TA Section Day/Time. Organic Chemistry EXAM 2A (200 points)

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1 UCC, Binder ame TA ection Day/Time rganic Chemistry EXAM 2A (200 points) D T WITE TE EXAM TU TE PAGE UTIL ITUCTED T D. In the meantime, please read the instructions below. Page 1 (25) Page 2 (25) Page 3 (40) Page 4 (35) Page 5 (40) Page 6 (35) Total (200) % In each of the following problems, use your knowledge of organic chemistry conventions to answer the questions in the proper manner. Be sure to read all instructions carefully. You have 1.5 hours to complete this exam. Point distributions are given throughout the exam so you can use your time wisely. Pencil is preferred, but blue or black ink is okay if you write neatly. Do not use colorful (red, purple, etc.) pens as this interferes with grading. We are happy to answer questions, but please read instructions twice before asking. Write your Last ame, First Initial at the top of each of the following pages. Make sure your belongings are in order now so that you can leave quietly when you are finished. Keep your eyes on your own paper. Cheat sheets and electronic devices are not allowed, including cell phones and calculators. Any student found using any of said devices, or found examining another student s exam, will be promptly removed from the exam room and at minimum will receive a zero on this exam. uch an incident will be reported to the UCC Judiciary Affairs Committee.

2 1. Fundamentals (a) (5 points) Provide the approximate pka s of the following compounds on the lines provided (b) (10 points) Circle the most acidic proton on each compound and estimate its pka. + 3 C 2 (c) (10 points) Advanced Functional Groups! Follow the arrows and fill in the box. Draw the missing enaminol (contains an alkene, amine, alcohol) in the box provided. 229 Lys C 2 P 2 3 C :B C 2 P 2 3 Iminium retroaldol C C 2 P 2 3 Glyceraldehyde 3phosphate (GAP) + Enaminol Draw the missing thiohemiacetal. is + Cys C 2 P 2 3 Glyceraldehyde 3phosphate (GAP) Covalent binding to enzyme Thiohemiacetal is 1

3 2. Carbohydrates (a) (15 points) The conversion of αdmannopyranose 6phosphate into Dfructofuranose 6 phosphate is a fourstep process involving (1) ring opening of the pyranose, (2) tautomerization of the aldose into an enediol, (3) tautomerization into the ketose, and finally (4) closing of the furanose ring. how the structures of these intermediates without abbreviations in the boxes provided (K to keep the phosphate in condensed form). o mechanisms necessary, but you re welcome to add them if it s helpful to you. nly the structures in the provided boxes will be graded. 2 3 P αdmannopyranose 6Phosphate P DFructofuranose 6 Phosphate DMannose 6Phosphate (an aldose) Enediol of DMannose 6Phosphate DFructose 6 Phosphate (a ketose) (b) (10 points) Draw the aworth projection for milk sugar (lactose): βdgalactopyranosyl(1à4)βdglucopyranoside disaccharide formed from Dgalactose and D glucose linked by a β1,4glycosidic bond. DGalactose is the C4 epimer of glucose. The ring template is provided for reference only. edraw the rings. 2

4 3. Mechanism Warmup (a) (15 points) The final stages in the biosynthesis of epiaristolochene are shown below. Follow the arrow in the first step to draw the intermediate in the box provided. Add arrows to complete the mechanisms in the remaining four steps. + Draw this intermediate, then add arrow(s) for all remaining steps :B epiaristolochene (stereochem incorporated along the way, not shown until now!) (b) (25 points) Cannabinoids are activated by heat through a decarboxylation reaction. Draw the keto tautomer of cannabidiolic acid (CBDA) in the box provided. Add the arrows in both steps, along with bases (:B) or acids ( + ) where appropriate to explain each step in the decarboxylation of CBDA to form cannabidiol (CBD). Cannabidiolic Acid (CBDA) add arrows, :B and/or + to explain keto formation keto tautomer of CBDA draw this structure, then add arrows with :B and/or + if appropriate to explain formation of CBD Δ C 2 Cannabidiol (CBD) 3

5 4. Fill in the Boxes o arrowpushing necessary, only structures in boxes graded. (a) (25 points) Draw each intermediate in beginning stages of the mavelonate pathway, in addition to the active portions (abbreviated forms) of ADP and ADP +. The active parts of ADP / AD and ADP + / AD + are the same. 1 + Claisen condensation aldollike reaction 2a (3)3ydroxy3 methylglutaryl CoA 2b ydrolysis ( 2 ) 2 ADP thioester reduction 3 ADP (same as AD abbreviated form) + ADP + (b) (10 points) how the intermediates involved in the activation of a carboxylate group with DCC followed by coupling with an amine. Intermediate in ucleophilic Acyl ubsitution Mechanism '=C=' (DCC) + 2 " :B ' ' " 4

6 5. eaction Mechanisms (40 points) how the mechanism for the conversion of α ketoglutarate into succinyl CoA. The reaction involves (1) nucleophilic addition reaction of TPP ylid to the ketone in α ketoglutarate, (2) decarboxylation to form an enaminol, (3) addition of alkene in the enaminol to the sulfur atom in lipoamide, (4) elimination of TPP ylid to produce a thioester, (5) transesterification of the thioester with coenzyme A. Use the structures below to complete each step in this transformation, adding arrows and amino acid residues as acids and/or bases where appropriate. o additional intermediates are needed aside from the structures provided and in the boxes. TPP Adduct An Enaminol 2 C C 2 αketoglutarate TPP ylide 1 C 2 2 C 2 A Thioester 3 TPP ylide 4 2 C 5a CoA C 2 5b CoA C 2 uccinyl CoA 5

7 6. Active ite Design (35 points) The citric acid cycle involves the attachment of an incoming acetyl CoA molecule to oxaloacetate. This occurs by an initial tautomerization of acetyl CoA followed by an aldollike reaction of the enol of acetyl CoA. Fill in the box with the structure of the enol of acetyl CoA, then complete the mechanisms Design separate active sites for each step below with the following criteria in addition to standard mechanistic arrowpushing to complete each transformation: edraw the given components within the active site. Please D T draw the active sites around the structures provided or around the boxed structure. Each substrate (starting material) must be held in place by at least one bond to the peptide backbone. Amino acid residues must be used as acids and bases. o These residues must start in their natural physiological state. o You may use the same residues in both steps, but this is not required. Complete each mechanism in one step no additional intermediates aside from the enol. ot necessary to explain stereochemistry in final product. Also not necessary to draw redraw products as complex with enzyme. Tautomerization Enol of Aldollike reaction 2 C C 2 xaloacetate 2 C C 2 ()Citryl CoA Active site for tautomerization: Active site for aldollike reaction: 6