Identification of 3-aminomethyl-1,2-dihydro-4-phenyl-1-isoquinolones: A new class of potent, selective, and orally active non-peptide dipeptidyl peptidase IV inhibitors that form a unique interaction with Lys554 Yoshihiro Banno a , Yasufumi Miyamoto a , Mitsuru Sasaki a , Satoru Oi a , Tomoko Asakawa a , Osamu Kataoka a , Koji Takeuchi a , Nobuhiro Suzuki a , Koji Ikedo a , Takuo Kosaka a , Shigetoshi Tsubotani a , Akiyoshi Tani a , Miyuki Funami a , Michiko Tawada a , Yoshio Yamamoto a , Kathleen Aertgeerts b , Jason Yano b , Hironobu Maezaki a,⇑ a Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, 17-85 Jusohonmachi 2-Chome Yodogawa-ku, Yodogawa-ku, Osaka 532-8686, Japan b Takeda San Diego, Inc., 10410, Science Center Drive, San Diego, CA 92121, USA article info Article history: Received 13 May 2011 Revised 20 June 2011 Accepted 20 June 2011 Available online 28 June 2011 Keywords: Dipeptidyl peptidase IV (DPP-4) Isoquinolone Anti-diabetic effects abstract The design, synthesis, and structure–activity relationships of a new class of potent and orally active non-peptide dipeptidyl peptidase IV (DPP-4) inhibitors, 3-aminomethyl-1,2-dihydro-4-phenyl-1-iso- quinolones, are described. We hypothesized that the 4-phenyl group of the isoquinolone occupies the S1 pocket of the enzyme, the 3-aminomethyl group forms an electrostatic interaction with the S2 pocket, and the introduction of a hydrogen bond donor onto the 6- or 7-substituent provides interaction with the hydrophilic region of the enzyme. Based on this hypothesis, intensive research focused on developing new non-peptide DPP-4 inhibitors has been carried out. Among the compounds designed in this study, we identified 2-[(3-aminomethyl-2-(2-methylpropyl)-1-oxo-4-phenyl-1,2-dihydro-6-isoquinoli- nyl)oxy]acetamide (35a) as a potent, selective, and orally bioavailable DPP-4 inhibitor, which exhibited in vivo efficacy in diabetic model rats. Finally, X-ray crystallography of 35a in a complex with the enzyme validated our hypothesized binding mode and identified Lys554 as a new target-binding site available for DPP-4 inhibitors. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Dipeptidyl peptidase IV (DPP-4, EC 3.4.14.5) is an extracellular membrane-bound serine protease expressed on the cell surface of a variety of organs, for example, intestine, kidney, and liver. 1 It catalyses the cleavage of N-terminal dipeptides from polypeptides with L-proline or L-alanine residues situated at the penultimate position of the substrates. 2,3 The unique aminopeptidase function of DPP-4 has been shown to modulate the biological activities of circulating regulatory peptides involved in the endocrine, neuroen- docrine, and immune systems in vitro. 4 It has been revealed that DPP-4 plays a principal role in the inactivation of glucagon-like peptide-1 (GLP-1 or GLP-1[7–36]amide), which contributes to the control of blood glucose levels in vivo. 4–13 GLP-1 is one of the gastrointestinal hormones (incretins) se- creted by intestinal L-cells in response to the ingestion of nutri- ents. 14–16 It is known as the most potent insulinotropic hormone that increases glucose-stimulated insulin secretion. Furthermore, numerous studies have indicated the importance of GLP-1 not only as a potent insulin secretagogue, but also as a multifunctional hypoglycemic hormone responsible for the stimulation of b-cell growth, survival, and differentiation, the inhibition of glucagon re- lease, the retardation of gastric emptying, etc. Actually, many clin- ical studies have shown that GLP-1 normalizes postprandial and fasting glycemia in subjects with type 2 diabetes. 17–21 On the basis of the above evidence, GLP-1 itself is one of the logical candidates for therapeutic agents in the treatment of diabetes. 22–25 However, active GLP-1 is rapidly metabolized by DPP-4 resulting in GLP-1[9–36]amide. 1 Therefore, alternative strategies to elicit the beneficial anti-diabetic effects of GLP-1 are required. One of the promising approaches is the inhibition of DPP-4 activity, which can extend the duration of GLP-1 action through the blockade of its degradation, resulting in improvement of the elevated glucose levels in diabetes. Accordingly, DPP-4 inhibitors have been expected to serve as a new type of glucose-lowering agent with little or no adverse effects observed with sulfonylureas. Many DPP-4 inhibitors, such as MK-403 (sitagliptin phosphate), 26 BMS- 477118 (saxagliptin), 27,28 LAF-237 (vildagliptin), 28 and SYR-322 0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2011.06.059 ⇑ Corresponding author. Tel.: +81 6 6300 6263; fax: +81 6 6300 6306. E-mail address: Maezaki_Hironobu@takeda.co.jp (H. Maezaki). Bioorganic & Medicinal Chemistry 19 (2011) 4953–4970 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry journal homepage: www.elsevier.com/locate/bmc