Selective chemical modification of cyclomalto-oligosaccharides via tert-butyldimethylsilylation

Selective reaction of cyclomaltoheptaose and cyclomalto-octaose with tert-butylchlorodimethylsilane in N,N-dimethylformamide in the presence of imidazole gave the heptakis(6-O-tert-butyldimethylsilyl) (21) and octakis(6-O-tert-butyldimethylsilyl) (27) derivatives in yields of 70 and 67%, respectively. The twelve partially methylated regioisomers of cyclomalto-oligosaccharides, namely, hexakis(2- and 3-O-methyl, and 2,6- and 3,6-di-O-methyl)cyclomaltohexaoses, heptakis(2-, 3-, and 6-O-methyl and 2,3-, 2,6- and 3,6-di-O-methyl)cyclomaltoheptaoses, and octakis(6-O-methyl and 2,3-di-O-methyl)cyclomalto-octaoses, have been prepared crystalline by unambiguous routes using hexakis(6-O-tert-butyldimethylsilyl)cyclomaltohexaose (2), 21, and 27, respectively, as the key intermediates. The synthesis of several heptakis- and octakis-(6-substituted) derivatives of cyclomalto-heptaose and -octaose is also described.