D-glucose exists as two epimeric cyclic hemiacetals: a-D-glucopyranose (left, labeled hydroxy group is in the axial position) and B-D-glucopyranose (right, the labeled hydroxy group is in equatorial position). The two anomers equilibrate via the open aldehyde form. Draw the curved arrows to show the complete reaction mechanism for the conversion of one anomer to the other under acidic catalysis. HOH HOH Ho HO HO HO HO- H H HO- OH!-- H H OH H OHI H

rivatives: Nucleophilic Acyl Substitution Reactions - EOC O C-O [References] One step in the gluconeogenesis pathway for the biosynthesis of glucose is the partial reduction of 3-phosphoglycerate to give glyceraldehyde 3-phosphate. The process occurs by phosphorylation with ATP to give 1,3-bisphosphoglycerate, reaction with a thiol group on the enzyme to give an enzyme-bound thioester, and reduction with NADH. H-C-OH ATP ADP CH₂OPO32- 3-phosphoglycerate 0= OPO32- C H-C-OH CH₂OPO32 1,3-bisphosphoglycerate Enz-SH PO43- O= C S-Enz H-C-OH CH₂OPO3² (Enzyme-bound thioester) NADH/H+ O=C NAD*, Enz-SH H H-C-OH CH₂OPO3²- glyceraldehyde 3-phosphate Propose a structure for the first intermediate in the reaction of the enzyme-bound thioester with NADH to form glyceraldehyde 3-phosphate. To simplify the drawing process, substitute the structure below for the enzyme-bound thioester. S-CH3 substitute for the CH2CH3 enzyme-bound thioester You do not have to consider stereochemistry. • You do not have…

How many stereoisomers are possible for an aldopentose?

Draw the two possible Haworth structures for each the following sugars in their cyclized form. Be sure to label each as an ? or a ? anomer.