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RS Liu

Publications and source records attributed to RS Liu.

17 recordsLinked to original sources
PubMed2000

Facile synthesis of oxa- and azacyclic dienes via cycloalkenation of alkynyltungsten compounds. Stereoselective construction of tricyclic furan and pyran derivatives via intramolecular diels-alder reaction

A convenient and short synthesis of functionalized oxacyclic and azacyclic dienes is developed on the basis of organotungsten chemistry. Alkynyltungsten compounds bearing a tethered alcohol and amine are treated with aldehydes and BF(3).Et(2)O in cold diethyl ether to give tungsten-heterocyclic carbenium salts, further leading to tungsten-heterocyclic dienes via deprotonation with Et(3)N. Hydrodemetalation of these tungsten-heterocyclic dienes is performed by the action of anhydrous Me(3)NO in CH(3)CN. This method is applicable to the synthesis of a number of oxa- and azacyclic dienes, including those tethered with an electron-deficient olefin. The oxacyclic 1,3,8-nonatrienes and 1,3,9-decatrienes undergo intramolecular Diels-Alder reactions upon heating in toluene, yielding tricyclic tetrahydropyran and -furan derivatives with excellent diastereoselectivities.

Journal Article↗
PubMed2000

Correlation of substituent effects and energy levels of the two lowest excited states of the azulenic chromophore

[structure: see text] Experimental and calculated data show that the relative energy levels of the two lowest excited states of azulene are sensitive to the nature and position of substituents on the nonalternant hydrocarbon. Extending such investigations led to a rational explanation for some of the baffling data on azulenic bacteriorhodopsin analogues in the literature.

Journal Article↗
PubMed2000

31. Clinical Application of

Background and Purpose: [F-18]FDG has long been used for detection of the malignant tumors and assessment of the metabolic activity of the tumors. However, there are several drawbacks of FDG including hyperglycemic effect, nonspecific uptake on inflammation, sink phenomenon due to high accumulation of FDG in urinary tract, and physiologic uptake of FDG in the bowels and muscles, which may cause false positive as well as false negative results. [C-11]acetate, as a metabolic substrate of beta-oxidation, precursors of amino acid, fatty acid and sterol, has been proved useful in detecting various malignancies. The aim of this study is to assess the feasibility of clinical application of [C-11]acetate in oncology.Methods: High quality whole body images could be obtained by using large dosage (20 mCi) of [C-11]acetate and modern PET scanner. In the recent years, [C-11]acetate PET studies have been performed in 513 patients with various malignancies.Results: The results showed that [C-11]acetate is more accurate in detecting meningioma (accuracy 97%), glioma (91%), nasopharyngeal cancer (93%), lymphoma (85%), non-small cell cancer (81%), colon cancer (78%), renal cell cancer (80%), ovarian cancer (76%), than in detecting small cell cancer of lung, thyroid cancer, and pancreas cancer. The advantages of [C-11]acetate are less time consuming (whole procedure completed within 45 min after injection), no hyperglycemic effect and no sink phenomenon. The disadvantages are increased uptake in salivary glands, pancreas, and sometimes the bowels, which may cause either false positive or false negative results, and on-site-cyclotron dependent.Conclusion: In summary, [C-11]acetate is clinically useful in detecting various malignant tumors clinically and may play a complementary role to FDG.

Journal Article↗