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631.
John Pal AP Kadigachalam P Mallick A Doddi VR Vankar YD 《Organic & biomolecular chemistry》2011,9(3):809-819
A series of sugar-derived spiroaminals has been synthesized by utilizing cross metathesis, ring closing metathesis and lactamization reactions as key steps from 1-C-alkylated glycosyl azides and important correlations in the spectral data between spiroaminals and their respective anomers are reported. 相似文献
632.
Kurhade SE Mengawade T Bhuniya D Palle VP Reddy DS 《Organic & biomolecular chemistry》2011,9(3):744-747
An efficient and convenient method for the synthesis of sugar-lactam conjugates is reported starting from readily available sugar azides using the Aubé reaction. Cyclic azido alcohols are used in the Aubé reaction for the first time in a carbohydrate setting. The resulting glycoconjugates could be further used to increase the chemical diversity on the sugar backbone, and may find potential applications as glycomimetics, peptidomimetics, in glycotargeting and in CNS drug delivery. 相似文献
633.
An efficient method for the stereoselective synthesis of l-ribose was accomplished starting from commercially inexpensive d-fructose. The intermediates in the process can serve as versatile precursors for the preparation of l-nucleoside analogues. 相似文献
634.
d-ribo-C18-phytosphingosine and l-arabino-C18-phytosphingosine were synthesised starting from commercially inexpensive d-fructose. Metal-mediated fragmentation and stereoselective reduction were used as key steps to provide the hydrophilic portion of d-ribo and l-arabino phytosphingosines. Grubbs’ cross-metathesis and hydrogenation allowed the incorporation of hydrophobic tail. 相似文献
635.
A 1,4 O→O silyl migration followed by nucleophilic substitution with phthalimide was observed under Mitsunobu reaction conditions. This one step secondary alcohol protection and primary alcohol substitution with N-nucleophiles was extended to a variety of 2-hydroxyethyl trialkylsilylether derivatives. A possible mechanism has been postulated based on the pKa values of the alcohol and nucleophile. The present one-pot silyl migration and substitution reaction might find application in the stereoselective synthesis of novel iminosugar derived anti diabetic agents. 相似文献
636.
The synthesis of 4 and 8 is reported. These intermediates are obtained by a one-pot tandem cyclization of 1 and 6, respectively, via Bischler Napieralski reaction followed by cyclopropylimine rearrangement. Compounds 4 and 8 were reduced by sodium borohydride in methanol to afford cytotoxic alkaloid (±)-crispine A and antileishmania compound (±)-harmicine. 相似文献
637.
An efficient, convenient, and novel one-pot method of 2,4,5-triaryl-1H-imidazoles synthesis using benzil, arene carbaldehydes, and ammonium acetate, catalyzed by uranyl nitrate hexahydrate [UO2(NO3)2·6H2O] supported on acidic alumina and resulting in good to excellent yields under heterogeneous conditions, is reported. Formation
of a reactants-catalyst complex was confirmed by UV-VIS spectral data. Antibacterial (MIC) and antioxidant activity of the
synthesized compounds was also studied. 相似文献
638.
Velvadapu V Paul T Wagh B Glassford I DeBrosse C Andrade RB 《The Journal of organic chemistry》2011,76(18):7516-7527
Novel sources of antibiotics are required to address the serious problem of antibiotic resistance. Telithromycin (2) is a third-generation macrolide antibiotic prepared from erythromycin (1) and used clinically since 2004. Herein we report the details of our efforts that ultimately led to the total synthesis of (-)-4,8,10-tridesmethyl telithromycin (3) wherein methyl groups have been replaced with hydrogens. The synthesis of desmethyl macrolides has emerged as a novel strategy for preparing bioactive antibiotics. 相似文献
639.
Analytical expressions are found for the wavenumbers and resonance frequencies in flexible, orthotropic shells using the asymptotic methods. These expressions are valid for arbitrary circumferential orders n. The Donnell-Mushtari shell theory is used to model the dynamics of the cylindrical shell. Initially, an in vacuo cylindrical isotropic shell is considered and expressions for all the wavenumbers (bending, near-field bending, longitudinal and torsional) are found. Subsequently, defining a suitable orthotropy parameter ?, the problem of wave propagation in an orthotropic shell is posed as a perturbation on the corresponding problem for an isotropic shell. Asymptotic expressions for the wavenumbers in the in vacuo orthotropic shell are then obtained by treating ? as an expansion parameter. In both cases (isotropy and orthotropy), a frequency-scaling parameter (η) and Poisson's ratio (ν) are used to find elegant expansions in the different frequency regimes. The asymptotic expansions are compared with numerical solutions in each of the cases and the match is found to be good. The main contribution of this work lies in the extension of the existing literature by developing closed-form expressions for wavenumbers with arbitrary circumferential orders n in the case of both, isotropic and orthotropic shells. Finally, we present natural frequency expressions in finite shells (isotropic and orthotropic) for the axisymmetric mode and compare them with numerical and ANSYS results. Here also, the comparison is found to be good. 相似文献
640.
I.N. PrakashB. Babu Ch. Venkata ReddyP. Narayana Murty Y.P. ReddyP. Sambasiva Rao R.V.S.S.N. Ravikumar 《Physica B: Condensed Matter》2011,406(17):3295-3298
EPR and optical absorption studies on Fe3+ and Mn2+ doped strontium tetraborate (SrB4O7) glasses are carried out at room temperature. The EPR spectrum of the Fe3+ doped glass consists of signals with g-values 9.04, 4.22 and 2.04, whereas the EPR spectrum of Mn2+ doped glass exhibits a characteristic hyperfine sextet around g=2.0. The spectroscopic analyses of the obtained results confirmed distorted octahedral site symmetry for the Fe3+ and Mn2+ impurity ions. Crystal field and Racah parameters evaluated from optical absorption spectra are: Dq=790, B=700 and C=3000 cm−1 for Fe3+doped glass and Dq=880, B=700 and C=2975 cm−1 for Mn2+ doped glass. 相似文献