Involvement of the S-aglycon in the conformational preferences of thioglucosides

The conformational preferences of two series of alkyl β-d-thioglucopyranosides in solution were investigated by NMR and CD. The rotamer populations of the hydroxymethyl group were found to depend on the structural nature of the S-aglycon. The population of the gt rotamer increased and that of the gg   rotamer decreased as the alkyl group attached to the S atom increased in size. These rotamer populations have a linear correlation with the Taft’ steric parameters, the nS–σC–O∗exo-anomeric interaction may express these rotational preferences. Comparative analysis of the hydroxymethyl populations between alkyl O- and S-glucosides revealed identical or slightly higher gt and smaller gg populations for the latter compounds.

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2,3-Di-O-Acetyl-1-S-acetyl-4,6-bis-O-(4-bromobenzoyl)-1-thio-β-d-glucopyranoseC26H24Br2O10S[α]D = +50.4 (c 0.6, CHCl3)CD (CH3CN) λext nm (Δε): 251 (+16.1), 233 (−6.3)Source of chirality: d-(+)-glucose

Methyl 2,3-di-O-acetyl-4,6-bis-O-(4-bromobenzoyl)-1-thio-β-d-glucopyranosideC25H24Br2O9S[α]D = +6.0 (c 0.8, CHCl3)CD (CH3CN) λext nm (Δε): 251 (+15.1), 234 (−6.8)Source of chirality: d-(+)-glucose

Ethyl 2,3-di-O-acetyl-4,6-bis-O-(4-bromobenzoyl)-1-thio-β-d-glucopyranosideC26H26Br2O9S[α]D = +1.7 (c 1.0, CHCl3)CD (CH3CN) λext nm (Δε): 251 (+14.6), 234 (−7.0)Source of chirality: d-(+)-glucose

Propyl 2,3-di-O-acetyl-4,6-bis-O-(4-bromobenzoyl)-1-thio-β-d-glucopyranosideC27H28Br2O9S[α]D = +1.9 (c 0.1, CHCl3)CD (CH3CN) λext nm (Δε): 251 (+13.8), 234 (−6.3)Source of chirality: d-(+)-glucose

Isopropyl 2,3-di-O-acetyl-4,6-bis-O-(4-bromobenzoyl)-1-thio-β-d-glucopyranosideC27H28Br2O9S[α]D = −6.3 (c 0.7, CHCl3)CD (CH3CN) λext nm (Δε): 251 (+13.1),233 (−6.5)Source of chirality: d-(+)-glucose

Cyclohexyl 2,3-di-O-acetyl-4,6-bis-O-(4-bromobenzoyl)-1-thio-β-d-glucopyranosideC30H32Br2O9S[α]D = +3.9 (c 0.9, CHCl3)CD (CH3CN) λext nm (Δε): 251 (+11.0), 233 (−4.8)Source of chirality: d-(+)-glucose

tert-Butyl 2,3-di-O-acetyl-4,6-bis-O-(4-bromobenzoyl)-1-thio-β-d-glucopyranosideC28H30Br2O9S[α]D = −13.7 (c 0.6, CHCl3)CD (CH3CN) λext nm (Δε): 252 (+9.2), 233 (−5.5)Source of chirality: d-(+)-glucose

Benzyl 2,3-di-O-acetyl-4,6-bis-O-(4-bromobenzoyl)-1-thio-β-d-glucopyranosideC31H28Br2O9S[α]D = −49.8 (c 0.8, CHCl3)CD (CH3CN) λext nm (Δε): 252 (+12.9), 234 (−8.5), 211 (−8.9)Source of chirality: d-(+)-glucose