Dimethyl sulfonium triflate DMTST

Scheme 5.1 Mechanism of thioglycoside activation (a) by thiophiles X1 such as /V-bromosuccinimicle (NBS), 11,12 methyl triflate,13 dimethyl(methylthio)sulfonium triflate (DMTST),14 phenylselenyl triflate (PhSeOTf),17,18 iV-iodosuccinimide/triflic acid (MS/TfOH),19 20 and iodonium di-sym-collidine perchlorate (IDCP)21 (b) by tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBPA,+)25 and (c) via anomeric sulfoxides.26 The stereochemical outcome of these glycosylations follows the same general trends as with many other glycosyl donor/promoter combinations (m-CPBA = mcta-chloroperbenzoic acid).

Scheme 8 Thioglycoside-based glycosidation reactions, (a) thiophile = JV-btvmosuccwimide (NBS) [35], methyl tnflate [38], dimethyl(methyIthto)sulfonium triflate (DMTST) [39], or AModo-succmiraide (NlS)-triflic acid [40]. (b) TBPA+- = tris (4-bromophenyl)ammoniumyl hexachloroanti-monate [42]. (c) mCPHA = m-chloroptrbenmic acid [43],...

Another popular promoter for glycosylation with thioglycosides is the reagent dimethyl(methylthio)sulfonium triflate (DMTST).60 A comparison between DMTST and NIS/TfOH for the formation of sialoglycoconjugates demonstrated that the iodine system provided superior yields and anomeric selectivity in nearly all cases.61 The yields and stereoselectivity also increased with an increase in solvent polarity, suggesting that enhanced stabilization of the oxacarbenium intermediate, the rate-limiting step in glycosylation, was responsible for the increased... 

Another concept for the activation of thioglycosides is their reaction with soft sulfur electrophiles. The first reagents of this type were dimethyl(methylthio)sulfonium triflate (DMTST, 83) and the corresponding tetrafluoroborate (DMTSF, 84) (Figure 4.4) [86,183-185], which are powerful methylsulfenylating agents (E = SMe) (Scheme 4.15), and are still extensively used. 

Similarly, reaction of a thioglycoside with a hydroxylic compound in the presence of an excess of a tetraalkylammonium bromide and the thiophilic promoter dimethyl(methylthio)sulfonium triflate (DMTST) proceeds with high stereoselectivity.131-133... 

Preparation of the oligosaccharide moiety was carried out with the 2-methylthio derivative of N-acetylneuraminic ester 158. The donor 158 was coupled with the acceptor 159 in the presence of dimethyl(methylthio)-sulfonium triflate (DMTST) and molecular sieves to give the disaccharide 160 (a p = 3 1). After isolation of the a-isomer, deprotection and then N-glycolylated with N-hydroxysuccinimide ester followed by methylation and acetylation gave the benzyl glycoside 162. 

Due to the possibility of side reactions of acceptors with MeOTf and safety considerations, a more specific promoter, dimethyl (methylthio)sulfonium triflate (DMTST), can be utilized instead of MeOTf it is produced by mixing MeOTf with dimethyl disulfide. ... 

Ito and coworkers have combined the soluble polymer-supported synthesis with the catch-and-release protocol using the chloroacetyl (ClAc) tag (Scheme 16.20). Glucosamine acceptor bound to a low molecular weight polyethylene glycol (PEG) 70 was glycosylated with a thiogalactoside donor 71 in the presence of dimethyl(methylthio) sulfonium triflate (DMTST) in CH2CI2 to provide the disaccharide 72 in 94% yield. 

SCHEME 14.14 Synthesis of PS A1 repeating tetrasaccharide unit from Bacteroides fragilis by Seeberger and coworkers. DMTST, dimethyl(methylthio)sulfonium triflate TTBP, 2,4,6-tri-terf-butylpyrimidine. 

Abbreviations Ac acetyl Bn benzyl BSP 1-benzenesulfinyl piperidine BTIB bis(trifluoroacetoxy)iodobenzene DAST (diethylamino)sulfur trifluoride DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTSF dimethyl(methylthio)sulfonium tetrafluoroborate DMTST dimethyl(methylthio)sulfonium triflate DTBMP 2,6-Ai-tert-butyl-4-methylpyridine DTBP 2,6-di-tert-butylpyridine DTBPl 2,6-di-tert-butylpyridinium iodide FDCPT l-fluoro-2,6-dichloropyridinium triflate FTMPT l-fluoro-2,4,6-trimethylpyridinium triflate IDCP iodonium dicollidine perchlorate IDCT idonium dicollidine triflate LPTS 2,6-lutidinium p-toluenesulfonate LTMP lithium tetramethylpiperidide Me methyl MPBT S-(4-methoxyphenyl) benzenethiosulflnate NBS A-bromosuccinimide NIS A-iodosuccinimide NlSac A-iodosaccharin PPTS pyridinium p-toluenesulfonate TBPA tris(4-bromophenyl)ammoniumyl hexachloroantimonate Tf trifluoromethanesulfonyl TMTSB methyl-bis(methylthio)sulfonium hexachloroantimonate TMU tetramethylurea Tr trityl TTBP 2,4,6-tri-tert-butylpyrimidine. 

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