Anhydro-3,4,6-tri-O-benzyl-/3-D-altropyranose (11) and 1,2-anhydro-3,4,6-tri-Obenzyl-ot-D-allopyranose (21) are useful monomers for stereoregular polymerization to aflbrd ot-(I -~ 2)-linked oΒ°aitropyranan o1" /3-(I ~ 2'l-linked D-allopyranan, which are valuable model compounds tbr immunological research [I], and may serve as glycosyl donors in the stereospecific synthesis of oligosaccharides [2] and other biomedical products [3]. According to the literature [4], altrose and allose derivatives occur
frequently as components of bioactive natural products. For example. Epipodophyllotoxin altrosides were used as antitumor agents to increase the mean survival time of mice inoculated with P388 k, ukaemia cells by 220% [5]. it was also reported that some oligosaccharides containing, altropyranose could be used as wound healing agents [6], and some aryl /3-D-allopyranosides were observed in the leaves of a higher plant (Protea rubropilosa) used in glycosidase-specificity studies [7]. These results have caused us to study the synthesis of the title anhydro sugars via an intramolecular SN2 reaction [8] of a C-2 alkoxide with a C-! bearing a leaving group, or an inverse ring closure [9] reaction of a C-I aikoxide with a C-2 attached to a leaving group. Thus, methyl 4,6Β°O-benzylidene-ot-D-altropyranoside (1) was prepared from D-glucose [10], and selective 2-O-allylation of l [11] gave methyl 2-O.allyl-4,6.0-benzylidene-a-Daltropyranoside (2) in satisfactory yield (78.7%). The structure of 2 was established from its ~H NMR spectrum by single frequency decoupling and further confirmed by the preparation of its derivatives (3,4). Carefully controlled acid-catalyzed debenzylidenation of 2 furnished methyl 2-O-allyl-a-o-altropyranoside (5), and benzylation of 5 " Corresponding author.