Photohalogenation of glycopyranosyl halides: An expedient route to c-1 gem dihalogenated sugars

Stereocontrolled Access to Higher Sugars (Non-1-en-4-ulopyranosyl Derivatives) and Glycomimetics [3-(β-D-Glycopyranosyl)-1-propenes and(3Z)-4,8-Anhydro-nona-1,3-dienitols]

“…[28] 3-Glycosyl-1-propenes could also be prepared using allyltrimethylsilane by Lewis acid-catalyzed opening of anhydro sugars (1,2-, [9] 1,4-, [29] and 1,6-anhydro sugars [7] ) of radical-mediated allylation of 1؊3, [59,60] we found it preferable to resort to photolytic conditions, where the temperature of the reaction mixture was maintained below ca. 35°C…”

“…Water was distilled twice. 5,6,7,9-Tetra-O-acetyl-1,2,3-trideoxy-α-D-gluco-non-1-en-4-ulopyranosyl Chloride and 5,6,7,9-Tetra-O-acetyl-1,2,3-trideoxy-α-Dgluco-non-1-en-4-ulopyranose (4 and 7): A mixture of the chlorobromo sugar 1 [59] (0.40 g, 0.90 mmol), allyltributyltin (0.596 g, 0.558 mL, 1.80 mmol) and a catalytic amount of AIBN in dry, deoxygenated benzene (9 mL) was introduced into a quartz tube (external diameter ഠ13 mm), flushed with argon. The tube was placed beside a medium pressure mercury lamp (Hanovia, 450 W), inserted into a two-walled cooling jacket with tap water cooling.…”

“…Hz, J 2,3Ј ϭ 6 9. Hz, 1 H, 2-H), 5.48 (q, J 6,7 ϭ Ͻ1 Hz, J 7,8 ϭ 1.3 Hz, 1 H, 7-H), 5.34 (d, 2 H, 5-H, 6-H), 5.18 [dd, J 1(Z),1(E) ϭ 1.4 Hz, 1 H, 1-H(E)], 5.14 [dd, 1 H, 1-H(Z)], 4.47 (dt, J 8,9 ϭ 6.7 Hz, J 8,9Ј ϭ 6.7 Hz, 1 H, 8-H), 4.13 (dd, 2 H, 9-H, 9Ј-H), 2.73 (dd, 2 H, 3-H, 3Ј-H), 2.14, 2.09, 2.03, 1.955,6,7,9-Tetra-O-acetyl-1,2,3-trideoxy-α-D-manno-non-1-en-4-ulopyranosyl Chloride and 5,6,7,9-Tetra-O-acetyl-1,2,3-trideoxy-α-Dmanno-non-1-en-4-ulopyranose (6 and 9): These compounds were prepared from 3,[59] as described for preparing the -galacto analogues 5 and 8.Compound 6: 31% yield; colourless syrup. Ϫ R f ϭ 0.53 (EtOAc/ petroleum ether 1:1).…”

Non-Stick Sugars: Synthesis of Difluorosugar Fluorides as Potential Glycosidase Inactivators

“…Treatment of the known [34] 1,1-difluoroglucose derivative 8 with N-bromosuccinimide (NBS) under photobromination conditions led to bromination at C5 (Scheme 2). It is worth noting that in this class of compound, the anomeric centre is not stereogenic, meaning that the compound lacks either an αor β-designation.…”

“…[34,35] These latter compounds also had potential as inactivators, with the additional fluorine located right at the anomeric centre, but functioned rather as substrates of the enzyme with no significant accumulation of a stabilized intermediate. [36][37][38] Changing the location and number of fluorine substituents on the sugar ring of an activated fluorosugar alters the corresponding rates of glycosylation and deglycosylation when these derivatives are reacted with a glycosidase.…”