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Keywords:

  • α-aminoacyl-containing proline derivatives;
  • dipeptidyl peptidase IV;
  • inhibitor;
  • molecular docking;
  • type 2 diabetes

Abstract

  1. Top of page
  2. Abstract
  3. Methods and Materials
  4. Experimental Section
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

On the basis of the enzyme-binding features of known potent inhibitors of dipeptidyl peptidase IV, novel α-aminoacyl-containing proline analogs (8Aa–8Ak, 8Ba–8Bj, 8Ca–8Ck, and 8Da–8Di) with the S configuration were designed, synthesized, and their activity profiled. Their structural features were determined by nuclear magnetic resonance (NMR) spectroscopy, low- and high-resolution mass spectroscopy. Five compounds (8Aa, 8Aj, 8Ch, 8Ck, and 8Dc) were shown to have promising inhibitory activities against dipeptidyl peptidase IV. Two of them, compounds 8Aa and 8Aj inhibited dipeptidyl peptidase IV with IC50 values of 4.56 and 8.4 μm, respectively, and displayed no inhibition at other dipeptidyl peptidase IV. The possible binding modes of compounds 6, 7, 8Aa, and 8Aj with dipeptidyl peptidase IV were also explored by molecular docking simulation. This study provides promising new templates for the further development of antidiabetic agents.

Dipeptidyl peptidase IV (DPP IV, also known as CD26, EC 3.4.14.5) is a prolyl dipeptidase involved in the in vivo degradation of two insulin-sensing hormones, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP), by cleaving the peptide bond in the penultimate position (1,2). GLP-1 is a potent antihyperglycemic hormone, inducing glucose-dependent stimulation of insulin secretion while suppressing glucagon secretion (3,4). The active form of GLP-1 is rapidly inactivated by plasma DPP IV through cleavage of the dipeptide from the N-terminus, limiting its duration of action. Inhibition of DPP IV results in elevated circulating levels of endogenous GLP-1, which is produced by L-cells in the small intestine in response to food intake (5–8). Thus, inhibition of DPP IV extends the half-life of endogenously secreted GLP-1, which in turn enhances insulin secretion and improves glucose tolerance. Dipeptidyl peptidase IV inhibitors offer several potential advantages over the existing therapies including decreased risk of hypoglycemia, potential for weight loss, and the potential for regeneration and differentiation of pancreatic β-cells. Therefore, DPP IV has become a validated target for the treatment of type 2 diabetes. Several DPP IV inhibitors are currently undergoing late-stage clinical trials. The first DPP IV inhibitor, sitagliptin 1 (Januvia; Merck, Rahway, NJ, USA), was approved by the Food and Drug Administration (FDA) in October 2006 (Figure 1) (9–11); vildagliptin 2 (Glavus; Novartis, Basel, Switzerland) was approved by the European Medicines Agency in September 2007 (12–14); saxagliptin 3 (Onglyza; Bristol-Myers Squibb, New York City, NY, USA) was approved by the FDA as a once-daily diabetes medication for the treatment of type 2 diabetes in August 2009 (15); alogliptin 4 (Nesina; Takeda, Osaka, Honshu, Japan) was launched in Japan as a potent and highly selective inhibitor of DPP IV in May 2010 (16); and linagliptin 5 (Tradjenta; Boehringer Ingelheim, Biberach, Baden-Württemberg, Germany) was approved by the FDA in June 2011 (17) and is indicated as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus.

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Figure 1.  Approved dipeptidyl peptidase IV (DPP IV) inhibitors.

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Recently, various classes of structurally different DPP IV inhibitors have been reported (18–20). Moriarty and colleagues (18) identified compound 6 (Figure 2) as a potent DPP IV inhibitor with high inhibitory activity (IC50 = 63 nm). Compound 7 was reported by Edmondson et al. (19) as a potent and highly selective inhibitor of DPP IV (IC50 = 18 nm). Clearly, inhibitor 6 has structural features similar to compound 7 because both of them contain a pyrrole scaffold. On the basis of the above findings, we speculated that a combination of segment A of compound 6 and segment B of compound 7 may result in novel α-aminoacyl-containing proline analogs as potential inhibitors of DPP IV. To verify our hypothesis, we firstly carried out biological evaluation of compound 8Aa against DPP IV. As expected, compound 8Aa showed moderate DPP IV inhibitory efficacy (IC50 = 4.56 μm). We continued our structure–activity relationship efforts around compound 8Aa. A series of α-aminoacyl-containing proline derivatives were designed and synthesized, and their biological activities against DPP IV and other DPPs were evaluated. Among these compounds, 8Aa, 8Aj, 8Ch, 8Ck, and 8Dc showed moderate DPP IV inhibitory activities. Compounds 8Aa and 8Aj inhibited DPP IV with IC50 values of 4.56 and 8.4 μm, respectively, and displayed no inhibition against other DPPs. The possible binding modes of compounds 6, 7, 8Aa, and 8Aj to DPP IV were also explored using molecular docking simulation. Herein, we report the design, synthesis, and biological activity of a series of novel α-aminoacyl-containing proline derivatives (8Aa8Ak, 8Ba8Bj, 8Ca8Ck, and 8Da8Di).

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Figure 2.  Design strategy of α-aminoacyl-containing proline derivatives as dipeptidyl peptidase IV (DPP IV) inhibitors.

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Methods and Materials

  1. Top of page
  2. Abstract
  3. Methods and Materials
  4. Experimental Section
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

Chemistry

Design of analogs

On the basis of the structural features of compound 8Aa, 41 compounds (8Aa8Ak, 8Ba8Bj, 8Ca8Ck, and 8Da8Di, Table 1) were designed and synthesized. Keeping the R2 as hydrogen, we obtained compounds 8Ab8Ak by introducing different electronic substituents at various positions of the benzene ring of compound 8Aa. When R2 is methyl (Me), ethyl (Et), or phenyl (Ph), further 30 compounds (8Ba8Bj, 8Ca8Ck, and 8Da8Di) were prepared (Table 1).

Table 1.   Chemical structures of compounds 8Aa–8Di and their inhibitory activities against DPP IV Thumbnail image of
Synthetic procedures of target compounds

The general synthetic procedures for target compounds are outlined in Scheme 1. The straightforward six-step synthetic route enabled us to vary positions R1 and R2. The initial step in the synthesis of 8Aa8Di was the coupling of phenol 9 and α-bromoesters 10 followed by N-deprotection. Amines 11 were then coupled with N-Boc-proline followed by deprotection to give compounds 12, which were subsequently coupled with compound 13 and deprotected to afforded analogs 8Aa8Di.

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Figure  Scheme 1: .  Synthetic route to α-aminoacyl-containing proline derivatives 8Aa–8Di. Reagents and conditions: (a) K2CO3, MeOH, r.t., overnight; (b) TFA, anhydrous CH2Cl2, r.t., 3 h; (c) TEA, THF, −15 °C, iso-butyl chloroformate, r.t., overnight; (d) HATU, DIPEA, r.t., overnight.

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Biological evaluation

Enzyme-based assay of DPP IV

To measure the activity of DPP IV, a continuous fluorometric assay was employed using Ala-Pro-aminomethylcoumarin (AMC), which is cleaved by the enzyme to release the fluorescent AMC (21). Liberation of AMC was monitored using an excitation wavelength of 355 nm and an emission wavelength of 460 nm using an Envision microplate reader (PerkinElmer, Waltham, MA, USA). A typical reaction contained 50 pm enzyme DPP IV, 10 μm Ala-Pro-AMC, different concentrations of test compounds, and assay buffer (100 mm HEPES, pH 7.5, 0.1 mg/mL BSA) in a total reaction volume of 50 μL. The DPP IV enzyme used in these studies was soluble human recombinant protein produced in a baculovirus expression system (Bac-To-Bac; Life Technologies, Grand Island, NE, USA).

Enzyme-based assay of DPPs inhibition selectivities

All DPP proteins were expressed in high five cells using a baculovirus system, and the activities of DPPs were assayed using a continuous fluorometric method. We used Nle-Pro-AMC as the substrate to measure the activities of DPP 7 and FAP, and Ala-Pro-AMC for DPP 8 and DPP 9 at the optimized pH (5.5 for DPP 7 and 8.0 for other members) assay system.

Molecular docking

The Glide program from the Schrödinger Suite was employed for the docking study.a All molecules were generated and minimized using sybyl 7.3, Tripos. The protein receptor was obtained from the worldwide Protein Data Bank (PDB ID: 2BUB) (22) and processed by removing all solvents, adding hydrogens, and carrying out minimal minimization with the OPLS2001 force field using protein preparation wizard. The grid was sized to 15 Å in each direction and centered using the original small molecule inhibitor. In all cases, all compounds were prepared for docking using LigPrep under its default parameters. The maximum number of heavy atoms permitted per compound was 120 with the maximum number of rotatable bonds set at 30. Docking was performed using Glide (23) in standard precision mode, with up to 40 conformers saved per molecule. The top-scoring conformer for each compound, as assessed by its Glide score, was exported to a Maestro-formatted output file.

Experimental Section

  1. Top of page
  2. Abstract
  3. Methods and Materials
  4. Experimental Section
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

The reagents (chemicals) were purchased from commercial sources, and used without further purification. Analytical thin-layer chromatography was HSGF254 (0.15–0.2 mm thickness). Yields were not optimized. Nuclear magnetic resonance (NMR) spectra were given on a Brucker AMX-400 and AMX-300 (internal standard as tetramethylsilane). Chemical shifts were reported in parts per million (ppm, d) downfield from tetramethylsilane. Proton-coupling patterns were described as singlet, doublet, triplet, quartet, multiplet, and broad. Low- and high-resolution mass spectra were given with an electric ionization (ESI) and electrospray and a LCQ-DECA spectrometer produced by Finnigan MAT-95.

General procedures for the preparation of compounds 8Aa8Di

A solution of compound 13 (0.10 mmol) in DMF (5 mL) was added HATU (0.10 mmol) and DIPEA (0.10 mmol). After stirring for 30 min, compound 12 (0.11 mmol) and additional DIPEA (0.11 mmol) were added. This solution was allowed to stir at room temperature for 20 h, and then, the saturated NaHCO3 was added. The mixture was extracted with EtOAc and washed with saturated NaCl, dried over Na2SO4 and concentrated. The residue was purified with flash chromatography on silica gel, eluted with a mixture of PE/EA (4/1, v/v) to afford target compound as a white solid. A solution of the target compound (100 mg) in dry CH2Cl2 (2 mL) was added CF3COOH (0.2 mL) at 0 °C and warmed to room temperature. After 3 h, the mixture was concentrated. The residue was purified with flash chromatography on silica gel, eluted with a mixture of CH2Cl2/MeOH (20/1, v/v) to afford compounds 8Aa8Di.

Ethyl-2-(4-(((S)-1-((S)-2-amino-(4-fluorophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Aa)

1H NMR (CDCl3, 300 MHz): δ 7.46–7.13 (m, 6H), 6.91–6.78 (m, 2H), 4.79 (s, 2H), 4.60–4.39 (m, 3H), 4.17–3.93 (m, 3H), 3.56–3.37 (m, 4H), 2.71–2.43 (m, 4H), 1.53–1.39 (m, 3H) ppm; ESI-MS m/z 472, [M + H]+. HRMS (ESI) m/z calcd C25H30FN3O5 [M + H]+ 472.2248, found 472.2239.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-3-p-tolylpropanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Ab)

1H NMR (CDCl3, 300 MHz): δ 7.41–7.32 (m, 2H), 7.24–7.13 (m, 4H), 6.75–6.63 (m, 2H), 4.61 (s, 2H), 4.35–4.21 (m, 3H), 4.15–4.01 (m, 3H), 3.42–3.15 (m, 4H), 2.20–1.85 (m, 7H), 1.34 (t, = 6.9 Hz, 3H) ppm; ESI-MS m/z 468, [M + H]+. HRMS (ESI) m/z calcd C26H33N3O5 [M + H]+ 468.2498, found 468.2487.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-(4-methoxyphenyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Ac)

1H NMR (CDCl3, 300 MHz): δ 7.38–7.09 (m, 4H), 6.90–6.73 (m, 4H), 4.69 (s, 2H), 4.49–4.30 (m, 3H), 4.17–3.97 (m, 3H), 3.88 (s, 3H), 3.50–3.33 (m, 4H), 2.41–2.18 (m, 4H), 1.38 (t, = 6.9 Hz, 3H) ppm; ESI-MS m/z 484, [M + H]+. HRMS (ESI) m/z calcd C26H33N3O6 [M + H]+ 484.2448, found 484.2449.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-(biphenyl-4-yl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Ad)

1H NMR (CDCl3, 300 MHz): δ 7.38–7.09 (m, 4H), 6.90–6.73 (m, 4H), 4.69 (s, 2H), 4.49–4.30 (m, 3H), 4.17–3.97 (m, 3H), 3.88 (s, 3H), 3.50–3.33 (m, 4H), 2.41–2.18 (m, 4H), 1.38 (t, = 6.9 Hz, 3H) ppm; ESI-MS m/z 484, [M + H]+. HRMS (ESI) m/z calcd C26H33N3O6 [M + H]+ 484.2448, found 484.2449.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-(4-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Ae)

1H NMR (CDCl3, 300 MHz): δ 7.41–7.21 (m, 2H), 7.18–7.00 (m, 4H), 6.98–6.77 (m, 2H), 4.89 (s, 2H), 4.56–4.21 (m, 3H), 4.11–3.98 (m, 3H), 3.42–3.15 (m, 4H), 2.32–1.86 (m, 4H), 1.44 (t, = 4.2 Hz, 3H) ppm; ESI-MS m/z 479, [M + H]+. HRMS (ESI) m/z calcd C26H30N4O5 [M + H]+ 479.2294, found 479.2283.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-(4-(trifluoromethyl)phenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Af)

1H NMR (CDCl3, 300 MHz): δ 7.49–7.34 (m, 2H), 7.21–7.17 (m, 2H), 7.10–7.01 (m, 2H), 6.90–6.81 (m, 2H), 4.73 (s, 2H), 4.49–4.39 (m, 3H), 4.21–3.93 (m, 3H), 3.59–3.37 (m, 4H), 2.89–2.78 (m, 4H), 1.43–1.21 (m, 3H) ppm; ESI-MS m/z 522, [M + H]+. HRMS (ESI) m/z calcd C26H30F3N3O5 [M + H]+ 522.2216, found 522.2208.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-phenylpropanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Ag)

1H NMR (CDCl3, 300 MHz): δ 7.34–7.30 (m, 2H), 7.28–7.11 (m, 5H), 6.87–6.81 (m, 2H), 4.84 (s, 2H), 4.43–4.31 (m, 3H), 4.14–4.01 (m, 3H), 3.32–3.11 (m, 4H), 2.10–1.91 (m, 4H), 1.41 (t, = 6.3 Hz, 3H) ppm; ESI-MS m/z 454, [M + H]+. HRMS (ESI) m/z calcd C25H29N3O5 [M + H]+ 454.2342, found 454.2338.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-(2-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Ah)

1H NMR (CDCl3, 300 MHz): δ 7.67–7.34 (m, 2H), 7.29–7.16 (m, 4H), 6.98–6.81 (m, 2H), 4.97 (s, 2H), 4.64–4.43 (m, 3H), 4.22–3.99 (m, 3H), 3.64–3.33 (m, 4H), 2.65–2.29 (m, 4H), 1.53–1.32 (m, 3H) ppm; ESI-MS m/z 479, [M + H]+. HRMS (ESI) m/z calcd C26H30N4O5 [M + H]+ 479.2294, found 479.2287.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-(2-(trifluoromethyl)phenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Ai)

1H NMR (CDCl3, 300 MHz): δ 7.53–7.27 (m, 2H), 7.19–7.03 (m, 4H), 6.88–6.73 (m, 2H), 4.83 (s, 2H), 4.53–4.43 (m, 3H), 4.24–3.89 (m, 3H), 3.54–3.23 (m, 4H), 2.45–2.09 (m, 4H), 1.45 (t, = 4.8 Hz, 3H) ppm; ESI-MS m/z 522, [M + H]+. HRMS (ESI) m/z calcd C26H30F3N3O5 [M + H]+ 522.2216, found 522.2209.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-(2-fluorophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Aj)

1H NMR (CDCl3, 300 MHz): δ 7.56–7.34 (m, 2H), 7.21–7.01 (m, 4H), 6.87–6.81 (m, 2H), 4.85 (s, 2H), 4.58–4.42 (m, 3H), 4.20–3.99 (m, 3H), 3.51–3.21 (m, 4H), 2.76–2.43 (m, 4H), 1.34–1.21 (m, 3H) ppm; ESI-MS m/z 472, [M + H]+. HRMS (ESI) m/z calcd C25H30N3O5 [M + H]+ 472.2248, found 472.2241.

Ethyl-2-(4-(((S)-1-((S)-2-amino-3-(3-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)acetate (8Ak)

1H NMR (CDCl3, 300 MHz): δ 8.01–7.73 (m, 3H), 7.51–7.26 (m, 3H), 6.88–6.73 (m, 2H), 4.79 (s, 2H), 4.59–4.41 (m, 3H), 4.29–4.07 (m, 3H), 3.59–3.37 (m, 4H), 2.43–2.01 (m, 4H), 1.49–1.28 (m, 3H) ppm; ESI-MS m/z 479, [M + H]+. HRMS (ESI) m/z calcd C26H30N4O5 [M + H]+ 479.2294, found 479.2291.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-phenylpropanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Ba)

1H NMR (CDCl3, 300 MHz): δ 7.45–7.39 (m, 2H), 7.23–7.11 (m, 5H), 6.98–6.89 (m, 2H), 4.85 (dd, J1 = 4.2 Hz, J2 = 9.6 Hz, 1H), 4.43–4.41 (m, 3H), 4.21–4.16 (m, 3H), 3.32–3.19 (m, 4H), 2.05–1.98 (m, 4H), 1.59–1.56 (m, 3H), 1.31–1.28 (m, 3H) ppm; ESI-MS m/z 468, [M + H]+. HRMS (ESI) m/z calcd C26H33N3O5 [M + H]+ 468.2498, found 468.2496.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-p-tolylpropanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Bb)

1H NMR (CDCl3, 300 MHz): δ 7.14–7.01 (m, 6H), 6.80–6.74 (m, 2H), 4.67 (dd, J1 = 9.0 Hz, J2 = 15.0 Hz, 1H), 4.32–4.31 (m, 3H), 4.23–4.14 (m, 3H), 3.21 (m, 2H), 3.09 (m, 2H), 2.27 (s, 3H), 2.00–1.94 (m, 4H), 1.59–1.53 (m, 3H), 1.28–1.22 (m, 3H) ppm; ESI-MS m/z 482, [M + H]+. HRMS (ESI) m/z calcd C27H35N3O5 [M + H]+ 482.2655, found 482.2651.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-methoxyphenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Bc)

1H NMR (CDCl3, 300 MHz): δ 7.14–7.09 (m, 4H), 6.81–6.74 (m, 2H), 4.69–4.67 (m, 1H), 4.28–4.15 (m, 6H), 3.75 (s, 3H), 3.47–3.18 (m, 4H), 2.00–1.99 (m, 4H), 1.59–1.55 (m, 3H), 1.29–1.23 (m, 3H) ppm; ESI-MS m/z 498, [M + H]+. HRMS (ESI) m/z calcd C27H35N3O6 [M + H]+ 498.2604, found 498.2611.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Bd)

1H NMR (CDCl3, 300 MHz): δ 7.60–7.55 (m, 2H), 7.46–7.43 (m, 2H), 7.14–7.11 (m, 2H), 6.78–6.73 (m, 2H), 4.68 (t, = 13.3 Hz, 1H), 4.36–4.09 (m, 6H), 3.44–3.24 (m, 4H), 2.05–2.02 (m, 4H), 1.60–1.51 (m, 3H), 1.30–1.24 (m, 3H) ppm; ESI-MS m/z 493, [M + H]+. HRMS (ESI) m/z calcd C27H32N4O5 [M + H]+ 493.2451, found 493.2449.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-(trifluoromethyl)phenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Be)

1H NMR (CDCl3, 300 MHz): δ 7.58–7.53 (m, 2H), 7.41–7.35 (m, 2H), 7.14–7.09 (m, 2H), 6.78–6.70 (m, 2H), 4.67 (dd, J1 = 9.3 Hz, J2 = 15.6 Hz, 1H), 4.31–4.10 (m, 6H), 3.21–3.04 (m, 4H), 2.03–1.85 (m, 4H), 1.59–1.52 (m, 3H), 1.28 (t, = 3.0 Hz, 3H) ppm; ESI-MS m/z 536, [M + H]+. HRMS (ESI) m/z calcd C27H32F3N3O5 [M + H]+ 536.2372, found 536.2367.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-fluorophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Bf)

1H NMR (CDCl3, 300 MHz): δ 7.65–7.55 (m, 2H), 7.45–7.42 (m, 2H), 7.16–7.13 (m, 2H), 6.78–6.72 (m, 2H), 4.68–4.63 (m, 1H), 4.38–4.18 (m, 6H), 3.53–3.21 (m, 4H), 1.99 (m, 4H), 1.63–1.53 (m, 3H), 1.29–1.22 (m, 3H) ppm; ESI-MS m/z 486, [M + H]+. HRMS (ESI) m/z calcd C26H32FN3O5 [M + H]+ 486.2404, found 486.2401.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(2-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Bg)

1H NMR (CDCl3, 300 MHz): δ 7.51–7.43 (m, 2H), 7.41–7.39 (m, 2H), 7.20–7.16 (m, 2H), 6.78–6.74 (m, 2H), 4.71–4.68 (m, 1H), 4.28–4.13 (m, 6H), 3.45–3.28 (m, 4H), 2.09–2.07 (m, 4H), 1.68–1.61 (m, 3H), 1.30–1.22 (m, 3H) ppm; ESI-MS m/z 493, [M + H]+. HRMS (ESI) m/z calcd C27H32N4O5 [M + H]+ 493.2451, found 493.2447.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(2-fluorophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Bh)

1H NMR (CDCl3, 300 MHz): δ 7.59–7.48 (m, 2H), 7.39–7.33 (m, 2H), 7.19–7.16 (m, 2H), 6.81–6.74 (m, 2H), 4.85–4.81 (m, 1H), 4.23–4.05 (m, 6H), 3.50–3.38 (m, 4H), 2.13–2.08 (m, 4H), 1.58–1.47 (m, 3H), 1.31–1.25 (m, 3H) ppm; ESI-MS m/z 486, [M + H]+. HRMS (ESI) m/z calcd C26H32FN3O5 [M + H]+ 486.2404, found 486.2410.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(3-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Bi)

1H NMR (CDCl3, 300 MHz): δ 7.64–7.63 (m, 1H), 7.55–7.44 (m, 3H), 7.15–7.13 (m, 2H), 6.77–6.74 (m, 2H), 4.67 (dd, J1 = 1.8 Hz, J2 = 6.6 Hz, 1H), 4.38–4.15 (m, 6H), 3.48–3.46 (m, 1H), 3.18–3.16 (m, 2H), 3.00–2.99 (m, 1H), 2.00 (m, 4H), 1.58 (d, 3H, = 3.0), 1.25 (t, 3H, = 6.9) ppm; ESI-MS m/z 493, [M + H]+. HRMS (ESI) m/z calcd C27H32N4O5 [M + H]+ 493.2451, found 493.2447.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(3-fluorophenyl)propanoyl) pyrrolidine-2-carboxamido)-methyl)phenoxy)propanoate (8Bj)

1H NMR (CDCl3, 300 MHz): δ 7.60–7.56 (m, 2H), 7.46–7.41 (m, 2H), 7.14–7.11 (m, 2H), 6.78–6.74 (m, 2H), 4.69–4.67 (m, 1H), 4.21–4.17 (m, 6H), 3.50–3.23 (m, 4H), 2.03 (m, 4H), 1.60–1.53 (m, 3H), 1.30–1.24 (m, 3H) ppm; ESI-MS m/z 486, [M + H]+. HRMS (ESI) m/z calcd C26H32FN3O5 [M + H]+ 486.2404, found 486.2401.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-phenylpropanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Ca)

1H NMR (CDCl3, 300 MHz): δ 7.29–7.10 (m, 7H), 6.80–6.75 (m, 2H), 4.52–4.14 (m, 7H), 3.14 (m, 1H), 3.09–2.91 (m, 3H), 1.98–1.87 (m, 6H), 1.32–1.23 (m, 3H), 1.07–1.01 (m, 3H) ppm; ESI-MS m/z 482, [M + H]+. HRMS (ESI) m/z calcd C27H35N3O5 [M + H]+ 482.2655, found 482.2651.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-p-tolylpropanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Cb)

1H NMR (CDCl3, 300 MHz): δ 7.11–6.98 (m, 6H), 6.80–6.75 (m, 2H), 4.51–4.47 (m, 1H), 4.34–4.23 (m, 3H), 4.22–4.14 (m, 3H), 3.42 (m, 1H), 3.07–2.91 (m, 3H), 2.00–1.80 (m, 6H), 1.28–1.23 (m, 3H), 1.09–1.02 (m, 3H) ppm; ESI-MS m/z 496, [M + H]+. HRMS (ESI) m/z calcd C28H37N3O5 [M + H]+ 496.2811, found 496.2803.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-methoxyphenyl)pyrrolidine-2-carbox amido)methyl)phenoxy)butanoate (8Cc)

1H NMR (CDCl3, 300 MHz): δ 7.13–7.07 (m, 4H), 6.83–6.75 (m, 4H), 4.50–4.47 (m, 1H), 4.23–4.14 (m, 5H), 3.76–3.74 (m, 1H), 3.70 (s, 3H), 3.19 (m, 1H), 3.07 (m, 2H), 2.91 (m, 1H), 2.04–1.89 (m, 6H), 1.27–1.21 (m, 3H), 1.06–1.01 (m, 3H) ppm; ESI-MS m/z 513, [M + H]+. HRMS (ESI) m/z calcd C28H37N3O6 [M + H]+ 513.2761, found 513.2754.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(biphenyl-4-yl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Cd)

1H NMR (CDCl3, 300 MHz): δ 8.00–7.98 (m, 3H), 7.53–7.49 (m, 2H), 7.37–7.26 (m, 2H), 7.10–7.08 (m, 2H), 6.78–6.72 (m, 4H), 4.50–4.16 (m, 6H), 3.55 (dd, J1 = 7.5 Hz, J2 = 14.4 Hz, 1H), 3.18–2.97 (m, 4H), 2.02–1.81 (m, 6H), 1.27–1.19 (m, 3H), 1.04–1.00 (m, 3H) ppm; ESI-MS m/z 558, [M + H]+. HRMS (ESI) m/z calcd C33H39N3O5 [M + H]+ 558.2968, found 558.2960.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Ce)

1H NMR (CDCl3, 300 MHz): δ 7.36–7.21 (m, 4H), 7.10–6.99 (m, 2H), 6.73–6.69 (m, 2H), 4.54–4.47 (m, 2H), 4.22–4.13 (m, 4H), 3.53–3.48 (m, 1H), 3.36–3.21 (m, 4H), 2.01–1.95 (m, 6H), 1.31–1.21 (m, 3H), 1.10–1.05 (m, 3H) ppm; ESI-MS m/z 507, [M + H]+. HRMS (ESI) m/z calcd C28H34N4O5 [M + H]+ 507.2067, found 507.2071.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-fluorophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Cf)

1H NMR (CDCl3, 300 MHz): δ 7.26–7.10 (m, 4H), 6.94 (m, 2H), 6.79–6.74 (m, 2H), 4.51–4.47 (m, 2H), 4.21–4.14 (m, 4H), 3.51–3.48 (m, 1H), 3.40–3.11 (m, 4H), 1.97–1.93 (m, 6H), 1.28–1.19 (m, 3H), 1.07–1.02 (m, 3H) ppm; ESI-MS m/z 500, [M + H]+. HRMS (ESI) m/z calcd C27H34FN3O5 [M + H]+ 500.2561, found 500.2557.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(2-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Cg)

1H NMR (CDCl3, 300 MHz): δ 7.67–7.63 (m, 2H), 7.60–7.51 (m, 2H), 7.47–7.41 (m, 2H), 6.79–6.74 (m, 2H), 4.48–4.18 (m, 6H), 3.83 (m, 1H), 3.54–3.52 (m, 2H), 3.20–3.16 (m, 2H), 2.06–1.90 (m, 3H), 1.65–1.63 (m, 1H), 1.38–1.29 (m, 2H), 1.25–1.08 (m, 3H), 1.05–1.00 (m, 3H) ppm; ESI-MS m/z 507, [M + H]+. HRMS (ESI) m/z calcd C28H34N4O5 [M + H]+ 507.2067, found 507.2071.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(2-(trifluoromethyl)phenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Ch)

1H NMR (CDCl3, 300 MHz): δ 7.66–7.64 (m, 1H), 7.46–7.39 (m, 3H), 7.15–7.13 (m, 2H), 6.78–6.75 (m, 2H), 4.48–4.15 (m, 6H), 3.54 (dd, J1 = 6.9 Hz, J2 = 14.1 Hz, 1H), 3.35–3.28 (m, 4H), 1.95–1.91 (m, 6H), 1.22 (dd, 3H, J1 = 6.9 Hz, J2 = 13.8 Hz), 1.02 (t, 3H, = 6.9 Hz) ppm; ESI-MS m/z 550, [M + H]+. HRMS (ESI) m/z calcd C28H34F3N3O5 [M + H]+ 550.2529, found 550.2520.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(2-fluorophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Ci)

1H NMR (CDCl3, 300 MHz): δ 7.63–7.54 (m, 2H), 7.47–7.36 (m, 4H), 7.28–7.11 (m, 2H), 6.83–6.78 (m, 2H), 4.59–4.01 (m, 6H), 3.78 (m, 1H), 3.41–3.30 (m, 2H), 3.20–3.10 (m, 2H), 2.19–1.80 (m, 6H), 1.30–1.13 (m, 3H), 1.08–0.98 (m, 3H) ppm; ESI-MS m/z 500, [M + H]+. HRMS (ESI) m/z calcd C27H34FN3O5 [M + H]+ 500.2561, found 500.2558.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(3-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Cj)

1H NMR (CDCl3, 300 MHz): δ 7.68–7.67 (m, 1H), 7.57–7.44 (m, 3H), 7.19–7.13 (m, 2H), 6.78–6.74 (m, 2H), 4.49–4.20 (m, 6H), 3.83 (m, 1H), 3.61–3.54 (m, 2H), 3.27–3.13 (m, 2H), 2.31–2.01 (m, 3H), 1.63–1.59 (m, 1H), 1.33–1.29 (m, 2H), 1.25–1.11 (m, 3H), 1.08–1.03 (m, 3H) ppm; ESI-MS m/z 507, [M + H]+. HRMS (ESI) m/z calcd C28H34N4O5 [M + H]+ 507.2067, found 507.2063.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(3-(trifluoromethyl)phenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)butanoate (8Ck)

1H NMR (CDCl3, 300 MHz): δ 7.64 (m, 1H), 7.58–7.44 (m, 3H), 7.29–7.18 (m, 2H), 6.81–6.70 (m, 2H), 4.31–4.17 (m, 6H), 3.81 (m, 1H), 3.61–3.41 (m, 2H), 3.27–3.13 (m, 2H), 2.33–2.13 (m, 3H), 1.61–1.51 (m, 1H), 1.37–1.31 (m, 2H), 1.25–1.20 (m, 3H), 1.08–1.01 (m, 3H) ppm; ESI-MS m/z 550, [M + H]+. HRMS (ESI) m/z calcd C28H34F3N3O5 [M + H]+ 550.2529, found 550.2521.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-phenylpropanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8Da)

1H NMR (CDCl3, 300 MHz): δ 7.54–7.52 (m, 2H), 7.41–7.34 (m, 3H), 7.19–7.08 (m, 7H), 6.87–6.80 (m, 2H), 5.55 (s, 1H), 4.36–4.20 (m, 3H), 4.19–4.08 (m, 3H), 3.19–3.04 (m, 3H), 2.71 (m, 1H), 1.86–1.73 (m, 4H), 1.17 (t, = 7.5 Hz, 3H) ppm; ESI-MS m/z 530, [M + H]+. HRMS (ESI) m/z calcd C31H35N3O5 [M + H]+ 530.2655, found 530.2651.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-methoxyphenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8Db)

1H NMR (CDCl3, 300 MHz): δ 7.54–7.51 (m, 2H), 7.38–7.36 (m, 3H), 7.14–7.05 (m, 4H), 6.92–6.73 (m, 4H), 5.56 (s, 1H), 4.30–4.10 (m, 6H), 3.72 (s, 3H), 3.14–3.08 (m, 4H), 2.00–1.89 (m, 4H), 1.22–1.16 (m, 3H) ppm; ESI-MS m/z 560, [M + H]+. HRMS (ESI) m/z calcd C32H37N3O6 [M + H]+ 560.2761, found 560.2753.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8Dc)

1H NMR (CDCl3, 300 MHz): δ 7.50–7.47 (m, 4H), 7.34–7.26 (m, 5H), 7.13–7.10 (m, 2H), 6.86–6.83 (m, 2H), 5.56 (s, 1H), 4.30–4.10 (m, 6H), 3.20–2.94 (m, 4H), 1.92–1.39 (m, 4H), 1.17 (t, = 6.9 Hz, 3H) ppm; ESI-MS m/z 555, [M + H]+. HRMS (ESI) m/z calcd C32H34N4O5 [M + H]+ 555.2602, found 555.2597.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-(trifluoromethyl)phenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8Dd)

1H NMR (CDCl3, 300 MHz): δ 7.53–7.50 (m, 4H), 7.38–7.36 (m, 5H), 7.13–7.08 (m, 2H), 6.86–6.82 (m, 2H), 5.56 (s, 1H), 4.37–4.40 (m, 3H), 4.21–4.07 (m, 3H), 3.20–3.03 (m, 4H), 2.00 (m, 4H), 1.19 (t, = 6.0 Hz, 3H) ppm; ESI-MS m/z 598, [M + H]+. HRMS (ESI) m/z calcd C32H34F3N3O5 [M + H]+ 598.2529, found 598.2521.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(4-fluorophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8De)

1H NMR (CDCl3, 300 MHz): δ 7.53–7.51 (m, 2H), 7.40–7.34 (m, 3H), 7.13–7.06 (m, 4H), 6.95–6.83 (m, 4H), 5.55 (s, 1H), 4.28–4.21 (m, 2H), 4.20–4.08 (m, 2H), 3.38–3.06 (m, 3H), 1.93–1.78 (m, 3H), 1.24–1.15 (m, 3H) ppm; ESI-MS m/z 548, [M + H]+. HRMS (ESI) m/z calcd C31H34FN3O5 [M + H]+ 548.2561, found 548.2559.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(2-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8Df)

1H NMR (CDCl3, 300 MHz): δ 7.57–7.52 (m, 4H), 7.42–7.39 (m, 5H), 7.15–7.13 (m, 2H), 6.84–6.81 (m, 2H), 5.53 (s, 1H), 4.28–4.11 (m, 6H), 3.51–3.14 (m, 4H), 1.91–1.80 (m, 3H), 1.57 (m, 1H), 1.18 (t, = 2.7 Hz, 3H) ppm; ESI-MS m/z 555, [M + H]+. HRMS (ESI) m/z calcd C32H34N4O5 [M + H]+ 555.2602, found 555.2595.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(2-(trifluoromethyl)phenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8Dg)

1H NMR (CDCl3, 300 MHz): δ 7.68–7.66 (m, 2H), 7.51–7.49 (m, 3H), 7.45–7.38 (m, 4H), 7.15–7.08 (m, 2H), 6.87 (m, 2H), 5.57 (s, 1H), 4.21–4.19 (m, 4H), 3.58–3.39 (m, 2H), 3.10–2.74 (m, 4H), 1.99–1.87 (m, 4H), 1.26–1.19 (m, 3H) ppm; ESI-MS m/z 598, [M + H]+. HRMS (ESI) m/z calcd C32H34F3N3O5 [M + H]+ 598.2529, found 598.2523.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(3-cyanophenyl)propanoyl)pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8Dh)

1H NMR (CDCl3, 300 MHz): δ 7.68–7.61 (m, 4H), 7.54–7.47 (m, 5H), 7.19–7.13 (m, 2H), 6.88–6.83 (m, 2H), 5.61 (s, 1H), 4.43–4.28 (m, 3H), 4.21–4.13 (m, 3H), 3.33–3.15 (m, 3H), 2.10–2.01 (m, 4H), 1.28 (t, = 6.9 Hz, 3H) ppm; ESI-MS m/z 555, [M + H]+. HRMS (ESI) m/z calcd C32H34N4O5 [M + H]+ 555.2602, found 555.2593.

Ethyl 2-(4-(((S)-1-((S)-2-amino-3-(3-(trifluoromethyl)phenyl)propanoyl) pyrrolidine-2-carboxamido)methyl)phenoxy)-2-phenylacetate (8Di)

1H NMR (CDCl3, 300 MHz): δ 7.58–7.56 (m, 4H), 7.53–7.49 (m, 5H), 7.13–7.11 (m, 2H), 6.86–6.84 (m, 2H), 5.58 (s, 1H), 4.31–4.22 (m, 3H), 4.21–4.11 (m, 3H), 3.24–3.01 (m, 3H), 2.02–1.91 (m, 4H), 1.20 (t, = 4.5 Hz, 3H) ppm; ESI-MS m/z 598, [M + H]+. HRMS (ESI) m/z calcd C32H34F3N3O5 [M + H]+ 598.2529, found 598.2526.

Ethyl 2-(4-(aminomethyl)phenoxy)acetate (11a)

1H NMR (CDCl3, 400 MHz): δ 7.20 (d, = 8.4 Hz, 2H), 6.86 (d, = 8.4 Hz, 2H), 4.60 (s, 2H), 4.25 (q, = 7.2 Hz, 2H), 4.15 (s, 2H), 1.30 (t, = 7.2 Hz, 3H) ppm; ESI-MS m/z 210, [M + H]+.

(S)-ethyl 2-(4-((pyrrolidine-2-carboxamido)methyl)phenoxy)acetate (12a)

1H NMR (DMSO-d6, 400 MHz): δ 7.19 (d, = 8.4 Hz, 2H), 6.87 (d, = 8.4 Hz, 2H), 4.25–4.14 (m, 4H), 2.50–2.49 (m, 6H), 1.39 (s, 1H), 1.27 (s, 2H), 1.20 (t, = 7.2 Hz, 3H) ppm; ESI-MS m/z 307, [M + H]+.

Results and Discussion

  1. Top of page
  2. Abstract
  3. Methods and Materials
  4. Experimental Section
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

Chemistry

In total, 41 compounds (8Aa–8Ak, 8Ba–8Bj, 8Ca–8Ck, and 8Da–8Di) were designed and synthesized based on structural features from compounds 6 and 7, and their chemical structures are shown in Table 1. These compounds were synthesized through the route outlined in Scheme 1, and the details of the synthetic procedures and structural characterizations are described in the Experimental section.

Biological evaluation

For the primary screening assay, the inhibition percentages of the compounds (8Aa–8Ak, 8Ba–8Bj, 8Ca–8Ck, and 8Da–8Di) at 20 μg/mL were measured. The results are summarized in Table 1 and illustrated that most of these compounds exhibited moderate inhibitory activities.

The initial compound 8Aa displayed potential inhibition activities toward DPP IV, with 98.7% inhibition at the concentration of 20 μg/mL. Introducing electron-donating and electron-withdrawing groups to the para-position of the benzene ring of R1 did not improve the inhibition activities. For instance, compounds 8Ab (4-Me), 8Ac (4-OCH3), 8Ad (4-Ph), 8Ae (4-CN), and 8Af (4-CF3) exhibited mild inhibition activities against DPP IV, with 25.9%, 27.7%, 48.1%, 29.3%, and 6.0% inhibitions at 20 μg/mL, respectively. Therefore, for the para-position substitutions, the fluorine group appeared to be essential for DPP IV inhibition. While electron-withdrawing groups were introduced at ortho- and meta-position of the benzene ring, the DPP IV activities were dramatically decreased. For instance, compounds 8Ah (2-CN), 8Ai (2-CF3), and 8Ak (3-CN) showed mild inhibition activity toward DPP IV. However, compound 8Aj, which was fluorine-substituted at ortho-position, provided an increase in inhibitory potency with 92.8% inhibition at 20 μg/mL. When R1 is fluorine, the inhibition against DPP IV was increased, as illustrated in compounds 8Aa and 8Aj, with IC50 values of 4.56 and 8.4 μm, respectively. All these indicated that the fluorine group was very important for the potency,

In the comparison of 8Aa–8Ak to 8Ba–8Bj, 8Ca–8Ck, and 8Da–8Di, it can be found that all of these compounds showed decreased inhibitory activities against DPP IV, and a few completely lost inhibitory activity. To some extent, compounds 8Ch, 8Ck, and 8Dc exhibited a better ability to inhibit DPP IV than the other compounds. These findings indicated that both the fluorine-substituted benzene and the R2 substitutions play important roles in the inhibitory activities against DPP IV.

Furthermore, compounds 8Aa and 8Aj were screened against a panel of four members of the DPPs family (Table 2). Both compounds 8Aa and 8Aj exhibited high selectivities against other DPPs (FAP, DPP 7, DPP 8, and DPP 9), with inhibition rates <50% against DPPs at 20 μg/mL.

Table 2.   Selectivity profiles of selected DPP IV inhibitors (IC50, μm)
CompoundDPP IVFAPDPP 7DPP 8DPP 9
  1. DPP IV, dipeptidyl peptidase IV; NI, no inhibition.

8Aa 4.56NINININI
8Aj 8.4NINININI

Binding models predicted by molecular docking simulation

To gain insight into the binding modes of these compounds against DPP IV, molecular modeling experiments were carried out to investigate the binding interactions between this series of compounds and the active site of DPP IV using Glide program. The crystal structure of DPP IV (PDB ID: 2BUB) was used in molecular docking simulation (22). Figure 3 represents the main interactions between compounds 6, 7, 8Aa, and 8Aj with DPP IV.

image

Figure 3.  Stereoview of the binding poses of compounds 6(A), 7(B), 8Aa(C), and 8Aj(D) at the dimmer interface site of dipeptidyl peptidase IV (DPP IV). Hydrogen atoms have been omitted for clarity. All structure figures were prepared using pymol (http://pymol.sourceforge.net/).

Download figure to PowerPoint

The binding structure shows that compounds 8Aa and 8Aj effectively occupy the S1 and S2 pockets of DPP IV and make extensive hydrophobic and hydrogen-bonding interactions with residues in these two pockets, thereby displayed inhibitory activity against DPP IV. For example, the amino of compounds 8Aa and 8Aj make favorable contacts with Tyr662 and Glu206 through hydrogen bonds. Similar to compound 7, the acetyl oxygens of compounds 8Aa and 8Aj form hydrogen bonds with Arg429. However, compounds 8Aa and 8Aj lack the interaction with Ser630 in the S1 pocket through hydrogen bonds, which may account for the decreased DPP IV activity compared with compounds 6 (IC50 = 63 nm) and 7 (IC50 = 18 nm).

On the basis of the above-mentioned docking results, we speculate that lengthening the carbon chain of compounds 8 by incorporating a carbonyl group at the β-position of the amino acid moiety may lead to increased DPP IV activity, which consequently allow better hydrogen-bonding interactions of the amino with Tyr662, Glu205, and Glu206, as well as a new hydrogen bond between the carbonyl and Tyr547. In addition, introducing difluoro substitution at ortho- and para-position of the benzene ring was expected to result in significant affinity gain by hydrogen-bonding interactions with Ser630 and Asn710.

Conclusions

  1. Top of page
  2. Abstract
  3. Methods and Materials
  4. Experimental Section
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

In summary, 41 novel α-aminoacyl-containing proline derivatives were designed and synthesized. The bioassay found a number of new compounds as highly selective inhibitors of DPP IV. Molecular docking results reveal that both hydrophobic and hydrogen-bonding interactions are important for the inhibitory potency. Therefore, this study provides a new promising scaffold with moderate inhibitory activities (IC50 values 4.56 and 8.4 μm) suitable for further development of new antidiabetic agents targeting DPP IV. The possible binding modes of compounds 6, 7, 8Aa, and 8Aj with DPP IV were also explored by molecular docking simulation.

Footnotes

Acknowledgments

  1. Top of page
  2. Abstract
  3. Methods and Materials
  4. Experimental Section
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

We gratefully acknowledge financial support from National Basic Research Program of China (Grants 2009CB940903 and 2009CB918502), the National Natural Science Foundation of China (Grants 20721003 and 81025017), National S&T Major Projects (2012ZX09103-101-072), and Silver Project (260644).

References

  1. Top of page
  2. Abstract
  3. Methods and Materials
  4. Experimental Section
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References
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