Synthesis and application of a highly branched, mechanism-based 2-deoxy-2-fluoro-oligosaccharide inhibitor ofendo-xyloglucanases

Abstract

Xyloglucan (XyG) is a complex polysaccharide that is ubiquitous and often abundant in the cell walls of terrestrial plants.

Orthogonal Active-Site Labels for Mixed-Linkage endo-β-Glucanases

“…102 Similarly, specifically engineered glycosynthase enzymes have been used to extend the nonreducing end of monosaccharide inhibitors to yield the corresponding disaccharide and trisaccharide inhibitors. 105 the other hand, we have previously been successful in stereoselectively 2-fluorinating a complex xyloglucan heptasaccharide (Xyl 3 Glc 4 , "XXXG") glycal with Selectfluor in the synthesis of an endo-xyloglucanase inhibitor, 21 which avoided tedious stepwise oligosaccharide construction. 106,107 Yet, prior to the present study, the use of Selectfluor on glycals containing β(1,3) glycosidic linkages had not been explored.…”

“…Notably, in our previous work, the reaction of a highly branched xyloglucan heptasaccharide glycal afforded exclusively the gluco epimer with an anomeric α/β mixture (as confirmed by 19 F nuclear magnetic resonance (NMR) spectroscopy). 21 Since we were unfortunately unable to bias the diastereoselectivity of fluorination here, the reactions of glycals 9 and 10 with Selectfluor were scaled-up using acetone/water (5:1) as a convenient solvent system to achieve moderate yields of diastereomeric mixtures. 19 F NMR spectra indicated that the diastereomeric ratios were similar to those observed in the small-scale reactions (11,Figure S27 in the Supporting Information; 12, Figure S28 in the Supporting Information).…”

“…58,90 The per-O-acetylated G3G glycal (9) and per-O-acetylated GG3G glycal (10) were synthesized by adapting previously established methods. 21,125 Thus, the corresponding glycosyl α-bromide (1000 mg 7 or 900 mg 8) was dissolved in 30 mL of acetic acid and slowly added to a suspension of Zn (31 equiv), NaOAc (18.5 equiv), and CuSO 4 •5H 2 O (0.2 equiv) in 20 mL of water, which had been stirring for 5 min. The solution was stirred vigorously for 3 h at RT and subsequently filtered through Celite.…”

“…1 H NMR (Figure S25 in the Supporting Information, 400 MHz, CDCl 3 ): δ 6.45 (d, J (H1−H2) = 6. 26 Utilizing established synthetic protocols 21,97,98 with modifications (see the Results and Discussion section), the glycals 9 (150 mg) and 10 (160 mg) were converted into a diastereomeric mixture of the corresponding (per-O-acetylated)-1-hydroxy 2-deoxy-2-fluoro-glycosides by dissolution in a minimum amount of acetone and addition to a stirring suspension of Selectfluor (1.2 equiv) in 18 mL of acetone/ water (5:1). The solution was stirred first at RT for 16 h, and then at 60 °C for 3 h. It was subsequently filtered over a Celite plug and concentrated under reduced pressure.…”

“…(per-OAc)-1-Hydroxy-2-deoxy-2-fluoro-G3G (11). The synthesis of the per-O-acetylated 2′,4′-dinitrophenyl-2-deoxy-2-fluoro-β-glycosides 13 and 14 followed previously reported glycosylation methods, 21,75 with modifications. The diastereomeric mixtures comprising 11 (60 mg) or 12 (90 mg) were individually dissolved in 5 mL of dry DMF containing 4 Å activated molecular sieves and anhydrous DABCO (5 equiv).…”