The Grignard condensation of pyrrolinedione (I) with 7-chloroindol-1-ylmagnesium bromide (II) in toluene gives the monoaddition product (III), which is condensed with indol-1-ylmagnesium bromide (IV) to yield the disubstituted compound (V). The hydrogenation of (V) with H2 over Pd/C in DMF affords the tetrahydro derivative (VI), which is condensed with the aminosugar (VII) in DMF and dehydrogenated with DDQ or DBU to afford the adduct (VIII). Finally, the methylamino group of (VIII) is deprotected by means of TBAF in THF.
The intermediate aminosugar (VII) has been obtained as follows: The protection of the alcohol (IX) with Bn-Br and NaH in DMF gives the benzyl ether (X), which is oxidized with OsO4 and NaIO4 in acetone/THF to yield the aldehyde (XI). The cyclization of (XI) by means of Ts-OH in dioxane/water affords the lactol (XII), which is treated with diethylamino sulfurtrifluoride (DAST) to provide the glycosyl fluoride (XIII). The condensation of (XIII) with the benzylated glucose derivative (XIV) by means of AgClO4 and SnCl2 in THF/ethyl ether gives the disaccharide (XV). The reduction of the carbamoyl group of (XV) with LiAlH4 in refluxing THF yields the methylamino derivative (XVI), which is protected at the methylamino group with trimethylsilylethyl(p-methylphenyl)carbonate (teoc-O-PNP) to afford the carbamate (XVII). Finally, this compound is debenzylated by hydrogenation over Pd/C in ethanol/THF to afford the target aminosugar (VIII).
The cyclization of 3,4-bis(3-indolyl)-1-methylpyrroline-2,5-dione (I) by hydrogenation with H2 over Pd/C in DMF, followed by a treatment with TFA, gives the hexacyclic dione (II), which then is condensed with aminosugar (III) in refluxing methanol and dehydrogenated with DDQ in THF to afford the target glycoside.
The intermediate aminosugar (III) has been obtained as follows: The protection of the alcohol (IV) with Bn-Br and NaH in DMF gives the benzyl ether (V), which is oxidized with OsO4 and NaIO4 in acetone/THF to yield the aldehyde (VI). The cyclization of (VI) by means of TsOH in dioxane/water affords the lactol (VII), which is treated with diethylamino sulfurtrifluoride (DAST) to provide the glycosyl fluoride (VIII). The condensation of (VIII) with the benzylated glucose derivative (IX) by means of AgClO4 and SnCl2 in THF/ethyl ether gives the disaccharide (X). The reduction of the carbamoyl group of (X) with LiAlH4 in refluxing THF yields the methylamino derivative (XI), which is finally debenzylated by hydrogenation over Pd/C in ethanol/THF to afford the target aminosugar (III).