P-glycoprotein (P-gp; ABCB1)-mediated drug efflux causes multidrug resistance in cancer. Previous synthetic methylated epigallocatechin (EGC) possessed promising P-gp modulating activity. In order to further improve the potency, we have synthesized some novel stereoisomers of methylated epigallocatechin (EGC) and gallocatechin (GC) as well as epicatechin (EC) and catechin (C). The (2R, 3S)-trans-methylated C derivative 25 and the (2R, 3R)-cis-methylated EC derivative 31, both containing dimethyoxylation at ring B, tri-methoxylation at ring D and oxycarbonylphenylcarbamoyl linker between ring D and C3, are the most potent in reversing P-gp mediated drug resistance with EC₅₀ ranged from 32 nM to 93 nM. They are non-toxic to fibroblast with IC₅₀ > 100 μM. They can inhibit the P-gp mediated drug efflux and restore the intracellular drug concentration to a cytotoxic level. They do not downregulate surface P-gp protein level to enhance drug retention. They are specific for P-gp with no or low modulating activity towards MRP1- or BCRP-mediated drug resistance. In summary, methylated C 25 and EC 31 derivatives represent a new class of potent, specific and non-toxic P-gp modulator.

P-糖蛋白（P-gp；ABCB1）介导的药物外流导致癌症的多药耐药性。以前的合成甲基化表没食子儿茶素 (EGC) 具有有希望的 P-gp 调节活性。为了进一步提高效力，我们合成了甲基化表没食子儿茶素 (EGC) 和没食子儿茶素 (GC) 以及表儿茶素 (EC) 和儿茶素 (C) 的一些新型立体异构体。(2R, 3S)-转甲基化 C 衍生物25和 (2R, 3R)-顺式-甲基化 EC 衍生物31均在环 B 处含有二甲氧基化，在环 D 处含有三甲氧基化，并且在环 D 和 C3 之间含有氧羰基苯基氨基甲酰基接头，用 EC ₅₀最有效地逆转 P-gp 介导的耐药性范围从 32 nM 到 93 nM。它们对成纤维细胞无毒，IC ₅₀  > 100 μM。它们可以抑制 P-gp 介导的药物流出并将细胞内药物浓度恢复到细胞毒性水平。它们不会下调表面 P-gp 蛋白水平以增强药物保留。它们对 P-gp 具有特异性，对 MRP1 或 BCRP 介导的耐药性没有调节活性或调节活性低。总之，甲基化 C 25和 EC 31衍生物代表了一类新的有效、特异性和无毒的 P-gp 调节剂。