Organic Chemistry

1032 CHAPTER 24 Catalysis

41. Proof that an imine was formed between aldolase and its substrate was obtained by using D-fructose-1,6-diphosphate, labeled at the
    C-2 position with as the substrate. was added to the reaction mixture. A radioactive product was isolated from the
    reaction mixture and hydrolyzed in an acidic solution. Draw the structure of the radioactive product obtained from the acidic
    solution. (Hint: reduces an imine linkage.)


42. 3-Amino-2-oxindole catalyzes the decarboxylation of -keto acids.
    a. Propose a mechanism for the catalyzed reaction.
    b. Would 3-aminoindole be equally effective as a catalyst?


43. a. Explain why the alkyl halide shown here reacts much more rapidly than do primary alkyl halides, such as butyl chloride and
    pentyl chloride, with guanine residues.

b. The alkyl halide can react with two guanine residues in two different chains, thereby cross-linking the chains. Propose a

mechanism for the cross-linking reaction.

44. Triosephosphate isomerase catalyzes the conversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate. The enzyme’s
    catalytic groups are Glu 165 and His 95. In the first step of the reaction, these catalytic groups function as a general-base and a
    general-acid catalyst, respectively. Propose a mechanism for the reaction.

2 −O

3 POCH 2 CCH 2 OH

triosephosphate isomerase

O

2 −O

3 POCH 2 CHCH

O

OH

glyceraldehyde-3-phosphate

dihydroxyacetone phosphate

Cl− Cl−

H 2 N N

R

N

N

O

ClCH 2 CH 2 NCH 2 CH 2 Cl 2 HN

CH 3

CH 2 CH 2 NCH 2 CH 2

+ CH^3

+

H 2 N N NH 2

R

N

N N

O O

+

N

R

N

HN NH

NH 2

N

H

O

3-amino-2-oxindole

a

NaBH 4

(^14) C, NaBH 4