors for N-centered radicals - Direct amidation of arenes and heteroarenes
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Readily prepared N-aminopyridinium salts are valuable precursors for the generation of N-centered radicals. Reduction of these salts by single electron transfer allows for clean generation of amidyl radicals. It is shown that direct radical C-H amination of heteroarenes and arenes can be achieved with N-aminopyridinium salts under mild conditions by using photoredox catalysis.
- Greulich, Tobias W.,Daniliuc, Constantin G.,Studer, Armido
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supporting information
p. 254 - 257
(2015/03/05)
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- Amide-Functionalized Naphthyridines on a RhII-RhII Platform: Effect of Steric Crowding, Hemilability, and Hydrogen-Bonding Interactions on the Structural Diversity and Catalytic Activity of Dirhodium(II) Complexes
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Ferrocene-amide-functionalized 1,8-naphthyridine (NP) based ligands {[(5,7-dimethyl-1,8-naphthyridin-2-yl)amino]carbonyl}ferrocene (L1H) and {[(3-phenyl-1,8-naphthyridin-2-yl)amino]carbonyl}ferrocene (L2H) have been synthesized. Room-temperature treatment of both the ligands with Rh2(CH3COO)4 produced [Rh2(CH3COO)3(L1)] (1) and [Rh2(CH3COO)3(L2)] (2) as neutral complexes in which the ligands were deprotonated and bound in a tridentate fashion. The steric effect of the ortho-methyl group in L1H and the inertness of the bridging carboxylate groups prevented the incorporation of the second ligand on the {RhII-RhII} unit. The use of the more labile Rh2(CF3COO)4 salt with L1H produced a cis bis-adduct [Rh2(CF3COO)4(L1H)2] (3), whereas L2H resulted in a trans bis-adduct [Rh2(CF3COO)3(L2)(L2H)] (4). Ligand L1H exhibits chelate binding in 3 and L2H forms a bridge-chelate mode in 4. Hydrogen-bonding interactions between the amide hydrogen and carboxylate oxygen atoms play an important role in the formation of these complexes. In the absence of this hydrogen-bonding interaction, both ligands bind axially as evident from the X-ray structure of [Rh2(CH3COO)2(CH3CN)4(L2H)2](BF4)2 (6). However, the axial ligands reorganize at reflux into a bridge-chelate coordination mode and produce [Rh2(CH3COO)2(CH3CN)2(L1H)](BF4)2 (5) and [Rh2(CH3COO)2(L2H)2](BF4)2 (7). Judicious selection of the dirhodium(II) precursors, choice of ligand, and adaptation of the correct reaction conditions affords 7, which features hemilabile amide side arms that occupy sites trans to the Rh-Rh bond. Consequently, this compound exhibits higher catalytic activity for carbene insertion to the C-H bond of substituted indoles by using appropriate diazo compounds, whereas other compounds are far less reactive. Thus, this work demonstrates the utility of steric crowding, hemilability, and hydrogen-bonding functionalities to govern the structure and catalytic efficacyof dirhodium(II,II) compounds.
- Sarkar, Mithun,Daw, Prosenjit,Ghatak, Tapas,Bera, Jitendra K.
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supporting information
p. 16537 - 16549
(2016/02/12)
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- NH4PF6-promoted cyclodehydration of α-amino carbonyl compounds: Efficient synthesis of pyrrolo[3,2,1-ij]quinoline and indole derivatives
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NH4PF6 is an inexpensive, safe, and low-toxicity inorganic salt; it was found to promote the cyclodehydration of α-amino carbonyl compounds in the absence of metal reagents. This simple cyclodehydration strategy enables highly atom-e
- Ji, Xiao-Ming,Zhou, Shu-Juan,Deng, Chen-Liang,Chen, Fan,Tang, Ri-Yuan
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p. 53837 - 53841
(2015/01/16)
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- Catalytic functionalization of indoles by copper-mediated carbene transfer
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The complex [TpBr3Cu(NCMe)] (TpBr3=hydrotris(3,4,5- tribromo)pyrazolylborate) efficiently catalyzes the C-H functionalization of indole derivatives at C3 by carbene transfer from different diazoesters in a high-yield transformation involving low catalyst loadings and short reaction times. This system has shown that the previously proposed dichotomy of carbene addition (to the double bond) vs carbene insertion (to the C-H bond) corresponds to two consecutive reaction steps: the cyclopropane intermediates, observed in the reaction mixtures, are the precursors of the final C-H functionalization derivatives in a ring-opening process involving acid catalysis. Those in situ generated cyclopropanes undergo nucleophilic ring opening with Me 2CuLi to afford both C2 and C3 functionalized indoles.
- Delgado-Rebollo, Manuela,Prieto, Auxiliadora,Perez, Pedro J.
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p. 2047 - 2052
(2014/08/05)
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- Synthesis and pharmacological evaluation of (indol-3-yl)alkylamides as potent analgesic agents
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A series of (indol-3-yl)alkylamides was synthesized and evaluated for analgesic activity. Two N-(pyridin-4-yl)acetamides, compounds 24 and 25, bearing benzyl or 4-fluorobenzyl moieties in 1-position of indole ring exhibited promising analgesic properties (ED50 = 8.1 and 11 mg/kg p.o., respectively), being as potent as the reference drugs flupirtine (CAS 56995-20-1), ibuprofen (CAS 15687-27-1) and diclofenac (CAS 15307-86-5). The two test compounds were tested for their anti-inflammatory activity by carrageenin-induced edema in rat paw test. 4-Fluorobenzyl derivative 25 whose ID50 was 0.085 ± 0.021 mmol/kg was selected as a lead compound for further pharmacomodulation.
- Fouchard,Marchand,Le Baut,Emig,Nickel
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p. 814 - 824
(2007/10/03)
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- Synthesis of 3,4-Bridged Indoles by Photocyclisation Reactions. Part 2. Photocyclisation of Halogenoacetyl Tryptophol Derivatives and α-Chloro Indol-3-ylalkanoate Esters
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Irradiation of the trichloroacetates 2, 4 and 5, derived from the corresponding tryptophols, in methanolic acetonitrile results in photocyclisation to the indole 4-position, and the formation of the pyrrolobenzoxocines 9-11.Attempted photocyclisation of the 'reversed' α-chloro esters 15a, 15b and 18 was thwarted by readily occurring elimination of HCl, although the dimethyl compound 15c did cyclise to give the cycloheptaindole 20 upon irradiation in acetonitrile.
- Beck, Anthony L.,Mascal, Mark,Moody, Christopher J.,Coates, William J.
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p. 813 - 822
(2007/10/02)
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