Synthesis, structure and sweetness of 4-chloro-4-deoxy-alpha-D-galactopyranosyl 1,4,6-trichloro-1,4,6-trideoxy-beta-D-tagatofuranoside

The reaction of 6-O-acetylsucrose with sulfuryl chloride was reexamined. The major product, after dechlorosulfation and acetylation, was determined by X-ray diffraction to be 2,3,6-tri-O-acetyl-4-chloro-4-deoxy-alpha-D- galactopyranosyl 3-O-acetyl-1,4,6-trichloro-1,4,6-trideoxy-beta-D- tagatofuranoside and not the corresponding sorbofuranoside, as reported earlier. The mechanism of chlorination at C-4' is discussed. The intensity of sweetness of the free 4'-chlorodeoxy tagato isomer is determined to be only about one-tenth the sweetness of the corresponding chlorodeoxy fructo isomer, which strongly suggests that the hydrophobic gamma-site is located at C-4'.