For the study described herein

For the study described herein, analogues of CID1792197 (2) were selected for exploration. There are a variety of reasons for this decision. First, the synthetic approach, described hereafter, is modular in nature to rapidly enable the independent modification of either end of the molecule. Second, there were not many commercially available derivatives of this molecule that explored modifications that we desired. Third, it was envisioned that synthetic derivatives of caged compounds 2 could remove the α,β-unsaturated amide, which could serve as an indiscriminate Michael acceptor with diverse off-target activities. Finally, this compound was a selective GPR55 agonist with no activity at CB1, CB2, or GPR35.
Results and discussion CID1792197 (2) was the scaffold chosen for further lead development due to synthetic feasibility to obtain analogues. Modifications of the lead (2) were targeted at the two termini in order to increase activity as a selective GPR55 agonist, enhance solubility, and eliminate the Michael acceptor functionality. In order to synthesize analogues that explored the role that each end of the molecule plays with respect to the overall activity of the analogue, a retrosynthesis was designed to be modular in nature (Scheme 1). By doing so, each end of the analogue could be independently modified and the total number of steps to analogues would be fewer. It was envisioned that the two parts of the molecule could be coupled by reacting an acylisothiocyanate with an aniline to generate the acylthiourea moiety of the analogues (6). The acylisothiocyanates could be synthesized from carboxylic acids 5. The anilines (7) could be prepared by substituting the chloride in p-nitrophenyl sulfonyl chloride with the proper amine (8), followed by catalytic hydrogenation of the nitro group. Many, but not all, of the carboxylic acids (5) and amines (8) were commercially available and the remainder were synthesized as described herein.
Conclusion Utilizing a modular synthesis, 22 unique compounds were synthesized. These included 12 different sulfonamide substitutions, five different acyl groups attached to the thiourea, and six hybrid analogues where both sections were modified. The activities of the compounds indicated both beneficial and detrimental interactions. For example, the potential and optimal positions of hydroxyl groups for hydrogen bonding to the receptor (analogues 6bv, 6cv, 6dv, 6ev, 6gv, 6jv, 6kv, 6fy, 6fz, 6bx, 6ex, 6gx, 6bz, and 6gz) and the position of aromatic nitrogen atoms (6av, 6iv, 6lv, 6fw, 6fx, 6ax, 6bx, 6ex, and gx) on either end of the ligand were analyzed. These data serve as a springboard for the design of even more potent and selective ligands to serve as agonists at GPR55.
Experimental
Acknowledgments This research was supported in part by the National Institutes of Health grants R01DA023204, P32DA013429, and P30DA029925. The authors thank Dr. Franklin J. Moy (UNCG) for assisting with the analysis of NMR data and Dr. Daniel A. Todd (UNCG) for acquisition of the high resolution mass spectrometry data at the Triad Mass Spectrometry Laboratory at the University of North Carolina at Greensboro.
Introduction 2-Lysophosphatidylcholines (1-acyl-glycero-3-phosphocholines, 2-LPCs, LPCs), which maintain the acyl chain in sn-1 position, are the most abundant lysophospholipid in nature (D'Arrigo and Servi, 2010). Lipidomic analysis has revealed a correlation of lower plasma concentrations of LPCs with impaired glucose tolerance and obesity (Zhao et al., 2010, Barber et al., 2012). LPC 16∶0 is the most abundant species in human plasma (146 ± 37 μM) followed by LPC 18∶0 (56.5 ± 14.9 μM) and LPC 18∶1 (28.4 ± 12.5 μM) (Heimerl et al., 2014). Although the presence of LPCs in plasma was observed at the beginning of the twentieth century (Kihara et al., 2015), the original observation from Metz's laboratory on dose-dependent lysophospholipid-induced insulin secretion was shown already in 1986 (Metz, 1986) while the involvement of G protein coupled receptor for the effect of LPC on insulin secretion was identified as GPR119 in 2005 (Soga et al., 2005). GPR119 is preferentially expressed on β-cells of the islets of Langerhans but its expression has also been demonstrated in intestinal L- and K-cells, where its activation was associated with secretion of glucagon-like peptide 1 and glucose-dependent insulinotropic peptide (Overton et al., 2006, Sakamoto et al., 2006, Ahlkvist et al., 2013). GPR119 has been shown to bind a variety of lipid-derived ligands, as well as a range of small synthetic molecules. Recent literature data indicate that lysophospholipids also have the ability to interact with other pancreatic receptors regulating carbohydrate metabolism. GPR55 activated by lysophosphatidylinositols may be another attractive target in type 2 diabetes mellitus (T2DM) (Liu et al., 2016). Treatment of diabetic rats with lysophoshatidylinositol has been found to counteract the symptoms of diabetes such as high blood glucose, lower body weight, increase amplitude of slow wave in stomach smooth muscle, and to improve gastric emptying (Lin et al., 2014). Both GPR119 and GPR55 receptors are stimulated by endocannabinoids such as palmitoylethanolamide (PEA), oleoylethanolamide (OEA), arachidonoylethanolamide (anandamide, AEA), and 2-arachidonoylglycerol (2-AG) (Godlewski et al., 2009). We have recently proved that ligand specificity of GPR55 is much wider and our studies evidence that GPR55 is activated also by LPC (Drzazga et al., 2017). However, GPR40 (also known as the free fatty acid receptor 1 or FFAR1) is the best-studied of the cell-surface receptors on β-cells. GPR40 is the most potently activated by endogenous free fatty acids (FFAs) with medium and long (C12-C22) aliphatic chains, resulting in amplification of insulin secretion only in the presence of elevated glucose levels (Itoh et al., 2003, Itoh and Hinuma, 2005, Briscoe et al., 2003). The glucose dependency of insulin secretion makes this receptor an excellent target for developing efficacious therapies with a desired safety profile for use in the treatment of T2DM.