Catalytic Glycosylation with Glycosyl Thioimidate Donors

Abstract

A new class of glycosyl thioimidates, glycosyl N-phenyl-trifluorothioacetimidates, were prepared from the readily available glycosyl thiols in excellent yields. These imidates exhibited very good donor properties under the action of catalytic amounts of BF 3 ·Et 2 O, and the corresponding glycosidation

Methyl 1,2‐Orthoesters as Useful Glycosyl Donors in Glycosylation Reactions: A Comparison with n‐Pent‐4‐enyl 1,2‐Orthoesters

“…Acetylation of this mixture (consisting of partially de‐ O ‐acetylated materials) resulted after additional chromatography (hexane/EtOAc 6:4) in the isolation of 1α,1′β‐disaccharide 6a (8 mg, 17 %) and disaccharide 23a (7 mg, 12 %). Spectral data for 23a are in agreement with those described previously 54 . 1 H NMR (300 MHz, CDCl 3 ): δ = 7.92–7.79 (m, 6 H), 7.48–7.19 (m, 9 H), 6.08 (t, J = 9.6 Hz, 1 H), 5.45 (t, J = 9.9 Hz, 1 H), 5.31 (dd, J = 10.2, 3.3 Hz, 1 H), 5.19 (m, 4 H), 4.77 (s, 1 H), 4.21 (m, 1 H), 4.12 (dd, J = 12.0, 5.4 Hz, 1 H), 3.97 (m, 2 H), 3.83 (dd, J = 10.8, 6.3 Hz, 1 H), 3.58 (dd, J = 10.8, 1.8 Hz, 1 H), 3.43 (s, 3 H), 2.07, 1.984, 1.978, 1.92 (4s, 12 H) ppm.…”

“…Methyl 6‐ O ‐(2,3,4,6‐Tetra‐ O ‐acetyl‐α‐ D ‐mannopyranosyl)‐2,3,4‐tri‐ O ‐benzoyl‐α‐ D ‐glucopyranoside (23a): 54 This compound was prepared from orthoester 4a (50 mg, 0.14 mmol) and methyl 2,3,4 tri‐ O ‐benzoyl‐α‐ D ‐mannopyranosyl ( 19 , 35 mg, 0.07 mmol) by the general procedure for glycosylation. Purification by flash chromatography (hexane/EtOAc 6:4) allowed the isolation of 23a (23 mg, 40 %) along with methyl 2,3,4,6‐tetra‐ O ‐acetyl‐α‐ D ‐mannopyranoside ( 7a , 5 mg, 10 %), and unchanged methyl 2,3,4‐tri‐ O ‐benzoyl‐α‐ D ‐mannopyranosyl ( 19 , 5 mg, 14 %), together with a lower running mixture of compounds appearing as a single spot on tlc.…”

New Principles for Glycoside‐Bond Formation

“…The glycosidation products were obtained in excellent yields. [181] Glycosyl thiols can be prepared readily from the corresponding reducing sugars by using the Lawesson reagent. [182] A highly stereoselective method for the synthesis of a-glycosyl thiols was also reported recently.…”

Neue Prinzipien für die Bildung von glycosidischen Bindungen

“…97 ) zu gewährleisten, welche leicht aus den entsprechenden Glycosylthiolen hergestellt werden konnten (Schema ). Die Glycosidierungsprodukte wurden in exzellenten Ausbeuten erhalten 181. Bemerkenswert ist, dass Glycosylthiole leicht aus den entsprechenden reduzierenden Zuckern mithilfe des Lawesson‐Reagens hergestellt werden können 182.…”