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.

Synthesis of mycothiol, 1D-1-O-(2-[N-acetyl-L-cysteinyl]amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol, principal low molecular mass thiol in the actinomycetes.

Members of the actinomycetes produce 1D-1-O-(2-[N-acetyl-L-cysteinyl]amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol or mycothiol 1 as principal low molecular mass thiol. Chemical synthesis of a biosynthetic precursor of mycothiol, the pseudodisaccharide 1D-1-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol 13 was achieved by the following steps: (1) Enantioselective synthesis gave the glycosyl acceptors (-)-2,3,4,5,6-penta-O-acetyl-D-myo-inositol D-7 and the corresponding L-isomer L-7. (2) Condensation of D-7 and L-7 with the glycosyl donor 3,4,6-tri-O-acetyl-2-deoxy-2-(2,4-dinitrophenylamino)-alpha-D-glucopyranosylbromide afforded the corresponding alpha and beta anomeric products, which could be resolved by silica gel chromatography.