MAQO和它的环糊精包结物的电子自旋共振研究

报导2-甲基-3乙酰基喹喔啉1，4-二氧化物（MAQO）和它与α-环糊精（α-CD），β-环糊精（β-CD）包结物在室温下应用紫外光（λ＝360nm）进行原位光化学反应生成自由基的电子自旋共振研究结果，推断MAQO在紫外光作用下首先生成激发态（MAQO）*，然后进一步发生光化学反应导致N＝C双键转移而生成氮氧自由基并为ESR所检测到．从ESR检测结果猜想，在非含氢溶剂中是生成较稳定的且又相距很远的氮氧双自由基；而在含氢溶剂中，由于发生夺氢反应而生成稳定的氮氧单自由基．当MAQO－α－CD包结物在含氢溶剂中发生光化学反应时亦生成氮氧单自由基；但其ESR谱的超精细结构（hfs）和线宽均发生了变化，推断环糊精包结在MAQO分子苯环一端，受环糊精的微环境空间阻碍效应．

ESR Studies on 2-Methyl-3-Acetyl Quinoxaline N, N-Dioxide and Its Cyclodextrin Inclusion Compounds

2-Methyl-3-acetyl quinoxaline N,N-dioxide (MAQO) is a novel medicine. However it easily undergoes photoreations such as deoxygenation, cyclization etc., resulting in the change of its pharmaceutical action. The problem about radical intermediates involved in the change process is still not well resolved, and the relevant studies are worthwhile.
In CCl4 and CS2 nonprotonic solvents, MAQO gives identical electron spin resonance (ESR) spectra at g=2.0063 with hyperfine (fh) constant aN=1.03mT under UV-irradiation at room temperature. The photochemical process can be depicted as formula(1).
As soon as the unimolecular nitroxide biradical produces, it rapidly couple into a dimmer biradical, 4.Because the two nitroxyl radical in the dimer are far from each other, no interaction between them is observed. Therefore, it can be recognized as two independent mono-radicals.
In protonic solvent, CHCl3, when MAQO was irradiated with ultraviolet light at room temperature, it gives a ESR signal at g=2.0058 with hyperfine constant aN=0.98mT, aH(5,7)=o.11mT, aH(6.8)=0.36mT. The hf structure from two groups of equivalent ringprotons can be clearly observed. According to formula (1)， the unimolecular nitroxyl biradical formed from a excited intermediate may abstract a H atom from CHCl3 to generate a hydrogenated nitroxyl mono-radical 5, which can elucidate the above ESR spectrum.
The ESR results of MAQO-α-CD, MAQO-β-CD and MAQO parent are similar in protonic solvent. The only difference is that the aH values, hf constant from protons on benzo-ring, decrease while the line widths increase, compared with that of MAQO parent. This result indicates that the benzo-ring, part of MAQO molecules, has been included in CD and CD have a microenvironmental effect on the proton on the ring.
The nitroxyl radicals detected by ESR are very reactive, they will polymerize, deoxygenate, cyclize, etc,. resulting in the deterioration of the medicine.