Background: Quinoxaline 1,4-dioxides have a broad range of biological activity that causes a growing interest in their derivatives for drug discovery. Recent studies demonstrated that quinoxaline 1,4- dioxides have a promising anticancer activity and good hypoxia-selectivity.

Objective: The preparation, isolation, structure characterization, and screening for anticancer activity of the first representatives of 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides have been described.

Materials and Methods: A series of 7- and 6-halogeno-3-phenylquinoxaline-2-carbonitrile 1,4-dioxides was synthesized by the Beirut reaction. The cytotoxicity was assessed by MTT test (72 h incubation) in normoxia (21% O2) and hypoxia (1% O2) conditions.

Results: We found that during the Beirut reaction between a benzofuroxan bearing an electron withdrawing group and benzoylacetonitrile in the presence of triethylamine, in addition to well-known 7-substituted quinoxaline-2-carbonitrile 1,4-dioxides 7-11a, the 6-isomers 7-11b are formed. Moreover, the yield of the 6- isomers increased with the increase in the electron-withdrawing character of the substituent. For benzofuroxans with CO2Me and CF3 groups, 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides 10-11b were the major products. Despite similarities in physicochemical and spectroscopic properties, the obtained isomers exhibit considerable differences in their anticancer activity and hypoxia selectivity.

Conclusion: Substituents and their electronic effects play a key role in the formation of 7- and 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides in the Beirut reaction and in the cytotoxicity properties of the obtained isomers.

背景：喹喔啉1,4-二氧化物具有广泛的生物学活性，这引起了人们对其衍生物用于药物开发的兴趣日益增长。最近的研究表明，喹喔啉1,4-二氧化物具有良好的抗癌活性和良好的低氧选择性。

目的：描述了6-取代的喹喔啉-2-甲腈1，4-二氧化物的第一个代表化合物的制备，分离，结构表征和抗癌活性的筛选。

材料与方法：通过贝鲁特反应合成了一系列的7-和6-卤代-3-苯基喹喔啉-2-腈1,4-二氧化物。在正常氧（21％O2）和低氧（1％O2）条件下，通过MTT试验（72小时孵育）评估细胞毒性。

结果：我们发现，在三乙胺存在下，带有吸电子基团的苯并呋喃与苯甲酰乙腈之间的贝鲁特反应期间，除了众所周知的7-取代的喹喔啉-2-腈1,4-二氧化物7-11a外，6形成异构体7-11b。此外，随着取代基的吸电子特性的增加，6-异构体的产率增加。对于具有CO2Me和CF3基团的苯并呋喃，主要产品是6-取代的喹喔啉-2-腈1,4-二氧化物10-11b。尽管理化性质和光谱性质相似，但所获得的异构体在其抗癌活性和低氧选择性方面显示出相当大的差异。

结论：在贝鲁特反应中，取代基及其电子效应在7和6位取代的喹喔啉-2-甲腈1,4-二氧化物的形成以及所获得异构体的细胞毒性中起关键作用。