- The multicomponent approach to N-methyl peptides: Total synthesis of antibacterial (-)-viridic acid and analogues
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Two syntheses of natural viridic acid, an unusual triply N-methylated peptide with two anthranilate units, are presented. The first one is based on peptide-coupling strategies and affords the optically active natural product in 20% overall yield over six steps. A more economical approach with only four steps leads to the similarly active racemate by utilizing a Ugi four-component reaction (Ugi-4CR) as the key transformation. A small library of viridic acid analogues is readily available to provide first SAR insight. The biological activities of the natural product and its derivatives against the Gram-negative bacterium Aliivibrio fischeri were evaluated.
- Neves Filho, Ricardo A. W.,Stark, Sebastian,Westermann, Bernhard,Wessjohann, Ludger A.
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supporting information
p. 2085 - 2090
(2013/02/22)
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- A flexible asymmetric approach to methyl 5-alkyltetramates and its application in the synthesis of cytotoxic marine natural product belamide A
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By using a methyl tetramate derivative (R)- or (S)-9 as a novel chiral building block, a direct, flexible, and highly enantioselective approach to methyl (R)- or (S)-5-alkyltetramates (2) is disclosed. Among the synthesized methyl 5-alkyltetramates 2, met
- Lan, Hong-Qiao,Ye, Jian-Liang,Wang, Ai-E,Ruan, Yuan-Ping,Huang, Pei-Qiang
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experimental part
p. 958 - 968
(2011/03/20)
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- Synthesis and use of 2H-azirin-3-amines as dipeptide synthons
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The synthesis of the new 2H-azirin-3-amines ('3-amino-2H-azirines') 11, 20, 28, and 33 as dipeptide synthons is described. The reactions of the starting amides with Lawesson reagent gave the corresponding thioamides, and consecutive treatment with COCl2, 1,4-diazabicyclo[2.2.2]octane (DABCO), and NaN3 led to the desired products. It is shown that these 2H-azirin-3-amines can conveniently be used as building blocks of the dipeptides Aib-(Me)Axx (Axx=alanine, valine), Aib-Homoproline, and Iva-Pro in the synthesis of several model peptides. However, some limitations apply for the synthesis of such 2H-azirin-3-amines. The starting material for the azirine synthesis, the corresponding thioamides, cannot generally be synthesized, and the 2H-azirin-3-amines could not be obtained in all cases from the thioamides prepared.
- Breitenmoser, Roland A.,Heimgartner, Heinz
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p. 885 - 912
(2007/10/03)
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- 1-Ethyl 2-halopyridinium salts, highly efficient coupling reagents for hindered peptide synthesis both in solution and the solid-phase
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1-Ethyl-2-halopyridinium salts, BEP, FEP, BEPH and FEPH, were synthesized and proved to be very effective for the synthesis of hindered peptides containing N-methylated or C(α),C(α)-dialkylated amino acid residues. HPLC monitoring of model reactions indicated that these pyridinium salts demonstrated higher reactivities, lower racemization than the commonly used halogenated uronium and phosphonium salts. The efficiency of these pyridinium type coupling reagents was further proved by the synthesis of a series of hindered oligopeptides and active esters with good yields and convenient workup. The 8-11 tetrapeptide fragment of Cyclosporin A (CsA) and the pentapeptide moiety of Dolastatin 15 were also successfully synthesized using these pyridinium salts. The efficiency of these pyridinium type coupling reagents for SPPS was also demonstrated by the solid-phase synthesis of the extremely hindered 8-11 peptide segment of CsA and the linear undecapeptide of CsO. The mechanism of the pyridinium salt mediated coupling reactions was also studied by 1H NMR, IR and HPLC. It was proposed that the major reactive intermediates were the corresponding acyl halide and acyloxypyridinium salts of the N-protected amino acid or peptide. (C) 2000 Elsevier Science Ltd.
- Li, Peng,Xu, Jie-Cheng
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p. 8119 - 8131
(2007/10/03)
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- An efficient synthesis of N-methylamino acids and some of their derivatives
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N-Methylamino acid derivatives are obtained in high yield by a stereoselective one-pot procedure from hexafluoroacetone protected amino acids via N-chloromethylation and treatment with triethylsilane/trifluoroacetic acid.
- Spengler, Jan,Burger, Klaus
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- Synthesis of Microcolin B, a Potent New Immunosuppressant Using an Efficient Mixed Imide Formation Reaction
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Microcolin B, a potent new immunosuppressant isolated from blue-green alga Lyngbya majuscula off the Venezuelan coast, has been made using a methyl-directed asymmetric hydrogenation reaction with rhodium on alumina catalyst on lactone 4 for the synthesis of the key (R,R)-2,4-dimethyl-octanoic acid fragment 1. A new, direct mixed imide formation reaction was also developed for the production of the unusual prolylpyrrolen-2-one 2 portion of microcolin. The pentafluorophenyl ester of CBZ-proline 5 was reacted with the lithium imidate of lactam 6, providing the mixed imide in 80% yield. Coupling of acid 1 with the N-terminus of the tripeptide, followed by coupling with pyrrolylproline 2, gave microcolin B. The new mixed-imide forming reaction was also applied to a formal total synthesis of microcolin A. The pentafluorophenyl ester of TBS-protected cis-hydroxyproline was coupled with lactam 6, and the resultant imide was converted to the key pyrrolylproline made previously for microcolin A.
- Andrus, Merritt B.,Li, Wenke,Keyes, Robert F.
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p. 5542 - 5549
(2007/10/03)
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- (-)-Sandramycin: Total synthesis and characterization of DNA binding properties
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Full details of the total synthesis of the potent antitumor antibiotic (-)-sandramycin (1), a cyclic decadepsipeptide possessing a 2-fold axis of symmetry, is described and constitutes the first total synthesis of a member of the growing class of naturall
- Boger, Dale L.,Chen, Jyun-Hung,Saionz, Kurt W.
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p. 1629 - 1644
(2007/10/03)
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- Coupling N-Methylated Amino Acids Using PyBroP and PyCloP Halogenophosphonium Salts: Mechanism and Fields of Application
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PyBroP (1) and PyCloP (2), two halotripyrrolidinophosphonium hexafluorophosphates, are peptidecoupling reagents highly efficient for coupling N-methylated amino esters, in contrast with PyBOP (3), the hydroxybenzotriazolyl analogue.These halogenophosphonium salts 1 and 2 are convenient (one-pot reactions) stable solids soluble in conventional solvents.Use of them gave an excellent peptide yield with essentially no epimerization.Activation with these reagents probably involves the formation of an (acyloxy)phosphonium, as shown in the case of 2,4,6-trimethylbenzoic acid activation.In the case of reagents 1 and 2, oxazolone and/or a symmetrical anhydride were intermediates which were rapidly aminolyzed.In contrast, the benzotriazolyl ester intermediate which was formed with PyBOP (3) was poorly reactive with N-methylated amino esters.PyBroP (1) and PyCloP (2) were less efficient in the coupling of some Boc-amino acids because of N-carboxyanhydride formation; this was particularly the case when Boc-Val-OH or Boc-MeVal-OH was coupled with MeVal-OMe.
- Coste, Jacques,Frerot, Eric,Jouin, Patrick
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p. 2437 - 2446
(2007/10/02)
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- Acetylation of Pyrrolidine-2,4-diones: A Synthesis of 3-Acyltetramic Acids. X-Ray Molecular Structure of 3--5-isopropyl-1-methylpyrrolidine-2,4-dione
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Pyrrolidine-2,4-diones, prepared from the corresponding α-amino acid esters by condensation with ethoxycarbonylacetic acid, Dieckmann cyclisation, and hydrolysis-decarboxylation, are acylated at C-3 by the acid chlorides of saturated, unsaturated, and are
- Jones, Raymond C. F.,Begley, Michael J.,Peterson, Graeme E.,Sumaria, Suresh
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p. 1959 - 1968
(2007/10/02)
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