- Enantioselective synthesis of a novel trans double bond ceramide analogue via catalytic asymmetric dihydroxylation of an enyne. The role of the trans double bond of ceramide in the fusion of Semliki Forest virus with target membranes
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Intensive interest is currently focused on the role of ceramide (1), a key lipid molecule that functions as a second messenger. The first asymmetric synthesis of a D-erythro-ceramide analogue that contains a C(5)C(6) trans double bond (3), together with its biological evaluation in a viral-liposome fusion system, is described. Sharpless asymmetric dihydroxylation of 4'- methoxyphenyl trans-5-octadecyn-2-enyl ether (enyne 8a), prepared by the coupling reaction of 1-[(E)-(4'-bromo-2'-butenyl)oxy]-4-methoxybenzene (7) with lithium tetradecyne, generated yne-diol 9 in 96% yield with the desired stereochemistry at the C(2) and C(3) positions and high enantiomeric purity (95% enantiomeric excess). Birch reduction (Li/EtNH2) of yne-diol 9 furnished (2R,3R,5E)octadecene-1,2,3-triol (10) stereospecifically. The latter was converted to 2-azido derivative 13 in three steps (via a 2-O- triflate-1,3-O-benzylidene intermediate) and 55% overall yield. Reduction of azide 13 and in situ N-acylation with p-nitrophenyl cis-hexadec-4-enoate provided D-erythro-Δ5-trans-ceramide (3) in 91% yield. The role of the trans double bond of ceramide in mediating fusion of an alphavirus (Semliki Forest virus) was assessed in a liposomal model system, using target phospholipid/cholesterol vesicles containing either D-erythroceramide 1 or 3. The kinetics of virus fusion, as monitored by a change in pyrene excimer fluorescence over a period of 60 s, showed that Δ5-trans-ceramide 3 was completely inactive, indicating that there is an absolute requirement for the trans double bond to be located between C(4) and C(5). These data indicate that the molecular determinants on the viral envelope glycoprotein are highly specific for recognition of the unsaturated site in the ceramide molecule.
- He, LinLi,Byun, Hoe-Sup,Smit, Jolanda,Wilschut, Jan,Bittman, Robert
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p. 3897 - 3903
(2007/10/03)
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- Regioselective and Stereospecific Azidation of 1,2- and 1,3-Diols by Azidotrimethylsilane via a Mitsunobu Reaction
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A one-pot regio- and stereospecific azidation reaction of 1,2- and 1,3-diols with azidotrimethylsilane (MB3SiN3) via a Mitsunobu reaction has been achieved. With 1,2- and 1,3-diols, the reaction of triphenylphosphine, diisopropyl azodicarboxylate, and Me3SiN3 in dichloromethane gave regioselective azidation at C-2 and C-3, respectively, in good yield (74-90% combined yield of 1a + 1b or of 2a + 2b). However, application of the same reaction conditions to a 1,4-diol led to the exclusive formation of the cyclic ether. The regioselectivity of this one-pot reaction is influenced by the solvent, the degree of steric bulk at C-2 of the 1,2-diol or at C-3 of the 1,3-diol, and the presence of electron-donating and electron-withdrawing groups near the secondary carbinol carbon. This selectivity is discussed in terms of the mechanistic model proposed by Mathieu-Pelta and Evans (Mathieu-Pelta, I.; Evans, S. A., Jr. J. Org. Chem. 1992, 57, 3409-3413), which involves reaction of the dioxaphospholane intermediate with Me3SiN3 to form oxyphosphonium ions 4 and 5.
- He, Linli,Wanunu, Meni,Byun, Hoe-Sup,Bittman, Robert
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p. 6049 - 6055
(2007/10/03)
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