Indirect approach to C-3 branched 1,2-cis-glycofuranosides: synthesis of aceric acid glycoside analogues.
Aceric acid (3-C-carboxy-5-deoxy-alpha-l-xylofuranose) residues are present in pectic polysaccharide rhamnogalacturonan II (RG II) in the form of synthetically challenging 1,2-cis-glycofuranosides. To access synthetic fragments of RG II incorporating aceric acid, a four-step procedure based on C-2 epimerisation of initially prepared 1,2-trans-glycofuranoside was developed. Readily available derivatives of branched-chain l-lyxofuranose bearing a 3-C-vinyl group as a masked 3-C-carboxyl group were investigated as potential precursors of aceric acid units. In the first step of the procedure, installation of a participating group at C-2 of the furanose ring ensured stereocontrol of the O-glycosylation, which was carried out with the thioglycoside of 2-O-acetyl-3,5-di-O-benzyl-3-C-vinyl-L-lyxofuranose. After the glycosylation step, the 2-O-acetyl group was removed, the free 2-OH group was oxidised and the resulting ketone was finally reduced to form the C-3-vinyl-L-xylofuranoside. The use of L-Selectride in the key reduction reaction was essential to achieve the required stereoselectivity to generate 1,2-cis-furanoside.
de Oliveira
Marcelo T
MT
School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK.
Hughes
David L
DL
Nepogodiev
Sergey A
SA
Field
Robert A
RA
D006027:Glycosides / Q000138:chemical synthesis*; D006031:Glycosylation; D010368:Pectins / Q000737:chemistry; D013237:Stereoisomerism; D013400:Sugar Acids / Q000737:chemistry*; D014994:Xylose / Q000031:analogs & derivatives* / Q000737:chemistry
C511260:3-C-carboxy-5-deoxyxylose; D006027:Glycosides; D013400:Sugar Acids; C042492:rhamnogalacturonan II; D010368:Pectins; D014994:Xylose