Since it was preferable to obtain at each step of the synthesis on the soluble support complete conversion of the starting material to the expected product, we decided to use a tosyl group as a nitrogen protecting group which also makes the amine proton more acidic for the alkylation reaction. Tosylation of commercially available (L)-allylglycine was adapted from a known procedure.6 Esterification of 1 with MeOH in the presence of TMSCl yielded 2 which was smoothly alkylated with allyl bromide in the presence of potassium carbonate to give 4. Bifunctional poly(ethylene glycol) with an average mass of 3400 was used as the soluble support because it presents the right compromise between loading and good precipitation properties.2b Since the Ts group made allylglycine sensitive to racemization, we preferred to avoid classical coupling conditions and we chose a Mitsunobu reaction for anchoring the Ts allylglycine 1 on both of the hydroxyl groups of the PEG to give 3.7 Alkylation with allyl bromide in the presence of potassium carbonate yielded the PEG supported allyl allylglycine 5a.
J.; Jahed, N.; Sarbu, T.; Matyjaszewski, K., Characterization of α,ω-dihydroxypolystyrene by gradient polymer elution chromatography and two-dimensional liquid chromatography.
Soluble polymer supported divergent synthesis of ..
Cao  performed modification of zinc oxide using silica and trimethyl siloxane (TMS). The finest particles of ZnO were obtained by calcination of the precursor zinc carbonate hydroxide (ZCH). ZHC was obtained in a process of precipitation from substrates such as zinc sulfate heptahydrate (ZnSO4·7H2O), ammonium solution (NH4OH) and ammonium bicarbonate (NH4HCO3). The surface of the ZCH was then successively modified by an method using TEOS and hexamethyldisilazane (HMDS) in water. The ZHC functionalized in this way was calcined, to obtain ultrafine particles of ZnO. Modification of the ZnO particles made possible a solution to the problem of their agglomeration. Functionalization of the ZnO surface with an inorganic compound (silica) reduced the photocatalytic action of the oxide, while the organic compound (HMDS) increased the compatibility of the ZnO with an organic matrix. The highly transparent modified zinc oxide surface was found to provide excellent protection against UV radiation, which represents a significant advantage of the use of these modifying agents. A schematic representation of the synthesis of surface-modified ZnO ultrafine particles using an modification method is shown in .
19/12/2017 · Soluble polymer supp..
Representative procedure: Synthesis of 11e : Cinnamyl bromide (11.8 mg, 0.06 mmol) was added to poly(ethylene glycol) 3400 N-(diphenylmethylene) glycinate (80 mg, 0.02 mmol) and Cs2CO3 (39 mg, 0.12 mmol). The mixture was heated under microwave for 45 minutes. After cooling, the product was dissolved in CH2Cl2, then filtered. The filtrate was concentrated, dissolved in CH2Cl2, filtered and then, precipitated in Et2O. The product was filtered and dried in vacuo to yield 80 mg (98 %) of the title compound : IR (KBr) 2865 (m), 1736 (s), 1655 (s), 1459 (s), 1100 (m), 954 (m) cm-1 ; 1H NMR (CDCl3, Me4Si) 2.70-2.90 (m, 2 H), 3.50-3.80 (s large, 310 H), 4.05 - 4.15 (m, 1 H), 4.20 - 4.30 (m, 2 H), 5.90-6.15 (m, 1 H), 6.30-6.45 (d, = 15.5 Hz, 1 H), 7.10-7.40 (m, 13 H), 7.55-7.70 (m, 2 H) ; 13C NMR (CDCl3, Me4Si) 37.48, 64.44, 65.78, 69.36, 126.40, 127.49, 128.27, 128.40, 128.83, 128.86, 129.03, 129.18, 130.73, 133.08, 136.72, 137.68, 139.85, 171.17, 171.99
Polymer-supported chemistry has undergone a dramatic revival
The enormous breadth of chemical reactions performed in biological systems can be attributed to nature’s ability to construct highly ordered arrangements of catalytic functional groups, or enzyme active sites. In addition, many organisms have evolved the ability to assemble polyketide synthases (PKSs), or multienzyme complexes that are capable of performing multistep synthesis in a linear fashion. Chemists have tried to mimic nature’s efficiency by constructing multifunctional catalysts or by designing multicomponent reactions or multi-catalyst systems. What is still lacking is a system that mimics nature’s ability to form structurally precise collections of functional groups (active sites) in a modular fashion that enables not only catalysis but also multistep synthesis. This project will investigate the use of short helical peptides to display catalytic functional groups in a stereocontrolled fashion to achieve enzyme-like catalysis. This template approach will provide a new strategy for catalyst design and optimization that takes advantage of substrate preorganization and proximity to improve catalytic activity. The helical scaffold will also make possible the design and construction of multifunctional catalysts capable of performing multistep synthetic processes.