Synthesis of α-d-Glcp-(1→3)-α-d-Galf-(1→2)-α-l- Rhap constituent of the CPS of Streptococcus pneumoniae 22F. Effect of 3-O-substitution in 1,2-cis α-d-galactofuranosylation
The synthesis of the trisaccharide α-d-Glcp-(1→3)-α-d- Galf-(1→2)-l-Rhap (3) constituent of Streptococcus pneumonia 22F was achieved with complete diastereoselectivity. This is the first example of a synthesis of an internal α-d-Galf containing oligosaccharide of a pathogen microorganism. Allyl α-d-...
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2014
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_20462069_v4_n7_p3368_Gola http://hdl.handle.net/20.500.12110/paper_20462069_v4_n7_p3368_Gola |
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| Sumario: | The synthesis of the trisaccharide α-d-Glcp-(1→3)-α-d- Galf-(1→2)-l-Rhap (3) constituent of Streptococcus pneumonia 22F was achieved with complete diastereoselectivity. This is the first example of a synthesis of an internal α-d-Galf containing oligosaccharide of a pathogen microorganism. Allyl α-d-galactofuranoside, used as novel precursor of the internal Galf, allowed the introduction of an orthogonal group at O-3. The trichloroacetimidate method was used for the construction of 1,2-cis-α-d-galactofuranosyl linkage. The influence of the 3-O-substituent (PMB, Bz, PFBz, PMBz, TIPS) was evaluated in benzylated galactofuranosyl trichloroacetimidate donors in terms of yield and selectivity of α-d-Galf-(1→2)-α-l-Rhap product as well as donor rearrangement by-product. Complete stereoselectivity was observed with all protecting groups used in the Galf donor, but the 3-O-benzoyl substitution gave the best yield. Protective groups were also evaluated in the rhamnoside acceptor, benzyl substitution was a requirement for complete stereoselectivity. |
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