Chemists discovered that when naturally occurring sugars were degraded to glyceraldehyde , the dhtrorotatory (+) enantiomer of glyceraldehyde was always obtained. on the other hand, the degradation of some synthetic sugars gave the levorotatory one (-). thus, carbohydrate chemists started using the fischer-rosanoff convention, which uses a D to designate the sugars that degrade to (+)-glyceraldehyde and a L to designate the sugars that degrade to (-)-glyceraldehyde.