Glucosamine was readily transformed into N-di-glycosyl donors β(1-4)and β(1-3)-linked disaccharides 13 and 15a-c, respectively. From 18 as galactosyl donor and 14a methylmaleoyl (DMM) protected derivative 1 which furnished trichloroacetimidate 4 as glycosyl donor. Reaction as acceptor β(1-3)-linked disaccharide 19 was obtained in high yield, which is a versatile building block for the with various acceptors (5a-g) in the presence of TMSOTf as the catalyst afforded the corresponding β-glycosides 6a-g important Galβ(1-3)GlcNAc unit. 19 was transformed into trichloroacetimidate 21; glycosylation with 5e as acceptor generally in high yields. Cleavage of the DMM group was readily accomplished by treatment with aqueous NaOH and gave trisaccharide 22 which furnished on partial deprotection Galβ(1-3)GlcNAcβ(1-4)Glc derivative 24. Thus, then with HCl (pH 5). Starting from 1 also DMM group containing glycosyl acceptors 9 and 14a-c were synthesized.
the wide applicability of DMM as amino protective group in oligosaccharide synthesis is exhibited. They furnished with trichloroacetimidates 12 and 4 as An important constituent of various glyconjugates is -gluparticipation to enforce β linkage, stability to acid and non nucleophilic bases and thus compatibility with an array of cosamine which is mainly found as an N-acetyl derivative in β-glycosidic linkage [1] . Glycoside bond formation with different functional groups and protective groups. Additionally, the cyclic DMM group is symmetric, thus easing donors derived from N-acetylglucosamine (GlcNAc) occurs generally by neighboring group participation to give a 1,3-structural assignments by NMR also in the case of hindered rotation of the DMM group. Our studies concentrated on oxazolinium intermediate [2] , which exhibits only weak glycosyl donor properties. Therefore, various alternatives have glucosamine, which was investigated as N-DMM-protected glycosyl donor and glycosyl acceptor in situations typically been investigated having, for instance, a phthalimido [1] [2] , a tetrachlorophthalimido [3] [4] a dithiasuccinylimido [5] , an found in oligosaccharide synthesis [15] . N,N-diacetylamino [6] , a trichloroacetylamino [7] , or a trichloroethoxycarbonylamino group [8] [9] in the 2-position, N-DMM-Protected Glucosamine as Glycosyl Donor thus supporting formation of the β anomer. Due to strong electron withdrawing character of the N substituents, these Treatment of glucosamine hydrochloride first with base glucosamine derivatives also exhibit increased glycosyl doand then with dimethylmaleic anhydride (DMMA) [16] led nor properties. Also the 2-azido group has gained wide use to N-acylation; upon treatment with acetic anhydride in in this regard [1] [2] [10] [11] [12] . However, all these groups also pyridine N-DMM-protected tetra-O-acetylglucosamine 1 exhibit some disadvantages which have been recently dis-(Scheme 1) was obtained as starting material for the followcussed in detail [3] [9] . Therefore, we investigated the dimething investigations; only the β isomer was found. ylmaleoyl (DMM) group [13] which to the best of our knowl-
The 1-O-acetyl group could be readily removed by treatedge has not been used for the protection of amino groups ment with hydrazinium acetate to afford compound 2. Rein sugars [14] . The reported ease of introduction and also action with tert-butyldimethylsilyl chloride (TBDMS-Cl) in ease of cleavage under weakly aqueous basic and then the presence of imidazole gave exclusively β-1-O-TBDMS acidic conditions [13] made it an interesting protective group protected compound 3. Reaction of 2 with trichloroacetonfor aminosugars because all the other beneficial properties itrile in the presence of 1,8-diaza[5.4.0]bicycloundec-7-ene of electron-withdrawing protective groups should be also (DBU) afforded β-trichloroacetimidate 4, which was used found: high glycosyl donor properties, neighboring group as glycosyl donor with various acceptors (5a؊g) [17] . Under standard conditions, i.e. activation of 4 with 0.01 equiva-