br Methods br Results and discussion br Acknowledgements br
Results and discussion
Introduction Diacylglycerol O-acyltransferase (DGAT) is a key enzyme that catalyzes the final committed step in triglyceride synthesis and is highly expressed in the small intestine, adipose tissue, liver and mammary gland.1, 2, 3, 4 Its imbalance could lead to the excessive accumulation of triglycerides, which is frequently associated with metabolic diseases, such as obesity, insulin resistance and hepatic steatosis.5, 6 Although the DGAT family contains two isozymes DGAT-1 and DGAT-2, their sequence homology is limited. A previous investigation revealed that DGAT-2 knockout (DGAT-2−/−) mice suffer from lipopenia and die soon after birth. However, DGAT-1−/− mice are healthy and significantly resistant to diet-induced obesity (DIO), hyperlipidemia and hepatic steatosis when fed a high-fat diet.9, 10, 11, 12 Thus, DGAT-1 could be a potential target for the modulation of triglycerides to treat hyperlipidemia and other metabolic disorders. Over the past decade, an increasing number of small-molecule DGAT-1 inhibitors had been developed with variable structural types.13, 14, 15 Most (Fig. 1) share a privileged structure with the heteroaryl-linker-acid, which is based on compounds 1 and 2 described in the early patents of Japan Tobacco/Tularik and Bayer.16, 17 Several inhibitors containing the phenylcyclohexylacetic H-9 dihydrochloride functional group from compound 1 have entered into clinical trials,18, 19, 20, 21, 22, 23, 24 and compound 3 (LCQ908) was included in a phase III study for the treatment of familial chylomicronemia syndrome (FCS) and showed high plasma exposure after oral dosing. Based on compound 2 with a keto acid moiety that was originally developed by Abbott, the terminal benzothiazole group was opened, creating lead compound 8 (A-922500), which showed highly potent inhibition of DGAT-1 (50% inhibitory concentration [IC50]=7nM) with oral efficacy. This compound was extensively applied in the study of DGAT-1, but it is poorly soluble. To increase the solubility of this lead compound, researchers attempted to exchange the keto acid moiety of compound 8 with a simple amino acid while retaining the functional acid group to reduce its LogP property and avoid possible isomerization (Fig. 2, 9 and 10).27, 28, 29, 30, 31 In our efforts to discover novel potent DGAT-1 inhibitors, we designed a series of compounds based on compound 8 in which the phenyl linker was replaced by a six-membered heteroaryl group with a five-membered amino acid scaffold. Here, we report the discovery of a new low-systemic-exposure DGAT-1 inhibitor 22, which bears a picolinoylpyrrolidine-2-carboxylic acid moiety targeting DGAT-1 specifically.32, 33 We found that this compound exhibited dose-dependent efficacy in an oral triglyceride uptake study in mice.
Results and discussion
Conclusions Herein, we described the design and synthesis of a series of DGAT-1 inhibitors with a picolinoylpyrrolidine-2-carboxylic acid moiety based on compound 8 in which the phenyl linker was replaced by a six-membered heteroaryl group with a five-membered amino acid scaffold. Among them, compound 22 exhibited good inhibitory activity for hDGAT-1 and effectively reduced the intracellular triglyceride contents in the 3T3-L1, Caco-2 and HepG2 cell lines. Furthermore, an acute lipid challenge test of compound 22 revealed that it exerts dose-dependent lipid-lowering effects in mice. DGAT-1 inhibitor 22, as an attractive lead candidate, warrants further investigation for the treatment of hyperlipidemia and other metabolic disorders because of its preferential distributions in the intestine and liver, which correlates perfectly with the location of DGAT-1.
Acknowledgments We are grateful for financial support from the National Natural Science Foundation of China (Grant No. 81225022, 81503124) and the Institutes for Drug Discovery and Development, Chinese Academy of Sciences (No. CASIMM0120162025).