Aldehydes, synthesis using galactose

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. 

An extension of the reaction of 6-acetoxy-5-enes leads to the use of alkenes with different substituents at C-6, a notable example being the extended chain sugar derivative 40 made from the D-galactose-based C-4 epimer of aldehyde 34 by an aryllithium addition reaction. Treatment with mercury(II) chloride in aqueous acetonitrile gives the expected alcohols in 75% yield, and these on acetylation then afford the enone 41 (70%) of relevance to the synthesis of pan-creastatin (42) which shows promising anti-cancer properties [42]. A very similar reaction, involving a 6-C-phenyl-5-ene,but one in which the C-1 substituent is not lost, is covered in the following section. 

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