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71.
Gaul C Njardarson JT Shan D Dorn DC Wu KD Tong WP Huang XY Moore MA Danishefsky SJ 《Journal of the American Chemical Society》2004,126(36):11326-11337
The first asymmetric total synthesis of (+)-migrastatin (1), a macrolide natural product with anti-metastatic properties, has been accomplished. Our concise and flexible approach utilized a Lewis acid-catalyzed diene aldehyde condensation (LACDAC) to install the three contiguous stereocenters and the trisubstituted (Z)-alkene of migrastatin (2 + 3 --> 21). Construction of the two remaining stereocenters and incorporation of the glutarimide-containing side chain was achieved by an anti-selective aldol addition of propionyl oxazolidinone 28 to angelic aldehyde 27, followed by a Horner-Wadsworth-Emmons (HWE) coupling of 32 with glutarimide aldehyde 5. Finally, the assembly of the macrocycle was realized by a highly (E)-selective ring-closing metathesis (35 --> 37). Utilizing the power of diverted total synthesis (DTS), a series of otherwise inaccessible analogues was prepared and evaluated for their potential as tumor cell migration inhibitors in several in vitro assays. These studies revealed a dramatic increase in activity when the natural motif was considerably simplified, presenting macrolactones 45 and 48, as well as macrolactam 55, macroketone 60, and CF(3)-alcohol 71 as promising anti-metastatic agents. 相似文献
72.
Constrained peptides are promising next-generation therapeutics. Peptide stapling is a particularly attractive technique to generate constrained macrocycles with improved biological activity and metabolic stability. We introduce a biocompatible two-component stapling approach based on the reagent 2,6-dicyanopyridine and a pseudo-cysteine amino acid. Stapling can proceed either directly on-resin during solid-phase synthesis or following isolation of the linear peptide. The stapling reaction is orthogonal to natural amino acid side chains and completes in aqueous solution at physiological pH, enabling its direct use in biochemical assays. We performed a small screening campaign of short peptides targeting the Zika virus protease NS2B-NS3, allowing the direct comparison of linear with in situ stapled peptides. A stapled screening hit showed over 28-fold stronger inhibition than its linear analogue, demonstrating the successful identification of constrained peptide inhibitors.A synthetically straightforward and biocompatible peptide-stapling strategy that can be used directly in biochemical assays to identify constrained enzyme inhibitors. 相似文献
73.
1-(2′-Deoxy-5′-O-dimethoxytrityl-′-D -ribofuranosyl)-1 H-benzimidazole 3′-[(p-chlorophenyl)(2-cyanoethyl) phosphate] ( 6 ) has been synthesized from 1-(β-D -ribofuranosyl)-1H-benzimidazole ( 3b ) using regiospecific 2′-deoxygenation. The latter compound was obtained by glycosylation of benzimidazole with the D -ribose derivative 2 leading exclusively of the β-D -anomer. 相似文献
74.
Christoph Elschenbroich Fabian Gerson Hiroaki Ohya-Nishiguchi Christoph Wydler Axel Nissen 《Helvetica chimica acta》1977,60(8):2530-2538
Proton hyperfine data are reported for the radical anions of 1,8-di (propyn-1-yl)-naphthalene (I), 7,8,12,13-tetradehydro-10,11-dihydro-9H-cyclodeca[d,e]naphthalene (II) and 2,2′-di(propyn-1-yl)-biphenyl (III), as well as of 5,6,11,12-tetradehydro-7,8,9,10-tetrahydro-dibenzo[a,c]cyclodecene (IV) and its 8,8,9,9-tetradeuterio-derivative (IV-d4). The triple bonds in I and II can be regarded as roughly parallel, while those in IV (and IV-d4) may be considered as crossed. The π-spin distributions in I? to IV? are discussed in terms of simple MO models which suggest a weekly bonding interaction between the acetylenic fragments in IV?, in contrast to III? where such an effect appears to be negligible. The importance of an analogous interaction in I? and II? is difficult to deduce, since its inclusion into a MO model does not substantially affect the π-spin distribution in these radical anions. 相似文献
75.
Christoph Lübbert 《Journal of Geometry》1980,14(1):59-70
According to Strubecker an affine metric n-space (Jn,g) over a field F of char. 2 (n2) is called simply-isotropic if Radg is one-dimensional; let Fu be the totally isotropic direction w.r. to g. The group Bg of motions of (Jn,g) contains an invariant (2n–1)-dimensional subgroup G, called thelimit group (Grenzgruppe) which maps planes parallel to Fu into parallel ones. In case n=3, n=5, F= Strubecker [12], [13], [14] gave several factorizations G=GL oGR of G into a commutative product of subgroups acting 1-transitively (=regularly) on Jn.This note deals with all factorizations of this kind; it followes that n must be odd. A factorization is invariant under Bg iff n=3. Finally it is shown for each factorization of G how the space Jn can be made into a two sided incidence group and into a kinematic space in the sense of Karzel [5], and how the two structures are related to each other.
Herrn Professor Dr. Karl Strubecker zum 75. Geburtstag gewidmet 相似文献
Herrn Professor Dr. Karl Strubecker zum 75. Geburtstag gewidmet 相似文献
76.
Lambert C Nöll G Zabel M Hampel F Schmälzlin E Bräuchle C Meerholz K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(17):4232-4239
Two highly substituted azulene derivatives were synthesised by Pd-mediated dimerisation from the corresponding tolan species. One azulene derivative (2) has donor functionalities (dianisylaminophenyl and dianisylamino) in the 1-, 2-, 3- and 6-positions, while the other (1) has donors (dianisylaminophenyl) in the 2- and 6-positions and acceptors (nitrophenyl) in the 1- and 3-positions. Each azulene derivative shows strong bond length alternation in the solid state, determined by X-ray crystal analysis, and an intense CT band around 450-500 nm in its UV/Vis spectrum. The first-order hyperpolarisability of 1 and of 2 was measured by hyper-Rayleigh scattering and is about that of disperse red DR1. Both azulene derivatives show multiple oxidation processes. The intramolecular adiabatic ET behaviour of the mixed valence radical cations of 1 and of 2 was investigated by UV/Vis/NIR spectroelectrochemistry. The intervalence-CT band of 1(+) could be analysed by the Generalised Mulliken-Hush theory, which yields an electronic coupling V=1140 cm(-1) for the optically induced adiabatic hole transfer. 相似文献
77.
Self-assembly of amphiphilic hexapyridinium cations at the air/water interface and on HOPG surfaces.
Haofei Gong Dr. Björn Bredenkötter Dr. Christoph Meier Carola Hoffmann‐ Richter Dr. Ulrich Ziener Dr. Dirk G. Kurth Dr. Dirk Volkmer Prof. Dr. 《Chemphyschem》2007,8(16):2354-2362
Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues. 相似文献
78.
Alexandra Tsybizova Christopher Brenig Christoph Kieninger Bernhard Kräutler Peter Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(25):7252-7264
Aryl-cobalamins are a new class of organometallic structural mimics of vitamin B12 designed as potential ‘antivitamins B12’. Here, the first cationic aryl-cobinamides are described, which were synthesized using the newly developed diaryl-iodonium method. The aryl-cobinamides were obtained as pairs of organometallic coordination isomers, the stereo-structure of which was unambiguously assigned based on homo- and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the ‘beta’ or at the ‘alpha’ face of the cobalt-center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas-phase bond dissociation energies (BDEs) of the coordination-isomeric phenyl- and 4-ethylphenyl-cobinamides were determined by ESI-MS threshold CID experiments, furnishing (Co−C )-BDEs of 38.4 and 40.6 kcal mol−1, respectively, for the two β-isomers, and the larger BDEs of 46.6 and 43.8 kcal mol−1 for the corresponding α-isomers. Surprisingly, the observed (Co−C )-BDEs of the Coβ-aryl-cobinamides were smaller than the (Co−C )-BDE of Coβ-methyl-cobinamide. DFT studies and the magnitudes of the experimental (Co−C )-BDEs revealed relevant contributions of non-bonded interactions in aryl-cobinamides, notably steric strain between the aryl and the cobalt-corrin moieties and non-bonded interactions with and among the peripheral sidechains. 相似文献
79.
Christoph Meinel 《Angewandte Chemie (International ed. in English)》1984,23(5):339-347
In 1751, the Swedish chemist Johan Gottschalk Wallerius first differentiated between “pure” and “applied” chemistry, a distinction which was quickly adopted by the other branches of science. Behind this was a new scientific concept of chemistry which emphasized the importance of applying chemistry's accumulated knowledge and its capabilities of providing for the general economic benefit. It also provided chemistry with a new position within the hierarchy of the sciences as well as with a new function in society. The reasons behind and causes of the change in scientific perspective associated with this concept point to the social and institutional conditions under which this field has developed into an independent academic discipline. 相似文献
80.
Raska CS Parker CE Sunnarborg SW Pope RM Lee DC Glish GL Borchers CH 《Journal of the American Society for Mass Spectrometry》2003,14(10):1076-1085
A method has been developed for rapid and sensitive identification of epitope-containing peptides, based on direct MALDI-MS/MS analysis of epitope-containing peptides affinity bound to affinity beads. This technique provides sequence information of the epitope that allows unambiguous identification of the epitope either by database searching or de novo sequencing. With MALDI-MS, affinity beads with bound peptides can be placed directly on the MALDI target and analyzed. Coupling a MALDI source to an orthogonal injection quadrupole time-of-flight (QqTOF) mass spectrometer allows direct sequencing of the bound peptides. In contrast to ESI-MS/MS, elution of the affinity-bound peptides followed by additional concentration and purification steps is not required, thus reducing the potential for sample loss. Direct mass spectrometric sequencing of affinity-bound peptides eliminates the need for chemical or enzymatic sequencing. Other advantages of this direct MALDI-MS/MS analysis of epitope-containing peptides bound to the affinity beads include its sensitivity (femtomole levels) and speed. In addition, direct analysis of peptides on affinity beads does not adversely affect the high mass accuracy of a QqTOF, and database searching can be performed on the MS/MS spectra obtained. In proof-of-principle experiments, this method has been demonstrated on beads containing immobilized antibodies against phosphotyrosine, the c-myc epitope tag, as well as immobilized avidin. Furthermore, de novo sequencing of epitope-containing peptides is demonstrated. The first application of this method was with anti-FLAG-tag affinity beads, where direct MALDI MS/MS was used to determine an unexpected enzymatic cleavage site on a growth factor protein. 相似文献