Novel Potent and Selective DPP-4 Inhibitors: Design, Synthesis and Molecular Docking Study of Dihydropyrimidine Phthalimide Hybrids

Abstract

Background: Dipeptidyl peptidase-4 (DPP-4) inhibitors have emerged as anti-hyperglycemic agents that improve glycemic control in type 2 diabetic patients, either as monotherapy or in combination with other antidiabetic drugs.

Methods: A novel series of dihydropyrimidine phthalimide hybrids was synthesized and evaluated for their in vitro and in vivo DPP-4 inhibition activity and selectivity using alogliptin as reference. Oral glucose tolerance test was assessed in type 2 diabetic rats after chronic treatment with the synthesized hybrids ± metformin. Cytotoxicity and antioxidant assays were performed. Additionally, molecular docking study with DPP-4 and structure activity relationship of the novel hybrids were also studied.

Results: Among the synthesized hybrids, 10g, 10i, 10e, 10d and 10b had stronger in vitro DPP-4 inhibitory activity than alogliptin. Moreover, an in vivo DPP-4 inhibition assay revealed that 10g and 10i have the strongest and the most extended blood DPP-4 inhibitory activity compared to alogliptin. In type 2 diabetic rats, hybrids 10g, 10i and 10e exhibited better glycemic control than alogliptin, an effect that further supported by metformin combination. Finally, 10j, 10e, 10h and 10d had the highest radical scavenging activity in DPPH assay.

Conclusions: Hybrids 10g, 10i and 10e are potent DPP-4 inhibitors which may be beneficial for T2DM treatment.

Keywords: DPP-4 inhibitors; DPPH; OGTT; T2DM; dihydropyrimidine; phthalimide.

Figure 1

Diagram represents design of novel DPP-4 inhibitors.

Scheme 1

Synthesis of the target compounds 10a–j. Reagents and conditions: (a) NaOH, dil. EtOH, rt; (b) NaOH, abs. EtOH; (c) DMF, reflux; (d) SOCl₂, reflux, dry benzene, distillation; (e) abs. dichloromethane, TEA, rt.

Figure 2

(a) Effect of hybrids 10a–e on viability of normal hepatic LO2 cells. (n = 5). (b) Effect of hybrids 10f–j on viability of normal hepatic LO2 cells (n = 5). *** Significant from control group at p < 0.001, ** Significant from control group at p < 0.01, * Significant from control group at p < 0.05.

Figure 3

(a). The in vivo DPP-4 activity of 10a–e hybrids and alogliptin within 48 h. (n = 3). (b) The in vivo DPP-4 activity of 10f–j hybrids and alogliptin within 48 h. (n = 3).

Figure 4

(a) Chronic effect of hybrids 10a–j and alogliptin administration on blood glucose levels during an OGTT in type 2 diabetic rats. Data are presented as mean ± SEM (n = 7). (b) Chronic effect of combined administration of 10a–j/MET, alogliptin/MET on blood glucose levels during an OGTT in type 2 diabetic rats. Data are presented as mean ± SEM (n = 7).

Figure 5

(a) Chronic effect of hybrids 10a–j and alogliptin administration on area under the curve (AUC) of OGTT in type 2 diabetic rats. Data are presented as mean ± SEM (n = 7). *** Significant from diabetic control group at p < 0.001, ** Significant from diabetic control group at p < 0.01. (b) Chronic effect of combined administration of 10a–j/MET, alogliptin/MET on area under the curve (AUC) of OGTT in type 2 diabetic rats. Data are presented as mean ± SEM (n = 7). *** Significant from diabetic control group at p < 0.001, * Significant from diabetic control group at p < 0.05.

Figure 6

Docking and binding pattern of compounds 10g (a,b), 10i (c,d), 10e (e,f) and alogliptin (g,h) showing interactions with different amino acid residues found in the active site of DPP-4 (PDB code: 3G0B).

Figure 6

Docking and binding pattern of compounds 10g (a,b), 10i (c,d), 10e (e,f) and alogliptin (g,h) showing interactions with different amino acid residues found in the active site of DPP-4 (PDB code: 3G0B).

Figure 7

Equivalence of positions 2 and 4 in dihydropyrimidine.