Synthesis using galactose derivative

Scheme 6.13 Synthesis of galactose-derived TcTs inhibitors using CuAAC reaction.

In the synthesis of the glycolipid asialo GMI described by Ogawa and co-workers [107] the trisaccharide derivative (215) (used in the synthesis of asialo GM2) was converted into the 4,6-O-benzylidene derivative (233) and this was condensed with aceto-bromogalactose in the presence of mercury(II) cyanide and molecular sieves to give the P-linked acetylated galactose derivative in 97 % yield. The product was deprotected and acetylated to give the peracetyl derivative (234) of the tetrasaccharide which was converted into the free sugar (235) with hydrazine hydrate. Compound (235) was converted into asialo GMI via the imidate as described above for the synthesis of asialo GM2 from the imidate (219). 

A synthesis of an enantiomerically and diastereomerically pure 3-thiazoline 214 from 215 has been reported via a modified Asinger reaction. The use of a galactose-derived chiral auxiliary 216 was involved (Scheme 85) <2000TL7289>. 

The aforementioned D-galactose-derived chiral imines 27 were used for the Strecker synthesis of D-a-amino nitriles and D-o -amino acids by the Kunz group. Various types of glycosylim-ines 27, prepared from 2,3,4,6-tetra-0-pivaloyl-/3-D-galacosylamine with aliphatic or aromatic aldehydes, were treated with TMSCN in the presence of SnCl4, providing a-amino nitriles... 

The procedure is remarkably effective for the coupling with cyclic ketones and provides a fast access to a-C-ketosides of Neu5Ac. The coupling efficiency is however moderate in the synthesis of C-disaccharides, as shown with the D-galactose-derived aldehyde 198 (O Scheme 44). Acetates 213 provide the expected compound 215 but much less efficiently than sulfide 204 (30 versus 82% yield, respectively). The moderate yield using acetates 213 is due to the competitive pinacol coupling of aldehyde 198 because the rate of the reductive metallation of the anomeric acetates is too slow. 

The presented review describes total syntheses directed towards 6-amino-6,8-dideoxy-D-eryt/iro-D-galacto-octose, commonly named lincosamine - the sugar component of the antibiotic lincomycin. In the first part we present total syntheses of lincosamine that start from carbohydrate precursors. The D-galactose-derived aldehyde is the most frequently used synthon. In the second part, total syntheses of lincosamine from non-carbohydrate precursors are presented. This part of the review is divided into two subsections. The first one groups syntheses based on the application of furan compounds. In the second one we present a hetero-Diels-Alder approach to the synthesis of lincosamine. 

P-D-abequoside) has been achieved by use of tris(trimethylsilyl)silane. A new synthesis of methyl p-D-abequoside derivative 16 proceeded via the D-galactose-derived intermediates 14 and 15, and involved deoxygenation at the 6-position by reduction of the tosylate with LAH and at the 3-positions by regioselective opening of the 3,4-cyclic sulfate (Scheme 4). The protected methyl 3,6-dideoxy-a-D-ara6mo-hexopyranoside 17 (methyl a-o-tyvelopyranoside) was similarly obtained by way of an a-o-mannose-derived 2,3-cyclic sulfate 6-tosylate."... 

The synthesis of tunicamycin V using a 2-azido-2-deoxy-D-galactose derivative as starting material for a multistep sequence has been described. ... 

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