Cysteine, reaction with aldoses

Another series of interesting thiosugars was prepared by Schubert by the action of cysteine on the aldoses. By analogy with the structure assigned by this same author to the reaction product of cysteine with ordinary aldehydes, these new compounds may be formulated as the open chain forms ... 

The earliest synthesis of members of these analogs (617) involved reaction of aldose sugars (34) with L-cysteine (39JBC601 53MI1 75LA1637 76-LA450) or 2-aminoethanethiol (61CB225) (Scheme 162). 

The OV-17 phase has been found to give improved separation of the diastereoisomerlc pertrimethylsilylated methyl 2-(polyhydroxy-alkyl)thiazolidine-(ilR)-carboxylates formed from enantiomeric pairs of nine aldoses after reaction with L-cysteine methyl ester (c.f. Vol.20, p.2il8). Although each pair of sugar enantiomers gave separate peaks, those from different sugars, e.g., D-xylose and L-arabinose, sometimes co-eluted, ... 

It was found that carbazole and phloroglucinol are unsuitable for determining the heptose content of sugar mixtures because of interference from other sugars similar interference is encountered with resorcinol. With orcinol, cysteine, and diphenylamine, however, specific reactions can be obtained at selected wavelengths. Ketoheptoses (and keto sugars in general) react under milder acid conditions than the aldoses, and this property can be used for identification purposes. In the orcinol test, for... 

Hara et al. [117] demonstrated an excellent separation of the enantiomers of nine aldoses by GC as their diastereomeric thiazolidine derivatives. The sugars were derivatized with L-cysteine methyl ester (49) and subsequently silylated. This simple derivatization, including the acylation, was carried out in pyridine at 60 C. The rapid reaction of thiols with the carbonyl group of sugars was also exploited by Little [118], who used (-k)-l-phenylethanethiol (50) to form acyclic dithioacetals. 

---