Abstract We have synthesized 35 N -phenyl- N ′-(4-pyridyl)urea derivatives and tested their cytokinin activity in the tobacco callus bioassay. Among them, N -phenyl- N ′- (2-chloro-4-pyridyl)urea is highly active, the optimum concentration of which is lower than 4 × 10 −9 M (0.001 ppm), 3 compounds, i.e. N -(2-methylphenyl)- N ′-(2-chloro-4-pyridyl)urea, N -(3-methylphenyl)- N ′-(2-chloro-4-pyridyl)urea and N -(3-chlorophenyl)- N ′-(2-chloro-4-pyridyl) urea are as active as N 6 -benzyladenine (concentration for optimum yield: 4.4 × 10 −8 M or 0.01 ppm), and N -phenyl- N ′-(2-methyl-4-pyridyl)urea and N -(2-chlorophenyl)- N ′-(2-chloro-4-pyridyl)urea are as active as N -phenyl- N ′-(4-pyridyl)urea (concentration for optimum yield: 4.7 × 10 −7 M or 0.1 ppm), while the activity of the other 29 compounds are not so remarkable and 11 of them are almost or completely inactive.

中文翻译：

---

N-苯基-N'-(4-吡啶基)脲衍生物的细胞分裂素活性

摘要 我们合成了 35 种 N-苯基-N'-(4-吡啶基)脲衍生物，并在烟草愈伤组织生物测定中测试了它们的细胞分裂素活性。其中，N-苯基-N'-(2-氯-4-吡啶基)脲具有高活性，其最佳浓度低于4×10 -9 M (0.001 ppm)，3种化合物，即N-( 2-甲基苯基)-N'-(2-氯-4-吡啶基)脲、N-(3-甲基苯基)-N'-(2-氯-4-吡啶基)脲和N-(3-氯苯基)-N '-(2-chloro-4-pyridyl) urea 与 N 6 -benzyladenine（最佳产率的浓度：4.4 × 10 -8 M 或 0.01 ppm）和 N-苯基-N '-(2-甲基- 4-吡啶基）脲和 N-（2-氯苯基）-N'-（2-氯-4-吡啶基）脲与 N-苯基-N'-（4-吡啶基）脲一样活跃（最佳产率的浓度： 4.7 × 10 -7 M 或 0.1 ppm），