440678-01-3Relevant academic research and scientific papers
Linear total synthetic routes to β-D-C-(1,6)-linked oligoglucoses and oligogalactoses up to pentaoses by iterative Wittig olefination assembly
Dondoni, Alessandro,Marra, Alberto,Mizuno, Mamoru,Giovannini, Pier Paolo
, p. 4186 - 4199 (2007/10/03)
Two complementary routes, A and B, have been followed for the stepwise iterative assembly of β-D-(1,6)-glucopyranose and galactopyranose residues through methylene bridges. In route A the building block was constituted by 2,3,4-tri-O-benzyl-6-O-tert-butyldiphenylsilyl (O-TBDPS) β-linked galactosylmethylenephosphorane, while in route B the building block was a β-linked formyl C-glycopyranoside with a similar orthogonal protection of hydroxy groups. In route A each cycle consisted of the reaction of the phosphorane building block with a sugar residue bearing a formyl group at the C-5 carbon atom (coupling) and transformation of the O-TBDPS-protected primary alcohol into the formyl group (arming). Accordingly, route A is defined as the aldehyde route. On the other hand, each cycle in route B involved the coupling of the sugar aldehyde building block with a substrate bearing a phosphorus ylide at C-6 and introduction of the phosphonium group in the arming step as a precursor of the ylide functionality. Accordingly, route B is defined as the ylide route. The efficiency of route A proved to be seriously hampered by the 1,2-elimination of BnOH under the basic reaction conditions of the Wittig olefination, giving rise to the formation of substantial amounts of enopyranose. On the other hand, the ylide route B proved to be more efficient since very good yields (70-93%) of the isolated Wittig products were obtained throughout four consecutive cycles. Individual olefins and polyolefins obtained by routes A and B using gluco and galacto substrates were reduced and debenzylated in one pot by H2/Pd(OH)2 to give the corresponding β-D-C-(1,6)-linked oligosaccharides up to the pentaose stage. The latter compounds were fully characterized by high-field NMR spectroscopy (500 MHz).
Improved iterative olefination approach to oligosaccharide mimics: Stereoselective synthesis of β-(1→6)-D-galactopentaose methylene isostere
Dondoni,Mizuno,Marra
, p. 6657 - 6660 (2007/10/03)
The title C-pentagalactoside featuring β-(1→6) ethylene bridges between the D-galactopyranose units has been prepared through four consecutive cycles comprising the Wittig reaction of a formyl C-galactoside building block with sugar phosphorane substrate
