Synthesis of N,N′-diglycosylated isoindigos

The first N,N′-diglycosylated isoindigos were prepared by P(NEt2)3-mediated dimerization of acetyl protected N-glycosyl-5-alkylisatins. Subsequent deacetylation yielded the corresponding deprotected N,N′-diglycosylated isoindigos. Isatine-N-glycosides containing an unsubstituted or alkyl-substituted heterocyclic moiety and β-D-manno- and β-L-rhamno configured carbohydrate substituents were successfully transformed into the corresponding isoindigos. In contrast, isatins with β-D-gluco- or β-D-xylo configured substituents failed to give the desired products.