Chemistry Exam: Amino Acids, Peptides, Terpines, and Organic Reactions - Prof. Tomikazu Sa, Exams of Organic Chemistry

Download Chemistry Exam: Amino Acids, Peptides, Terpines, and Organic Reactions - Prof. Tomikazu Sa and more Exams Organic Chemistry in PDF only on Docsity! CHEM 239A Summer, 2007 FINAL EXAM Name . Prof. Sasaki 175 points TOTAL Good Luck! Note: Only answers in the box will be graded. ______________________________________________________________________ 1. (45) (a) Draw the complete structure of the dipeptide, Ala-Glu, in the form that is predominant at pH = 7. Ala is alanine, and Glu is glutamic acid. (b) Amino acid analysis of a tripeptide showed two peaks, Gly and Asp with the ratio of 2 : 1. The N-terminal residue of the tripeptide was identified to be Gly by the Sanger method. Draw all possible sequences that are consistent with the N-terminal residue analysis and the amino acid composition. Label N-terminal and C-terminal residues in the sequences. Gly is glycine. Asp is aspartic acid. (c) Draw a stepwise mechanism for the reaction of Ala and 2,4-dinitrofluorobenzene. CHEM 239U page 2 Name . 2. (40) (a) Carefully circle the isoprene units in the following terpines, and label each as a monoterpine, sesquiterpine, or diterpine. (i) (ii) O O (iii) O O CH3 CH3 O CH3 (b) Retrovirus like HIV I, the pathogen responsible for AIDS, incorporate an RNA template that is copied into DNA during infection. The reverse transcriptase enzyme that copies RNA into DNA is relatively nonselective and error-prone, leading a high mutation rate. Its lack of selectivity is exploited by the anti-HIV drug AZT (3'-azido-2',3'-dideoxythymidine), which becomes phosphorylated and is incorporated by reverse transcriptase into DNA, where it acts as a chain terminator. Mammalian DNA polymerases are more selective, having a low affinity for AZT, so its toxicity is relatively low. Draw the structures of AZT and AZT 5'-triphosphate, the derivative that inhibits reverse transcriptase. AZT AZT 5'-triphosphate