Structures in equilibrium at point A: Structures in equilibrium at point B: (ii) Structure at the isoelectric point: O O

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1 ame 21 F10-Final Exam Page 2 I. (42 points) (1) (16 points) The titration curve for L-lysine is shown below. Provide (i) the main structures in equilibrium at each of points and B indicated below and (ii) the structure at the isoelectric point. Draw the structures using the Fischer projections. (i) Structures in equilibrium at point : Structures in equilibrium at point B: (ii) Structure at the isoelectric point: (2) (16 points) Draw the full structure (including stereochemistry) for the tri-peptide Tyr-e-rg (all L amino acids) in the predominant form it would exist at its isoelectric point. Use the Fischer projections. Structure at the isoelectric point: The predominant form of this tripeptide at p 1 has a net charge of: (circle one) The predominant form of this tripeptide at p 11 has a net charge of: (circle one) (3) (10 points) omplete the following reaction sequence by providing in each of the boxes the structure of the product [J. rg. hem. 2010, 7, 3027]. 1. 4M aq l 2. ( 2 3 ) 3 D 2

2 ame 21 F10-Final Exam Page 3 II. (42 points) (1) (16 points) Treatment of enone with a/ 2 results in the formation of cyclohexanone () and acetone (D) via β-hydroxy ketone intermediate B. Provide in the box below a stepby-step mechanism using the curved arrow convention for the following transformation. You do not need to show a for each step. a/ 2 a/ 2 B D Mechanism for -> B: Mechanism for B -> and D: a B a D 2 pts for the intermediate 2 pts for each set of mech. arrows 2 pts for each intermediate B 2 pts for each set of mech. arrows 6 10 (2) (26 points) Provide in the box below a step-by-step mechanism using the curved arrow convention for the following transformation. You do not need to show a for each step. Mechanism: a a enantiomer a pts for each intermediate 2 pts for each set of mech. arrows a

3 ame 21 F10-Final Exam Page 4 III. (6 points) Provide in the boxes below a step-by-step mechanism using the curved arrow convention for each of the following transformations. You may use - as your ønsted acid and - as its conjugate base. (1) (26 points) 2 Mechanism: pts for each intermediate 2 pts for each set of mech. arrows (2) (30 points) [rg. Lett. 2010, 12, 904] l/ l 2 l Ts (catalytic) 2 3 Mechanism: pts for each intermediate 2 pts for each set of mech. arrows 30

4 ame 21 F10-Exam Exam Page IV. (38 points) Shown below is a trisaccharide recently isolated from Securidaca welwitschii [elv. him. cta 2010, 93, 2237]. nswer the following questions about this trisaccharide, 1. α β B 1 (1) (4 points) Label each of the glycosidic bonds in trisaccharide 1 using a small arrow ( ). (2) (4 points) lassify each glycosidic linkage in 1 as α or β right next to each of the arrows you have shown. (3) (3 points) ow many D-sugar units does trisaccharide 1 have? (circle one) (4) (3 points) Is the hemi-acetal in trisaccharide 1 α or β? (circle one) α β () (3 points) Is trisaccharide 1 a reducing sugar? (circle one) Yes o (6) (4 points) Describe the linkages between the following sugar units [e.g., α(1 -> 6)]: For and B: α(1 -> 2) For B and : β(1 -> 4) (7) (17 points) Draw Fischer projections for the open-chain forms of the three carbohydrates produced when trisaccharide 1 is hydrolyzed with a warm dilute aqueous acidic solution. arbohydrate arbohydrate B arbohydrate

5 ame 21 F10-Final Exam Page 6 V. (32 points) omplete the following reactions by providing in each of the boxes the structure of the reagent, intermediate, or product. Indicate stereochemistry for the product/intermediate and if more than one stereoisomer is formed, draw one structure and write enantiomer or diastereomer. (1) [Synthesis 2010, 3004] 3 Ts (catalytic) 3 (2) (gas) 2 l 2 (solvent) α-anomer 2 (1 equiv) K 2 3 S 2 (3) [rg. Lett. 2010, 12, 904] a 3 (catalytic) 4 x 3 3 (sovent) K l 3 3 diastereomer 4 Kl (4) [J. m. hem. Soc. 2010, 132, 14064] LD (2 equiv) Li Li 1. 3 I (1 equiv) Si 2 3 TF, l Si 2 3 dilithium dianion 4 diastereomer 4 LiI Lil

6 ame 21 F10-Final Exam Page 7 VI. (30 points) omplete the following reactions by providing in each of the boxes the structure of the product or intermediate. Indicate stereochemistry for the product/intermediate and if more than one stereoisomer is formed, draw one structure and write enantiomer or diastereomer. (1) [Synlett 2010, 3011] K 2 3 (2) 2 3 trans! enantiomer (excess) heat (3) aq 4 l (protonation) Li 3 P 3 (4) a () Li Li aq 4 l (protonation) (1 equiv) 2 3 Li Li