- Sphingosine and Phytosphingosine from D-Threose Synthesis of a 4-Keto-Ceramide
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Reaction of 2,4-O-benzylidene-D-threose 3 with tetradecyl magnesium bromide furnished D-arabino- and L-xylo-octadecane-1,2,3,4-tetrols 5a,x.Regioselective oxidation of the 4-OH group gave 4-keto-D-erythro-derivative 6 which can be reduced with acetaldehyde in a SmI2-catalyzed Tishtshenko reaction to afford exclusively 5a.Regioselective 2-O-mesylation of 5a ( -> 7a) and then acid catalyzed debenzylation afforded exclusively 2-O-mesyl-tetrol 9a.Reaction with NaN3 and ensuing azide reduction furnished D-ribo-C18-phytosphingosine (2) in high overall yield.Treatment of 2-O-mesyl derivatives 7a,x with NaN3 and then with 4-nitrobenzenesulfonyl chloride in pyridine afforded 11r,l.Elimination with DBU or, alternatively, by treatment with phenylselenide and then with H2O2, gave known 1,3-O-benzylidene protected azidosphingosine 14, which can be readily converted into sphingosine (1).Transformation of 2 into ceramide 15, selective 1,3-O-silyl protection, oxidation of the 4-OH group ( -> 17) and then desilylation afforded the 4-keto ceramide 18 found in a marine sponge.Reduction of 17 offers a convenient possibility for radioactive labelling of ceramides with tritium.
- Wild, Robert,Schmidt, Richard R.
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p. 2195 - 2208
(2007/10/02)
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- SYNTHESIS OF D-ribo- AND L-lyxo-PHYTOSPHINGOSINE: TRANSFORMATION INTO THE CORRESPONDING LACTOSYL-CERAMIDES
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2,4-O-Benzylidene-D-threose (2) reacted with tetradecylmagnesium bromide to give the D-arabino- and the L-xylo-octadecanetetrol derivatives 3a and 3x as a readily separable mixture.Each of these compounds was transformed, via regioselective mesylation, azide displacement, benzylidene cleavage, and azide reduction, into D-ribo- (1r) and L-lyxo-phytosphingosine (1l), respectively. 3,4-O-Isopropylidenation of the intermediate azido derivatives 7r and 7l afforded the 1-O-glycosyl acceptors 2-azido-3,4-O-isopropylidene-D-ribo-1,3,4-octadecanetriol (8r) and 2-azido-3,4-O-isopropylidene-L-lyxo-1,3,4-octadecanetriol (8l), respectively.With the trichloroacetimidate-activated lactosyl donor 9, the expected glycosydes 2-azido-1-O-(2,3,6,2',3',4'6'-hepta-O-acetyl-β-lactosyl)-3,4-O-isopropylidene-D-ribo- and L-lyxo-1,3,4-octadecanetriol (10r and 10l) were obtained, which were conveniently transformed into the corresponding unprotected glycosphingolipids 14r and 14l.
- Schmidt, Richard R.,Maier, Thomas
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p. 169 - 180
(2007/10/02)
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