Optimization of a pyrazole hit from FBDD into a novel series of indazoles as ketohexokinase inhibitors Xuqing Zhang ⇑ , Fengbing Song, Gee-Hong Kuo, Amy Xiang, Alan C. Gibbs, Marta C. Abad, Weimei Sun, Lawrence C. Kuo, Zhihua Sui Johnson & Johnson Pharmaceutical Research and Development, Welsh & McKean Roads, PO Box 776, Spring House, PA 19477, United States article info Article history: Received 2 May 2011 Revised 14 June 2011 Accepted 15 June 2011 Available online 29 June 2011 Keywords: FBDD (fragment based drug discovery) KHK (ketohexokinase) Pyrazole Indazole abstract A series of indazoles have been discovered as KHK inhibitors from a pyrazole hit identified through frag- ment-based drug discovery (FBDD). The optimization process guided by both X-ray crystallography and solution activity resulted in lead-like compounds with good pharmaceutical properties. Ó 2011 Elsevier Ltd. All rights reserved. Ketohexokinase (KHK, also known as fructokinase) catalyzes, with adenosine triphosphate (ATP) and a potassium ion (K + ), the conversion of the furanose form of D-fructose to fructose-1-phos- phate. 1 It initiates the intracellular catabolism of a large proportion of dietary carbohydrate and is an important regulator of hepatic glucose metabolism. 2 Due to its role in dietary fructose metabo- lism, inhibition of KHK would suppress carbon supply for fatty acid and very low density lipoprotein synthesis. Hence, modulation of KHK will help relieve some metabolic syndromes such as obesity, hypertriglyceridemia, insulin resistance and hypertension, which makes KHK an important target in drug discovery. 3 Recently, a novel series of pyrimidinopyrimidines have been discovered by using a combination of high-throughput screening (HTS) and structure-based drug design (SBDD). 4 Along with HTS approach, we also described a different approach for lead genera- tion of KHK inhibitors through a FBDD protocol. 5 The entire process includes X-ray crystallographic screening of three stages of itera- tive design and synthesis of fragment libraries. We have described the discovery of unique and structurally diverse hits through this pathway. Herein we focus on a medicinal chemistry approach to drive one hit into lead-like structures. Unlike the early libraries solely guided by electron density information from X-ray crystallography, the follow-up compounds were evaluated in a KHK-mediated enzymatic assay. Selected compounds were ad- vanced into lead optimization or late lead generation according to their bio-activity, pharmacokinetic and selectivity profiles. Fragment evolution has been by far the most successful method of fragment optimization. 6–9 When allied with a high degree of structural information such as X-ray crystallography, it gives medicinal chemists valuable tools in the validation and subsequent optimization of a hit. Pyrazole 1 (Fig. 1) was identified as a hit binding to the ATP binding site of KHK by X-ray crystallographic screening of the fragment libraries. Without KHK enzyme activity tested, fragment 1 was optimized in the follow-up chemistry. Figure 1 illustrates the combination of fragment fusion and evolu- tion of pyrazole 1 to yield indazole 2. Evidence supporting incorpo- ration of an indazole core was an intra-molecular H-bonding between the 4-carboxamide and 5-amine functional groups of pyrazole 1, as revealed by X-ray crystallography, molecular mechanics and virtual docking experiments. Furthermore, as indicated by X-ray crystallography, these two functional groups 0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2011.06.067 ⇑ Corresponding author. Tel.: +1 215 488 7866. E-mail address: xzhang5@its.jnj.com (X. Zhang). N N MeS R 2 N N MeS O NH 2 NH 2 1 FBDD hit 2 Figure 1. From pyrazole to indazole. Bioorganic & Medicinal Chemistry Letters 21 (2011) 4762–4767 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl