Optimization of Monocarboxylate Transporter 1 Blockers through Analysis and Modulation of Atropisomer Interconversion Properties Simon D. Guile, †, * John R. Bantick, † Martin E. Cooper, †,§ David K. Donald, † Christine Eyssade, † Anthony H. Ingall, † Richard J. Lewis, ‡ Barrie P. Martin, † Rukhsana T. Mohammed, † Timothy J. Potter, ‡ Rachel H. Reynolds, † Stephen A. St-Gallay, ‡ and Andrew D. Wright ‡ Department of Medicinal Chemistry, AstraZeneca R&D Charnwood, Bakewell Road, Loughborough, LE11 5RH, UK, and Department of Physical & Metabolic Science, AstraZeneca R&D Charnwood, Bakewell Road, Loughborough, LE11 5RH, UK ReceiVed August 17, 2006 We have previously described a novel series of potent blockers of the monocarboxylate transporter, MCT1, which show potent immunomodulatory activity in an assay measuring inhibition of PMA/ionomycin-induced human PBMC proliferation. However, the preferred compounds had the undesirable property of existing as a mixture of slowly interconverting rotational isomers. Here we show that variable temperature NMR is an effective method of monitoring how alteration to the nature of the amide substituent can modulate the rate of isomer exchange. This led to the design of compounds with increased rates of rotamer interconversion. Moreover, some of these compounds also showed improved potency and provided a route to further optimization. Introduction An important component of the immune response is activation of T cells following antigen challenge. However, undesirable activation can lead to graft rejection following transplantation and to autoimmune diseases such as rheumatoid arthritis. We became interested in a report 1 describing a series of pyrrolopyrimidines as potential immunosuppressive agents. From this lead, following an extensive structural investigation, we identified a novel series of compounds exemplified by quinoline amide 1. 2 Furthermore, through compound-led target identification 3 using photoaffinity labeling and proteomic characterization, we were able to show the previously unknown molecular target of these compounds to be the monocarboxylate transporter, MCT1. This was supported by a strong correlation between binding at MCT1 and in Vitro immunomodulatory activity in an assay measuring inhibition of PMA/ionomycin- induced human PBMC proliferation. 4 The monocarboxylate transporters are a family of proteins which transport lactate and other small monocarboxylates. 5 We have shown that MCT1 expression is rapidly upregulated upon T lymphocyte activation in order to meet the demand for lactate efflux resulting from an increased glycolytic rate. Inhibition of lactate efflux by potent blockade of lactate transport results in the accumulation of lactate within the cell and feedback inhibition of glycolysis. This suppression of cellular metabolism results in the inability of T lymphocytes to sustain the rapid rate of cell division occurring during the early immune response to antigen recognition, without being cytotoxic. Blockade of MCT1 is thus a novel mechanism of immunosuppression distinct from current therapies. Quinoline amide 1 resulted from an optimization strategy which focused on reducing logD of highly potent but lipophilic leads. It was concluded that, in order to achieve a good balance of properties, assisted by maintaining low lipophilicity, such compounds require a heteroaryl group at the 6-position in combination with an amide group at the 5-position. 2 The preferred 5-amide was found to be the (R)-hydroxypyrrolidine amide. However, compounds containing this amide existed in solution as a mixture of atropisomers 6 (slowly equilibrating conformational isomers), due to restricted rotations at the amide (CO-N) and aryl-carbonyl (Ar-CO) bonds (Figure 1). For quinoline 1 and the closely related fluoro analogue 2, we have been able to isolate, assign conformations, and, in the case of 2, measure MCT1 potencies for each of the atropisomers. Despite their good properties, progression of compounds such as 1 as potential drugs would be complicated by the existence of multiple conformational forms. These could present signifi- cant challenges due to potential safety, analytical, and manu- facturing concerns. 7 There are numerous examples in the literature of atropisomers encountered during drug discovery programs. 8-13 Reports describe how atropisomerism has been simplified through symmetrization 9 or eliminated by making interconversion rapid. 10 Alternatively, restricting rotation has allowed isolation of a single conformer. 11,12 To investigate the most suitable approach for our compounds, we prepared a range of amides with different electronic and steric properties. This led to an understanding of the factors affecting rates of conformer interconversion allowing the design of new amides which not only exhibited fast interconversion but also had other advantages over the previously preferred amides. We went on to make further modification resulting in highly optimized drug-like compounds. Chemistry While the synthesis of quinoline 1 has been previously described, the other target compounds 2-13 were prepared as shown in Schemes 1-4 below. The N-1 isopropyl compounds 3 and 4 were prepared as shown in Scheme 1. The commercially available chloropyrim- idinedione 14 was alkylated under forcing conditions with isopropyl iodide to give a mixture of the O-alkylated and desired N-alkylated products 15 and 16, respectively. The substituted thiophene ring was incorporated in a three-step process to give the ester 17 which was then saponified to the acid 18. Reaction * Corresponding author: Tel: +44-1509-645308. Fax: +44-1509- 645512. e-mail: simon.guile@astrazeneca.com. † Department of Medicinal Chemistry. ‡ Department of Physical & Metabolic Science. § Current address: 7TM Pharma A/S, Fremtidsvej 3, 2970 Horsholm, Denmark. 254 J. Med. Chem. 2007, 50, 254-263 10.1021/jm060995h CCC: $37.00 © 2007 American Chemical Society Published on Web 12/21/2006