radical reactions in biological systems
TRANSCRIPT
Organic Pedagogical Electronic Network
Radical Reactions in Biological Systems
Created by Rowan Arave and Alexandra ButlerEdited by Margaret Hilton
Honors Organic Chemistry CHEM 2321 (Sigman), 2013
Radical Organic Chemistry
Wiki Page: http://en.wikipedia.org/wiki/Radical_(chemistry)
Overview: Free Radicals are atoms without a full set of valence electrons. This causes the outer electron shell to be ‘open’, and thus, more reactive. Radical reactions take place in a series of three steps: initiation, propagation, and termination. Mechanism Cl Cl heat or light Cl• Cl•+
Cl• HCl
+ Cl Cl + Cl•
Cl• Cl• Cl Cl
+
+
+
CH3CH2• Cl•+ CH3CH2Cl
HH
HH3C
H
HH3C
H
HH3C
H
HH3C Cl
H
HH3C
H
HCH3
Initiation
Propagation
Termination
Radical Organic Chemistry
Wiki Page: http://en.wikipedia.org/wiki/Radical_(chemistry)
Overview: Free Radicals are atoms without a full set of valence electrons. This causes the outer electron shell to be ‘open’, and thus, more reactive. Radical reactions take place in a series of three steps: initiation, propagation, and termination.
Early Examples
Moses Gomberg discovered the first free radical, a Triphenyl Methyl Radical, in 1900.
Friedrich Paneth pioneered free radical decomposition in organic compounds. In 1929 he discovered the free methyl radical.
Synthesis and Repair of DNA
M. Kolbergr et al. / Biochimica et Biophysica Acta 1699 (2004) 1–34
The reduction of ribonucleotides to deoxyribonucleotides (RNA DNA) is the result of a radical reaction. Ribonucleotide reductase (RNR) is an enzyme that helps to catalyze this transformation. The reduction of RNA to DNA is the rate limiting step in synthesis of DNA. Therefore, this reaction plays a large part in cell growth and maintenance.
OPP(P)
baseHO H
OH
H
Cys 439
S
Cys 462SH
Cys 225SH
Asn 437N HH 441Glu
CO
O
OPP(P)
base
O HO
H
H
Cys 439
HS
Cys 462SH
Cys 225SH
Asn 437N HH 441Glu
CO
O H2O
OPP(P)
base
O HH
Cys 439
HS
Cys 462SH
Cys 225S
Asn 437N H
H 441Glu
CO
O
OPP(P)
base
O HH
Cys 439
HS
Cys 462S
Cys 225S
Asn 437N H
H 441Glu
CO
OH
OPP(P)
base
O HH
Cys 439
HS
Cys 462S
Cys 225S
Asn 437N H
H 441Glu
CO
OH
OPP(P)
base
O HH
Cys 439
S
Cys 462S
Cys 225S
Asn 437N H
H 441Glu
CO
OH
H
Problems
1.The Journal of Organic Chemistry DOI: 10.1021/jo40014332. Modern physical organic chemistry3. Smith pg. 557
1. Lipid peroxidation occurs due to oxidative stress. Polyunsaturated fatty acids and sterols undergo radical chain oxidation to complete this process. Draw an arrow-pushing mechanism for the following reaction of triphenylmethyl radical with molecular oxygen.
2. The trityl radical is in equilibrium with an unsymmetrical dimer (note: not Ph3C-CPh3). Propose a mechanism for the formation of this unsymmetrical dimer.
3. BHT (butylated hydroxy toluene) is a synthetic anti-oxidant that interrupts radical chain reactions. Propose a mechanism for how this could occur and predict the resulting products. (Hint: think resonance)
BHT
+ ?
O2 OO
OH
+ R ?
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Contributed by: Created by Rowan Arave and Alexandra Butler (Undergraduates)
Edited by Margaret HiltonHonors Organic Chemistry CHEM 2321 (Sigman),
University of Utah
2013