For instance, Guan
et al. [
96] substituted the 1-(4-(difluoromethoxy)phenyl)propyl group attached to N in the diflumetorim molecule with 2-(6-phenoxypyridin-3-yl)ethan-1-amine, leading to the identification of compound
63 (
Fig. 6). The inhibitory activity of compound
63a against cucumber downy mildew (EC
50 = 0.19 mg/L) was notably better than that of diflumetorim (half maximal effective concentration (EC
50) = 23.06 mg/L), flumorph (EC
50 = 7.77 mg/L), and cyazofamid (EC
50 = 1.01 mg/L). Additionally, it showed significant inhibitory activity against southern corn rust and wheat powdery mildew. The structural relationships indicated that the substitution position of the chlorine atom on the phenyl group had a strong influence on the antimicrobial activity of the compounds. Subsequent structural optimization showed that compound
63b with a difluoromethyl group exhibited better inhibitory activity against downy mildew (EC
50 = 0.10 mg/L) compared to compound
63a (EC
50 = 0.19 mg/L) and common fungicides like diflumetorim, dimethomorph, and cyazofamid (EC
50 = 1.01
–23.06 mg/L). The field efficacy of compound
63b was also superior to compound
63a, cyazofamid, and flumorph, making it a potential candidate as a fungicide [
97]. Following the structural optimization of compound
63b in the same year, Guan
et al. [
98] observed that compound
64 (
Fig. 6) demonstrated an EC
50 value of 2.16 mg/L against southern corn rust, surpassing the control diflumetorim (EC
50 = 53.26 mg/L). It was deemed a promising lead compound for antirust purposes. The conformational relationship indicated that enhancing the fungicidal activity of compound
64 was favored by adding an electron-donating group at the
para-position of the benzene ring, an electron-withdrawing group at the
meta-position of the benzene ring, and substituting the pyrimidine amine group at the 4-position on the pyridine ring. Yan
et al. [
99] added the pyrimidine ring containing the phenyl thiazole group to pyrimidine ring 2 of diflumetorim, and discovered that compound
65 (
Fig. 6) had a greater effect on the antimicrobial activity of
Puccinia sorghi (EC
50 = 0.93 mg/L) and
Blumeria graminis (EC
50 = 1.24 mg/L) compared to diflumetorim, tebuconazole, and flusilazole. The cytotoxicity tests revealed that compound
65 was less toxic than diflumetorim. Compound
66 (
Fig. 6) [
100] demonstrated outstanding fungicidal activity against
Pseudoperonospora cubensis (EC
50 = 0.422 mg/L), surpassing the effectiveness of commercially available fungicides such as cyazofamid, flumorph, and diflumetorim. The activity of the entire molecule is thought to be boosted by the presence of the substituted F atom on the phenyl ring in compound
66. Additionally, compound
67 (
Fig. 6) [
101] demonstrated control efficacy exceeding 80% against cucumber downy mildew, wheat powdery mildew, and colletotrichum orbiculare.