Draw the Haworth projection of the disaccharide made by joining D-galactose and D-ribose with a B(1-3) glycosidic bond. Ift one anomer, you can draw any of them
The Correct Answer and Explanation is :
iturn0image0turn0image1turn0image3turn0image5The disaccharide formed by linking D-galactose and D-ribose through a β(1→3) glycosidic bond is a rare and specific linkage. In this bond, the anomeric hydroxyl group of D-galactose (at C1) is connected to the hydroxyl group on C3 of D-ribose.
Haworth Projections of D-Galactose and D-Ribose:
1. **D-Galactose:**
- D-galactose is an aldohexose that forms a six-membered pyranose ring.
- In its β-anomeric form, the hydroxyl group on the anomeric carbon (C1) is equatorial (up) relative to the ring.
- The hydroxymethyl group (-CH₂OH) on C6 is axial (down).
2. **D-Ribose:**
- D-ribose is an aldopentose that forms a five-membered furanose ring.
- In its β-anomeric form, the hydroxyl group on the anomeric carbon (C1) is equatorial (up) relative to the ring.
- The hydroxymethyl group (-CH₂OH) on C5 is axial (down).
Formation of the β(1→3) Glycosidic Bond:
- The anomeric hydroxyl group of D-galactose (C1) reacts with the hydroxyl group on C3 of D-ribose. - This reaction results in the formation of a β(1→3) glycosidic bond, where the anomeric carbon of D-galactose is connected to C3 of D-ribose.
Haworth Projection of the Disaccharide:
- The disaccharide consists of the D-galactose and D-ribose units linked by the β(1→3) glycosidic bond. - In the Haworth projection, the D-galactose unit is on the left, with its anomeric hydroxyl group pointing up (equatorial). - The D-ribose unit is on the right, with its anomeric hydroxyl group also pointing up (equatorial). - The glycosidic bond connects the anomeric carbon of D-galactose to C3 of D-ribose.
Explanation:
The β(1→3) glycosidic bond is less common than other glycosidic linkages, such as β(1→4) or α(1→4), which are prevalent in disaccharides like lactose and maltose. This rarity is due to the specific orientation required for the hydroxyl groups on C1 of D-galactose and C3 of D-ribose to undergo condensation. The β-anomeric forms of both sugars facilitate this linkage, as the hydroxyl groups are positioned equatorially, allowing for the necessary spatial alignment.
Understanding the formation and structure of such disaccharides is crucial in biochemistry, as it provides insights into the diversity of carbohydrate structures and their potential biological functions. The β(1→3) glycosidic bond contributes to the structural complexity of polysaccharides and glycoproteins, influencing their properties and interactions in biological systems.
For a visual representation and further details on Haworth projections, you can refer to resources like Master Organic Chemistry’s article on the Haworth Projection. citeturn0search1