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101.
J. Stephen Clark Rebecca P. Freeman Andrew W. Thomas Claire Wilson 《Tetrahedron letters》2004,45(47):8639-8642
A concise enantioselective synthesis of the cyclic ether core of the marine natural product (+)-laurenyne has been accomplished using ring-closing metathesis for medium-ring construction. 相似文献
102.
Venkatraman S Njoroge FG Girijavallabhan V McPhail AT 《The Journal of organic chemistry》2002,67(8):2686-2688
A novel synthesis of cis and trans substituted 4-tert-butoxycarbonyl cyclohexylglycines via asymmetric aminohydroxylation of vinyl styrene followed by reduction of the aromatic ring and subsequent oxidation is reported. 相似文献
103.
Bashall A Bond AD Doyle EL García F Kidd S Lawson GT Parry MC McPartlin M Woods AD Wright DS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(15):3377-3385
Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported. 相似文献
104.
Blackmore IJ Gibson VC Hitchcock PB Rees CW Williams DJ White AJ 《Journal of the American Chemical Society》2005,127(16):6012-6020
The 2,6-bis(alpha-iminoalkyl)pyridines 2,6-[ArNC(CR(3))](2)C(5)H(3)N [R = H, D; Ar = 2,6-i-Pr(2)C(6)H(3) (DIPP), 2,6-Me(2)C(6)H(3) (DMP)] react with MeLi in Et(2)O to give a binary mixture of products: the pyridine N-methylated species 2,6-[ArNC(CR(3))](2)C(5)H(3)N(Me)Li(OEt(2)) and the deprotonated/dedeuterated species 2-[ArNC(CR(3))],6-[ArNC(=CR(2))]C(5)H(3)NLi(OEt(2)). For R = D, the product ratio is 2:1 in favor of the N-methylated product, while, for R = H, the deprotonated product is favored by 5:1, increasing to 8:1 in toluene solvent. Warming solutions of the N-methylated species leads to clean conversion to the thermodynamically preferred deprotonated species. Crossover experiments show that MeLi is re-formed and dissociates from the terdentate ligand before deprotonating the ketimine methyl unit. For MgR(2) (R = Et, i-Pr) and ZnR(2) (R = Et) reagents, N-alkylation products are formed exclusively, but derivatives containing bulky aryl substituents are found to undergo further rearrangement to 2-alkylated species, arising by migration of the alkyl group of the N-alkyl moiety to the adjacent ring carbon atom. The reversibility of the N-alkylation process has been probed using deuterio-labeled Mg alkyl reagents and mixed alkyl zinc species. A cationic zinc derivative is shown to undergo "reverse" alkyl migration, from the heterocycle nitrogen atom to the zinc center. EPR spectroscopy reveals a paramagnetic intermediate in which the unpaired electron is delocalized over the heterocycle and di-imine moieties of the ligand, indicating that the N-alkylation reactions proceed via single electron-transfer processes. 相似文献
105.
Reactions of trialkylboranes with 2-lithio-2-alkyl-1,3-benzodithioles followed by oxidation give ketones in good yields. This method is far less subject to steric hindrance than the analogous reactions using anions derived from bis(phenylthio)alkanes. 相似文献
106.
Gunnlaugsson T Leonard JP Sénéchal K Harte AJ 《Chemical communications (Cambridge, England)》2004,(7):782-783
The cationic cyclen based Eu(III)-phen conjugated 1.Eu was synthesised as a chemosensor for Cu(II), where the recognition in water at pH 7.4 gave rise to quenching of the Eu(III) luminescence and the formation of tetranuclear polymetallic Cu(II)-Eu(III) macrocyclic complexes in solution where Cu(II) was bound by three 1.Eu conjugates. 相似文献
107.
A reagent panel comprised of seven aryl beta-D-N-acetylneuraminides was synthesized and then used to probe the mechanisms of nonenzymatic hydrolysis. These reactions proceeded via four independent pathways: (1) acid-catalyzed hydrolysis of the neutral molecule; (2) acid-catalyzed hydrolysis of the anionic form, or its kinetic equivalent spontaneous hydrolysis of the neutral form; (3) spontaneous hydrolysis of the anionic form; and (4) a base-promoted pathway. The pH-independent spontaneous hydrolysis of 4-nitrophenyl alpha-D-N-acetylneuraminide (5) occurs at a rate that is over 100 times faster than that of the corresponding reaction of 4-nitrophenyl beta-D-N-acetylneuraminide (4a). Spontaneous hydrolyses of four aryl beta-D-N-acetylneuraminides displayed a beta(lg) value of -1.24 +/- 0.16 (pH = 8.1, T = 100 degrees C), and at a pH value of 1.0 (50 degrees C), all seven panel members gave a beta(lg) value of 0.14 +/- 0.08. The aqueous ethanolyses of 4a and 5 gave similar products and displayed sensitivity parameters (m) in a standard Winstein-Grunwald analysis of -0.04 +/- 0.01 and +0.23 +/- 0.02, respectively. These results, plus the activation parameters calculated for the spontaneous hydrolyses of the anionic forms of 5 (DeltaH() = 116 +/- 2 kJ mol(-1) and DeltaS = 27 +/- 4 J mol(-1) K(-1)) and 4a (DeltaH = 138 +/- 3 kJ mol(-1) and DeltaS = 59 +/- 8 J mol(-1) K(-1)), are inconsistent with anomeric carboxylate assistance occurring during the hydrolysis reactions, and the likely cause for the enhanced reactivity of 5 in comparison to that of 4a is an increase in ground-state steric strain. 相似文献
108.
Bond AD Derossi S Jensen F Larsen FB McKenzie CJ Nelson J 《Inorganic chemistry》2005,44(17):5987-5989
Treatment of cryptand L(1) with Cu(II) generates a H3O2(-)-bridged dicopper(II) cryptate, 2, where the guest anion has responded to steric constraint by a significant shortening of the O-O distance to 2.325(9) A; computational optimization at the B3LYP/6-31(d) level suggests that the bridging O-H...O H-bond is bent (approximately 157 degrees) but that the barrier to interchange of the bridging H atom is low (<4 kJ mol(-1)). This cryptate, rather than the [Cu2L(1)muCN]3+ species recently claimed to derive from cleavage of the C-C bond of the solvent, is the product of acetonitrile recrystallization of the initially formed reaction product, 1. 相似文献
109.
Yuko Ogata Pamela M. Quizon Nancy S. Nightlinger Pongkwan Sitasuwan Casey Snodgrass L. Andrew Lee Jeffrey D. Meyer Richard S. Rogers 《Rapid communications in mass spectrometry : RCM》2022,36(3):e9222
Rationale
The multi-attribute method (MAM) has become a valuable mass spectrometry (MS)-based tool that can identify and quantify the site-specific product attributes and purity information for biotherapeutics such as monoclonal antibodies (mAbs) and fusion molecules in recent years. As we expand the use of the MAM at various stages of drug development, it is critical to enhance the sample preparation throughput without additional chemical modifications and variability.Methods
In this study, a fully automated MAM sample preparation protocol is presented, where rapid desalting in less than 15 minutes is achieved using miniaturized size-exclusion chromatography columns in pipette tips on an automated liquid handler. The peptide samples were analyzed using an electrospray ionization (ESI) orbitrap mass spectrometer coupled to an ultra-high-performance liquid chromatography (UHPLC) system with a dual column switching system.Results
No significant change was observed in product attributes and their quantities compared with manual, low-artifact sample preparation. The sample recovery using the buffer exchange tips was greatly enhanced over the manual spin cartridges while still demonstrating excellent reproducibility for a wide variety of starting sample concentrations. Unlike a plate desalting system, the individual columns provide flexibility in the number of samples prepared at a time and sample locations within plates.Conclusions
This automated protocol enables the preparation of up to 96 samples with less “at-bench” time than the manual preparation of a smaller batch of samples, thereby greatly facilitating support of process development and the use of the MAM in quality control.110.
The product from the fluorination of pyridine by KCoF4 at ca. 220° contains eleven fluoropyridines, two fluoro-2-azahex-enes, three azahexa- dienes, and two fluoro-N-methylpyrrolidines, besides an azacyclohexa-1,3- diene. Four products were isolated from a fluorination of pyridine by CoF3 at ca. 150°, a 2-azahexene, two N-methylpyrrolidines, and 4H-nona- fluoropiperidine. 相似文献