koofer(6) - other using the Gabriel sequence to accomplish...

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Week 4, set 1; chem. 109C summer 06 1. The acid promoted (viz., using hydronium ion/water) conversion of an amide to a carboxylic acid, and of an ester to a carboxylic acid constitute integral portions of the Gabriel synthesis of alpha amino acids. Be sure that you are clear of the relationships. In this context, please formulate a mechanism to account for the following transformations. Show, too, the by- products. R NR 2 O H 3 O H 2 O R OH O – this transformation provides an example of specific acid catalysis. Be mindful of the fact that the mechanism for chymotrypsin promoted cleavage of a peptide uses a general acid catalysis pathway instead. More to come. R OR O H 3 O H 2 O R OH O 2. Formulate a mechanism to show how an alkylated malonic acid (see below) undergoes loss of carbon dioxide when heated. As you recall, this transformation is also part of the Gabriel sequence. HO OH O O R heat HO O R + CO 2 3. Devise two synthetic routes to leucine, one using the HVZ reaction as an important step, the
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Unformatted text preview: other using the Gabriel sequence to accomplish the task. 4. Supply reagents that could be used to accomplish the sequence illustrated below. CH 2 (CO 2 Et) 2 CO 2 Et CO 2 Et CO 2 H 5. Given a pH of 7.3, determine the net charge on aspartic acid, histidine, arginine. You’re your work. Would it be possible to separate these substances using gel electrophoresis (at this pH)? Explain. 6. Determine the pI for asparagine. Show your reasoning – in the manner illustrated in today’s class. 7. Determine the equilibrium constant for the acid-base reaction of diethyl malonate and sodium ethoxide. Show your work. [Hint: You will have to consult Appendix II of your text to determine the appropriate pKa values for the component acids; use values that are rounded-off.] Generalize, in words, what you have discovered....
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