H CH 2 -OH (4) H b. (5) H H. (6) a. b.

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1 ame Key 15 F010-Exam o. Page I. (15 points) For each of the following pairs of compounds, predict which compound is more acidic. Compare the two underlined s for each pair and circle the compound that is more acidic for each pair. The more acidic compound for each pair will be (circle one): (1) F a. F C C - F C C - () a. () a. Cl C (5) a. C C C () a. S S (6) a. C II. (a) (9 points) Show the structures of the three possible conjugate acids of and explain, in several words, as to which of the three conjugate acids is most stable and would be expected to form preferentially. Use drawings of pertinent resonance form(s) and several words to explain your answer. three possible conjugate acid structures: 1... explanation: #1 is the most stable conjugate acid. Unlike the other two, #1 has two idential resoance structures where the positive charge is delocalized over the two atoms. 6 (b) (6 points) The pk a values of indole and are estimated to be 0.1 and 11.9, respectively. Explain this difference in pk a values using resonance structures of the conjugate bases of the two compounds. indole explanation: pk a ~0.1 The conjugate base of has two identical resonance structures where the negative charge is delocalized over the two atoms pk a ~11.9 indole 6

2 ame Key 15 F10-Exam o. Page III. (8 points) Glycoside 1 is a new steroidal saponins isolated from the rhizomes of Polygonatum kinigianum, one of the original plants commonly known as uang-jing in traditional Chinese medicine [elv. Chhem. cta 010, 9, 1086]. Treatment of the glycoside, 1, with the enzyme β glycosidase provides trisaccharide. nswer the following questions about this glycoside 1 and trisaccharide. α β α 1 enzyme (1) ( points) Label each of the glycosidic bonds in glycoside 1 using a small arrow ( ). C B () ( points) Classify each glycosidic linkage in 1 as α or β right next to each of the arrows you have shown. () ( points) ow many D-sugar units does trisaccharide have? (circle one) 0 1 () ( points) Is the hemi-acetal in trisaccharide α or β? (circle one) α β (5) ( points) Is trisaccharide a reducing sugar? (circle one) Yes o (6) ( points) Describe the linkages between the following sugar units [e.g., α(1 -> 6)]: For and C: α(1 >) For B and C: α(1 >) (7) (1 points) Draw Fischer projections for the open-chain forms of the three carbohydrates produced when glycoside 1 is hydrolyzed with a warm dilute aqueous acidic solution. Carbohydrate Carbohydrate B Carbohydrate C C C C

3 ame Key 15 F10-Exam o. Page IV. (1 points) Treatment of glycosyl trichloroacetimidate 1 with isopropyl alcohol () in the presence of a catalytic amount of a strong acid results in the formation of an anomeric mixture of glycosides [ngew. Chem. Int. Ed. 010, 9, 87]. Propose in the box below a step-by-step, curved-arrow reaction mechanism for this transformation from 1 to. You may use - and - for the catalytic acid and its conjugate base, respectively. You do not need to balance each step. PhC PhC PhC Mechansim: PhC 1 PhC PhC PhC CCl CCl PhC PhC 1 acid catalyst () C Cl (solvent) PhC PhC PhC PhC CCl PhC PhC PhC PhC PhC PhC PhC anomeric mixture mech. arrows for each step: pts each intermediate: pts PhC V. ( points) Treatment of hydroxy ester with a catalytic amount of p-toluenesulfonic acid (Ts; pka -0.51) results in the formation of its lactone derivative, 5, shown below [ngew. Chem. Int. Ed. 010, 9, 5887]. Provide in the box below a step-by-step, curved-arrow reaction mechanism for this transformation from the hydroxy ester. You may use - and - for the acid Ts and its conjugate base, respectively. Mechanism: C Ts (catalytic) 5 + C 1 C mech. arrows: pts/set interm. structure: pts each C C C C 5

4 ame Key 15 F10-Exam o. Page 5 VI. (18 points) Complete the following reaction schemes by providing in the boxes the structures of the corresponding products. Make sure to indicate the stereochemistry where applicable. (1) [Synthesis 010, 51] K C ( equiv) C I ( equiv) C C + KI () [Synthesis 010, 51] C C C C + C C () [J. Med. Chem. 010, 5, 777] C C + () [J. Med. Chem. 010, 5, 777] ac C C (5) [Chem. Eur. J. 010, 16, 1788] C 1 6 C 1 17 ac C C C or C

5 ame 15 F10-Exam o. Page 6 VII. (18 points) Complete the following reaction schemes by providing in the boxes the structures of the corresponding products. Make sure to indicate the stereochemistry where applicable. (1) [J. Med. Chem. 010, 5, 796] a (1 equiv) a or the enolate form + Br w/o stereo. designation acceptable + abr + enatiomer () [J. rg. Chem. 010, 75, 716] 5% K C C + K + () [Chem. sian J. 010, 5, 19] C 11 1 BrMg MgBr 1.. aq Cl meso! C 8 16 () [rg. Lett. 007, 9, 01] C Ph 1. LD -78 C. I C Ph + LiI C C