Question

The sugar D-gulose is a sweet-tasting syrup. O=CC(O)C(O)C(O)C(O)C(O)C(O)CO D-Gulose a. Draw the Fisher projection for \(\mathrm{L}\) -gulose. b. Draw the Haworth structures for \(\alpha\) - and \(\beta\) -D-gulose.

Short answer

Draw Fisher projection for L-gulose by inverting chiral centers of D-gulose. For Haworth structures, form cyclic structures and position the -OH group downward for \(\alpha\)-D-gulose and upward for \(\beta\)-D-gulose.

Step-by-step solution

Understand the given SMILES structure

The given SMILES structure represents D-gulose. It describes the molecular structure of the sugar with hydroxyl groups (-OH) attached to the carbon atoms. The structure has six carbon atoms, which is typical for hexoses.

Determine the D-gulose Fisher Projection

A Fisher projection is a two-dimensional representation of a molecule. For D-gulose, place the -OH groups according to their position and orientation (right or left) relative to the main carbon chain. Ensure all chiral centers (carbon atoms with four different groups attached) are shown properly.

Convert D-gulose Fisher Projection to L-gulose

Change the chiral centers of D-gulose to their mirror image to obtain the Fisher projection of L-gulose. This is done by inverting the positions of the -OH groups (left to right and right to left) in the Fisher projection.

Draw Fisher Projection of L-gulose

Construct the Fisher projection of L-gulose from the inverted positions. Ensure that the -OH groups are correctly positioned relative to each chiral center.

Convert Fisher Projection of D-gulose to Haworth Projection

To draw the Haworth structures for \(\alpha\) and \(\beta\)-D-gulose, the Fisher projection of D-gulose must first be transformed into a cyclic form. The fifth hydroxyl group (OH) attacks the aldehyde carbon (C1) forming a hemiacetal. This creates a six-membered ring structure.

Draw \(\alpha\)-D-gulose Haworth Projection

In the \(\alpha\)-anomer, the -OH group on the anomeric carbon (C1) is positioned downward (trans to the CH2OH group at C5). Draw the six-membered ring with this orientation.

Draw \(\beta\)-D-gulose Haworth Projection

In the \(\beta\)-anomer, the -OH group on the anomeric carbon (C1) is positioned upward (cis to the CH2OH group at C5). Draw the six-membered ring with this orientation.

Key concepts

Fischer projection

A Fischer projection is a method for representing three-dimensional structures of molecules in two dimensions. It is particularly useful for depicting sugars, as it shows the relative orientations of all the substituents. In a Fischer projection, the molecule is imagined to be oriented so that the main carbon chain is vertical, with the most oxidized carbon atom at the top. Horizontal lines represent bonds coming out of the plane towards the viewer, while vertical lines represent bonds going behind the plane.