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Kent S. Gates - One of the best experts on this subject based on the ideXlab platform.
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application of suzuki miyaura and buchwald hartwig cross coupling reactions to the preparation of substituted 1 2 4 Benzotriazine 1 oxides related to the antitumor agent tirapazamine
Journal of Heterocyclic Chemistry, 2017Co-Authors: Ujjal Sarkar, Charles L. Barnes, Roman Hillebrand, Kevin M. Johnson, Andrea H. Cummings, Ngoc Linh Phung, Anuruddha Rajapakse, Haiying Zhou, Jordan R. Willis, Kent S. GatesAbstract:Many 1,2,4-Benzotriazine 1,4-dioxides display the ability to selectively kill the oxygen-poor cells found in solid tumors. As a result, there is a desire for synthetic routes that afford access to substituted 1,2,4-Benzotriazine 1-oxides that can be used as direct precursors in the synthesis of 1,2,4-Benzotriazine 1,4-dioxides. Here we describe the use of Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions for the construction of various 1,2,4-Benzotriazine 1-oxide analogs bearing substituents at the 3-, 6-, and 7-positions.
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Application of Suzuki–Miyaura and Buchwald–Hartwig Cross‐coupling Reactions to the Preparation of Substituted 1,2,4‐Benzotriazine 1‐Oxides Related to the Antitumor Agent Tirapazamine
Journal of heterocyclic chemistry, 2015Co-Authors: Ujjal Sarkar, Charles L. Barnes, Roman Hillebrand, Kevin M. Johnson, Andrea H. Cummings, Ngoc Linh Phung, Anuruddha Rajapakse, Haiying Zhou, Jordan R. Willis, Kent S. GatesAbstract:Many 1,2,4-Benzotriazine 1,4-dioxides display the ability to selectively kill the oxygen-poor cells found in solid tumors. As a result, there is a desire for synthetic routes that afford access to substituted 1,2,4-Benzotriazine 1-oxides that can be used as direct precursors in the synthesis of 1,2,4-Benzotriazine 1,4-dioxides. Here we describe the use of Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions for the construction of various 1,2,4-Benzotriazine 1-oxide analogs bearing substituents at the 3-, 6-, and 7-positions.
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Toward Hypoxia-Selective DNA-Alkylating Agents Built by Grafting Nitrogen Mustards onto the Bioreductively Activated, Hypoxia-Selective DNA-Oxidizing Agent 3‑Amino-1,2,4-Benzotriazine 1,4-Dioxide (Tirapazamine)
2015Co-Authors: Kevin M. Johnson, Zachary D. Parsons, Charles L. Barnes, Kent S. GatesAbstract:Tirapazamine (3-amino-1,2,4-Benzotriazine 1,4-dioxide) is a heterocyclic di-N-oxide that undergoes enzymatic deoxygenation selectively in the oxygen-poor (hypoxic) cells found in solid tumors to generate a mono-N-oxide metabolite. This work explored the idea that the electronic changes resulting from the metabolic deoxygenation of tirapazamine analogues might be exploited to activate a DNA-alkylating species selectively in hypoxic tissue. Toward this end, tirapazamine analogues bearing nitrogen mustard units were prepared. In the case of the tirapazamine analogue 18a bearing a nitrogen mustard unit at the 6-position, it was found that removal of the 4-oxide from the parent di-N-oxide to generate the mono-N-oxide analogue 17a did indeed cause a substantial increase in reactivity of the mustard unit, as measured by hydrolysis rates and DNA-alkylation yields. Hammett sigma values were measured to quantitatively assess the magnitude of the electronic changes induced by metabolic deoxygenation of the 3-amino-1,2,4-Benzotriazine 1,4-dioxide heterocycle. The results provide evidence that the 1,2,4-benzotiazine 1,4-dioxide unit can serve as an oxygen-sensing prodrug platform for the selective unmasking of bioactive agents in hypoxic cells
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Isotopic Labeling Experiments That Elucidate the Mechanism of DNA Strand Cleavage by the Hypoxia-Selective Antitumor Agent 1,2,4-Benzotriazine 1,4-Di‑N‑oxide
2014Co-Authors: Xiulong Shen, Anuruddha Rajapakse, Rainer Glaser, Fabio Gallazzi, Venkatraman Junnotula, Tarra Fuchs-knotts, Kent S. GatesAbstract:The 1,2,4-Benzotriazine 1,4-dioxides are an important class of potential anticancer drugs that selectively kill the low-oxygen (hypoxic) cells found in solid tumors. These compounds undergo intracellular one-electron enzymatic reduction to yield an oxygen-sensitive drug radical intermediate that partitions forward, under hypoxic conditions, to generate a highly reactive secondary radical that causes cell killing DNA damage. Here, we characterized bioreductively activated, hypoxia-selective DNA-strand cleavage by 1,2,4-Benzotriazine 1,4-dioxide. We found that one-electron enzymatic activation of 1,2,4-Benzotriazine 1,4-dioxide under hypoxic conditions in the presence of the deuterium atom donor methanol-d4 produced nondeuterated mono-N-oxide metabolites. This and the results of other isotopic labeling studies provided evidence against the generation of atom-abstracting drug radical intermediates and are consistent with a DNA-damage mechanism involving the release of hydroxyl radical from enzymatically activated 1,2,4-Benzotriazine 1,4-dioxides
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Isotopic labeling experiments that elucidate the mechanism of DNA strand cleavage by the hypoxia-selective antitumor agent 1,2,4-Benzotriazine 1,4-di-N-oxide.
Chemical research in toxicology, 2013Co-Authors: Xiulong Shen, Anuruddha Rajapakse, Rainer Glaser, Fabio Gallazzi, Venkatraman Junnotula, Tarra Fuchs-knotts, Kent S. GatesAbstract:The 1,2,4-Benzotriazine 1,4-dioxides are an important class of potential anticancer drugs that selectively kill the low-oxygen (hypoxic) cells found in solid tumors. These compounds undergo intracellular one-electron enzymatic reduction to yield an oxygen-sensitive drug radical intermediate that partitions forward, under hypoxic conditions, to generate a highly reactive secondary radical that causes cell killing DNA damage. Here, we characterized bioreductively activated, hypoxia-selective DNA-strand cleavage by 1,2,4-Benzotriazine 1,4-dioxide. We found that one-electron enzymatic activation of 1,2,4-Benzotriazine 1,4-dioxide under hypoxic conditions in the presence of the deuterium atom donor methanol-d4 produced nondeuterated mono-N-oxide metabolites. This and the results of other isotopic labeling studies provided evidence against the generation of atom-abstracting drug radical intermediates and are consistent with a DNA-damage mechanism involving the release of hydroxyl radical from enzymatically activated 1,2,4-Benzotriazine 1,4-dioxides.
William A Denny - One of the best experts on this subject based on the ideXlab platform.
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Radical properties governing the hypoxia-selective cytotoxicity of antitumor 3-amino-1,2,4-Benzotriazine 1,4-dioxides
Organic & biomolecular chemistry, 2005Co-Authors: Robert F. Anderson, Michael P. Hay, Swarna A Gamage, Sujata S. Shinde, William A DennyAbstract:Revealing the free radical mechanism by which the anticancer drug tirapazamine (3-amino-1,2,4-Benzotriazine 1,4-dioxide) induces hypoxia-selective cytotoxicity, is seen as a way forward to develop clinically useful bioreductive drugs against chemo- and radiation-resistant hypoxic tumor cells. Our previous studies point to the formation of an active benzotriazinyl radical following the one-electron reduction of tirapazamine and its elimination of water from the initial reduction intermediate, and have suggested that this species is a cytotoxin. In this paper we have used pulse radiolysis to measure the one-electron reduction potentials of the benzotriazinyl radicals E(B*,H(+)/B) of 30 analogues of tirapazamine as well as the one-electron reduction potentials of their two-electron reduced metabolites, Benzotriazine 1-oxides E(B/B*-). The redox dependencies of the back-oxidation of the one-electron reduced Benzotriazine 1,4-dioxides by oxygen, their radical prototropic properties and water elimination reactions were found to be tracked in the main by the one-electron reduction potentials of the Benzotriazine 1,4-dioxides E(A/A*-). Multiple regression analysis of published aerobic and hypoxic clonogenic cytotoxicity data for the SCCVII murine tumor cell line with the physical chemistry parameters measured in this study, revealed that hypoxic cytotoxicity is dependent on E(B*, H(+)/B) thus providing strong evidence that the benzotriazinyl radicals are the active cytotoxic species in hypoxia, while aerobic cytotoxicity is dependent on E(B/B*-). It is concluded that maximizing the differential ratio between these two controlling parameters, in combination with necessary pharmacological aspects, will lead to more efficacious anticancer bioreductive drugs.
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Oxidation of 2-Deoxyribose by Benzotriazinyl Radicals of Antitumor 3-Amino-1,2,4-Benzotriazine 1,4-Dioxides
Journal of the American Chemical Society, 2004Co-Authors: Sujata S. Shinde, Michael P. Hay, Swarna A Gamage, Robert F. Anderson, William A DennyAbstract:Tirapazamine (3-amino-1,2,4-Benzotriazine 1,4-dioxide) is the lead bioreductive drug in clinical trials as an anticancer agent to kill refractory hypoxic cells of solid tumors. It has long been known that, upon metabolic one-electron reduction, tirapazamine induces lethal DNA double strand breaks in hypoxic cells. These strand breaks arise from radical damage to the ribose moiety of DNA, and in this pulse radiolysis and product analysis study we examine mechanistic aspects of the dual function of tirapazamine and analogues in producing radicals of sufficient power to oxidize 2-deoxyribose to form radicals, as well as the ability of the compounds to oxidize the resulting deoxyribose radicals to generate the strand breaks. Both the rate of oxidation of 2-deoxyribose and the radical yield increase with the one-electron reduction potentials of the putative benzotriazinyl radicals formed from the Benzotriazine 1,4-dioxides. Subsequent oxidation of the 2-deoxyribose radicals by the Benzotriazine 1,4-dioxides and 1-oxides proceeds through adduct formation followed by breakdown to form the radical anions of both species. The yield of the radical anions increases with increasing one-electron reduction potentials of the compounds. We have previously presented evidence that oxidizing benzotriazinyl radicals are formed following one-electron reduction of the Benzotriazine 1,4-dioxides. The reactions reported in this work represent the kinetic basis of a short chain reaction leading to increased oxidation of 2-deoxyribose, a process which is dependent on the one-electron reduction potential of the benzotriazinyl radicals that are above a threshold value of ca. 1.24 V.
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dna targeted 1 2 4 Benzotriazine 1 4 dioxides potent analogues of the hypoxia selective cytotoxin tirapazamine
Journal of Medicinal Chemistry, 2004Co-Authors: Michael P. Hay, Frederik B Pruijn, Swarna A Gamage, H Sarath D Liyanage, Mary S Kovacs, Adam V Patterson, William R Wilson, Martin J Brown, William A DennyAbstract:Tirapazamine (TPZ, 1,2,4-benzotriazin-3-amine 1,4-dioxide) is a bioreductive hypoxia-selective cytotoxin, currently in phase II/III clinical trials in combination with radiotherapy and with cisplatin-based chemotherapy. We have prepared a series of 1,2,4-Benzotriazine 1,4-dioxide (BTO) analogues of TPZ where a DNA-targeting chromophore is attached at the 3-position via a flexible linker. DNA binding affinity was modified through variation of the chromophore or the pKa of the linker chain. The association constants (KDNA) for calf thymus DNA ranged from 1 × 102 to 5.6 × 105 M-1 (ionic strength of 0.01 M). DNA binding affinity was dependent on the presence of a positive charge, either in the linker chain or in the chromophore, and (for a series of 4-acridine carboxamide chromophore analogues) correlated strongly with linker chain pKa. The efficacy of these BTOs in killing aerobic and hypoxic mouse SCCVII tumor cells in vitro was determined by clonogenic survival. Cytotoxicity was measured as the concentrati...
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Activation of 3-amino-1,2,4-Benzotriazine 1,4-dioxide antitumor agents to oxidizing species following their one-electron reduction.
Journal of the American Chemical Society, 2003Co-Authors: Robert F. Anderson, Michael P. Hay, Swarna A Gamage, Sujata S. Shinde, William A DennyAbstract:The mechanism by which a Benzotriazine 1,4-dioxide class of anticancer drugs produce oxidizing radicals following their one-electron reduction has been investigated using tirapazamine (3-amino-1,2,4-Benzotriazine 1,4-dioxide, 1) and its 6-methoxy (6), 7-dimethylamino (7), and 8-methyl (8) analogues. By measuring the changes in absorption with pH, we found that the radical anions undergo protonation with radical pK(r) values of 6.19 +/- 0.05, 6.10 +/- 0.03, 6.45 +/- 0.04, and 6.60 +/- 0.04, respectively. The one-electron reduced species underwent a first-order reaction, with increased rate constants from 112 +/- 23 s(-)(1) for 1 to 777 +/- 12 s(-)(1)(6), 1120 +/- 29 s(-)(1) (7), and 825 +/- 89 s(-)(1) (8) at pH 7. No overall change in conductance was observed following the one-electron reduction of 6, and 8 at pH 4.5, consistent with the protonation of the radical anions, but a loss in conductance was seen for one-electron reduced 7 because of further protonation of the initially formed radical. This is assigned to the protonation of the dimethylamino group of the radical species, which has a pK(a) of 8.8 +/- 0.3. All conductance changes take place on a time-scale shorter than those of the above first-order reactions, which are not associated with the formation or loss of charged species. The absorption spectra present at the end of the unimolecular reactions were found to be similar to those formed immediately upon the one-electron oxidation of the respective substituted 3-amino-1,2,4-Benzotriazine 1-oxides, and it is suggested that common benzotriazinyl radicals are formed by both routes. All these intermediate radicals underwent dismutation to produce final spectra matched by equal contributions of the parent compound and their respective substituted 3-amino-1,2,4-Benzotriazine 1-oxides. By establishing redox equilibria between the intermediate radicals formed on the one-electron oxidation of the respective 3-amino-1,2,4-Benzotriazine 1-oxides of the compounds and reference compounds, we found the one-electron reduction potential of the oxidizing radicals to range from 0.94 to 1.31 V. The benzotriazinyl radical of tirapazamine was found to oxidize dGMP and 2-deoxyribose with rate constants of (1.4 +/- 0.2) x 10(8) M(-)(1) s(-)(1) and (3.7 +/- 0.5) x 10(6) M(-)(1) s(-)(1), respectively.
Charles L. Barnes - One of the best experts on this subject based on the ideXlab platform.
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application of suzuki miyaura and buchwald hartwig cross coupling reactions to the preparation of substituted 1 2 4 Benzotriazine 1 oxides related to the antitumor agent tirapazamine
Journal of Heterocyclic Chemistry, 2017Co-Authors: Ujjal Sarkar, Charles L. Barnes, Roman Hillebrand, Kevin M. Johnson, Andrea H. Cummings, Ngoc Linh Phung, Anuruddha Rajapakse, Haiying Zhou, Jordan R. Willis, Kent S. GatesAbstract:Many 1,2,4-Benzotriazine 1,4-dioxides display the ability to selectively kill the oxygen-poor cells found in solid tumors. As a result, there is a desire for synthetic routes that afford access to substituted 1,2,4-Benzotriazine 1-oxides that can be used as direct precursors in the synthesis of 1,2,4-Benzotriazine 1,4-dioxides. Here we describe the use of Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions for the construction of various 1,2,4-Benzotriazine 1-oxide analogs bearing substituents at the 3-, 6-, and 7-positions.
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Application of Suzuki–Miyaura and Buchwald–Hartwig Cross‐coupling Reactions to the Preparation of Substituted 1,2,4‐Benzotriazine 1‐Oxides Related to the Antitumor Agent Tirapazamine
Journal of heterocyclic chemistry, 2015Co-Authors: Ujjal Sarkar, Charles L. Barnes, Roman Hillebrand, Kevin M. Johnson, Andrea H. Cummings, Ngoc Linh Phung, Anuruddha Rajapakse, Haiying Zhou, Jordan R. Willis, Kent S. GatesAbstract:Many 1,2,4-Benzotriazine 1,4-dioxides display the ability to selectively kill the oxygen-poor cells found in solid tumors. As a result, there is a desire for synthetic routes that afford access to substituted 1,2,4-Benzotriazine 1-oxides that can be used as direct precursors in the synthesis of 1,2,4-Benzotriazine 1,4-dioxides. Here we describe the use of Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions for the construction of various 1,2,4-Benzotriazine 1-oxide analogs bearing substituents at the 3-, 6-, and 7-positions.
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Toward Hypoxia-Selective DNA-Alkylating Agents Built by Grafting Nitrogen Mustards onto the Bioreductively Activated, Hypoxia-Selective DNA-Oxidizing Agent 3‑Amino-1,2,4-Benzotriazine 1,4-Dioxide (Tirapazamine)
2015Co-Authors: Kevin M. Johnson, Zachary D. Parsons, Charles L. Barnes, Kent S. GatesAbstract:Tirapazamine (3-amino-1,2,4-Benzotriazine 1,4-dioxide) is a heterocyclic di-N-oxide that undergoes enzymatic deoxygenation selectively in the oxygen-poor (hypoxic) cells found in solid tumors to generate a mono-N-oxide metabolite. This work explored the idea that the electronic changes resulting from the metabolic deoxygenation of tirapazamine analogues might be exploited to activate a DNA-alkylating species selectively in hypoxic tissue. Toward this end, tirapazamine analogues bearing nitrogen mustard units were prepared. In the case of the tirapazamine analogue 18a bearing a nitrogen mustard unit at the 6-position, it was found that removal of the 4-oxide from the parent di-N-oxide to generate the mono-N-oxide analogue 17a did indeed cause a substantial increase in reactivity of the mustard unit, as measured by hydrolysis rates and DNA-alkylation yields. Hammett sigma values were measured to quantitatively assess the magnitude of the electronic changes induced by metabolic deoxygenation of the 3-amino-1,2,4-Benzotriazine 1,4-dioxide heterocycle. The results provide evidence that the 1,2,4-benzotiazine 1,4-dioxide unit can serve as an oxygen-sensing prodrug platform for the selective unmasking of bioactive agents in hypoxic cells
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Synthesis, Crystal Structure, and Rotational Energy Profile of 3-Cyclopropyl-1,2,4-Benzotriazine 1,4-Di-N-oxide
Journal of Chemical Crystallography, 2010Co-Authors: Ujjal Sarkar, Charles L. Barnes, Rainer Glaser, Zack D. Parsons, Kent S. GatesAbstract:1,2,4-Benzotriazine 1,4-di- N -oxides are potent antitumor drug candidates that undergo in vivo bioreduction leading to selective DNA damage in the low oxygen (hypoxic) cells found in tumors. Tirapazamine (TPZ) is the lead compound in this family. Here we report on the synthesis, crystal structure, and conformational analysis of a new analog, 3-cyclopropyl-1,2,4-Benzotriazine 1,4-di- N -oxide ( 3 ). Compound 3 (C_10H_10N_3O_2) crystallized in the monoclinic space group C 2/ c . Unit cell parameters for 3 : a = 16.6306 (12), b = 7.799 (5), c = 16.0113 (11) Å, α = 90, β = 119.0440 (10), γ = 90, and z = 8. Graphical Abstract 1,2,4-Benzotriazine 1,4-di- N -oxides are antitumor drug candidates that undergo in vivo bioreduction to yield DNA-damaging radical intermediates in hypoxic tumor cells. Here we report on the synthesis, crystal structure, and conformational analysis of a new analog, 3-cyclopropyl-1,2,4-Benzotriazine 1,4-di- N -oxide ( 3 ).
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Synthesis, Crystal Structure, and Rotational Energy Profile of 3-Cyclopropyl-1,2,4-Benzotriazine 1,4-Di- N -oxide
Journal of chemical crystallography, 2010Co-Authors: Ujjal Sarkar, Charles L. Barnes, Rainer Glaser, Zack D. Parsons, Kent S. GatesAbstract:Abstract1,2,4-Benzotriazine 1,4-di-N-oxides are potent antitumor drug candidates that undergo in vivo bioreduction leading to selective DNA damage in the low oxygen (hypoxic) cells found in tumors. Tirapazamine (TPZ) is the lead compound in this family. Here we report on the synthesis, crystal structure, and conformational analysis of a new analog, 3-cyclopropyl-1,2,4-Benzotriazine 1,4-di-N-oxide (3). Compound 3 (C 10 H 10 N 3 O 2 ) crystallized in the monoclinic space group C2/c. Unit cell parameters for 3: a = 16.6306 (12), b = 7.799 (5), c = 16.0113 (11) A, α = 90, β = 119.0440 (10), γ = 90, and z = 8.Graphical Abstract1,2,4-Benzotriazine 1,4-di-N-oxides are antitumor drug candidates that undergo in vivo bioreduction to yield DNA-damaging radical intermediates in hypoxic tumor cells. Here we report on the synthesis, crystal structure, and conformational analysis of a new analog, 3-cyclopropyl-1,2,4-Benzotriazine 1,4-di-N-oxide (3).[IMAGE]
Tarra Fuchs - One of the best experts on this subject based on the ideXlab platform.
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A mass spectrometry study of tirapazamine and its metabolites: Insights into the mechanism of metabolic transformations and the characterization of reaction intermediates
Journal of the American Society for Mass Spectrometry, 2003Co-Authors: Dmitri Zagorevskii, Kent S. Gates, Tarra Fuchs, Minghu Song, Curt Breneman, Yang Yuan, C. Michael GreenliefAbstract:Tandem mass spectrometry methods were used to study the sites of protonation and for identification of 3-amino-1,2,4-Benzotriazine 1,4-dioxide ( 1 , tirapazamine), and its metabolites (3-amino-1,2,4-Benzotriazine 1-oxide ( 3 ), 3-amino-1,2,4-Benzotriazine 4-oxide ( 4 ), 3-amino-1,2,4-Benzotriazine ( 5 ), and a related isomer 3-amino-1,2,4-Benzotriazine 2-oxide ( 6 ). Fragmentation pathways of 3 and 5 indicated the 4-N-atom as the most likely site of protonation. Among the N-oxides studied, the 4-oxide ( 4 ) showed the highest degree of protonation at the oxygen atom. The differences in collision-induced dissociation of isomeric protonated 1-, 2- and 4-oxides allowed for their identification by LC/MS/MS. Gas phase and liquid phase protonation of tirapazamine occurred exclusively at the oxygen in the 4-position. A loss of OH radical from these ions ( 2 ^+) resulted in ionized 3 . Neutralization-reionization mass spectrometry (NR MS) experiments demonstrated the stability of the neutral analogue of protonated tirapazamine in the gas phase in the μs time-frame. A significant portion of the neutral tirapazamine radicals ( 2 ) dissociated by loss of hydroxyl radical during the NR MS event, which indicates that previously proposed mechanisms for redox-activated DNA damage are reasonable. The activation energy for loss of hydroxyl radical from activated tirapazamine ( 2 ) was estimated to be ∼14 kcal mol^−1. Stable neutral analogues of [ 3 +H]^+ and [ 5 +H]^+ ions were also generated in the course of NR MS experiments. Structures of these radicals were assigned to the molecules having an extra hydrogen atom at one of the ring N-atoms. Quantum chemical calculations of protonated 1 , 3 , 4 and 5 and the corresponding neutrals were performed to assist in the interpretation of experimental results and to help identify their structures.
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3-Amino-1,2,4-Benzotriazine 4-Oxide: Characterization of a New Metabolite Arising from Bioreductive Processing of the Antitumor Agent 3-Amino-1,2,4-Benzotriazine 1,4-Dioxide (Tirapazamine)
The Journal of organic chemistry, 2001Co-Authors: Tarra Fuchs, Charles L. Barnes, Goutam Chowdhury, Kent S. GatesAbstract:Tirapazamine (1) is a promising antitumor agent that selectively causes DNA damage in hypoxic tumor cells, following one-electron bioreductive activation. Surprisingly, after more than 10 years of study, the products arising from bioreductive metabolism of tirapazamine have not been completely characterized. The two previously characterized metabolites are 3-amino-1,2,4-Benzotriazine 1-oxide (3) and 3-amino-1,2,4-Benzotriazine (5). In this work, 3-amino-1,2,4-Benzotriazine 4-oxide (4) is identified for the first time as a product resulting from one-electron activation of the antitumor agent tirapazamine by the enzymes xanthine/xanthine oxidase and NADPH:cytochrome P450 oxidoreductase. As part of this work, the novel N-oxide (4) was unambiguously synthesized and characterized using NMR spectroscopy, UV-vis spectroscopy, LC/MS, and X-ray crystallography. Under conditions where the parent drug tirapazamine is enzymatically activated, the metabolite 4 is produced but readily undergoes further reduction to the Benzotriazine (5). Thus, under circumstances where extensive reductive metabolism occurs, the yield of the 4-oxide (4) decreases. In contrast, the isomeric two-electron reduction product 3-amino-1,2,4-Benzotriazine 1-oxide (3) does not readily undergo enzymatic reduction and, therefore, is found as a major bioreductive metabolite under all conditions. Finally, the ability of the 4-oxide metabolite (4) to participate in tirapazamine-mediated DNA damage is considered.
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3 amino 1 2 4 Benzotriazine 4 oxide characterization of a new metabolite arising from bioreductive processing of the antitumor agent 3 amino 1 2 4 Benzotriazine 1 4 dioxide tirapazamine
Journal of Organic Chemistry, 2001Co-Authors: Tarra Fuchs, Charles L. Barnes, Goutam Chowdhury, Kent S. GatesAbstract:Tirapazamine (1) is a promising antitumor agent that selectively causes DNA damage in hypoxic tumor cells, following one-electron bioreductive activation. Surprisingly, after more than 10 years of study, the products arising from bioreductive metabolism of tirapazamine have not been completely characterized. The two previously characterized metabolites are 3-amino-1,2,4-Benzotriazine 1-oxide (3) and 3-amino-1,2,4-Benzotriazine (5). In this work, 3-amino-1,2,4-Benzotriazine 4-oxide (4) is identified for the first time as a product resulting from one-electron activation of the antitumor agent tirapazamine by the enzymes xanthine/xanthine oxidase and NADPH:cytochrome P450 oxidoreductase. As part of this work, the novel N-oxide (4) was unambiguously synthesized and characterized using NMR spectroscopy, UV−vis spectroscopy, LC/MS, and X-ray crystallography. Under conditions where the parent drug tirapazamine is enzymatically activated, the metabolite 4 is produced but readily undergoes further reduction to the...
Michael P. Hay - One of the best experts on this subject based on the ideXlab platform.
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complete 1h 13c and 15n nmr assignment of tirapazamine and related 1 2 4 Benzotriazine n oxides
Magnetic Resonance in Chemistry, 2006Co-Authors: Maruta Boyd, Michael P. Hay, Peter D. W. BoydAbstract:1H, 13C and 15N NMR measurements (1D and 2D including 1H15N gs-HMBC) have been carried out on 3-amino-1, 2,4-Benzotriazine and a series of N-oxides and complete assignments established. N-Oxidation at any position resulted in large upfield shifts of the corresponding N-1 and N-2 resonances and downfield shifts for N-4 with the exception of the 3-amino-1,2,4-Benzotriazine 1-oxide in which a small upfield shift of N-4 was observed. Density functional GIAO calculations of the 15N and 13C chemical shifts [B3LYP/6-31G(d)//B3LYP/6-311 + G(2d,p)] gave good agreement with experimental values confirming the assignments. The combination of 13C and 15N NMR provides an unambiguous method for assigning the 1H and 13C resonances of N-oxides of 1,2,4-Benzotriazines. Copyright © 2006 John Wiley & Sons, Ltd.
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Complete 1H, 13C and 15N NMR assignment of tirapazamine and related 1,2,4‐Benzotriazine N‐oxides
Magnetic resonance in chemistry : MRC, 2006Co-Authors: Maruta Boyd, Michael P. Hay, Peter D. W. BoydAbstract:1H, 13C and 15N NMR measurements (1D and 2D including 1H15N gs-HMBC) have been carried out on 3-amino-1, 2,4-Benzotriazine and a series of N-oxides and complete assignments established. N-Oxidation at any position resulted in large upfield shifts of the corresponding N-1 and N-2 resonances and downfield shifts for N-4 with the exception of the 3-amino-1,2,4-Benzotriazine 1-oxide in which a small upfield shift of N-4 was observed. Density functional GIAO calculations of the 15N and 13C chemical shifts [B3LYP/6-31G(d)//B3LYP/6-311 + G(2d,p)] gave good agreement with experimental values confirming the assignments. The combination of 13C and 15N NMR provides an unambiguous method for assigning the 1H and 13C resonances of N-oxides of 1,2,4-Benzotriazines. Copyright © 2006 John Wiley & Sons, Ltd.
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Radical properties governing the hypoxia-selective cytotoxicity of antitumor 3-amino-1,2,4-Benzotriazine 1,4-dioxides
Organic & biomolecular chemistry, 2005Co-Authors: Robert F. Anderson, Michael P. Hay, Swarna A Gamage, Sujata S. Shinde, William A DennyAbstract:Revealing the free radical mechanism by which the anticancer drug tirapazamine (3-amino-1,2,4-Benzotriazine 1,4-dioxide) induces hypoxia-selective cytotoxicity, is seen as a way forward to develop clinically useful bioreductive drugs against chemo- and radiation-resistant hypoxic tumor cells. Our previous studies point to the formation of an active benzotriazinyl radical following the one-electron reduction of tirapazamine and its elimination of water from the initial reduction intermediate, and have suggested that this species is a cytotoxin. In this paper we have used pulse radiolysis to measure the one-electron reduction potentials of the benzotriazinyl radicals E(B*,H(+)/B) of 30 analogues of tirapazamine as well as the one-electron reduction potentials of their two-electron reduced metabolites, Benzotriazine 1-oxides E(B/B*-). The redox dependencies of the back-oxidation of the one-electron reduced Benzotriazine 1,4-dioxides by oxygen, their radical prototropic properties and water elimination reactions were found to be tracked in the main by the one-electron reduction potentials of the Benzotriazine 1,4-dioxides E(A/A*-). Multiple regression analysis of published aerobic and hypoxic clonogenic cytotoxicity data for the SCCVII murine tumor cell line with the physical chemistry parameters measured in this study, revealed that hypoxic cytotoxicity is dependent on E(B*, H(+)/B) thus providing strong evidence that the benzotriazinyl radicals are the active cytotoxic species in hypoxia, while aerobic cytotoxicity is dependent on E(B/B*-). It is concluded that maximizing the differential ratio between these two controlling parameters, in combination with necessary pharmacological aspects, will lead to more efficacious anticancer bioreductive drugs.
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Oxidation of 2-Deoxyribose by Benzotriazinyl Radicals of Antitumor 3-Amino-1,2,4-Benzotriazine 1,4-Dioxides
Journal of the American Chemical Society, 2004Co-Authors: Sujata S. Shinde, Michael P. Hay, Swarna A Gamage, Robert F. Anderson, William A DennyAbstract:Tirapazamine (3-amino-1,2,4-Benzotriazine 1,4-dioxide) is the lead bioreductive drug in clinical trials as an anticancer agent to kill refractory hypoxic cells of solid tumors. It has long been known that, upon metabolic one-electron reduction, tirapazamine induces lethal DNA double strand breaks in hypoxic cells. These strand breaks arise from radical damage to the ribose moiety of DNA, and in this pulse radiolysis and product analysis study we examine mechanistic aspects of the dual function of tirapazamine and analogues in producing radicals of sufficient power to oxidize 2-deoxyribose to form radicals, as well as the ability of the compounds to oxidize the resulting deoxyribose radicals to generate the strand breaks. Both the rate of oxidation of 2-deoxyribose and the radical yield increase with the one-electron reduction potentials of the putative benzotriazinyl radicals formed from the Benzotriazine 1,4-dioxides. Subsequent oxidation of the 2-deoxyribose radicals by the Benzotriazine 1,4-dioxides and 1-oxides proceeds through adduct formation followed by breakdown to form the radical anions of both species. The yield of the radical anions increases with increasing one-electron reduction potentials of the compounds. We have previously presented evidence that oxidizing benzotriazinyl radicals are formed following one-electron reduction of the Benzotriazine 1,4-dioxides. The reactions reported in this work represent the kinetic basis of a short chain reaction leading to increased oxidation of 2-deoxyribose, a process which is dependent on the one-electron reduction potential of the benzotriazinyl radicals that are above a threshold value of ca. 1.24 V.
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dna targeted 1 2 4 Benzotriazine 1 4 dioxides potent analogues of the hypoxia selective cytotoxin tirapazamine
Journal of Medicinal Chemistry, 2004Co-Authors: Michael P. Hay, Frederik B Pruijn, Swarna A Gamage, H Sarath D Liyanage, Mary S Kovacs, Adam V Patterson, William R Wilson, Martin J Brown, William A DennyAbstract:Tirapazamine (TPZ, 1,2,4-benzotriazin-3-amine 1,4-dioxide) is a bioreductive hypoxia-selective cytotoxin, currently in phase II/III clinical trials in combination with radiotherapy and with cisplatin-based chemotherapy. We have prepared a series of 1,2,4-Benzotriazine 1,4-dioxide (BTO) analogues of TPZ where a DNA-targeting chromophore is attached at the 3-position via a flexible linker. DNA binding affinity was modified through variation of the chromophore or the pKa of the linker chain. The association constants (KDNA) for calf thymus DNA ranged from 1 × 102 to 5.6 × 105 M-1 (ionic strength of 0.01 M). DNA binding affinity was dependent on the presence of a positive charge, either in the linker chain or in the chromophore, and (for a series of 4-acridine carboxamide chromophore analogues) correlated strongly with linker chain pKa. The efficacy of these BTOs in killing aerobic and hypoxic mouse SCCVII tumor cells in vitro was determined by clonogenic survival. Cytotoxicity was measured as the concentrati...