Total Syntheses of Optically Active Carbohydrates

In previous Sections of this Chapter, total syntheses of sugars have been described which led to pure diastereoisomers in racemic form. 

There are reports in the literature describing the resolution of substrates, as well as of products. 

2-(2-Furyl)glycolic acid (605), a substrate for the synthesis of hex-oses (see Section IV) was resolved119 into both enantiomeric forms by recrystallization of its 2(R)-menthyl ester. From the R enantiomer of 605, methyl a-D-glucopyranoside320 and methyl a-D-mannopyrano-side227 were obtained by a sequence of reactions discussed in Section IV. No racemization occurred at any stage of the synthesis. 

Another substrate for the synthesis of hexoses, frons-5,6-dihydro-6-(hydroxymethyl)-2-methoxy-2/7-pyran (211), was obtained in both optically active forms by resolution of its 6-camphanyl ester.1 2 From the levorotatory enantiomer, methyl 2,3,6-tri-0-acetyl-4-deoxy-a-D-.r //o-hexopyranoside (606) was synthesized, thus confirming its (2S) (6S) configuration, corresponding to the D configurational series. 

3(R)-Hydroxy-4-pentenoic44,322 (R-94) and 3(R)-hydroxy-3(R)-methyl-4-hexenoic (R-99, R = H)4S acids were obtained from the racemic acids by recrystallization of their quinine salts. Compound R-94 served322 as the substrate for the synthesis of 2-deoxy-L-eri/t/iro-pen-tose as in 94 — 98. The enantiomeric acid R-99 was employed46 for the preparation of D-everniicose (see 99 — 105). 

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