TopCAT

Representative Procedure for Lewis Acid Promoted Clycosylation with TOPCAT Glycosyl Donor Using Silver Triflate [335]... 

Enslein, K., Gombar, V., Blake, B. Use of SAR in computer-assisted prediction of carcinogenicity and mutagenicity of chemicals by the TOPCAT program. Mutat. Res. 1994, 305, 47—61. 

Details pertaining to the design, preparation, reactivity, and oligosaccharide synthesis technology based on the MOP and TOPCAT leaving groups are discussed in the following four chapters [Chaps. 17-20],... 

II. THE METHODS GLYCOSYL 2-THIOPYRIDYLCARBONATES (TOPCAT) AS GLYCOSYL DONORS... 

Encouraged by the reactivity of bis(2-pyridyl) carbonate 2, we also explored the use of bis(2-thiopyridyl) carbonate 8 in the formation of anomeric 2-thiopyridyl carbonates. The reagent 8, prepared in quantitative yield from triphosgene and 2-pyridinethiol, was used to prepare several glycosyl 2-thiopyridylcarbonates (TOPCAT) in high yields (Scheme 3). 

To date, all TOPCAT donors prepared in our laboratory were isolated by column chromatography as pure (3-anomers (see Scheme 3), and they exhibited much higher stability compared with glycosyl 2-pyridylcarbonates. They are often crystalline and they can be stored for extended periods without a detectable change. These features are extremely important for their synthetic applications as versatile glycosyl donors in oligosaccharide and glycoside synthesis. 

Scheme 4 Synthesis of 1,2-cu-disaccharides using TOPCAT glycosyl donors. ...

Scheme 5 I,2,-/ram-glycoside synthesis using the TOPCAT-leaving group.

In the previous chapter, we briefly discussed the relevance of sialyl Le and we showed a synthesis of a protected derivative that was assembled from a MOP glycosyl donor [see Chap. 18]. This complements several other recently reported syntheses. Herein we describe a straightforward synthesis of sialyl Le employing the TOPCAT activation method as shown in Scheme 6. 

Scheme 6 Synthesis of a sialyl Lex derivative and intermediate disaccharide by TOPCAT donors.

Scheme 7 Synthesis of Le trisaccharide derivative via TOPCAT-mediated glycosylation.

Table 1 Glycosylation with TOPCAT and Imidate Donors...

C. General Procedures for the Synthesis of 1,2-c/s-Disaccharides Using TOPCAT Glycosyl Donors... 

D. General Procedure for the Synthesis of 1,2-frans-Giycosldes Using the TOPCAT-Leaving Group... 

Oligosaccharide Synthesis by Selective Anomeric Activation with MOP- and TOPCAT-Leaving Groups... 

Scheme 3 Selective activation of TOPCAT glycosyl donors in the presence of MOP acceptors TOPCAT versus MOP.

We have shown that the selective activation of the TOPCAT donors is possible with AgOTf in the presence of MOP acceptors. In a typical iterative process, one can use O-benzyl TOPCAT donors with partially ether or ester O-pro tec ted MOP acceptors for the synthesis of di-, tri-, or oligosaccharides with predetermined anomeric configurations in the major... 

Scheme 4 Rapid and efficient iterative oligosaccharide assembly using MOP- and TOPCAT-leaving groups.

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