THEORETICAL STUDY OF THE
METABOLISM OF FLAVANONE
Dr. Erin Dahlke
Flavonoids are polyphenolic compounds that
have been linked to many important health benefits,
including anti-bacterial, anti-viral, and anti-
inflammatory properties. It is believed that their
metabolism may play a key role in these beneficial
property. The metabolism of flavonoids is believed
to be carried out by cytochrome P450. This
purpose of this study is to use density functional
theory to study the metabolism of two specific
flavonoids, flavanone and 4’-methoxyflavanone, by
cytochrome P450 in the hopes of better
understanding their metabolism. A comparison of
our results to available experimental data on this
system will provide valuable information about the
mechanism behind this reaction.
• Flavonoids are naturally occurring, polyphenolic compounds
present in fruits, vegetables, and some beverages.
• The basic flavonoid structure includes a flavan nucleus, which
consists of 15 carbon atoms arranged in three rings derived
from a C6—C3—C6 skeleton and identified as A, B, and C.
– Flavonoids are classified based on their level of oxidation
and the pattern of substitution of the C ring.1
• Various substitutions on the A, B, and C rings account for
more than 5000 naturally-occurring flavonoid compounds.
• Flavonoids are responsible for a variety of health
benefits including protection against cancer and
cardiovascular disease and have varied physiological
and pharmacological activities.
• Flavonoid molecules can also inhibit the activities of
an array of enzymes through their free radical-
scavenging anti-oxidative activities and metal ion-
• It has been proposed that the metabolism of
flavonoids by cytochrome P450 may produce
metabolites that are more bioactive than the parent
molecule and that these metabolites may be
responsible for their pharmacological properties.3
• Another possible explanation is that the interaction of
either flavonoids or their metabolites may interact with
cytochrome P450 to inhibit or stimulate the
metabolism of other xenobiotic or drug compounds
which may be the cause of much of their biological
Kawaga et al.5 carried out a study investigating the
metabolism of two flavonoids, flavanone and 4’-
methoxyflavanone by cytochrome P450.
Based on the results of their study, the following mechanism
The mechanism is believed to proceed via a
hydrogen atom abstraction based on experimental
kinetic isotope effects.
It was also found that the metabolism of flavanone
resulted in three products while the metabolism of
4’-methoxyflavanone resulted in only two.
In order to better understand the mechanism
behind the metabolism of flavanone and 4’-
methoxyflavanone, quantum mechanical
calculations will be carried out to answer the
Does the mechanism really proceed by a hydrogen
atom transfer (HAT) or does it proceed via a single
electron transfer (SET) followed by a proton transfer.
Why does the flavanone molecule produce an
isoflavone product while the 4’methoxyflavanone does
What effect would different or additional substitutions
Optimized structures will be calculated for the
reactant, product, and transition state for the
first step in each branch of the mechanism.
Examination of the spin density and charge of
the transferred hydrogen and the flavonoid
radical will be examined to determine whether
the mechanism is a HAT or a SET.
Frequency calculations carried out on the
transition state with hydrogen and deuterium
for the transferred hydrogen atom will be used
to calculate kinetic isotope effects for the two
A six-coordinate oxo-ferryl species [Fe4+O2-
(C20N4H12)-(SH)-] is being used to model the
reactivity of Compound I of cytochrome P450.
The B3LYP is being used with two basis sets:
LANL2DZ(Fe)/6-31G (for optimization) and
LACV3P+*(Fe)/6-311+G*(the rest) (for single
points energies on the optimized structures)
All calculations are being carried out with the
Gaussian03 suite of program.
Results so far (Branch 1)
R=H, OCH3 R R
O O .
O +. O
Following the work of Wang et al.6 we have optimized
the reactant complex in both the doublet and quartet
spin state for flavanone.
We are close to having optimized product complexes
for both spin states as well; however all efforts to
optimize the transition states have failed.
We are also close to having optimized reactant
complexes for the two spin states of 4’-
Results so far (Branch 2 and 3)
R=H, OCH3 R R
O +. O
We have optimized the reactant complex in
both the doublet and quartet spin state for
All efforts to optimize the product complexes
and transition states have failed for the
We are in the process of optimizing reactant
complexes for the two spin states for the 4’-
Finish the optimizations of all reactant and product
complexes and transition states in the gas-phase.
Use implicit solvent models to mimic the protein
environment (in chlorobenzene, =5.62) and also
to mimic the reaction in a nonenzymatic aqueous
environment (in water, =78.39).
Calculate kinetic isotope effects using the
imaginary frequency of the transition state with
and without a deuterium substitution for the
transferred hydrogen atom.
The calculated kinetic isotope effects can be
compared to experimental data in order to help
validate our model chemistry.
Minnesota Supercomputing Institute
Dr. Joseph Scanlon, Ripon College
Loras College Chemistry and Biochemistry
Zhai, S.; Dai, Renke, D.; Friedman, F. K.; Vestal, R.
E. Drug Metab. Dispos. 1998, 26, 989.
Kawaga, H,; Takahashi, T.; Ohta, S,; and Harigaya,
Y. Xenobiotica 2004, 34, 797.
Wang, Y.; Kumar, D.; Yang, C.; Han, K.; Shaik, S. J.
Phys. Chem. B 2007, 111, 7700.
Otake, Y.; Walle, T. Drug Metab. Dispos. 2002, 30,
Das, S.; Rosazza, J. P. N. J. Nat. Prod. 2006, 69,
Pietta, P.-G. J. Nat. Prod. 2000, 63, 1035.