Complete 1H, 13C and 15N NMR assignment of tirapazamine and related 1,2,4-benzotriazine N-oxides

1H, 13C and 15N NMR measurements (1D and 2D including 1H--15N 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.     

Crystal structure of 3-amino-5-methyl-1,2,4-benzotriazine 1-oxide: Evidence for formation of a covalent attachment between a carbon-centered radical and the antitumor agent tirapazamine

The compound 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine, 1) is a potent antitumor agent. We isolated 3-amino-5-methyl-1,2,4-benzotriazine 1-oxide (5) from the reaction tirapazamine with methyl radical and characterized this compound by X-ray crystallography. The crystal structure of 5 provides clear evidence that this carbon-centered radical forms a covalent attachment with the drug tirapazamine. Given that tirapazamine generates carbon-centered DNA radicals as part of its mechanism of action, this finding may provide a chemical basis for understanding the small but significant levels of drug that become covalently associated with DNA during the damage process. The title compound C₈H₈N₄O crystallized in the monoclinic space group P2₁/c with unit cell parameters: a = 15.670(8), b = 7.381(4), c = 13.491(7) Å, = 90(1), = 95.623(9), = 90(1)°, and Z = 8.     

快速合成Bi@ZIF-8复合纳米材料用于近红外二区光热治疗以及可控药物释放

随着纳米技术的发展及其向医学领域的渗透,纳米技术为肿瘤的治疗开辟了新的途径,构建有效的纳米载体体系对于肿瘤的治疗具有十分重要的意义.本工作报道了一种铋纳米粒子嵌入ZIF-8的纳米材料Bi@ZIF-8@TPZ(BZT),联合近红外二区(NIR-Ⅱ)的光热治疗与化疗,达到了良好的治疗效果.BZT纳米材料高效地装载了抗癌药物替拉扎明(TPZ),同时嵌入的铋纳米点使得该纳米材料具有NIR-Ⅱ光热的能力.因ZIF-8具有良好的pH响应能力,所以在酸性和光照条件下能实现药物的可控释放,实现了化疗与NIR-Ⅱ光热治疗的协同治疗,使得BZT纳米材料在临床上具有很高的应用价值.     

Reactions in Tirapazamine Induced by the Attachment of Low‐Energy Electrons: Dissociation Versus Roaming of OH

Tirapazamine (TPZ) has been tested in clinical trials on radio‐chemotherapy due to its potential highly selective toxicity towards hypoxic tumor cells. It was suggested that either the hydroxyl radical or benzotriazinyl radical may form as bioactive radical after the initial reduction of TPZ in solution. In the present work, we studied low‐energy electron attachment to TPZ in the gas phase and investigated the decomposition of the formed TPZ^? anion by mass spectrometry. We observed the formation of the (TPZ–OH)^? anion accompanied by the dissociation of the hydroxyl radical as by far the most abundant reaction pathway upon attachment of a low‐energy electron. Quantum chemical calculations suggest that NH₂ pyramidalization is the key reaction coordinate for the reaction dynamics upon electron attachment. We propose an OH roaming mechanism for other reaction channels observed, in competition with the OH dissociation.     

Cyclophosphamides as hypoxia-activated diffusible cytotoxins: A theoretical study

Cyclophosphamides have been in clinical use as anti-cancer drugs for a long time and much research has been directed towards reducing their side effects. Here we have performed a theoretical investigation into the possibility of designing bioreductive analogues of cyclophosphamides. Our calculations have employed semiempirical molecular orbital AM1-SM2 and PM3-SM3 calculations, as implemented in MOPAC 93, which include a modified Born method for the treatment of solvation. We have investigated the effect of bioreductive activation on the -elimination reaction that is central to the activation of cyclophosphamides. The approach was tested on two known bioreductive agents, including CB1954, and gave results in agreement with experiment. Non-local density functional calculations on CB1954 and its metabolites, including the radical anion, were in agreement with the semiempirical calculations. The calculations have identified a number of potentially novel bioreductive cyclophosphamides. In particular, our calculations identified compounds in which the initial one-electron reduction was not activating. Such compounds are likely to be more effective bioreductive agents, as the -elimination will not compete under oxic conditions with the important re-oxidation required for the protection of oxic tissue.     

高效液相色谱法检测替拉扎明中的有关物质

替拉扎明（TPZ）是一种肿瘤放疗增敏剂,其中已知杂质SR4317为TPZ的合成中间体,SR4330为TPZ的可能降解物。TPZ中有关物质的检测目前尚未见文献报道。本文建立的检测TPZ中有关物质的高效液相色谱法（HPLC）,准确、灵敏、快速,可用于TPZ原料药的质量控制。     

Spin Trapping Hydroxyl and Aryl Radicals of One-Electron Reduced Anticancer Benzotriazine 1,4-Dioxides

Hypoxia in tumors results in resistance to both chemotherapy and radiotherapy treatments but affords an environment in which hypoxia-activated prodrugs (HAP) are activated upon bioreduction to release targeted cytotoxins. The benzotriazine 1,4-di-N-oxide (BTO) HAP, tirapazamine (TPZ, 1), has undergone extensive clinical evaluation in combination with radiotherapy to assist in the killing of hypoxic tumor cells. Although compound 1 did not gain approval for clinical use, it has spurred on the development of other BTOs, such as the 3-alkyl analogue, SN30000, 2. There is general agreement that the cytotoxin(s) from BTOs arise from the one-electron reduced form of the compounds. Identifying the cytotoxic radicals, and whether they play a role in the selective killing of hypoxic tumor cells, is important for continued development of the BTO class of anticancer prodrugs. In this study, nitrone spin-traps, combined with electron spin resonance, give evidence for the formation of aryl radicals from compounds 1, 2 and 3-phenyl analogues, compounds 3 and 4, which form carbon C-centered radicals. In addition, high concentrations of DEPMPO (5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide) spin-trap the •OH radical. The combination of spin-traps with high concentrations of DMSO and methanol also give evidence for the involvement of strongly oxidizing radicals. The failure to spin-trap methyl radicals with PBN (N-tert-butylphenylnitrone) on the bioreduction of compound 2, in the presence of DMSO, implies that free •OH radicals are not released from the protonated radical anions of compound 2. The spin-trapping of •OH radicals by high concentrations of DEPMPO, and the radical species arising from DMSO and methanol give both direct and indirect evidence for the scavenging of •OH radicals that are involved in an intramolecular process. Hypoxia-selective cytotoxicity is not related to the formation of aryl radicals from the BTO compounds as they are associated with high aerobic cytotoxicity.