Galactopyranoside, methyl 6-tosylate

A second series of experiments which are described in the same publication made use of the following route. Methyl 3-methyl-j9-D-galacto-pyranoside — methyl 3-methyl-6-trityl-/ -D-galactopyranoside —> methyl 2,4-diacetyl-3-methyl-6-trityl-/3-D-galactopyranoside. The trityl group was then removed and replaced by a tosyl residue, the product was treated with sodium iodide in acetone and the 6-deoxy iodide was reduced to form methyl 2,4-diacetyl-3-methyl- 8-D-fucopyranoside, from which the free sugar was obtained by suitable treatment. It cannot be said that the final product of these syntheses was highly pure or that the yields were satisfactory. 

Methyl-D-fucose has been prepared by two methods.68 In the first, methyl a-D-galactopyranoside was converted into the 6-tosyl derivative, from which by condensation with acetone methyl 3,4-isopropylidene-6-tosyl-a-D-galactopyranoside (LXIV) was obtained. Methylation gave the corresponding 2-methyl ether which was converted into the 6-deoxy iodide (LXV) by heating with sodium iodide in acetone solution at 140°. Reduction with Raney nickel gave sirupy methyl 2-methyl-3,4-isopro-pylidene-a-D-fucopyranoside (LXVI) from which 2-methyl-D-fucose was obtained on hydrolysis. 

Selective trimethylation at positions 2, 3 and 4 is obtainable by the use of (a) the 6-trityl derivatives of the methyl a- and /S-2 D-galacto-pyranosides or 6-trityl-D-galactopyranose3 itself, (f>) the 1,6-anhydro-/S-D-galactopyranose,4 M (c) the methyl /9-D-galactopyranoside 6-nitrate,7 and id) the methyl 6-tosyl-a-D-galactopyranoside.M... 

Some examples are known where the formation of alternative, anhydro-ring structures is possible, and the deformation of the molecule required in the alternative reactions is approximately the same, so that entropy changes may be largely neglected. In such cases the ethylene oxide ring is not favored. The action of bases on methyl 3,4-di-0-acetyl-2,6-di-0-tosyl-/J-D-glucopyranoside and on methyl 2,6-di-0-mesyl- -D-galactopyranoside affords predominantly the 3,6-anhydro-2-0-sulfonyl derivative in each case. 

Several methyl 6-deoxy-hexopyranoside 2- and 4-tosylates undergo rearrangement to branched-chain sugars on treatment with lithium triethylborohydride, e.g. (37)—a(38) and (39)-+(40)Methyl 6-deoxy-2,3-di-O-tosyl-o(-D-galactopyranoside yielded both a 3-deoxy-... 

Methyl 2-0-benzyl-6-deoxy-3,4-bis-0-tosyl-j -D-galactopyranoside in anhydrous hydrazine heated under briefly at 130° until dissolved, then 3 hrs. at 80-100° -> methyl 2-0-benzyl-4,6-dideoxy-y -D-gryf/zro-hexopyranosid-3-ulose hydra-zone in anhydrous methanol treated with glacial acetic acid and salicylaldehyde, and refluxed 1 hr. methyl 2-0-benzyl-4,6-dideoxy-j -D-ery /zro-hexopyranosid-3-ulose. Overall Y 66%. H. Paulsen and H. Redlidi, B. 107, 2992 (1974). 

Conversion of a d-galactose derivative into the corresponding enopyranoside is depicted in Scheme 12.23. The primary hydroxy group in 95, prepared from methyl 4,6-0-benzylidene-a-d-galactopyranoside 94 by 0-benzylation followed by acid hydrolysis of the benzylidene acetal, was selectively tosylated to give 96. Displacement of the OTs group with iodide followed by O-acetylation of the secondary alcohol provided 97. Treatment of 97 with DBU afforded methyl 4-0-acetyl-2,3-di-0-benzyl-6-deoxy-(3-l-arabino-hex-5-enopyranoside 98. 

Selective tosylation of methyl a-D-galactopyranoside with toluene-p-sulphonyl chloride (2 molar equivalents) in pyridine gave the 2,6-ditosylate (26.6%), the 2,3,6-tritosyIate (17.2%), and the 3,6-ditosylate (2.2%). Sucrose with 4 molar equivalents of toluene-p-sulphonyl chloride gave sucrose 6, l, 6 -tritosylate (33%) and 2,6,1,6-tetratosylate (32%) the latter was previously reported by Long but was here characterized for the first time. ... 

Me glycoside, 3,4,6-tribenzyl, Fi-tosyl Methyl 3,4,6-tri-0-benzyl-2-deoxy-2-C-(tosylcarbamoyl)-fS-D-galactopyranoside [135735-82-9]... 

Me glycoside, ditosyl Methyl 4,6-dichloro-4,6-dideoxy-2,3-di-0-tosyl-a-D-galactopyranoside [20550-17-8]... 

Tosyl Methyl 4,6-0-benzylidene-3-0-tosyl-a-D-galactopyranoside C21H24O8S 436.482... 

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