ame Key W06-Exam o. Page I. ( points) A disaccharide is cleaved by a β-glycosidase, an enzyme that specifically hydrolyzes a β- glycosidic linkage. When the disaccharide is treated with excess dimethyl sulfate [(C ) S ]/a/ and then hydrolyzed under aqueous acidic conditions at around 90 C, two monosaccharide products are formed:,,-tri--methyl-d-mannopyranose () and,,,6-tetra--methyl-d-galactopyranose (). C C!-D-mannopyranose!-D-galactopyranose () Draw in the box below the structure of the disaccharide. Each of the monosaccharide units should be drawn in the aworth projection formula and the stereochemistry of the anomeric hydroxyl group in the β- form. C C 6 () Draw in the boxes given below the structures of the two methylated monosaccharide products and in their most stable chair conformers. Assume the stereochemistry at the anomeric hydroxyl group to be in the β-form. For : For : C C C C C C C
ame Key W06-Exam o. Page II. ( points) Draw a Fischer projection formula for each of the following two compounds and assign its absolute stereochemistry using the D/L-designation. () C C C C C C () C C stereochemical designation: (C ) stereochemical designation: D ; L Circle the one that applies. D ; L Circle the one that applies. C Draw in an open-chain aldehyde form. C Draw in an open-chain aldehyde form. III. (0 points) Provide in the boxes below the structure of the expected reaction product from each of the following carbohydrate molecules (J. rg. Chem. 00, 67, 6). () C C C C C -I ( mol equiv) (anhydrous) CCl C C C!-anomer C I C () C C C BF (C C ) C (catalytic) PhS (. mol equiv) C CCl C C C C SPh C L-saccharide!!-anomer
ame Key W06-Exam o. Page IV. (9 points) For each of the following pairs of compounds, predict which compound is the more acidic. Compare the two underlined protons for each pair. The more acidic compound for each pair will be (circle one): () BrC C () C () () () (6) C - C C C C (C ) V. (7 points) The pk a values of the two acidic hydrogens of the enediol part of L-ascorbic acid (vitamin C) are.0 and.79. Which one of the two hydroxyl hydrogens at C- and C- is expected to be more acidic? C L-ascorbic acid - or - Circle one that applies. Explain briefly in the box below why the hydroxy hydrogen you selected is more acdic than the other by using resonance structures of their conjugate bases. C C The conjugate base from the - has the resonance form that places the negative charge at C-, whereas the negative charge in the conjugate base from the - can be delocalized over the larger area. VI. ( points) Complete each of the following Aldol condensation reaction sequences as necessary. () Tetrahedron Lett. 006, 7, 67. C C C C Br a 0 C C 88% C C C Br
VI. (continued) () rg. Lett. 006, 8, 87. ame Key W06-Exam o. Page ac C 60 C C C C C C ~60% () Tetrahedron Lett. 006, 7, 08. TP MEM (PhC ) - C(=)CF benzene, 0 C 6% TP MEM MEM = C C C C VII. (6 points) Treatment of enone with a/ in ethanol resulted in the formation methyl ketone and sodium acetate (J. Med. Chem. 006, 9, ). In the box below draw a stepwise mechanism by the use of the curved arrow convention. You may use as the base. You don t need to balance each step. C a/ C C C C - a C C - a C C C R C C C C C C C R (R = or C C C ) C C C C C C C - a C C - a 6
VIII. (9 points) Complete each of the following reaction sequences as necessary. ame Key W06-Exam o. Page 6 ()!(rg. Lett. 006, 8, 9).. LDA ( mol equiv) ( mol equiv) TF - Li Li-enolate ( mol equiv) C. workup C 8 p-ts toluene (solvent) 90 C C C () C heating. LiAl. aqueous workup C Provide the reagents. () J. Med. Chem. 006, 9, 67. Boc DCC C Ph ote: Boc = DCC = C Boc C Ph CF C C Ph CF C - salt