Chitobiose derivatives, synthesis

The last method is by intramolecular delivery (Scheme 43, d) 422-425 although elegant, this method has not yet found practical application in the synthesis of complex oligosaccharides. It remains to be seen if the method will work with the rather unreactive 4 -hydroxy group of chitobiose derivatives. This reactivity has been increased both by application of phthaloyl protection of the 2-amino groups and by application of the inverted conformation of l,6-anhydro-2-azido-2-deoxyglucopyranose. 8 ... 

Finally, Kren and coworkers have proposed the use of selectively acylated glycosides to be used as acceptors in a bi-enzymatic approach to the synthesis of di- and trisaccharides exploiting lipases/proteases and glycosidases (for instance, 6-0-acetyl-N-acetyl-D-glucosamine, 14, to give the corresponding chitobiose derivative 15) [44]. 

Chitin deacetylase has been used in the synthesis of partially and fully N-deacetylated 4-methyl umberlliferyl chitobiose derivatives as fluorogenic substrates for chitinase. Conversely, the reverse acylating action of chitin deacetylase has been used to prepare a partially N-acetylated chitosamine tetramer. The preparation of a 4-0-acetyl sialic acid derivative by a lipase OF-catalysed deacetylation of the peracetylated precursor has been reported. ... 

Sakamoto J, Kobayashi S. Enzymatic synthesis of 3-0-Methylated chitin oligomers from new derivatives of a chitobiose oxazoline. Chem. Lett. 2004 33 698-699. 

SCHEME 15.19 Synthesis of glycosyl amine 167 by amination of chitobiose and subsequent transformation into chitobiosyl-aspargine derivative 168. 

The glycosynthase methodology has been successfully extended to the enzymatic synthesis of /3-mannoside. The Glc519Ser mutant of the retaining /3-mannosidase (Man2a) proved to afford a catalytic conversion of the various acceptors with the a-mannosyl fluoride 97 as a readily accessible donor [159] (O Scheme 49). The chitobiose and GlcNAc derivatives, however, would not function as the acceptor. 

Synthesis of fluorinated chitin derivatives using chitinase from Bacillus sp. as a catalyst was carried out by Kobayashi and co-workers [227]. 6 -fluoro-, 6-fluoro-and 6,6 -difluoro-chitobiose oxazoline derivatives were newly prepared as TSAS monomers for chitinase. Ring-opening polyaddition of these monomers proceeded effectively at pH 8.0-9.0 and 30-40 C, giving rise to alternating 6-fluorinated chitin derivatives and fully 6-fluorinated chitin derivatives, under total control of region selectivity and stereoselectivity. 

Figure 8. Enzymatic synthesis of chitin using Bacillus sp. chitinase with the oxazoline derivative of chitobiose as donor. 

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