Chiral transformations of D-ribose to 2-(β-D-ribofuranosyl)-L and D-glycine and an anhydroallose hemiacetal used in C-nucleoside synthesis

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Abstract
Conversion of D-ribose to the epimeric 3,6-anhydro-4,5,7-tri-O-benzyl-D-glycero-D-(allo and altro)-heptonamides (5) followed published methods. Mesylation of 5 allowed convenient separation of the 2-O-methanesulfonyl D-allo (6a) and D-altro (6b) diasteromers. Individual treatment of 6a and b with lithium azide in DMF provided the inverted 2-azido D-altro (7a) and D-allo (7b) products. Acid catalyzed hydrolysis of the amide funciton of 7a and b followed by catalytic hydrogenolysis of the benzyl protecting and azide groups gave the target glycosyl amino acids, 2-β-D-ribofuranosyl)-L-glycine (2-amino-3,6-anhydro-2-deoxy-D-glycero-D-altro-heptonic acid) (9a) and its D-glycine (D-allo) epimer (9).Deacylation of the known 2-(5-O-benzoyl-2,3-O-isopropylidene-β-D-ribofuranosyl)-1,3-diphenylimidazolidine (10a) followed by mild acid catalyzed deprotection of the masked aldehyde function of 10b gave 3,4-O-isopropylidene-2,5-anhydro-D-allose (11), a compound prepared previously in racemic form and used in C-nucleoside synthesis.