Winter 2007 blank-4 - Name: Page 1(W.07.215.FE p1) | (50...

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Unformatted text preview: Name: Page 1(W.07.215.FE p1) | (50 points) Complete the following reaction sequences, including stereochemistry as required. Label any multistep sets of reagents. 8) J00 2006, 71, 9622 CH30 \ 'w/O O H30+, H20 Why won't the product undergo an intramolecular acylation reaction? C7H1004 5 5 b) J. Chem. Educ. 2006, 83, 1821 1) CH CH —c=CM Br '14 PBr 3 2 _ g CH3CH2—CEC—IC—CH3—3» 2) H30+ OH W 5 o NEC\CH/2U\OCHZCH3 NaOCHZCH3 H20=CHCHzBr HOCHZCHg NaOCHZCH3 HOCHZCH3 5 C) JOC, 2007, 72, 2 M H20 BnO )1 CH3 OH C11H14O4 5 l \ %/ Cf207-2 H 2 (PDC) _ 5 (COC|)2. DMSO, Et3N (Swern) These first two reactions yield different singly oxidized products ll (42 points) Name: Page 2(W.07.215.FE p2) a) (JOC 2006, 71, 337) The antitumor antibiotic Belactosin-C was synthesized using the same chemistry that we presented for protein synthesis. Fill in the reactant/s and the i O HOJSlO O 8 b) L OH O\ /o- Triosephosphate HWO\ x0- HOCH2 O//P\Q‘ isomerase O//P\O' O ntermediate below. H2 Pd/CJ (double deprotection) H O \k/ HZN NVNJWZL H O O O Belactosin-C The enzyme triosephophate isomerase converts dihydroxy acetone phosphate to glyceraldehyde— 3-phosphate. The active site of the enzyme is shown below. In the first box, show the four mechanistic arrows which convert the dihydroxyacetone to an enediol intermediate. In the seco nd box, show the enediol intermediate. Then show the four arrows which convert the enediol to gcheraldehyde-3-phosphate. Note the Lys-13 is solely used to to hold the molecules in place and is not pan‘ of the mechanism. Four arrow mechanism to enediol o *9 H a“; o H G Gly-165 o l H_N/\\ — i=0 R” CHZOPO3'2 His-195 G) l‘“3 Lys-13 E Enedio/ intermediate and four arrow mechanism W _ _ 9 Iy 165 O H N/\\ R” \ His-195 G) l‘“3 Lys—13 c) The following reaction was proposed. Br OCH3 92“ > HO OCH3 %o H + O 3) H3O. H (protonatlon) O However, this plan was flawed and another product was observed that is a hemiketal isomer of the one that was predicted. What is it ? Name: Page 3(W.07.215.FE p3) III (54 points) Angew. Chem. Int. Ed. 2006, 45, 7481. Aniline has been shown to act as a nucleophilic catalyst for the formation of oximes. First an imine is formed: >03 + QM = xffl * W: aniline This is followed by a transimination under acidic, aqueous conditions: ff” — O + H2NOCH3 : >N‘OCH3 + QNHz aniline The imine formation (first step) is carried out in a pH 4.5 buffer. The authors state. "Since the pKa of a protonated carbonyl is in the range of —4 to —10, the concentration of this highly reactive electrophile is extremely low at pH 4.5." They suggest that the pH could be lowered to increase the concentration of the electrophile, but that there would be a resulting counteraction of this effect. Explain this counteraction. Show the mechanism for the acid catalyzed transimination. Please use HB for acid and B' for its conjugate base. Name: Page 4(W.07.215.FE p4) IV (60 points) a) (CL, 2007, 9, 727) The following alkyne undgoes rearrangement under acid conditions to an a,B-unsaturated ketone. The mechanism is described as an E1 loss of water followed by a carbocation rearrangement, addition of water to form the enol and isomerization to the keto form. Show the mechanism using HB for Bronstead acid and B' for its conjugate base. OH “'3 PhEPh Ph O Ph>:81\Ph Ph H @ b) The product of the rearrangement is used in an aldol condensation reaction. Show the product: 0 o TsOH Ph>:gkph + Ph H 0 + H20 0) Provide the IUPAC name for the following molecule: O H OOH CH30W HO H d) (Angew. Chem. Int. Ed. 2006, 45, 7481) Draw the structure of the pentapeptide Leu-Tyr—Arg-Ala-Gly at pH 7. Please use Draw the Fischer projection of Fischer projections. (S)—cysteine at its isoelectric point (pl): The pl of cystine is: WW la V (44 points) Name: Page 5(W.07.215.FE p5) (JOC 2007, 72, 1962) Aminoglycoside antibiotics such as neomycin B are widely used for treatment of a variety of infections including tuberculosis and pneumonia. They bind to RNA sequences in the bacteria ribosome which impedes mRNA translation, resulting in miscoding and ultimately bacteria cell death. The hydrolysis of neomycin B yields four molecules. H NH2 a) Draw the Fischer .0 Ho , Eg‘flfif’éih‘fifiiélfi HO NHZ H NH ng B furanose (Ring C) from H O 2 H / neomycm. I HOCH2 O o H OH H NH2 Ring 0/ H H NHzo OaH neomycin B ,/:1H ’0 CHZNHZ ngD 0: HH b) Draw the Fischer projection of the open chain form of the top pyranose ring (Ring A). I d) How many hemiacetals are in neomycin B? 0) Write the IUPAC name of the molecule in a. E (Circle one): 0 1 2 3 4 How many acetals are in neomycin B ? (Circle one): 0 1 2 3 4 6 e) (OL 2007, 7, 1227) UDP-a-(D)—mannopyranose was synthesized by creating a phosphoester link between the C1 of the sugar and the terminal phosphate of the nucleotide. UDP is uridine 5'-diphosphate and mannose is the CZ epimer of glucose. Draw UDP-a-(D)—mannopyranose. 10 1) 2) NaO—||3|’—O—||:|’—ONa (CH3(CH2)3)3N3 f) (CL 2007, 7, 1161) Complete the following parts of a synthesis of a dinucleotide disulfide. H0 T 1) NaOH koj 2) I2, py H Ph 8 Note, the thioester is Y hydrolyzed, then |2 acts 0 as a mild oxidant to form 0 dithymidine disulfide. T = | NH O O CNa CNa ‘ diTTP disulfide 6 3) |2 ,Hzo, Dy ...
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Winter 2007 blank-4 - Name: Page 1(W.07.215.FE p1) | (50...

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