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51.
52.
A convergent stereoselective synthesis of the C13-C34 fragment of (−)-mucocin is described. The salient features include (a) the bidirectional synthesis of the C-2 symmetric C13-C21 subunit, (b) regio- and stereoselective preparation of a 1,3-diol derivative from a diene activated by NBS via intramolecular nucleophilic sulfinyl group participation, (c) utilizing the self-metathesis reaction to prepare a functionalized C10 alkene, and (d) regio- and stereoselective intermolecular epoxide opening to construct the ether bond between C20 and C24. An organocatalytic α-hydoxylation has been employed to create the C4 stereogenic center of C1-C12 subunit. Attempted union of the two subunits utilizing the B-alkyl Suzuki coupling did not succeed. 相似文献
53.
Amir E Antoni P Campos LM Damiron D Gupta N Amir RJ Pesika N Drockenmuller E Hawker CJ 《Chemical communications (Cambridge, England)》2012,48(40):4833-4835
Incorporation of orthogonal functional groups into biodegradable polymers permits the fabrication of multi-layered thin films with improved adhesion and tunable degradation profiles. The bi-layer structure also allows for accurate control over small molecule release. 相似文献
54.
We prove lower bounds for the entropy of limit measures associated to non-degenerate sequences of eigenfunctions on locally symmetric spaces of non-positive curvature. In the case of certain compact quotients of the space of positive definite n × n matrices (any quotient for n = 3, quotients associated to inner forms in general), measure classification results then show that the limit measures must have a Haar component. This is consistent with the conjecture that the limit measures are absolutely continuous. 相似文献
55.
A stereoselective synthesis of the macrolactone core of the potent anticancer agent neopeltolide is disclosed. The key steps of the synthesis include asymmetric allylation using Krische' protocol, conjugate reduction using MacMillan's methodology, and an asymmetric hetero-Diels-Alder reaction using Jacobsen's catalyst. Substrate controlled diastereoselective 1,3-anti reduction of a keto alcohol, Luche reduction followed by Ireland-Claisen rearrangement, oxymercuration, and reductive lithiation are other key steps. 相似文献
56.
Raj Kumar Dubey Avadhesh Pratap Singh Nalini Dwivedi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):1038-1045
Abstract Reaction of tri-n-butyl tin(IV) chloride with the sodium salt of Schiff bases [salicylidene-2-aminopyridine (sapH), salicylidene-2-amino-4-picoline (sapicH), salicylidene-2-methyl-1-aminobenzene (o-smabH), salicylidene-4-methyl-1-aminobenzene (p-smabH), salicylidene-1- aminobenzene (sabH), salicylidene-3-nitro-1-aminobenzene (snabH)] in MeOH-C6H6 mixture in 1:1 molar ratio produced complexes of the type [Bun 3Sn(sb)] (where sb = Schiff bases). All complexes obtained were characterized by elemental analysis (C, H, N, and Sn), infrared (IR), nuclear magnetic resonance (NMR; 1H, 13C, and 119Sn), and TOF-MS spectroscopic studies. These complexes were found to be monomeric, colored viscous liquids and are soluble in polar solvents (methanol, ethanol, DMSO, and DMF). On the basis of 119Sn NMR observations, a five coordination geometry around tin(IV) atom in these complexes is proposed tentatively. 相似文献
57.
Nalini Joshi 《Studies in Applied Mathematics》1999,102(4):345-373
In this article, we find all possible asymptotic behaviors of the solutions of the second Painlevé equation y "=2 y 3 + xy +α as the parameter α→∞ in the local region x ≪α2/3 . We prove that these are asymptotic behaviors by finding explicit error bounds. Moreover, we show that they are connected and complete in the sense that they correspond to all possible values of initial data given at a point in the local region. 相似文献
58.
59.
Investigation of EDTA anticoagulant in plasma to improve the throughput of liquid chromatography/tandem mass spectrometric assays 总被引:2,自引:0,他引:2
Sadagopan NP Li W Cook JA Galvan B Weller DL Fountain ST Cohen LH 《Rapid communications in mass spectrometry : RCM》2003,17(10):1065-1070
In this study, EDTA and heparin are compared as anticoagulants with respect to their efficiency in preventing clot formation in plasma samples that were subsequently analyzed by liquid chromatography/tandem mass spectrometry (LC/MS/MS). A pilot in vivo pharmacokinetic study for the drug chlorpheniramine was conducted in which both EDTA and heparin plasma samples were collected simultaneously. All conditions except the anticoagulant were held constant during the pharmacokinetic study. Bioanalytical results were compared from samples transferred by manual pipette and by an automated liquid handler workstation. The concentration of chlorpheniramine in samples was determined by LC/MS/MS. Results from the analysis of variances (ANOVA) of log-transformed plasma chlorpheniramine concentrations were used to calculate 90% confidence intervals for the ratio least-squares mean values for anticoagulants and for transfer methods. Analytical concentrations of the drug chlorpheniramine were equivalent in heparin- and EDTA-containing plasma. Results suggest that the failure rate for transfer of EDTA plasma (50 micro L by automated workstation or manually) is less than that for heparinized plasma. As a consequence of these results, the vast majority of plasma samples in our laboratories are now collected in EDTA, which allows for use of automated sample transfer resulting in a three-fold timesaving over manual transfer using a single-channel pipette. The ability to use automation has resulted in improved efficiency and cost savings. 相似文献
60.
Raghavan S Reddy SR Tony KA Kumar ChN Varma AK Nangia A 《The Journal of organic chemistry》2002,67(16):5838-5841
Bromohydrins have been prepared from beta-methyl-gamma,delta-unsaturated sulfoxides with high regio- and stereoselectivity. The reaction proceeds via neighboring group participation of the sulfinyl moiety with inversion of sulfoxide configuration as proven by an (18)O labeling study and X-ray crystallography. 相似文献