Protic Acid Catalyzed Stereoselective Glycosylation Using Glycosyl Fluorides

Abstract

A catalytic and stereoselective glycosylation of various glycosyl acceptors, such as methyl glycosides, thioglycosides, or a disarmed glycosyl fluoride, with benzyl-protected armed glycosyl fluoride was successfully carried out by using various protic acids in the presence of MS 5A. In the cases when trifluoromethanesulfonic acid (TfOH) or perchloric acid (HClO4) was used in diethyl ether (Et2O), α-glycosides were obtained as major products, while β-stereoselectivity was observed when tetrakis(pentafluorophenyl)boric acid [HB(C6F5)4] was used in a mixed solvent of trifluoromethylbenzene (BTF)–pivalonitrile (tBuCN) = 5 : 1. Stereoselectivity of this glycosylation was controlled by the properties of counter anions of the catalyst as well as by those of solvents. Also, one-pot trisaccharide synthesis was performed by successive addition of NIS and third-sugar to afford Glcα or β1–6Glcβ1–6Glc and Glcα or β1–6GlcNβ1–6Glc in excellent yields.

The C‐4 Configuration as a Probe for the Study of Glycosidation Reactions

“…[21] The reaction was also performed with a carbohydrate alcohol. Allowing the imidates 7 and 8 to compete for methyl 2,3,4-tri-O-benzyl-α--glucopyranoside (9) [22] catalyzed by TMSOTf at 0°C gave a 1:1 ratio of the glucoside 10 [23,24] and galactoside 11 [25,26] (Scheme 4) predominantly as β-glycosides. The triflate effect is thus also observed in disaccharide synthesis.…”

“…Products 3, [15] 4, 5, [16] 6, [17] 10, [23,24] 11, [25,26] 15, [33] and 20 [32] were made as reference compounds by known methods. Reference compounds 18, 19, and 21 were made as described below.…”

Completely β-Selective Glycosylation Using 3,6-O-(o-Xylylene)-Bridged Axial-Rich Glucosyl Fluoride

“…19 These facts prompted the following question: which species is the real catalyst of this reaction: 8 or 10? To clarify the actual catalytic species experimentally, we utilized the properties of molecular sieves: acidic 5A MS 20 and basic 4A and 3A MS. 21,22 Table 2 summarizes the results of comparative experiments using the acidic and basic MS.…”

Thio-arylglycosides with various aglyconpara-substituents: a probe for studying chemical glycosylation reactions

“…Donors bearing electron donating protective groups have much higher anomeric reactivities towards a promoter than those bearing electron withdrawing and conformational restricting protective groups. This phenomenon was first observed with the glycosyl halides,3 which has been subsequently found to be general for a variety of donors including pentenyl glycosides,4 thioglycosides,2, 5, 6 glycosyl fluorides,7 glycosyl thioimidates8 and glycosyl sulfoxides 9. The understanding of protective group effect on glycosylation rate led to the development of reactivity based chemoselective glycosylation method, where a thioglycoside donor with higher anomeric reactivity (armed) is mixed together with a less reactive (disarmed) thioglycosyl acceptor 2, 6.…”