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Identifying the Tautomeric Form of a Deoxyguanosine-Estrogen Quinone Intermediate.

Stack DE - Metabolites (2015)

Bottom Line: This tautomeric form was further verified by use of deuterium labelling of the catechol precursor use to form the estrogen o-quinone.HPLC-MS analysis indicates a reactive intermediate with a m/z of 552.22 consistent with a tautomeric form containing no deuterium.This intermediate is consistent with a reaction mechanism that involves: (1) proton assisted Michael addition; (2) re-aromatization of the estrogen A ring; and (3) glycosidic bond cleavage to form the known estrogen-DNA adduct, 4-OHE₁-1-N7Gua.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Nebraska at Omaha, 6001 Dodge Street, Omaha, NE 68182, USA. dstack@unomaha.edu.

ABSTRACT
Mechanistic insights into the reaction of an estrogen o-quinone with deoxyguanosine has been further investigated using high level density functional calculations in addition to the use of 4-hyroxycatecholestrone (4-OHE₁) regioselectivity labeled with deuterium at the C1-position. Calculations using the M06-2X functional with large basis sets indicate the tautomeric form of an estrogen-DNA adduct present when glycosidic bonds cleavage occurs is comprised of an aromatic A ring structure. This tautomeric form was further verified by use of deuterium labelling of the catechol precursor use to form the estrogen o-quinone. Regioselective deuterium labelling at the C1-position of the estrogen A ring allows discrimination between two tautomeric forms of a reaction intermediate either of which could be present during glycosidic bond cleavage. HPLC-MS analysis indicates a reactive intermediate with a m/z of 552.22 consistent with a tautomeric form containing no deuterium. This intermediate is consistent with a reaction mechanism that involves: (1) proton assisted Michael addition; (2) re-aromatization of the estrogen A ring; and (3) glycosidic bond cleavage to form the known estrogen-DNA adduct, 4-OHE₁-1-N7Gua.

No MeSH data available.


Revised mechanism of the reaction of E1-3,4-Q with dG.
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metabolites-05-00475-f008: Revised mechanism of the reaction of E1-3,4-Q with dG.

Mentions: Figure 8 shows the refined mechanism based on the results present in this article. The reaction starts with a 1,4-conjugate addition of the guanine nucleophile at the C1-poisition of E1-3,4-Q resulting in tautomeric form 1. Tautomeric form 1 quickly loses the proton at C1 to form the aromatic A ring. This tautomerization/re-aromatization step has a strong thermodynamic driving force of ca. 20 kcal/mol with a small energy barrier of 2 kcal/mol and is essentially irreversible. The C1 proton loss is followed by a slower glycosidic bond cleavage. Future modeling studies designed to explore the difference in rates observed between guanine adducted by estrogen quinones versus adenine should use the isomeric form 2.


Identifying the Tautomeric Form of a Deoxyguanosine-Estrogen Quinone Intermediate.

Stack DE - Metabolites (2015)

Revised mechanism of the reaction of E1-3,4-Q with dG.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588807&req=5

metabolites-05-00475-f008: Revised mechanism of the reaction of E1-3,4-Q with dG.
Mentions: Figure 8 shows the refined mechanism based on the results present in this article. The reaction starts with a 1,4-conjugate addition of the guanine nucleophile at the C1-poisition of E1-3,4-Q resulting in tautomeric form 1. Tautomeric form 1 quickly loses the proton at C1 to form the aromatic A ring. This tautomerization/re-aromatization step has a strong thermodynamic driving force of ca. 20 kcal/mol with a small energy barrier of 2 kcal/mol and is essentially irreversible. The C1 proton loss is followed by a slower glycosidic bond cleavage. Future modeling studies designed to explore the difference in rates observed between guanine adducted by estrogen quinones versus adenine should use the isomeric form 2.

Bottom Line: This tautomeric form was further verified by use of deuterium labelling of the catechol precursor use to form the estrogen o-quinone.HPLC-MS analysis indicates a reactive intermediate with a m/z of 552.22 consistent with a tautomeric form containing no deuterium.This intermediate is consistent with a reaction mechanism that involves: (1) proton assisted Michael addition; (2) re-aromatization of the estrogen A ring; and (3) glycosidic bond cleavage to form the known estrogen-DNA adduct, 4-OHE₁-1-N7Gua.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Nebraska at Omaha, 6001 Dodge Street, Omaha, NE 68182, USA. dstack@unomaha.edu.

ABSTRACT
Mechanistic insights into the reaction of an estrogen o-quinone with deoxyguanosine has been further investigated using high level density functional calculations in addition to the use of 4-hyroxycatecholestrone (4-OHE₁) regioselectivity labeled with deuterium at the C1-position. Calculations using the M06-2X functional with large basis sets indicate the tautomeric form of an estrogen-DNA adduct present when glycosidic bonds cleavage occurs is comprised of an aromatic A ring structure. This tautomeric form was further verified by use of deuterium labelling of the catechol precursor use to form the estrogen o-quinone. Regioselective deuterium labelling at the C1-position of the estrogen A ring allows discrimination between two tautomeric forms of a reaction intermediate either of which could be present during glycosidic bond cleavage. HPLC-MS analysis indicates a reactive intermediate with a m/z of 552.22 consistent with a tautomeric form containing no deuterium. This intermediate is consistent with a reaction mechanism that involves: (1) proton assisted Michael addition; (2) re-aromatization of the estrogen A ring; and (3) glycosidic bond cleavage to form the known estrogen-DNA adduct, 4-OHE₁-1-N7Gua.

No MeSH data available.