Armed–disarmed effect on the stability of cysteine thioglucosides

Thioglucosides of cysteine show variable stability depending on the nature of the protecting groups on the glycosyl donor. Armed protecting groups (benzyl) lead to products that decompose readily while disarmed protecting groups (acetyl) lead to more stable products. Since this armed/disarmed effect of the protecting group on the stability of the thioglucosides is more pronounced for cysteine with an unprotected carboxylic group, the proposed mechanism is that decomposition is initiated by an intramolecular protonation of glycosyl sulfide and subsequent displacement of the sulfide by adventitious nucleophiles.

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► Cysteine glucosides have variable stabilities depending on the glycosyl donor protecting groups.
► Armed cysteine thioglucosides with free carboxylic acid group decompose readily.
► The mechanism explains the decomposition of armed cysteine thioglucosides.