Synthetic Studies of Cellulose.

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For the synthesis of cellulose, We have to solve two problems ; 1) regiospecific control : glycosylation of the hydroxyl group at the 0-4 position of the glucopyranosyl residue has to be performed, 2) stereospecific control : glucosidic linkage of glucopyranosyl residues of beta-configuration has to be made. The first problem is solved by use of 2, 3, 6-tri-0-substituted glucopyranose derivatives as a starting material, but the main obstacle in the synthesis lies in the second problem, beta-glycosylation, although there are many newly-developed glycosylation methods and extensive data on glycosylation reactions. First of all, we have planned the synthesis of cello-oligosaccharides for obtaining information about beta-glycosylation before the synthesis of cellulose, and succeeded in the synthesis of a series of cello-oligosaccharides derivatives up to octamer. Now, we have following useful information about glycosylation reactions. 1) The imidate method is the best one for beta-glycosylation. 2) Benzyl protective groups introduced into hydroxyl groups at 2, 3, 6-positions of glucose are more effective than acyl groups for the high yield beta-glycosylation. 3) In the cade of acyl derivatives, an alkyl substituent group, especially benzyl group, introduced into 3-0-position of aglycon is indispensable for the highly selective beta-glycosylation with high yield. 4) On the other hand, electron-donating substituent group introduced into 4-0-position of glycon is extremely effective for the beta-glycosylation, but the electron-withdrawing acyl group decreases the yield of beta-glucoside.Consequently, we have found that the most suitable selection of the protective groups of the starting glucose after considering susbstituent effects enable us to success the synthesis of cellulose.