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Peptide Metal–Organic Frameworks for Enantioselective Separation of Chiral Drugs
2017
We report the ability of a chiral Cu(II) 3D MOF based on the tripeptide Gly-L-His-Gly (GHG) for the enantioselective separation of metamphetamine and ephedrine. Monte Carlo simulations suggest that chiral recognition is linked to preferential binding of one of the enantiomers as result of either stronger or additional H-bonds with the framework that lead to energetically more stable diastereomeric adducts. Solid phase extraction (SPE) of a racemic mixture by using Cu(GHG) as extractive phase permits isolating more than 50% of the (+)-ephedrine enantiomer as target compound in only four minutes. To the best of our knowledge, this represents the first example of a MOF capable of separating ch…
Towards Waltheriones C and D: Synthesis of the Oxabicyclic Core
2017
A route to the oxabicyclic cores of the HIV cytoprotective quinolone alkaloids, waltheriones C and D, is described. The approach relies on a stereospecific transannular bromoetherification followed by reductive debromination. The route can also be rendered enantioselective via enzymatic reduction of a key intermediate (>99:1 er).
Allylpalladium( II ) Complexes with Aminophosphane Ligands: Solution Behaviour and X‐ray Structure of cis ‐[Pd(η 3 ‐CH 2 CHCHPh){Ph 2 PCH 2 CHPhNH(2,…
2004
A new β-aminophosphane L2 [Ph2PCH2CH(Ph)NH(2,6-C6H3iPr2)], bearing an asymmetric carbon atom and a vicinal prochiral nitrogen centre and (η3-allyl)palladium complexes of general formula [Pd(η3-C3H4R){η2-Ph2PCH2CH(Ph)NHAr}][PF6] (1−6) (R = H, Me or Ph and Ar = Ph or 2,6-C6H3iPr2) have been synthesised. NMR spectroscopic studies and a crystal structure analysis of complex 6 (R = Ph, Ar = 2,6-C6H3iPr2) confirmed the highly diastereoselective coordination of the nitrogen atom. Because of the allyl fluxionality and the presence of asymmetric centres, all the complexes exist in solution as mixtures of up to four diastereomers. For the monosubstituted allyl complexes [Pd(η3-C3H4R){Ph2PCH2CH(Ph)NHA…
Experimental and theoretical investigations for the tandem alkylation–isomerization reactions between unsaturated carboxylic acids and allyl halides
2003
Abstract—Alkylation of dienediolates from unsaturated carboxylic acids with allylic halides when followed by solventless thermaltreatment at 150 to 2008C afford rearranged products on a trend highly dependent on the acarbon substitution. Thus, 2,2-bisallylated acidswith H atoms at C-2 lead to its 1,3-shift, whereas 2-methyl-2,2-bisallylated acids lead to the corresponding Cope rearrangement product. Inthe latter case, this tandem allylation-Cope reaction lead, in a highly regio and diastereoselective way, to products not accessible from directalkylation. B3LYP/6-31G p energies for the compounds involved at these isomerizations are in reasonable agreement with the experiments,allowing to exp…
Synthesis and application of new iminopyridine ligands in the enantioselective palladium-catalyzed allylic alkylation
2014
A variety of iminopyridines were obtained by condensation of chiral amines with pyridine-2-carboxaldehyde and quinoline-8-carbaldehyde, or of aminoalkylpyridine derivatives with chiral ketones. These ligands were assessed in the enantioselective palladium catalyzed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate affording the product dimethyl 1,3-diphenylprop-2-enylmalonate in good yields and moderate enantioselectivities (up to 62% ee). Catalytic activity and enantioselectivity were found to be highly dependent upon the steric properties of the ligands. The best enantioselectivity (62% ee) was obtained by an iminopyridine based on a camphane skeleton. © 2014 …
Photochemical Generation of Cyclophanes from 1,3,5-Trisubstituted Benzenes with Chalcone Chromophores
2007
(E,E,E)-1,3,5-Tricinnamoylbenzene (7a) photodimerizes in solution to the [4.4.4](1,3,5)cyclophane 8a. The process consists of three consecutive steps in which cisoid enone conformations of 7a react in regio- and stereoselective anti-head-to-head cycloadditions. (E,E,E)-1,3,5-Tris(3-oxo-3-phenylpropenyl)benzene (13a), an isomer of 7 with reversed enone units, shows a single [2π+2π] cycloaddition of the same type. Due to steric reasons, it is afterwards not capable of intramolecular processes and oligomerizes by intermolecular photocycloadditions. Photolyses in the crystalline state yield dimers by topochemically controlled syn-head-to-tail processes (7a → 10a, 13a → 15a). An efficient dimeri…
Synthesis and Conformational Properties of Nonsymmetric Pillar[5]arenes and Their Acetonitrile Inclusion Compounds
2010
The catalytic cyclocondensation of 1-butoxy-4-methoxy-2,5-bis(methoxymethyl)benzene (1d) affords a statistical mixture of the regioisomeric pillar[5]arenes 3a–d in high yield. The alkoxy groups are arranged stereoselectively in a mode so that they avoid steric interactions. The rotation of the benzene rings is, at room temperature, fast in terms of the NMR timescale and leads to a de facto Cs symmetry for 3a–c and a C5h symmetry for 3d. All four structural isomers can encapsulate two CH3CN guest molecules. The structure determinations are based on four crystal structure analyses (constitutions) and NMR spectroscopic measurements (conformations).
Structure elucidation of the adducts formed by fjord region Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxides with deoxyguanosine.
1999
Model adducts to be used in the identification of biologically formed adducts were synthesized by reaction of fjord-region dibenzo[a,l]pyrene 11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE) and deoxyadenosine (dA). The (+/-)-anti-DB[a,l]PDE was reacted with dA in dimethylformamide at 100 degrees C for 30 min to give four DB[a, l]PDE-14-N(6)dA adducts: (-)-anti-trans (26%), (+)-anti-trans (26%), (-)-anti-cis (17%), and (+)-anti-cis (17%). The (+/-)-syn-DB[a,l]PDE was reacted with dA under the same conditions to yield four DB[a, l]PDE-14-N(6)dA adducts and one N7Ade adduct: (+)-syn-cis (19%), (+)-syn-trans (13%), (-)-syn-cis (19%), (-)-syn-trans (13%), and (+/-)-syn-DB[a,l]PDE-14-N7Ade (22%). T…
ChemInform Abstract: Catalytic Activity of Large-Pore High Si/Al Zeolites: Cracking of Heptane on H-Beta and Dealuminated HY Zeolites
1988
Abstract The catalytic activity, selectivity, catalyst decay, thermal and hydrothermal stability, and acidity of H-Beta and HY zeolites with Si Al ratios of 7.5 and 10, respectively, have been studied during cracking of n-heptane at 450 °C and atmospheric pressure. It has been found that the H-Beta zeolite is more active and decays more slowly than HY. H-Beta presents a higher steric hindrance for dibranched molecules and therefore its open structure should be smaller than that of HY. A lower hydrogen transfer activity and hydrothermal stability is observed for H-Beta in comparison with the corresponding HY.
Ligand Effects on the Chemoselectivity of Ortho-Metalated Rhodium(II) Catalyzed α-Diazo Ketone Transformations
1997
Rh2(OOCR)2(PC)2 complexes (PC = orthometalated phosphines, OOCR = carboxylates) with very polarizable ligands, such as aromatic rings directly joined to the rhodium atoms, control chemoselectivity in competitive metal carbene transformations of α-diazo ketones. These catalysts have a mixed set of ligands that allows choosing among a big selection of ligands to gradually affect the electronic and steric properties of the catalyst. Their selectivity depends on the electrophilicity of the ligands and the polarizability of the metalated aromatic rings. Thus, Rh2(OOCR)2(PC)2 compounds [PC = (C6H4)P(CH3)(C6H5), (p-CH3C6H3)P(p-CH3C6H4)2, (C6H4)P(C6H5)2; R = C3F7 or CF3] exhibit an exceptional sele…