The chiral bicyclic imidazol derivatives 7 and X were obtained from D-glucose derivative 9 by a sequence of selective protection/deprotection and intramolecular SN2 reactions. Triols 7 and X are analogues of 6-epicastanospermine (4) and of 3,7a-diepialexine (6), respectively, and are potential glycosidase inhibitors. However, their anti-HIY activity proved to be only marginal.Introduction. -Naturally occurring N-containing 1 -deoxysugars have been discovered in several plants during the last decade [l]. They can be considered as polyhydroxylated piperidines (e.g. DNJ (l)), pyrrolidines (e.g. DMDP (2)), octahydroindolizines (e.g. castanospermine (3) and 6-epicastanospermine (4)), and hexahydro-1 H-pyrrolizines (e.g.
Some naturally occurring carbohydrates, of which several hydroxy groups had been selectively protected, were condensed with formamidine to give the expected imidazole derivatives in the D‐arabino (9), D‐lyxo (12), L‐xylo (17), D‐threo (21), and in the L‐ and D‐erythro (24) series. Introduction of a strong leaving group at the remaining free alcohol function of these products led at once to intramolecular SN2 cyclisation to the corresponding bicyclic aza sugar derivatives. This was followed by total deprotection to give the target aza sugars in the L‐xylo (7), L‐ribo (14), D‐arabino (19), as well as in the D‐threo (22) and the L‐ and D‐erythro (26) series. Inhibitory assays with four glycosidases showed that the D‐arabino aza sugar 19 is the only potent inhibitor (for an α‐mannosidase of jack bean).
The syntheses of all four imidazolo-piperidino-pentoses in the L-series ent-2 to ent-5, and of three out of the four possible stereomers in the D-series 3, 4, and 5, are reported. The linear imidazolo sugar precursors were prepared, either by double condensation of formamidine with protected aldohexoses, or by nucleophilic addition of a lithiated imidazole derivative to protected aldotetroses. Cyclisation of these linear imidazolo-carbohydrates was performed by intramolecular S N 2 reactions. These were followed by deprotection to
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