Derivatives of β-D-fructofuranosyl α-D-galactopyranoside

Tin(IV)-functionalised polymer supports; non-toxic and practical reagents for regioselective acetylation of sucrose

Polymer-supported butyltin(IV) reagents have been surveyed for regioselectivity in acetylation of sucrose. Polymer-supported butyltin(IV) dichloride 8 catalysed the acetylation of sucrose to give a 59% yield of 6-O-acetyl sucrose 3, the precursor of sucralose. The yield is close to that of a previously reported process involving dibutyltin(IV) oxide (Bu2SnO). The spent polymeric resin could readily be regenerated and can be subsequently used in further synthetic reactions.

[Periodate oxidation of sucrose derivatives]

The periodate oxidation of some derivatives of sucrose at primary positions is generally selective for the D-glucopyranoside group. A cleavage at C-2-C3 or C-3-C-4 positions was observed for the 6,1',6'-tri-O-trityl and 6,1',6'-tri-O-(tert-butyldemethylsilyl) derivatives, respectively. The periodate oxidation was more complete for all other derivatives with a cleavage at C-2-C-3 and C-3-C-4.

Cyclic acetals of 4,1',6'-trichloro-4,1',6'-trideoxy-galacto-sucrose and their conversion into methyl ether derivatives

The acid-catalysed reaction of 4,1',6'-trichloro-4,1',6'-trideoxy-galacto- sucrose (1) with 5.5 equiv. of 2-methoxypropene in N,N-dimethylformamide followed by acetylation gave 3',4'-di-O-acetyl-4,1',6'-trichloro-4,1',6'-trideoxy-2,3-O- isopropylidene-6-O-(1-methoxy-1-methylethyl)-galacto-sucrose (2, 2%), 6,3',4'- tri- O-acetyl-4,1',6'-trichloro-4,1',6'-trideoxy-2,3-O-isopropylidene-galacto -sucrose (3, 31%), 3',4'-di-O-acetyl-4,1',6'-trichloro-4,1',6'-trideoxy-2,3-O- isopropylidene- galacto-sucrose (4, 38%), 3'-O-acetyl-4,1',6'-trichloro-4,1',6'-trideoxy-2,3-O- isopropylidene- galacto-sucrose (5, 13%), and 2,3',4'-tri-O-acetyl-4,1',6'-trichloro- 4,1',6'-trideoxy-galacto-sucrose (6, 13%). Methylation of 4 followed by removal of the protecting groups gave 4,1',6'-trichloro-4,1',6'-trideoxy-6-O-methyl- galacto- sucrose (8). 4,1',6'-Trichloro-4,1',6'-trideoxy-3-O-methyl-galacto-sucrose (11) was synthesised from 6 by preferential tert-butyldiphenylsilylation of HO-6 followed by methylation and removal of the protecting groups. Likewise, 4,1',6'-trichloro- 4,1',6'-trideoxy-4'-O-methyl-galacto-sucrose (14) was synthesised from 5. Treatment of 3 with aqueous acetic acid followed by methylation and removal of the protecting groups afforded 4,1',6'-trichloro-4,1'6'-trideoxy-2,3-di-O-methyl- galacto-sucrose (17).

Synthesis and ring-opening reactions of 4-chloro-4-deoxy-alpha-D-galactopyranosyl 3,4-anhydro-1,6-dichloro-1,6-dideoxy-beta-D-lyxo-hexulofuranoside

Treatment of 4-chloro-4-deoxy-alpha-D-galactopyranosyl 1,6-dichloro-1,6-dideoxy-beta-D-fructofuranoside (1) with 2.3 mol. equiv. of diethyl azodicarboxylate (DEAD) and 1.3 mol. equiv. of triphenylphosphine (TPP) in toluene gave a mixture of 3,6-anhydro-4-chloro-4-deoxy-alpha-D-galactopyranosyl 3,4-anhydro-1,6-dichloro-1,6-dideoxy-beta-D-lyxo-hexulofuranosi de (2, 55%) and 4-chloro-4-deoxy-alpha-D-galactopyranosyl 3,4-anhydro-1,6-dichloro-1,6-dideoxy-beta-D-lyxo-hexulofuranosi de (3, 35%). Compound 3 was also synthesised from 6-O-tert-butyldiphenylsilyl-4-chloro-4-deoxy-alpha-D-galactopyrano syl 1,6-dichloro-1,6-dideoxy-beta-D-fructofuranoside by epoxidation with DEAD-TPP and removal of the silyl ether group with tetrabutylammonium fluoride. The SN2 reactions of 2,3,6-tri-O-acetyl-4-chloro-4-deoxy-alpha-D-galactopyranosyl 3,4-anhydro-1,6-dichloro-1,6-dideoxy-beta-D-lyxo-hexulofuranosi de (5) with fluoride, chloride, bromide, iodide, and azide ions gave the corresponding 4'-derivatives 10, 12, 14, 18, and 20, respectively. Reduction of 4-chloro-4-deoxy-alpha-D-galactopyranosyl 4-bromo-1,6-dichloro-1,4,6-trideoxy-beta-D-fructofuranoside (15) gave 4-chloro-4-deoxy-alpha-D-galactopyranosyl 1,6-dichloro-1,4,6-trideoxy-beta-D-fructofuranoside (16). A similar reduction of 4-chloro-4-deoxy-alpha-D-galactopyranosyl 4-azido-1,6-dichloro-1,4,6-trideoxy-beta-D-fructofuranoside (21) gave 4-chloro-4-deoxy-alpha-D-galactopyranosyl 4-amino-1,6-dichloro-1,4,6-trideoxy-beta-D-fructofuranoside (22).