Lecture 37 Chapter 25 Carbohydrates Fischer projections Cyclic

Lecture 37 – Chapter 25 : Carbohydrates • Fischer projections • Cyclic forms – hemiacetal formation, 6 vs. 5 • Mutarotation • Glycosides – formation and examples • Disaccharides • Oligosaccharides and Polysaccharides • Miscellaneous reactions

Simple monosaccharides – Fischer depictions D-glucose D-galactose D-Fuc. NAc D-Man. Ac. A D-glucosamine D-Ribose N-acetyl-D-glucosamine 2 -Deoxy-D-ribose

Aldohexoses – cyclic forms and their interconversion All present in solution, free sugars can interconvert

Mutarotation • dissolve dextrose in water, measure [a]D : +112. 2 • dissolve b-D-glucopyranose in water, measure [a]D : +18. 7 • allow either to equilibrate, measure [a]D : +52. 5

Glycosides • Free sugar + alcohol + acid gives a glycoside • Glycosides are no longer free sugars and do not mutarotate

Glycosides - disaccharides • Organic synthesis limited by protecting group chemistry needed • Bioorganic enzymatic synthesis now making oligosaccharides

Disaccharides – examples

Oligosaccharides – examples • Blood group antigens – extremely subtle differences in sugars in the epitope lead to important consequences in blood biochemistry

Polysaccharides – examples cellulose amylose

Synthetic vaccines Danishefsky et. al. Sloan-Kettering/Columbia – Synthetic vaccine against 3 types of cancer

Miscellaneous reactions of free sugars

Friday • Chapter 26 – Lipids and fats