1 / 11

25.13 Glycosides

25.13 Glycosides. Glycosides. Glycosides have a substituent other than OH at the anomeric carbon. Usually the atom connected to the anomeric carbon is oxygen. Glycosides. O -Glycosides are mixed acetals. CH. O. OH. O. H. CH 2 O H. O-Glycosides are mixed acetals. hemiacetal. CH. O.

darby
Download Presentation

25.13 Glycosides

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 25.13Glycosides

  2. Glycosides • Glycosides have a substituent other than OH at the anomeric carbon. • Usually the atom connected to the anomeric carbon is oxygen.

  3. Glycosides • O-Glycosides are mixed acetals.

  4. CH O OH O H CH2OH O-Glycosides are mixed acetals hemiacetal

  5. CH O OH O H CH2OH OR O H O-Glycosides are mixed acetals hemiacetal ROH acetal

  6. Preparation of Glycosides • Glycosides of simple alcohols (such as methanol) are prepared by adding an acid catalyst (usually gaseous HCl) to a solution of a carbohydrate in the appropriate alcohol. • Only the anomeric OH group is replaced. • An equilibrium is established between the a and b-glycosides (thermodynamic control). The more stable stereoisomer predominates.

  7. CH O HOCH2 O HO OH H HO OCH3 H HO OH OH H OH H HOCH2 O HO CH2OH HO OH OCH3 Preparation of Glycosides CH3OH HCl + D-Glucose

  8. HOCH2 O HO HO OCH3 OH HOCH2 O HO HO OH OCH3 Preparation of Glycosides Methylb-D-glucopyranoside + Methyla-D-glucopyranoside(major product)

  9. HOCH2 •• O HO •• HO OH OH HOCH2 •• O HO •• HO + H OH Mechanism of Glycoside Formation • carbocation is stabilized by lone-pair donation from oxygen of the ring HCl

  10. HOCH2 HOCH2 •• CH3 O O HO •• HO HO O HO •• + OH H OH + O •• H H3C CH3 HOCH2 •• O O •• •• HO •• H HO + H OH Mechanism of Glycoside Formation +

  11. HOCH2 HOCH2 •• CH3 O O HO •• HO HO O HO •• + OH H OH + + O –H •• H H3C HOCH2 •• HOCH2 O •• HO •• O •• HO HO •• HO OCH3 OH •• OH OCH3 •• •• Mechanism of Glycoside Formation + +

More Related