1,6-thio linkages

One of the most unusual carbohydrate - amino acid linkages so far found in Nature is the thio linkage between glucose or galactose and cysteine.35,40 41 This glycopeptide has not yet been isolated or synthesized. Therefore, in order to obtain 13C-n.m.r. chemical-shift data for... 

The phenothiazines and thioxanthenes have the characteristic of two phenyl groups fused to a central six-member ring giving a so-called 6-6-6 system. An ethylene is a commonly used bioisostere for a thio linkage in medicinal chemistry. Continued research in... 

DNAs containing a-phosphorothioate nucleotide analogs are not effectively hydrolyzed by the 3 — 5 -exonuclease activity. With Pol Ik, the thio linkage... 

Both traditional and new approaches (often used in the preparation of O-glycosides) have been applied to the establishment of thio linkages. Here, the synthesis of thiodisaccharides and thiooligosaccharides is described with reference to linkage specificity and method of generation. 

An approach to the synthesis of 1,6-thio linkages to mannose residues has recently been reported whereby the manno-1,2-epoxide (16) was opened with the thiolate of 17 to generate the thiodisaccharide (18) in moderate yield (63%) [34] (Scheme 7). 

Although there are many other synthetic possibilities for the preparation of 1,6-thio linkages, arguably none is easier or more effective than the displacement of a 6-deoxy-6-iodo derivative with a 1-thiolate. Recalling the poor yield of the methyl... 

The first report of SN2-like displacement of glycosyl halides by sugar thiolates for generating 1,4-thio linkages emerged in 1978 [14],... 

Most 1,2-thio linkages have been established via Sn2 displacement of a triflate of either glucosyl or mannosyl acceptor molecules with 1-thiolates. 

Pinto and co-workers [75] have chosen a more traditional approach toward establishing 1,2-thio linkages and ultimately the production of thiokojibiosides and related derivatives. The thiol 187 was coupled to the P-trichloroacetimidate 188 thereby yielding the protected allyl kojibioside 189 [75] (Scheme 37). Interestingly, when the a-trichloroacetimidate 190 was used as donor the thiosophorose derivative 191 was obtained as the major product (191 192, 2.3 1) in a reaction proceeding via the stable orthoester 193. 

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