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1.
Adducts of the conjugate addition of benzylamine to enantiopure amides of aroylacrylic acid possess high enantiomeric and diastereomeric purity. A high degree of stereoselectivity has been achieved by means of crystallization-induced asymmetric transformation. A practical synthesis leading to dipeptides containing homophenylalanine is depicted. 相似文献
2.
Larisa Kuznetsova 《Journal of fluorine chemistry》2004,125(4):487-500
Enantiopure 1-acyl-3-hydroxyl-4-CF2H-azetidin-2-ones and 1-acyl-3-hydroxy-4-CF3-azetidin-2-ones serve as versatile intermediates for the syntheses of CF2- and CF3-containing α-hydroxy-β-amino acids, dipeptides, and taxoid anticancer agents. Both enantiomers of 3-hydroxy-4-CF2H-β-lactams can be obtained in high yields through the diethylaminosulfur trifluoride (DAST) reaction of the corresponding enantiopure 4-formyl-β-lactam that is prepared through [2+2] cycloaddition of acetoxyketene to a 3-methyl-2-butenaldimine, followed by enzymatic optical resolution and ozonolysis. (+)-3-Hydroxy-4-CF3-β-lactams and (−)-3-hydroxy-4-CF3-β-lactams can also be readily obtained in enantiopure form through [2+2] cycloaddition of a CF3-imine with a ketene, followed by enzymatic optical resolution. Practical processes for the preparations of these enantiopure 3-hydroxy-4-Rf-β-lactams as well as their synthetic applications are described. 相似文献
3.
Microcolumns with self-assembled particle frits for proteomics 总被引:1,自引:0,他引:1
LC-MS-MS experiments in proteomics are usually performed with packed microcolumns employing frits or outlets smaller than the particle diameter to retain the packing material. We have developed packed microcolumns using self-assembled particles (SAPs) as frits that are smaller than the size of the outlet. A five to one ratio of outlet size to particle diameter appears to be the upper maximum. In these situations the particles assembled into an arch over the outlet like the stones in a stone bridge. When 3 microm particles were packed into a tapered column with an 8 microm outlet, two particles bridged the outlet with 0.3 pl dead volume and perfect success rate. In peptide analysis by LC-MS, the peak width at half height was normally less than 6 s, compared to 12 s without SAPs. The LC-MS-MS system provided 37% sequence coverage (21 matched peptides) for a tryptically-digested sample of 10 fmol bovine serum albumin. We also describe application of the SAP principle to make disposable pipette tip columns with short pieces of fused-silica capillary as the outlet. 相似文献
4.
《Journal of Saudi Chemical Society》2014,18(5):520-527
The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin under varying conditions has been studied spectrophotometrically at 70 °C and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Gly-Tyr] and [ninhydrin], respectively. Increase in total concentration of CTAB from 0 to 70 × 10−3 mol dm−3 resulted in an increase in the pseudo-first-order rate constant (kψ) by a factor of ca. 3. Quantitative kinetic analysis of kψ − [CTAB] data was performed on the basis of pseudo-phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton) and Piszkiewicz model. A possible mechanism has been proposed and the kinetic data have been used to evaluate the micellar binding constants KS (268 mol−1 dm3 for Gly-Tyr) and KN (64 mol−1 dm3 for ninhydrin). 相似文献
5.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(35):10603-10606
A simple heat/cool cycle can be used to significantly affect the properties of a solution of a low‐molecular‐weight gelator at high pH. The viscosity and extensional viscosity are increased markedly, leading to materials with very different properties than when the native solution is used. 相似文献
6.
Dr. Carlos Cabezas Dr. Marcelino Varela Prof. José L. Alonso 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(23):6520-6525
Among the hundreds of peptide compounds for which conformations have been determined by using different spectroscopic techniques, the structure of the simplest dipeptide glycylglycine (Gly-Gly) is conspicuously absent. Herein, for the first time, solid samples of Gly-Gly have been vaporized by laser ablation and three different structures have been revealed in a supersonic expansion by Fourier transform microwave spectroscopy. The intramolecular hydrogen bonding interactions that stabilize the observed forms have been established based on the 14N nuclear quadrupole hyperfine structure. We have illustrated how conformer interconversion distorts the equilibrium conformational distribution, giving rise to missing conformers in the conformational landscape. 相似文献
7.
Vanessa L. Campo 《Tetrahedron》2009,65(27):5343-7358
This work describes the synthesis in solution of a series of related diketopiperazines with potential biological activities: cyclo(l-Pro-l-Ser), cyclo(l-Phe-l-Ser), cyclo(d-Phe-l-Ser) and the corresponding glycosylated analogs of the latter, cyclo[d-Phe-l-Ser(αGlcNAc)] and cyclo[d-Phe-l-Ser(βGlcNAc)]. The synthetic approach involved coupling reactions of -OH or O-glycosylated serine benzyl esters with NFmoc-protected amino acids (Pro or Phe), followed by one-pot deprotection-cyclization reaction in the presence of 20% piperidine in DMF. 相似文献
8.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(10):2704-2707
Controlled molecular assembly is an important approach for the synthesis of single‐component materials with diverse functions. Unlike traditional heat treatment or solvent modulation, cryogenic treatment at 77 K enabled the tunable transition of a self‐assembled diphenylalanine organogel into a hexagonal crystal. Under these conditions, the assembled molecules undergo an internal rearrangement in the solid state to form a well‐defined chiral crystal structure. Moreover, these assemblies exhibit enhanced emission. This strategy for the synthesis of single‐component supramolecular assemblies can create new functions by manipulating phase transitions. 相似文献
9.
《Tetrahedron letters》2019,60(38):151058
Due to the hazardous nature of CH2Cl2, regulatory authorities have imposed restrictions to minimize or even stop its use. It has therefore become imperative to identify environmentally benign solvents to replace it. Here we report on a bio derived solvent, γ-valerolactone, for the incorporation of the first amino acid onto p-alkoxybenzyl alcohol resin in solid-phase peptide synthesis. Satisfactory loading values (by a spectrophotometric method) were achieved. Furthermore, racemization and dipeptide formation were also checked and found to be acceptable. 相似文献
10.