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171.
A concise total synthesis of (+)-deoxocassine (1) and (−)-deoxoprosophylline (2) has been achieved for the first time from d-xylose. The key steps involved in these synthesis are alkyl Grignard reaction, SN2 substitution of mesylate by azide, Wittig reaction, and reductive amination. 相似文献
172.
Bhaskar Kandagatla Vetukuri Venkata Naga Kali Vara Prasada Raju Ganta Madhusudhan Reddy Sirigiri Chandrakanth Rao Javed Iqbal Rakeshwar Bandichhor Srinivas Oruganti 《Tetrahedron letters》2012,53(52):7125-7127
Agomelatine was synthesized from 8-aminonaphthalen-2-ol by diazotization-iodination, formylation, C–C bond formation by nitroaldol and Pd/C hydrogenation of β-nitrovinylnaphthalene followed by N-acetylation. The route reported employs readily and commercially viable starting materials and reagents, and can potentially be utilized for process synthesis of agomelatine. 相似文献
173.
A convenient and practical InCl3 catalyzed three-component reaction of 4-hydroxy coumarin/1,3 diones, aromatic aldehyde, and secondary amine for the synthesis of α-benzylamino coumarins and diketones in good yields has been reported. 相似文献
174.
High efficiency and less run time are the basic requirements of high-speed chromatographic separations. To fulfill these requirements, a new separation technique, ultra-performance liquid chromatography (UPLC), has shown promising developments. A rapid, specific, sensitive, and precise reverse-phase UPLC method is developed for the determination of nabumetone in tablet dosage form. In this work, a new isocratic chromatographic method is developed. The newly developed method is applicable for assay determination of the active pharmaceutical ingredient. The chromatographic separation is achieved on a Waters Acquity BEH column (100 mm, i.d., 2.1 mm, 1.7 μm) within a short runtime of 2 min using a mobile phase of 5 mM ammonium acetate-acetonitrile (25:75, v/v), at a flow rate of 0.3 mL/min at an ambient temperature. Quantification is achieved with photodiode array detection at 230 nm, over the concentration range of 0.05-26 μg/mL. Forced degradation studies are also performed for nabumetone bulk drug samples to demonstrate the stability-indicating power of the UPLC method. Comparison of system performance with conventional high-performance liquid chromatography is made with respect to analysis time, efficiency, and sensitivity. The method is validated according to the ICH guidelines and is applied successfully for the determination of nabumetone in tablets. 相似文献
175.
Vikas?D.?GhuleEmail author Dharavath?Srinivas S.?Radhakrishnan Pandurang?M.?Jadhav Surya?P.?Tewari 《Structural chemistry》2012,23(3):749-754
Density functional theory has been used to investigate geometries, heats of formation (HOFs), C-NO2 bond dissociation energies (BDEs), and relative energetic properties of nitro derivatives of azole substituted furan. HOFs for a series of molecules were calculated by using density functional theory (DFT) and Møller–Plesset (MP2) methods. The density is predicted using crystal packing calculations; all the designed compounds show density above 1.71 g/cm3. The calculated detonation velocities and detonation pressures indicate that the nitro group is very helpful for enhancing the detonation performance for the designed compounds. Thermal stabilities have been evaluated from the bond dissociation energies. Charge on the nitro group was used to assess the impact sensitivity in this study. According to the results of the calculations, tri- and tetra-nitro substituted derivatives reveal high performance with better thermal stability. 相似文献
176.
M. Ramesh B. Raju M. George K. Srinivas V. Jayathirtha Rao K. Bhanuprakash R. Srinivas 《Journal of mass spectrometry : JMS》2012,47(7):860-868
The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6‐tris(benzylamino)‐1,3,5‐triazine (1) and 2,4,6‐tris(benzyloxy)‐1,3,5‐triazine (6) show abundant product ion of m/z 181 (C14H13+). The likely structure for C14H13+ is α‐[2‐methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the ‘N’ analog (1) but low for the ‘O’ analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M + H‐toluene]+ and [M + H‐benzene]+ for compounds 1 and 6, respectively. The protonated 2,4,6‐tris(4‐methylbenzylamino)‐1,3,5‐triazine (4) exhibits competitive eliminations of p‐xylene and 3,6‐dimethylenecyclohexa‐1,4‐diene. Moreover, protonated 2,4,6‐tris(1‐phenylethylamino)‐1,3,5‐triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring ‘N’. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H‐shift from ring carbon to ‘O’ generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium‐labeling and CAD experiments combined with DFT calculations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
177.
DFP, a highly selective and potent COX-2 inhibitor, has been synthesized by a modified approach. Three modifications of the existing method enabled us to prepare DFP in good quantity. 相似文献
178.
Girish Chandra G. Rajaram Shiva Prasad V. Srinivas S. N. Shringi R. Krishnanc 《Hyperfine Interactions》1986,27(1-4):305-308
The distribution of hyperfine fields (HF) is obtained at room temperature for Fe37.5Ni37.5Cr5Mo2Si10B8 annealed at temperatures between 641 K and 744 K. P(H,T) is also derived for samples annealed at 744 K for over 70 hours.
Three steps are noted in the evolution of the crystalline phases: (1) separation of ∼ 35% of Fe atoms into environments with
low and high HF's, with increase in Tc for the remainder (2) nearly complete separation of the P(H) into these two components on further annealing at a higher temperature
and (3) at yet higher annealing temperatures, conversion of the high field phase into one with a lower HF. The observations
are tentatively explained in terms of preferential presence of Cr in one of the phases and its subsequent migration into the
other phase. 相似文献
179.
Hallur GurulingappaPhillip Buckhaults Srinivas K. KumarKenneth W. Kinzler Bert VogelsteinSaeed R. Khan 《Tetrahedron letters》2003,44(9):1871-1873
Aminophosphinic acid derivatives were synthesized as potential inhibitors of renal dipeptidase, an enzyme overexpressed in benign and malignant colon tumors. Several compounds showed potent enzyme-inhibitory activity. 相似文献
180.
R. Srikanth K. Bhanuprakash R. Srinivas Cathy Y. Wong Johan K. Terlouw 《Journal of mass spectrometry : JMS》2004,39(3):303-311
Protonated silanoic acid, HSi(OH)2+, 1a +, is cleanly generated by the dissociative electron ionization of triethoxysilane, HSi(OC2H5)3, and tetraethoxysilane, Si(OC2H5)4. This follows from tandem mass spectrometric experiments and CBS-QB3 model chemistry calculations. The calculations predict that 1a + (ΔHf(298 K) = 205 kJ mol−1) is separated by high barriers from its isomers HOSiOH2+, 1b + and HSi(O)OH2+, 1c +. Low-energy (metastable) ions 1a + dissociate by loss of H2O via the pathway 1a + → 1b + → SiOH+ + H2O. Analysis of the metastable peak for this process confirms that the isomerization step 1a + → 1b + is rate determining. The calculations further predict that the incipient ions 1b + communicate via a low barrier with the proton-bound dimer SiO···H···OH2+, 1d +. This dimer ion is much lower in energy than its counterpart OSi···H···OH2+, 1e +, which is calculated to be only marginally stable. A comparison of the potential energy diagram for the silicon-containing ions 1a +– 1e + with that of their carbon analogues reveals that the dissociation chemistries of HSi(OH)2+ and HC(OH)2+ are only superficially similar. Neutralization–reionization experiments confirm the theoretical prediction that the HSi(OH)2• radical (ΔHf(298 K) = −455 kJ mol−1) is a stable species in the rarefied gas phase. However, owing to a mismatch of Franck–Condon factors a large fraction of the neutralized ions dissociates by loss of H• yielding Si(OH)2. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献