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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.


Modeling the kinetics of proton transfer at C1.
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metabolites-05-00475-f005: Modeling the kinetics of proton transfer at C1.

Mentions: Most exergonic proton transfers have free energy barriers much less than the 26.8 kcal/mol measure previously for this reaction using UV/VIS spectroscopy. The two proton transfer steps that converts tautomer 1 to 2 are shown in Figure 5. Since proton transfers from carbon have higher energy barriers than proton transfers involving heteroatoms, we chose to model the transition state structure in going from T-1mα to phenolic form 4 (Figure 5). Scans of the potential energy surface are computationally more expensive than single geometry minimization calculations, thus we employed Hartree-Fock theory using the reduced MIDI! basis set of Truhlar and coworkers. Although smaller than the popular 6-31G(d) basis set, MIDI! has been shown to produce more accurate geometries [21]. The energies of the starting structure and transition state were then refined with a SPE calculation at the M06-2X/QZVP calculation as done previously (Figure 4). Both the geometry optimization and SPE were simulated in an aqueous environment.


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

Stack DE - Metabolites (2015)

Modeling the kinetics of proton transfer at C1.
© Copyright Policy
Related In: Results  -  Collection

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

metabolites-05-00475-f005: Modeling the kinetics of proton transfer at C1.
Mentions: Most exergonic proton transfers have free energy barriers much less than the 26.8 kcal/mol measure previously for this reaction using UV/VIS spectroscopy. The two proton transfer steps that converts tautomer 1 to 2 are shown in Figure 5. Since proton transfers from carbon have higher energy barriers than proton transfers involving heteroatoms, we chose to model the transition state structure in going from T-1mα to phenolic form 4 (Figure 5). Scans of the potential energy surface are computationally more expensive than single geometry minimization calculations, thus we employed Hartree-Fock theory using the reduced MIDI! basis set of Truhlar and coworkers. Although smaller than the popular 6-31G(d) basis set, MIDI! has been shown to produce more accurate geometries [21]. The energies of the starting structure and transition state were then refined with a SPE calculation at the M06-2X/QZVP calculation as done previously (Figure 4). Both the geometry optimization and SPE were simulated in an aqueous environment.

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.