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 A 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 A: Structures in equilibrium at point B: (ii) Structure at the isoelectric point: 6 6 4 (2) (16 points) Draw the full structure (including stereochemistry) for the tri-peptide Tyr-Phe-Arg (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) +2 +1 0-1 -2 The predominant form of this tripeptide at p 11 has a net charge of: (circle one) +2 +1 0-1 -2 (3) (10 points) Complete the following reaction sequence by providing in each of the boxes the structure of the product [J. rg. Chem. 2010, 7, 3027]. Ph 1. 4M aq Cl 2. (C 2 C 3 ) 3 8 DCC 4 4 + C 2 + +
ame 21 F10-Final Exam Page 3 II. (42 points) (1) (16 points) Treatment of enone A with a/ 2 results in the formation of cyclohexanone (C) 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 A B C D + Mechanism for A -> B: a A Mechanism for B -> C and D: B a B 6 (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. D C 10 Mechanism: C 3 C 2 ac 2 C 3 C 2 C 3 a C 2 C 3 + enantiomer C 3 C 2 C 2 C 3 a a C 2 C 3 26
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 -A as your Brønsted acid and A- as its conjugate base. (1) (26 points) 2 Mechanism: 2 Cl/ 2 2 2 + Cl 2 2 A 2 2 Cl 26 (2) (30 points) [rg. Lett. 2010, 12, 904] C 3 C 3 Ts (catalytic) + 2 C 3 Mechanism: C 3 A C 3 30
ame 21 F10-Exam Exam Page IV. (38 points) Shown below is a trisaccharide recently isolated from Securidaca welwitschii [elv. Chim. Acta 2010, 93, 2237]. Answer the following questions about this trisaccharide, 1. A C B 1 (1) (4 points) Label each of the glycosidic bonds in trisaccharide 1 using a small arrow ( ). (2) (4 points) Classify 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) 0 1 2 3 (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 A and B: For B and C: (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. Carbohydrate A Carbohydrate B Carbohydrate C 6 6
ame 21 F10-Final Exam Page 6 V. (32 points) Complete 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] C 3 Ts (catalytic) + C 3 (2) Ph Ph Ph Ph Ph Br (gas) C 2 Cl 2 (solvent) α-anomer 2 (1 equiv) K 2 C 3 S 2 + 4 x Ph C 3 ac 3 (catalytic) C 3 (sovent) (3) [rg. Lett. 2010, 12, 904] K + KCl Cl C 3 4 (4) [J. Am. Chem. Soc. 2010, 132, 14064] LDA (2 equiv) 1. C 3 I (1 equiv) C 2 C 3 TF, -78 C 2. Cl Si dilithium dianion 4 4 + LiI + LiCl
ame 21 F10-Final Exam Page 7 VI. (30 points) Complete 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] C 2 C 3 K 2 C 3 (2) C 2 C 3 C 3 C 2 2 (excess) heat + 2 + C 3 C 2 (3) 1. 3 C C C 2. aq 4 Cl (protonation) Li PCC (4) C 3 C 3 C 3 C 3 + Br a C 3 + 2 () Li Li C 2 C 3 1. 2. aq 4 Cl (protonation) (1 equiv) Br + LiBr + Li +
The Reagent List Page 10 Shown below is a list of key reagents (not always the whole recipe) that may be useful for solving questions on the final exam. reagent classification or specialized use From s 4 oxidation Chem 210 KMn 4 oxidation peroxyacid epoxidation (e.g., 3- or meta-chloroperoxybenzoic acid) i. 3 ; ii. (C 3 ) 2 S or Zn ozonolysis i. 3 ; ii. 2 2 ozonolysis a 2 base, nucleophile a base KC(C 3 ) 3 bulky base 2 /Pd hydrogenation 2 /Pd, BaS 4, quinoline hydrogenation i. B 3 or 9-BB; ii. 2 2, a hydroboration PBr 3 e.g., R- R-Br SCl 2 e.g., R- R-Cl p-c 3 C 6 4 S 2 Cl (p-tscl) tosylate formation C 3 S 2 Cl (MsCl) mesylate formation -bromosuccinimide (BS) Br source of electrophilic Br =========================================================================== Ch. 13 C + ClCr 3 - (PCC) oxidant Cr 3 / 2 S 4 / 2 /acetone oxidant i. ClC(=)-C(=)Cl, (C 3 ) 2 S; ii. (C 2 C 3 ) 3 oxidant Ch. 14 ab 4 nucleophilic hydride LiAl 4 nucleophilic hydride diisobutylaluminum hydride (DIBAL) nucleophilic hydride RMgX nucleophilic carbon RLi nucelophilic carbon 4-C 3 C 6 4 S 3 (p-ts) (pka ~ -1) organic-soluble acid Raney i SC 2 C 2 S; SC 3 BF 3 (C 2 C 3 ) 2 Lewis acid 2 2 2 desulfurization thioacetal/thioketal formation hydrazone formation oxime formation
Page 11 Ch. 1 SCl 2 R-C(=) R-C(=)Cl Ag 2, a, 2 2 oxidant - + C2 2 (diazomethane) e.g., R-C(=) R-C(=)C 3 Ch. 17 Li[C(C 3 ) 2 ] (LDA) bulky base K 2 C 3 weak base Amino acids & proteins C 6 11 =C=C 6 11 (DCC; dicyclohexylcarbodiimide) PhC 2 C(=)Cl (benzyl chloroformate) RC(=) 3 (R = tert-butyl) [tert-butyl--c(=)-] 2 (Boc 2 ) RC(=) activation -protection -protection -protection 3 C C C C 3 3 C 3 C C 3 C 3 (9-fluoromethyl)methoxycarbonyl chloride (Fmoc) -protection Cl C 2 Cl 3 CC(=) 2, Pd/C Sanger s reagent -deprotection catalytic hydrogenolysis -terminus AA determination 2 F 2
The 20 naturally occurring amino acids Page 12 eutral amino acids 2 C 3 Alanine 2 2 Asparagine 2 2 Leucine Isoleucine 2 Serine 2 Threonine Acidic amino acids 2 Aspartic acid 2 Glutamic acid 2 S Cysteine 2 2 Glutamine 2 Glycine 2 SC 3 Methionine 2 Phenylalanine Proline 2 2 2 Tryptophan Tyrosine Valine Basic amino acids 2 Arginine 2 istidine 2 2 Lysine 2 pka Values for the Ionizable Functional Groups of an α-amino Acid Amino acid α-c(=) + α- 3 side chain Alanine 2.3 9.87 - Arginine 2.01 9.04 12.48 Asparagine 2.02 8.80 - Aspartic acid 2.10 9.82 3.86 Cysteine 2.0 10.2 8.00 Glutamic acid 2.10 9.47 4.07 Glutamine 2.17 9.13 - Glycine 2.3 9.78 - istidine 1.77 9.18 6.10 Isoleucine 2.32 9.76 - Leucine 2.33 9.74 - Lysine 2.18 8.9 10.3 Methionine 2.28 9.21 - Phenylalanine 2.8 9.24 - Proline 2.00 10.60 - Serine 2.21 9.1 - Threonine 2.09 9.10 - Tryprophan 2.38 9.39 - Tyrosine 2.20 9.11 10.07 Valine 2.29 9.72 -