The effects of structural modifications of 6-substituted N-(1H-tetrazol-5-yl)-2-pyrazinecarboxamides on their anti-allergic activity was analyzed quantitatively by means of the Hansch-Fujita method. The activity of these compounds was correlated with hydrophobic (π) and steric (molecular refractivity and STERIMOL B1) effects of the 6-substituent on the pyrazine ring. The 6-substituents with a length greater than n-propylamino possess an extra effect enhancing the activity. Moreover, the activity increased progressively from 6-non-amino via alkylamino- to dialkylamino-substituted compounds, other factors being equal. This could be attributable to an electronic effect of substituents. Electron-donating small and yet symmetric substituents with high hydrophobicity longer than n-propylamino seemed to be favorable to the activity. By compromising these contradictory requirements, small dialkylamino (including cyclic amino) groups were decided to be the most favorable substituents. This analysis was in agreement with the observation that the most effective compounds were the 6-dimethylamino (I-27) and 6-(1-pyrrolidinyl) (I-34) derivatives.
通过汉斯-藤田法对6-取代N-(
1H-四唑-5-基)-2-
吡嗪甲酰胺的结构修饰对其抗过敏活性的影响进行了定量分析。这些化合物的活性与
吡嗪环上6-取代基的疏
水(π)和空间(分子折射率和STERIMOL B1)效应相关。长度大于正丙基
氨基的6-取代基具有增强活性的额外效应。此外,在其他因素相同的情况下,活性从6-非
氨基到烷基
氨基和二烷基
氨基取代的化合物逐渐增加。这可能是由于取代基的电子效应。具有高疏
水性且长度大于正丙基
氨基的供电子小而对称取代基似乎有利于活性。通过权衡这些矛盾的要求,决定小二烷基
氨基(包括环状
氨基)基团是最有利的取代基。这一分析结果与观察结果一致,即最有效的化合物是6-二甲基
氨基(I-27)和6-(1-
吡咯烷基)(I-34)衍
生物。