Organic Chemistry III
	Professor Carl C. Wamser
Chem 336 - Spring 2006	Exam 3 Answer Key

1. (20 points) Give complete structures for the following, including stereochemistry. Assume the compounds are at pH 7.

a) BOC-Trp

b) isopentenylpyrophosphate

c) Val-Pro

d) (R) stereoisomer of the monoglyceride of octadecanoic acid

e) the H-bonding pattern in a G-C base pair

2a. (6 points) Penicillins typically include the structure shown below. Name the two amino acids that are the likely precursors to penicillin. Put circles around the atoms that come from each one.

2b. (8 points) Nitrous acid (or nitrite) can act as a mutagen by reacting with amine groups to form diazonium ions that decompose in water. Cytosine and adenine react to form uracil and inosine. Show the structures of these reactants and products (i.e., the four underlined compounds).

3a. (4 points) L-Threonine is named for its analogous structure to the sugar threose (shown below). Show the expected stereochemistry at both stereocenters of L-threonine. (Remember L in amino acids refers to the alpha position.)

3b. (5 points) Identify (circle) the isoprene units in beta-ionone (a perfume ingredient). Compared to a typical terpene, what modification has apparently taken place?

There is an incomplete isoprene unit (only 3 carbons), which was probably the result of an oxidation reaction.

3c. (7 points) Number the atoms in the compound shown below, and illustrate how acid catalysis could convert it to beta-ionone (shown above).

4. (15 points) Complete each of the following reactions by writing the structures of the products, including stereochemistry:

a) Glu + excess CH3OH (H2SO4 catalyst) --->

b) Cys + excess CH3COCl --->

c) CBZ-Leu + SOCl2 , then Ala --->

d) Asn + Sanger’s reagent --->

e) acetyl-CoA + cyclohexylamine --->
(OK to write CoA without structure)

5. (10 points) Identify the unknown heptapeptide based on the following information:

* Complete hydrolysis gives equal amounts of Ala, Arg, Cys, Glu, Lys, Ser, Tyr
* Edman degradation releases Ser, then Tyr
* Chymotrypsin cleavage gives a dipeptide containing Ser and Tyr, plus X
* X is a pentapeptide with N-terminal Ala and C-terminal Glu
* Trypsin cleavage of X gives a tripeptide plus free Lys and Glu

Ser-Tyr-Ala-Cys-Arg-Lys-Glu

6. (15 points) In the metabolism of fatty acids the following steps are followed. For each step, add what is needed to balance the reaction. Use NADH / NAD+ for redox reactions.

7a. (5 points) Indicate what products would be expected from the transamination reaction of pyruvic acid and aspartic acid.

7b. (5 points) Select any naturally occurring molecule and explain why its molecular structure makes it particularly well suited to its function.

Lots of possibilities here.