Synthesis of Fucosyl Saccharides under Neutral Conditions in Solutions of Lithium Perchlorate in Dichloromethane

Abstract

Trisaccharides embodying the Fuc ± a-(1-2)-Gal or the Fuc ± a-(1-2)-Glc substructure can be built up under neutral conditions by glycosylation of selectively deprotected glycosyl acceptor disaccharides with 2,3,4-tri-O-benzyl fucosyl fluoride in 0.07 m solutions of LiClO 4 in CH 2 Cl 2 . The glucosyl and the galactosyl trisaccharides, which are stereoisomers of the carbohydrate determinant of the human blood group H, are obtained in high yield and with complete a-selectivity. The glycosyl acceptor disaccharides with a deblocked 2-OH group in the saccharide unit are obtained by treatment of the respective 1,2-anhydro carbohydrates with glycosyl acceptors in 0.07 m LiClO 4 /CH 2 Cl 2 .

Stereoselective 1,2-cis Glycosylation of 2-O-Allyl Protected Thioglycosides

“…[ α ]$\rm{_{D}^{22}}$ =+82 (c=0.85 in CHCl 3 ); 1 H NMR (400 MHz, CDCl 3 , 25 °C): δ =7.39–7.13 (m, 30 H; Ar‐H), 5.00, 4.81 (ABq, 2 J (H,H)=10.9 Hz, 2 H; PhC H 2 ), 4.93 (d, 3 J (H,H)=3.4 Hz, 1 H; H‐1 b ), 4.93, 4.82 (ABq, 2 J (H,H)=11.1 Hz, 2 H; PhC H 2 ), 4.92, 4.58 (ABq, 2 J (H,H)=10.7 Hz, 2 H; PhC H 2 ), 4.82, 4.47 (ABq, 2 J (H,H)=10.9 Hz, 2 H; PhC H 2 ), 4.79, 4.68 (ABq, 2 J (H,H)=12.2 Hz, 2 H; PhC H 2 ), 4.60 (d, 3 J (H,H)=3.4 Hz, 1 H; H‐1 a ), 4.58, 4.44 (ABq, 2 J (H,H)=12.3 Hz, 2 H; PhC H 2 ), 4.00 (at, 3 J (H,H)=9.3 Hz, 1 H; H‐3 a ), 3.93 (dd, 2 J (H,H)=11.3 Hz, 3 J (H,H)=4.5 Hz, 1 H; H‐6′ a ), 3.79–3.76 (m, 1 H; H‐5 a ), 3.75–3.61 (m, 6 H; H‐2 b , H‐3 b , H‐4 b , H‐5 b , H‐6′ b , H‐6 a ), 3.54 (dd, 2 J (H,H)=10.8 Hz, 3 J (H,H)=1.9 Hz, 1 H; H‐6 b ), 3.51 (dd, 3 J (H,H)=9.7 Hz, 3.4 Hz, 1 H; H‐2 a ), 3.48 (at, 3 J (H,H)=9.7 Hz, 1 H; H‐4 a ), 3.36 (s, 3 H; OCH 3 ). The spectroscopic and analytical data were in agreement with those reported in the literature 28…”

Glycosyl Dithiocarbamates: β-Selective Couplings without Auxiliary Groups

“… 26 , 27 However, initial attempts to treat tri- O -benzyl epoxyglucal 1 with Et 2 DTC diethylammonium salt (prepared in situ from a 2:1 ratio of Et 2 NH and CS 2 ) resulted in little to no glycosyl DTC formation. The addition of Lewis acids such as LiClO 4 , which has been reported to catalyze epoxyglycal ring opening under aprotic conditions, 28 did not lead to significant improvements. However, epoxide ring openings with DTC salts in protic solvents proved to be highly effective.…”

Regioselective Benzylation of 2‐Deoxy‐2‐aminosugars using Crown Ethers: Application to a Shortened Synthesis of Hyaluronic Acid Oligomers

“…BaO/Ba(OH) 2 has been reported to perform ether formation in the presence of an amide bond. [31] Using BaO/Ba(OH) 2 only gave trace amounts of the 4,6-di- O -benzyl product 2 (entry 3, Table 1). No tribenzylated product was isolated.…”

“…A combination of CsOH/TBAI (tetrabutylammonium iodide) only gave an 18% yield of the dibenzylated product under similar conditions, along with triols from the starting materials in which the acetyl groups were cleaved by the treatment of base (entry 2, Table 1). BaO/Ba(OH) 2 has been reported to perform ether formation in the presence of an amide bond 31. Using BaO/Ba(OH) 2 only gave trace amounts of the 4,6‐di‐ O ‐benzyl product 2 (entry 3, Table 1).…”