Cyanoacetohydrazide linked to 1,2,3-triazole derivatives: a new class of α-glucosidase inhibitors

In this work, a novel series of cyanoacetohydrazide linked to 1,2,3-triazoles (9a–n) were designed and synthesized to be evaluated for their anti-α-glucosidase activity, focusing on the fact that α-glucosidase inhibitors have played a significant role in the management of type 2 diabetes mellitus. All synthesized compounds except 9a exhibited excellent inhibitory potential, with IC50 values ranging from 1.00 ± 0.01 to 271.17 ± 0.30 μM when compared to the standard drug acarbose (IC50 = 754.1 ± 0.5 μM). The kinetic binding study indicated that the most active derivatives 9b (IC50 = 1.50 ± 0.01 μM) and 9e (IC50 = 1.00 ± 0.01 μM) behaved as the uncompetitive inhibitors of α-glucosidase with Ki = 0.43 and 0.24 μM, respectively. Moreover, fluorescence measurements were conducted to show conformational changes of the enzyme after binding of the most potent inhibitor (9e). Calculation of standard enthalpy (ΔHm°) and entropy (ΔSm°) values confirmed the construction of hydrophobic interactions between 9e and the enzyme. Also, docking studies indicated desired interactions with important residues of the enzyme which rationalized the in vitro results.


Scientific Reports
| (2022) 12:8647 | https://doi.org/10.1038/s41598-022-11771-y www.nature.com/scientificreports/ critical binding site residues including Trp481, Asp518, Met519, Arg600 and can be considered as an ideal and novel fragment against α-glucosidase. Pharmacophoric hybridization is known as one of the most efficient strategies in designing novel α-glucosidase inhibitors with improved affinity and efficacy. As a result, the benzyl-1,2,3-triazole moiety which seems to participate in π-stacking and hydrophobic interactions with the enzyme, was linked to the cyanoacetohydrazide pharmacophore. In vitro enzyme inhibition and the mechanism of action as well as docking studies were executed to determine plausible protein-ligand interactions.
Chemistry. Synthesis of the target compounds 9a-n was schematically described in Fig. 2.
The corresponding derivatives were prepared by the reaction of 1,2,3-triazole-methoxy-benzaldehyde 5 and 2-cyanoacetohydrazide 8 in methanol in the presence of a few drops of acetic acid (HOAc) under microwave irradiation at 700 W for 10-12 min. Aldehyde 5 was prepared by the click reaction of compound 1 and in situ prepared azide derivatives 4 in the presence of triethylamine (NEt 3 ), CuSO 4 .5H 2 O, and sodium ascorbate in H 2 O/tert-BuOH for 24-48 h. It should be mentioned that aldehyde 1 was prepared by the reaction of 4-hydroxy benzaldehyde or 4-hydroxy-3-methoxybenzaldehyde and propargyl bromide in DMF at 80 °C for 4-5 h 36 . Compound 8 was also obtained by the reaction of excess amount of hydrazine hydrate 6 and ethyl 2-cyanoacetate 7 at room temperature 40 .
All synthesized compounds were characterized by FTIR, 1 H-NMR, 13 C-NMR, elemental analysis, and HPLC (Supplementary Information). It should be noted that 1 H and 13 CNMR spectra of most compounds indicated the presence of two isomers probably due to restricted C-N amide bond rotation 41 . Also, the presence of two isomers was obvious in HPLC chromatograms.
To explain the structure and observed activity correlations, cyanoacetohydrazide-1,2,3-triazole hybrids were divided into three categories based on the presence of methoxy group at X-position (9a-g), the unsubstituted group at X-position (9h-n) along with the substituents at the Y position of benzyl moiety to extract structure-activity relationships (SARs) of α-glucosidase inhibition.
(I) Among the 9a-g bearing OMe at X-position, compound 9e with 4-Cl substituent on the benzyl ring showed the most potent inhibitory activity (IC 50 = 1.00 ± 0.01 µM) among all the synthesized com- www.nature.com/scientificreports/ pounds. It is worth mentioning that the most active compound 9e recorded 754-fold better potency than the standard drug acarbose (IC 50 1.0 Vs 754.1 μM). Changing the chlorine position from para to ortho (9d) led to the decrease of inhibitory activity with an IC 50 value of 13.97 ± 0.80 µM. Compound 9b as the second most active analog (Y: 2-F, IC 50 = 1.50 μM), showed similar activity compared to the most potent derivatives, 9e (Y: 4-Cl, IC 50 = 1.00 μM). Replacing halogen groups with methyl as an electrondonating group in 9f (IC 50 = 28.00 μM) and 9g (IC 50 = 22.80 μM) caused to decrease of inhibitory activity. Noteworthy, the removal of any substitution from Y position (compounds 9a IC 50 > 750 μM) resulted in considerable deterioration of the activity. Overall, it was understood that any substitution at the Y-position improved the inhibitory activity. Also, the electron-donating substituent is less effective compared to electron-withdrawing groups. The presence of halogen groups (2-F and 4-Cl) might play a key role in this inhibition of enzyme due to the high electronegativity, which makes the whole molecule more polar, and the enzyme might have better interaction with it. (II) Similar to the previous set, among derivatives 9h-n, any substitutions at the Y-position improved the activity significantly as compared with the unsubstituted analog. This trend can easily be seen . The minor difference in the activity of the last three analogs may be due to the difference in the position and electron-withdrawing power of the substituents on the benzyl moiety. By comparing the IC 50 values in this set, it can be implied that ortho-methyl group as electrondonating substituent caused a significant improvement in the α-glucosidase inhibition with an IC 50 value of 11.28 μM. (III) Comparison of derivatives bearing the same substitution group at Y while X varies revealed that 9h as an unsubstituted derivative at Y exhibited better potency compared to the 9a counterpart. However, this trend was not followed in the rest of the derivatives as 9i, 9j, 9k, 9l, and 9n were not more potent than their counterparts 9b, 9c, 9d, 9l, and 9g. It can be understood that the SAR was mainly affected by the difference in substituents (Fig. 3).
Overall, it was perceived that any substitution at the Y position is favorable. Among the first set of compounds bearing OMe at X, it can be found that 4-Cl and 2-F substituents on the benzyl moiety played a substantial role in the anti-α-glucosidase activity. Although the presence of 2-CH 3 at the Y-position had destructive effect on the first category, this derivative showed the highest activity in the second category.
To correlate the activity of present molecules with the previously published reports, different interesting SARs were obtained. The comparison of IC 50 values of phenoxy derivatives with their corresponding methoxyphenyl analogs of biscoumarin derivatives (Compound A, Fig. 1) revealed that phenoxy analogs of biscoumarin (with 2-chloro and 4-nitro substituents) were more active than 4-methoxyphenoxy counterparts 38 . These results were supported in other studies on hydrazineylideneindolinone derivatives (Compound C, Fig. 1) so that phenoxy Table 1. α-Glucosidase inhibitory activity of compounds 9a-n. a Data represented in terms of mean ± SD. www.nature.com/scientificreports/ derivatives were more potent than methoxyphenoxy compounds 16 . Noteworthy, unlike the previous studies, in this work phenoxymethyl-1,2,3-triazole derivatives were more potent inhibitors than phenoxy-1,2,3-triazole counterparts.
Comparison of the benzyl substitutions showed that 2-fluorobenzyl of hydrazineylideneindolinone linked to phenoxymethyl-1,2,3-triazole derivatives (Compound C, Fig. 1) induced better α-glucosidase inhibitory activity than other derivatives 16 . Also, the same trend was observed by Xie et al., so the 2-fluorobenzyl moiety of isatinthiazole scaffold disclosed better potency in comparison to different derivatives 42 . These results are in line with the current study. However, assessments on biscoumarin-1,2,3-triazole hybrids exhibited that 2-Cl substitution on the benzyl pendant recorded better potency than the rest of the derivatives 38 .

Enzyme kinetic studies.
Kinetic studies were conducted for compounds 9b, 9e, 9i, and 9l to identify the type of inhibition. According to Fig. 4, the Lineweaver-Burk plot showed that the K m and V max gradually decreased with increasing the inhibitor concentration, indicating an uncompetitive inhibition for compounds 9b and 9e with K i = 0.43 and 0.24 µM, respectively. However, investigation of their compartments 9i and 9l demonstrated different manner of α-glucosidase inhibition. As can be seen in Figs. 5 and 6, they revealed a competitive inhibition. The K i value for compound 9i was calculated as 75.0 µM and the corresponding value for compound 9l was obtained as 85.0 µM.
Fluorescence spectroscopy measurements. The intrinsic fluorescence property of α-glucosidase is generally due to the presence of tryptophan, tyrosine, and phenylalanine amino acids. α-Glucosidase has 18 tryptophan residues that eight are exposed to the solvent, and four are found in the proposed active site pocket (Trp381, Trp710, Trp715, and Trp789). Therefore, the conformation of the enzyme affected by the local tryptophan environment, can be followed by the change of fluorescence intensity 43,44 . In fact, fluorescence spectroscopy measurements could be used to predict the tertiary structure of the enzyme. To demonstrate the effect of compound 9e on α-glucosidase activity, fluorescence spectra of the enzyme in the presence of various concentrations of 9e were recorded (Fig. 7). As can be seen in Fig. 7, no shift was observed in the emission maximum (λ max    Thermodynamic analysis of binding of compound 9e to α-glucosidase. Noncovalent interactions including hydrogen bonding, hydrophobic, electrostatic, and van der Waals forces are common forces between ligand and protein. To get insight into binding forces in the 9e-α-glucosidase complex, the thermodynamic study was conducted and the thermodynamic parameters of the noncovalent interactions, i.e., standard enthalpy change (ΔH°), standard entropy change (ΔS°), and standard free energy change (ΔG°) were calculated. For this purpose, the stability of α-glucosidase in the presence or absence of compound 9e was investigated by screening the fluorescence intensity at 340 nm at different temperatures (298-338 K) based on the equilibrium model (Native state ↔ Unfolded state). The start and end temperature points were 298 and 338 K, respectively. Denaturation profiles of α-glucosidase were then obtained by thermal scanning in the presence of various concentration of 9e. As shown in Fig. 8, a sigmoidal curve observed by each profile indicated a single denaturantdependent step based on the two-state theory. The values of ΔH°m and ΔS°m were calculated as reported in Table 2. T m was estimated to be the lowest for α-glucosidase that incubated in the presence of compound 9e at the concentration of 1.0 µM (311 K), but in the case of concentrations of 0.5 and 0 µM, T m was estimated to be 315 and 317 K, respectively. These results revealed that the most instability occurred at the higher concentration of compound 9e.
The forces between the protein and ligand can be categorized into I: ΔH° > 0, ΔS° > 0 for hydrophobic interactions; II: ΔH° < 0, ΔS° < 0 for van der Waals forces; III: ΔH° < 0, ΔS° < 0 for hydrogen bond and van der Waals interactions and IV: ΔH° < 0, ΔS° > 0 for electrostatic interactions; as non-covalent interactions. According to our results (Table 2), the presence of compound 9e in aqueous solutions of α-glucosidase indicated the formation of hydrophobic interactions between nonpolar amino acid residues and the enzyme, confirming the unfolded state of the protein.
Docking studies. Molecular docking studies were performed for compounds 9b and 9e to investigate the mode of their interactions with α-glucosidase (PDB ID: 5NN8) using the maestro molecular modeling platform of Schrödinger package. First to validate the in-silico procedure, the acarbose as a crystallographic inhibitor was docked into human lysosomal acid-α-glucosidase. The superimposed structure of acarbose and its crystallographic conformation recorded an RMSD value of 1.69 Å. Next, the docking assessments of the compounds were done based on the same protocol performed on the crystallographic inhibitor.  www.nature.com/scientificreports/ Figure 9 presented the binding pattern of derivative 9b with the binding site of α-glucosidase (glide score = -− 7.04 kcal/mol). Derivative 9b oriented within the α-glucosidase active site so that phenoxy-cyanoacetohydrazide penetrated the deep gorge of the binding site and the substituted moiety oriented toward the entrance of the active site. In detail, the nitrogen of cyanoacetohydrazide pendant was fixed between the Trp616 (essential residue) and Arg672. Carbonyl and hydrazine moieties of cyanoacetohydrazide group also participated in H-bound interactions with Arg600 (essential residue). The ortho-fluorobenzyl ring was stacked with Phe525 thus stabilizing the molecule at the entrance of the active site to get the suppressed conformation of α-glucosidase.
According to molecular docking study, 9e recorded the glide score of − 6.89 kcal/mol. As shown in Fig. 10, phenoxy-cyanoacetohydrazide oriented toward the inner core of the binding pocket, while the para-chlorobenzyl part (substituted moiety) of the compound bonded near the active site entrance. Focusing on the cyanoacetohydrazide pendant, confirmed our designing strategy so that nitrogen of the cyano group exhibited two H-bonding interactions with Trp613 (essential residue) and Arg672. Also, NH of hydrazide participated in H-bonding interaction with Asp616 (essential residue). There were π-π stacking and π-cation interactions between Arg600 (essential residue) and the phenoxy linker. Also, 1,2,3-triazole ring recorded a π-π stacking interaction with Phe525.  www.nature.com/scientificreports/ ADME-toxicity profiles and physicochemical properties. The pkCSM server 45 was used to predict the ADME-toxicity properties of synthesized compounds. As shown in Table 3, all derivatives showed good human intestinal absorption, low clearance values, and low toxicity. The results of drug-likeness properties were shown in Table 4. All compounds exhibited appropriate molecular properties with no drug-likeness rules violations 46 .

Conclusion
Novel cyanoacetohydrazide linked to 1,2,3-triazoles were designed, synthesized, and characterized via spectroscopic techniques and evaluated for their α-glucosidase inhibitory potential. These compounds except 9a demonstrated considerable inhibitory activity against α-glucosidase with IC 50 value of 1.0 to 271.17 µM compared to acarbose as the positive control (IC 50 value of 754.1 µM). Compound 9e (IC 50 = 1.00 ± 0.01 μM) with having para chlorobenzyl ring and 9b (IC 50 = 1.50 ± 0.01 μM) bearing ortho fluorobenzyl pendant group were found to be the most potent α-glucosidase inhibitors. Kinetic studies revealed that they 9b and 9e behaved uncompetitively against the enzyme with K i = 0.43 and 0.24 μM, respectively. Also, the binding affinity between compound 9e at different concentrations and α-glucosidase was recorded using fluorescence measurements. It indicated the inhibition of α-glucosidase due to conformational changes of the enzyme. According to the thermodynamic studies, hydrophobic interactions were found to be responsible for the formation of 9e-α-glucosidase complex. The in-silico studies confirmed the designing strategy so that cyanoacetohydrazide group was able to form several important interactions within the cavity which supported the high potency of these compounds and  www.nature.com/scientificreports/ phenoxy-1,2,3-triazole moiety stabilized the derivatives through several hydrophobic and hydrophilic interactions. Interestingly substituted moiety at Y position occupied the entrance of the active site to get the suppressed conformation of α-glucosidase. These results were in accordance with enzymatic assessments that any substitution at the Y position was favorable. As expected, developed pharmacophores used in the design of these hybrids, are involved in the interactions with the enzyme.

Materials and methods
All chemicals and reagents were purchased from Merck and Aldrich. Melting points were determined using Kofler hot stage apparatus and are uncorrected. The IR spectra were obtained on a Nicolet Magna FTIR 550 spectrometer (potassium bromide disks). NMR spectra were recorded on a Varian-INOVA 500 MHz and chemical shifts were expressed as δ (ppm) with tetramethylsilane as internal standard. Analytical HPLC evaluation was performed on a YL9100 HPLC system (Korea) equipped with UV detectors using a RP column (Teknokroma, C18, 5 μm, 150 × 4.6 mm) and solvent: methanol (solvent A) and water, a gradient of 0-100% solvent A in 11 min, 1 min at 0%, to 50% within 3 min, to 100% at 6 min, to 0 within 5 min (total run time 11 min); flow rate, 1 mL/ min; detection, 254 nm; injection volume, 20 μL.
Synthesis of compounds 9. The click reaction was conducted by a mixture of aldehyde 1 and in situ prepared azide derivative 4 to obtain compound 5 16 . For this purpose, benzyl chloride/bromide derivative 2 (1.1 mmol) and sodium azide 3 (0.06 g, 0.9 mmol) in the presence of triethylamine (0.13 g, 1.3 mmol) in the mixture of water (4 mL) and tert-butyl alcohol (4 mL) was stirred at room temperature for 30 min. Next, compound 1 (0.5 mmol) and CuSO 4 ·5H 2 O (7 mol%) were added to the reaction mixture and it was continued for 24-48 h. After completion of the reaction (checked by TLC), the mixture was poured on crushed ice, the precipitates were filtered off and washed with water. Compound 5 was used for further steps with no purification. A mixture of compound 5 (1 mmol) and 2-cyanoacetohydrazide 8 (1 mmol) in methanol (8 mL), in the presence of a few drops of HOAc was irritated under microwave irradiation at 700 W for 10-12 min (1 min interval). After completion of the reaction (checked by TLC), the mixture was poured on crushed ice, the precipitates were filtered off and washed frequently with water (Supplementary Information).      ((1-(4-chlorobenzyl)-1H-1,2,3-triazol-4-yl)         In vitro α-glucosidase inhibition assay. α-Glucosidase (Saccharomyces cerevisiae, EC3.2.1.20, 20 U/mg) and the substrate, p-nitrophenyl-β-D-glucopyranoside (p-NPG) were purchased from Sigma-Aldrich and the assay was performed exactly according to our previous report 14 . In this respect, various concentrations of each synthesized compound dissolved in DMSO, were added to potassium phosphate buffer (50 mM, pH 6.8) including enzyme (at final concentration of 0.1 U/mL), in a 96-well plate. After a 10-min incubation at 37 °C, p-NPG was added to each well to achieve final concentration of 4 mM. Then, the plate was re-incubated at 37 °C for 20 min. It should be noted that the final concentration of DMSO in each enzymatic solution was 10%. Finally, the change in the absorbance was measured at 405 nm using spectrophotometer (Synergy HTX Multi-Mode Microplate Reader-BioTek, Germany). Acarbose, the standard inhibitor of α-glucosidase was used as the positive control and the enzyme activity in the absence of each inhibitor was considered as the negative control. The percentage of inhibition for compounds and control was calculated using Eq. (1):
Fluorescence spectroscopy measurements. Compound 9e at different concentrations (0-1.0 µM) was added into the 3 mL solution containing a fixed amount of α-glucosidase (0.1 U/mL). All mixtures were held for 10 min to equilibrate before measurements. Then, the fluorescence emission spectra were measured from 300 to 450 nm at the excitation wavelength of 280 nm on a Synergy HTX multi-mode reader (Biotek Instruments, Winooski, VT, USA) equipped with a 1.0 cm quartz cell holder. The fluorescence spectra of the buffer containing compound 9e in the absence of the enzyme were subtracted as the background fluorescence 47 .
Thermodynamic analysis against α-glucosidase. Thermodynamic analysis was performed as described by Mojtabavi et al., the fluorescent intensity data were plotted as a function of temperature, and the thermodynamic profile was computed 48,49 . Therefore, the denatured fraction (F D ) of protein was calculated from Eq. (2), assuming a two-state mechanism for the protein denaturation: In Eq. (2), Y obs , Y N , and Y D are the observed absorbance, the values of absorbance characteristics of a fully native and denatured conformation, respectively. Equation (3) was used to calculate the apparent equilibrium constant (K) for a reversible denaturation process between native and denatured protein states: The standard Gibbs free energy change (ΔG°) for protein denaturation is given by the Eq. (4): (1) Inhibition% = OD negative control − OD sample /OD negative control ×100 OD = optical density at 405 nm .   www.nature.com/scientificreports/ where T and R are the absolute temperature and the universal gas constant, respectively. The Gibbs free energy (ΔG°) is the most valuable standard of protein conformational stability in thermal denaturation. The integrated Gibbs-Helmholtz equation was utilized for measuring changes in the Gibbs energy of a system as a function of temperature (Eq. (5)): where ΔC p is the heat capacity of protein denaturation. The ΔC p (11.6 kJ/mol K) of the α-glucosidase denaturation was taken from van der Kamp et al. report 48 . In thermal denaturation, T m is the temperature at which the protein is half denatured. ΔH°m and ΔS°m are the standard enthalpy and entropy of denaturation. The standard entropy was calculated from a relation between the standard enthalpy (ΔS) and entropy (ΔH) of denaturation as bellow: Molecular docking. The molecular docking of compounds 9b and 9e was performed using the maestro molecular modeling platform (version 10.5), Schrödinger suites 50 . X-ray crystallographic structure of α-glucosidase in complex with acarbose (PDB ID: 5NN8) was obtained from www. rcsb. com 44 . A protein preparation wizard was used to remove water molecules and co-crystallized atoms from the protein and prepare the receptor. Moreover, heteroatom states were generated at pH: 7.4 by EPIK, and H-bonds were assigned using PROPKA at the same pH. 2D structure of ligands was drawn in Hyperchem and the energies were minimized using molecular mechanics and molecular quantum approaches. Next, the ligand preparation wizard was used to prepare the ligand using the OPLS_2005 force field 51 . Acarbose, compounds 9b and 9e were docked into the binding sites using glide tasked to report ten poses per ligand with flexible ligand sampling and extra precision 52 .