A series of novel dipeptidyl boronic acid inhibitors of 20S proteasome were designed and synthesized. Aliphatic groups at R¹ position were designed for the first time to fully understand the SAR (structure–activity relationship). Among the screened compounds, novel inhibitor 5c inhibited the CT-L (chymotrypsin-like) activity with IC₅₀ of 8.21 nM and the MM (multiple myeloma) cells RPMI8226, U266B and ARH77 proliferations with the IC₅₀ of 8.99, 6.75 and 9.10 nM, respectively, which showed similar in vitro activities compared with the compound MLN2238 (biologically active form of marketed MLN9708). To investigate the oral availability, compound 5c was esterified to its prodrug 6a with the enzymatic IC₅₀ of 6.74 nM and RPMI8226, U266B and ARH77 cell proliferations IC₅₀ of 2.59, 4.32 and 3.68 nM, respectively. Furthermore, prodrug 6a exhibited good pharmacokinetic properties with oral bioavailability of 24.9%, similar with MLN9708 (27.8%). Moreover, compound 6a showed good microsomal stabilities and displayed stronger in vivo anticancer efficacy than MLN9708 in the human ARH77 xenograft mouse model. Finally, cell cycle results showed that compound 6a had a significant inhibitory effect on CT-L and inhibited cell cycle progression at the G2M stage.

设计并合成了一系列新型的20S蛋白酶体二肽基硼酸抑制剂。首次设计R ¹位置的脂族基团以充分了解SAR（结构-活性关系）。在筛选的化合物中，新型抑制剂5c抑制CT-L（胰凝乳蛋白酶样）活性，IC ₅₀为8.21 nM，而MM（多发性骨髓瘤）细胞RPMI8226，U266B和ARH77增殖，IC ₅₀为8.99、6.75和9.10 nM。与化合物MLN2238（市售MLN9708的生物活性形式）相比，它们分别显示出相似的体外活性。为了研究口服药物的可用性，化合物5c用酶促IC ₅₀为6.74 nM酯化其前药6a，RPMI8226，U266B和ARH77细胞增殖IC _50分别为2.59、4.32和3.68 nM。此外，前药6a表现出良好的药代动力学特性，口服生物利用度为24.9％，与MLN9708相似（27.8％）。此外，在人ARH77异种移植小鼠模型中，化合物6a显示出良好的微粒体稳定性，并比MLN9708表现出更强的体内抗癌功效。最后，细胞周期结果表明，化合物6a对CT-L具有显着的抑制作用，并在G2M阶段抑制了细胞周期进程。