Cancer cells, in comparison to somatic cells, are characterized by overexpression of lectine receptors which can recognize and internalize molecules containing carbohydrate targeting moiety [1]. Therefore we can use suitable carbohydrate targeting moiety grafted to fluorescent nanodiamond particles for diagnosis of malignant process [2]. Oxime ligation was employed for grafting of carbohydrate moiety to fluorescent nanodiamonds. This reaction is based on condensation of aldehyde (carbohydrate part) with aminooxy group (bound on nanodiamonds) under very mild conditions in water through formation of oxime bonds. For the synthesis of polysaccharide chain consisting of glucosamine units we used the “Troc” protection. The glycosyl donors are protected on nitrogen by 2,2,2-trichloroethoxycarbonyl group [3]. Limiting factor of Troc protecting group is low stability under alkaline conditions. Therefore selective preparation of orthogonally protected glycosyl donors in this way was rather complicated. Easy deprotection of Troc protecting group and the possibility of stereoselective preparation of α- vs. β-glycosides were, however, the main advantages of presented synthesis. In connection with the preparation of pent-4’-en-1-yl-3,4,6-tri-O-acetyl-2-deoxy-2-{[(2,2,2-trichlorethoxy)carbonyl]amino}-ß-D-glucopyranoside was necessary to optimize the 1,2-trans glycosylation process. Best yields of the glycosylation were achieved by reaction of glycosyl bromide prepared from 1,3,4,6-tetra-O-acetyl-2-deoxy-2-{[(2,2,2-trichlorethoxy)-carbonyl]amino}-ß-D-glucopyranoside. In the case of glycosylation using pentenylglycosides with N-Troc glycosylbromide we observed unexpected rearrangement of the glycosyl acceptor aglycone to the glycosyl donor. Oxidative cleavage of the pentenyl group on oligosaccharide by ozone afforded aldehyde which is essential for the above mentioned oxime ligation.
Acknowledgments: This work was partly-financed by grants TA02010760 and Academy of Sciences of Czech Republic No.: RVO 61388963.
References:
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2. 2. Petrakova, V. et al. Adv. Functional Mat.,2012, 22, 4, 812-819.
3. 3. Ellervik, U. Magnusson, G. Carbohydr. Res., 1996, 280, 2, 251-260
