| Autor: |
Madern JM; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands., Hansen T; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands., van Rijssel ER; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands., Kistemaker HAV; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands., van der Vorm S; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands., Overkleeft HS; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands., van der Marel GA; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands., Filippov DV; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands., Codée JDC; Leiden Institute of Chemistry , Leiden University , Einsteinweg 55 , CC Leiden 2333 , The Netherlands. |
| Abstrakt: |
Thiosugars, sugars that have their endocyclic oxygen substituted for a sulfur atom, have been used as stable bioisosteres of naturally occurring glycans because the thiosugar glycosydic linkage is supposed to be stabilized toward chemical and enzymatic hydrolysis. We have performed an in-depth investigation into the stability and reactivity of furanosyl thiacarbenium ions, by assessing all four diastereoisomeric thiofuranosides experimentally and computationally. We show that all furanosyl thiacarbenium ions react in a 1,2- cis-selective manner with triethylsilane, reminiscent of their oxo counterparts. The computed conformational space occupied by the thiacarbenium ions is strikingly similar to that of the corresponding furanosyl oxycarbenium ions, indicating that the stereoelectronic substituent effects governing the stability of furanosyl oxocarbenium ions and thiacarbenium ions are very similar. While the thio- ribo-furanose appears to be less reactive than its oxo counterpart, the thio- ara-, lyxo-, and xylo-furanosides appear to be more reactive than their oxygen equivalents. These differences are accounted for using the conformational preference of the donors and the carbocation intermediates. The lower reactivity of the thio- ribo furanosides in (Lewis) acid-mediated reactions and the similarity of the thia- and oxocarbenium ions make thio- ribo-furanosides excellent stabilized analogues of the naturally occurring ribo-furanose sugars. |
