To gain insights for further

To gain insights for further improvement of the agonistic activity, we compared the structural features of the -carbamate piperidine moiety in with that of the spirocyclic moiety in –. Obviously, the substituent corresponding to an isopropyl group on the -carbamate in was lacking in the spirocyclic structure in –. Additionally, as Arena researchers presented in their previous paper, the bulkiness of the terminal group in the right side part is important for potent agonistic activity. Therefore, we expected introduction of lipophilic groups in the spirocyclic structure would increase the potency. To explore this idea, we used and as parent compounds for synthetic accessibility and introduced a -dimethyl group on the spirocyclic structure of these compounds. As anticipated, a 5-fold boost in activity was observed in compound by introduction of a -dimethyl group at the 4-position of the spiro[5.5] system of , and this activity was equivalent to that of -carbamate piperidine derivative . This effect was also found in the spiro[4.5] system of . Introduction of a -dimethyl group at the 3-position of the spiro[4.5] system of boosted the activity by more than 20-fold, and the thus-obtained showed EC of 4 nM. On the other hand, compound having a -dimethyl group at the 2-position of had significantly reduced agonistic activity (EC = 511 nM), indicating that the position of -dimethyl group was critical for agonistic activity. Finally, we synthesized compound to investigate the position of an oxygen mi2 on the spirocyclic structure in . As a result, showed agonistic activity equivalent to that of , indicating that the position of the ether oxygen atom is not critical for the activity. We therefore succeeded in identifying a highly potent novel GPR119 agonist with a spirocylic structure at the right side (). Further investigation was conducted on (clogP = 5.10) which exhibited lower lipophilicity than (clogP = 5.26) and good solubility (441.5 μM in FeSSIF). Inhibitory activities of against six CYP isoforms were evaluated (). As described above, showed IC values of less than 10 μM against the three CYP isoforms (2C8, 2C9, and 2C19). In contrast, with a somewhat higher three-dimensionality (Fsp value = 0.72) as compared with (Fsp value = 0.65) showed no inhibitory activities against all six CYP isoforms (IC >10 μM). Compound was also evaluated in an intraperitoneal glucose tolerance test (ipGTT) model in Sprague-Dawley rats (). Glucose was intraperitoneally administrated 30 min after the oral administration of . After administration of glucose, the plasma concentration of glucose up to two hours and the plasma concentration of insulin up to one hour were measured. As a result, showed a hypoglycemic effect with glucose concentration-dependent insulin secretion. The area under the curve (AUC) of glucose decreased by 14% and 33% when dosed at levels of 0.3 mg/kg and 1 mg/kg, respectively. In summary, we have designed and synthesized novel GPR119 agonists having a spirocyclic structure instead of the substituted piperidine or piperazine ring found in other compounds. The representative showed potent GPR119 agonistic activity (EC = 4 nM, IA = 104%) with no CYP inhibitory activity (IC >10 μM), taking advantage of its higher three-dimensionality as compared with piperidine derivative which showed CYP inhibitory activities. Compound also displayed hypoglycemic activity with insulin secretion dependent on glucose concentration in the rat ipGTT test. These results demonstrate that has potential as a new treatment agent for type 2 diabetes for patients with low-risk of hypoglycemia. Acknowledgments
Introduction The hormone glucagon-like peptide-1 (GLP-1) is released from the intestine under postprandial conditions and it stimulates insulin secretion from the pancreatic β-cell in a glucose-dependent manner. Although GLP-1 mimics are already being used in the clinic to treat type 2 diabetic (T2D) patients, these have raised several safety issues such as risk of developing pancreatitis and medullary carcinoma of the thyroid [1]. Therefore, an alternative strategy, based on the possibility to increase endogenous GLP-1 secretion rather than administering exogenous GLP-1, is an attractive therapeutic option. It has been reported that glucose-stimulated insulin secretion (GSIS) of GLP-1 can be further modulated by amino acids, fatty acids and lipids [[2], [3], [4]]. Interestingly, most of the endogenous GLP-1 secretion is suggested to be mediated by G protein-coupled receptors (GPCRs) such as GPR119 [5, 6], GPR40 [7] and GPR120 [8]. Of these three, GPR119 seems to be the most important inducer of gastric inhibitory polypeptide or glucose-dependent insulinotropic peptide (GIP) and GLP-1 secretion after fat ingestion [9]. GPR119 is a member of class A GPCRs, which can bind to long-chain fatty acids including oleoylethanolamide (OEA), 2-oleoylglycerol (2-OG) and lysophosphatidylcholine (LPC) [6]. The expression of GPR119 mRNA has been reported in a number of tissues including brain, heart, spleen and stomach [10, 11]. The highest level of GPR119 expression has been reported in islets of Langerhans, pancreatic β-cell lines, and intestinal L-cells [12, 13]. Activation of GPR119 has been shown to positively modulate incretins and insulin secretion in humans [4, 14]. In rodents, this effect results in reduction of food intake and body weight gain [15, 16]. GPR119 expression in pancreatic β-cells led to the hypothesis that this receptor could play a role in modulating insulin secretion. Therefore, GPR119 agonists, which have been shown to raise intracellular cyclic AMP (cAMP) levels in vitro in different pancreatic β-cell systems expressing endogenous GPR119, would be expected to potentiate GSIS in a similar manner as GLP-1 and GIP, hormones which also act via GPCRs in β-cells. The insulinotropic actions of GPR119 agonists have been demonstrated in different models of pancreatic β-cells [17]. Although OEA has been identified as the main ligand for GPR119, other phospholipids such as lysophospholipids are potential ligands for this receptor [11]. The lysophospholipid lysophosphatidylinositol (LPI), initially discovered as ligand for GPR55 [18], has multiple GPR55-independent physiological and pathological roles [19].