Chapter 24 - Carbohydrates. After completing this chapter, students will be able to: Given a molecule in a fisher projection, be able to convert it to a wedge/dash representation and vice versa; given a hexopyranose, be able to determine the configuration of the anomeric carbon stereocenter as α or β. | Carbohydrate = Cn(H2O)n Carbohydrates occur in nature in nucleic acids, fats, cellulose, fibers, starch, “table sugar,” antibiotics, and other biological molecules. “Hydrated carbon” A pentahydroxyaldehyde Important recognition molecules on the cell surface: Chapter 24: Carbohydrates Naming The simplest carbohydrates are the sugars or saccharides. They constitute polyhydroxy-aldehydes (aldoses) or -ketones (ketoses); they form oligomers by ether bridges (hence di-, tri-, tetrasaccharide, etc.). The simplest sugars, both C3(H2O)3: 2,3-Dihydroxypropanal (Glyceraldehyde) An aldotriose 1,3-Dihydroxyacetone A ketotriose Chain length: Triose, tetrose, pentose, etc. Chiral Fischer projections: Review chapter 5 Some important monosaccharides: Dextrose, blood sugar, grape sugar Sweetest natural sugar; fruits Ribonucleic acids 4 Stereo-centers 3 Stereo-centers * * * * * * * * * * Fischer Projection: A flat stencil CH3 CH2CH3 H Br Eyes in the plane of the board Depending on your starting . | Carbohydrate = Cn(H2O)n Carbohydrates occur in nature in nucleic acids, fats, cellulose, fibers, starch, “table sugar,” antibiotics, and other biological molecules. “Hydrated carbon” A pentahydroxyaldehyde Important recognition molecules on the cell surface: Chapter 24: Carbohydrates Naming The simplest carbohydrates are the sugars or saccharides. They constitute polyhydroxy-aldehydes (aldoses) or -ketones (ketoses); they form oligomers by ether bridges (hence di-, tri-, tetrasaccharide, etc.). The simplest sugars, both C3(H2O)3: 2,3-Dihydroxypropanal (Glyceraldehyde) An aldotriose 1,3-Dihydroxyacetone A ketotriose Chain length: Triose, tetrose, pentose, etc. Chiral Fischer projections: Review chapter 5 Some important monosaccharides: Dextrose, blood sugar, grape sugar Sweetest natural sugar; fruits Ribonucleic acids 4 Stereo-centers 3 Stereo-centers * * * * * * * * * * Fischer Projection: A flat stencil CH3 CH2CH3 H Br Eyes in the plane of the board Depending on your starting dashed-wedged line structure, several Fischer projections are possible for the same molecule. Br H C CH3 CH2CH3 H Br Rules reminder: 180 º turn or double exchange leaves stereochemistry intact Most sugars are chiral and occur enantiomerically pure. Simplest case, one stereocenter: In almost all natural sugars, the stereocenter furthest away from carbonyl (drawn at the top) has the same absolute configuration as D-glyceraldehyde: “D-sugars” D and L are an older nomenclature (predates the knowledge of the absolute configuration of glyceraldehyde). The dextrorotatory enantiomer was called D, the other L. Later, D was found to be R, L therefore S. Commonly: Natural Unnatural Rules for arranging the Fischer stencil: Carbonyl on top, places bottom C*OH on the right in the D sugars. D-Threose L-Threose D-Erythrose L-Erythrose The Family of D-Aldoses rare unnatural rare unnatural unnatural rare L-form more common 11/20/2014 7 L-arabinose is in fact more common than D-arabinose in nature and is found
