Design, synthesis and molecular docking study of novel pyrrole-based α-amylase and α-glucosidase inhibitors

MEDICINAL

CHEMISTRY

RESEARCH

Med Chem Res

DOI 10.1007/s00044-017-1965-z

ORIGINAL RESEARCH

Design, synthesis and molecular docking study of novel pyrrole-

based α-amylase and α-glucosidase inhibitors

Nikhil C. Jadhav¹Akshata R. Pahelkar¹Neha V. Desai¹Vikas N. Telvekar¹

●

Received: 10 March 2017 / Accepted: 19 June 2017

Abstract In an effort to design and synthesize a new class

of α-glucosidase and α-amylase inhibitors, we have syn-

thesized novel pyrrole based molecules using molecular

hybridization approach. These novel analogs were synthe-

sized by the novel methodology developed in our lab which

comprises of the multi-component direct synthesis route

using hypervalent iodine reagent. The compounds were

Graphical abstract

1

characterized by infrared, H nuclear magnetic resonance

(NMR), ¹³C NMR and Mass Spectroscopy. These com-

pounds were screened for their α-amylase and α- glucosi-

dase activity. They showed a varying degree of inhibition

with IC₅₀values ranging between 0.4 to 4.14 µmol/mL and

0.8 to 4.14 µmol/mL for α-amylase and α-glucosidase

respectively. Compounds 3, 7, 12, and 18 showed excel-

lent activity as compared to standard acarbose. This has

identiﬁed a new class of α-amylase and α-glucosidase

inhibitor which can be further developed as anti-

hyperglycemic agents. The molecular docking analysis was

carried out to better understand of interaction between

α-amylase and α-glucosidase target and inhibitors in this

series. We also generated a homology model for human

α-glucosidase enzyme and identiﬁed the key residues at the

binding site. The outcome of the study could be used for

the rational design of potent and selective α-amylase and

α-glucosidase inhibitors, respectively.

●

Keywords α-glucosidase

Pyrrole derivatives

●

Multicomponent synthesis Molecular hybridization

approach Docking Homology modeling

●

Introduction

The increasing worldwide incidence of diabetes mellitus

constitutes a global public health problem and is a principal

cause of morbidity and mortality in human populations

(Florence et al. 2014). It is expected that the total number of

people with diabetes increase from 176 million in 2000 to

366 million in 2030 (Wild et al. 2004).

Diabetes mellitus is a metabolic disorder characterized

by hyperglycemia caused by an absolute or relative deﬁ-

ciency of insulin and insulin resistance. Chronic

Electronic supplementary material The online version of this article

(doi:10.1007/s00044-017-1965-z) contains supplementary material,

which is available to authorized users.

* Vikas N. Telvekar

vikastelvekar@rediffmail.com

1

Department of Pharmaceutical Sciences and Technology, Institute

of Chemical Technology, Matunga, Mumbai 400 019, India

Med Chem Res

hyperglycemia during diabetes causes glycation of body

proteins which in turn leads to secondary complications

affecting vital organs of the body. These may be inhibited

or lowered by maintaining blood glucose levels close to

normal. The therapeutic treatment includes use of insulin

and various oral anti-diabetic agents such as sulphonylureas

(e.g., glibenclamide), biguanides (e.g., metformin), thiazo-

lidinediones (e.g., pioglitazone), glinides (e.g., repaglinide)

and α-glycosidase inhibitors like acarbose, miglitol, and

voglibiose etc. The different classes of anti-diabetic drugs

exert their effect in different ways. These drugs also have

certain adverse effects like causing hypoglycemia at higher

doses, liver problems, lactic acidosis and diarrhea, and fail

to signiﬁcantly alter the course of diabetic complications. In

order to overcome these problems, it is essential to search

new class of compounds which are more efﬁcacious with

lesser side effects (Antre et al. 2012).

The alpha-amylases (Kaushik 2015) are the calcium

metalloenzymes which can’t function in the absence of

calcium. There are many digestive enzymes in humans and

among them the most important one is pancreatic alpha-

amylase (EC 3.2.1.1), that act as a catalysis in the reaction

which involves the hydrolysis of the alpha-1,4 glycosidic

linkages of the starch, amylopectin, amylose, glycogen, and

numerous maltodextrins and is responsible for starch

digestion. The other important enzyme is alpha-glucosidase

or maltase (EC 3.2.1.20) which catalyzes the ﬁnal step of

the digestive process of carbohydrates mainly starch by

acting upon 1,4-alpha bonds and producing glucose as the

ﬁnal product (Tundis 2010) The large molecules like starch

cannot cross the blood brain barrier as glucose has to reach

the brain thus; to overcome this problem alpha-amylase

cleaves the large starch molecules into smaller fragments of

sugars in order to cross the blood brain barrier. If there will

be excess conversion of starch to sugars, it will increase the

sugar level in blood, then the role of insulin will come into

action by ordering cells to metabolize the excess sugar

moieties and store as energy sources ie., glycogen. This

cycle is endlessly happening in a healthy person. But in

some cases, due to excess activity of amylase enzyme and

insulin deﬁciency or resistance to insulin, level of blood

glucose arises which might result in hyperglycemia. To

control hyperglycemia several studies on inhibition of

amylase enzyme activity is being studied. However, if there

will be excessive inhibition of pancreatic alpha amylase, it

might cause abnormal bacterial fermentation of undigested

carbohydrates in the colon resulting in ﬂatulence and diar-

rhea (Horii 1986).

α-glucosidase (EC 3.2.1.20) acts upon 1,4- α bonds. α-

glucosidase hydrolyze terminal, non-reducing,1–4 linked α-

glucose residues to release a single α-glucose molecule

(Bruni et al. 1970) and thus breaks down starch and dis-

accharides to glucose. As proven in the literature, inhibition

of α-glucosidase leads to the retardation of glucose

absorption and decrease in postprandial blood glucose

levels. This indicates that effective α-glucosidase inhibitors

may serve as therapeutic agents to treat diabetes and obesity

making it a target of special interest in the pharmaceutical

research community (Dwek et al. 2002).

Pyrroles are of paramount importance in the ﬁeld of

medicinal chemistry having various biological activities

including antimicrobial (Ballard et al. 2009), anti-

hyperglycemic (Goel et al. 2004), selective aldose reductase

inhibitors (Pegklidou et al. 2010). Pyrroles being important

class of heterocycles and pharmacophore of many active

pharmaceutical ingredients, various methods have been

reported for its synthesis. Some very promising multi-

component reactions are introduced for preparation of pyr-

roles. One of the published procedure used nano CoFe₂O₄

supported molybdenum (fCoFe₂O₄2SiO₂–NH₂–Mo(acac)₂)

catalysis for one pot synthesis of pyrrol but procedure

of synthesis nano CoFe₂O₄supported molybdenum

(fCoFe₂O₄2SiO₂–NH₂–Mo(acac)₂) catalysis was tedious

and time consuming (Bao-Le et al. 2014). As we are con-

tinuously working on development of efﬁcient routes for

synthesis of heterocycles, we have developed the multi-

component (three-component) direct synthesis route for

substituted pyrroles from easily available chemical moieties

using hypervalent iodine reagent like (diacetoxyiodo)ben-

zene (DIB) (Jadhav et al. 2013). We herein explored our

facile, efﬁcient route for synthesis of novel analogs of pyr-

role pharmacophores.

The therapeutic applications of amino acids have

received a considerable attention in metabolic disorders,

renal failure, respiratory physiology, cardiology, neurolo-

gical disorders, and congenital defects (Sensl et al. 1989).

Free amino acids have been found to have antiglycating

property. They improve the insulin sensitivity by promoting

insulin receptor tyrosine kinase activity (Sulochana et al.

2001). Phenyl alanine and tyrosine derivatives have been

reported for antihyperglycemic activity (Antre et al. 2012).

Glycine and proline derivatives are reported for antiglyca-

tion activity (Shantharam et al. 2013) Essential and bran-

ched chain amino acid (BCAA) leucine have anticataractous

effects possibly through antiglycation mechanism (Sulo-

chana et al. 1998). Beneﬁciary effects of BCAA like

valine, isoleucine, leucine has been proven in managing

long term complications of diabetes (Xiao et al. 2014)

(Adams 2011).

Glucosidases play a vital role in the digestive process of

carbohydrates by mediating the catalytic cleavage of a

glycosidic bond with substrate speciﬁcity (Kimura et al.

2004). α and β-glucosidases are most extensively studied

glucosidases in literature. In contrast to β-glucosidase,

The objective of present work was to synthesize active,

novel anti-diabetic chemical entities through molecular

Med Chem Res

Table 1 QikProp analysis data of novel pyrrole derivatives

Title Mw^ah#Stars QPlogPo/w^kQPPCaco % Human

oral

Rule

of

absorption ﬁve

1

241.33

255.36

269.39

285.39

289.8

0

1

0

1

0

1

0

1

0

1

0

4.18

4.62

4.54

4.82

4.58

5

4594.33 100

0

1

0

1

0

1

0

1

0

1

0

2

4419.15 100

4453.22 100

4452.58 100

4391.57 100

4459.44 100

4459.01 100

4460.32 100

4452.06 100

525.49 100

4407.16 100

4440.15 100

4439.56 100

531.64 100

4447.02 100

4457.66 100

4491.62 100

4434.76 100

4377.26 100

4341.66 100

4342.79 100

531.08 100

3

4

5

6

7

273.35

334.26

300.36

315.41

269.39

283.41

314.38

348.28

255.36

269.39

285.39

315.41

303.38

364.28

330.38

299.41

317.4

4.74

5.08

5

8

9

Fig. 1 Pictorial representation of designed pyrrole derivatives

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

3.73

4.68

4.92

5.3

hybridization concept of drug discovery. Molecular hybri-

dization is a valuable structural modiﬁcation tool, wherein

two pharmacophoric moieties of bioactive substance are

combined to give hybrid molecule with improved efﬁcacy

than parent compound (Viegas et al. 2007). This concept

can also deliver hybrid with speciﬁc selectivity proﬁle, low

side effects, and having dual/ multiple modes of action. In

present work, with the aim to have hybrids with improved

afﬁnity and efﬁcacy, we combined the branched aliphatic

feature of essential amino acids, valine and leucine to the

pyrrole ring and designed the novel analogs (Fig. 1).

ADME properties of designed molecules were found out by

using software Qikprop version 4.0. From the QikProp

analysis (QikProp 2014), it was observed that the designed

molecules exhibited good drug likeliness (Table 1). As

evidenced from # stars being 0–2, the molecules exhibited

good physicochemical properties which fall in the range of

known drugs. The partition coefﬁcient exhibited by

QPlogPo/w, were within range 2–6.5. The next parameter of

interest considered by QikProp analysis was QPPCaco. The

value of QPPCaco parameter <25 is considered poor and

>500 is considered excellent. Most of the designed mole-

cules exhibited QPPCaco within acceptable limits.

According to QikProp analysis, it was observed that per-

centage Human oral absorption of most of compounds is

100, which was considered to be good. The designed

molecules also obey the Lipinski’s rule of ﬁve and all the

molecules have MW within acceptable range 130.0–725.0.

Compounds showed good ADME results and hence were

further considered for synthesis and were synthesized using

our novel methodology (Ali et al. 2006). In our paper,

we are now reporting a modeling study for the discovery

of dual-functional inhibitors against α-amylase and

α-glucosidase activity. These studies can provide useful

information for the design of new compounds with

improved potency towards α-amylase and α- glucosidase or

those are potentially active against the α-amylase and

4.24

5.51

4.37

4.86

5.24

5.25

5.45

5.76

4.43

5.61

5.86

4.87

2.56

2.17

2.06

4342.6

4345.6

584.9

100

344.41

227.26

257.29

241.29

845.23

945.44

1718.34

88.45

92.94

96.88

#Stars: Number of property or descriptor values that fall outside the

95% range of similar values for known drugs. Outlying descriptors and

predicted properties are denoted with asterisks (*) in the out ﬁle. A

large number of stars suggests that a molecule is less drug-like than

molecules with few stars

QPlogPo/w: Predicted octanol/water partition coefﬁcient

QPPCaco: Predicted apparent Caco-2 cell permeability in nm/s. Caco-

2 cells are a model for the gut-blood barrier. QikProp predictions are

for non-active transport

Percent human oral absorption: Predicted human oral absorption on

0–100% scale. The prediction is based on a quantitative multiple linear

regression model. This property usually correlates well with human

oral absorption, as both measure the same property

Rule of Five: Number of violations of Lipinski’s rule of ﬁve. The rules

are: mol-MW < 500, QPlogPo/w < 5, donorHB ≤ 5, accptHB ≤ 10.

Compounds that satisfy these rules are considered drug like

α-glucosidase. A reported crystal structures 1OSE (for

amylase) were obtained from protein data bank and per-

formed docking study. Docking procedures basically aim to

identify the correct conformation of ligands in the binding

Med Chem Res

pocket of a protein and to predict the afﬁnity between the

ligand and the protein. Docking is one method in which the

binding of an inhibitor to a receptor can be explored. In our

paper, a theoretical 3D model of human α-glucosidase was

elaborated by homology modeling. The α-glucosidase

active site was then characterized sitemap and used to

study the docking of selected inhibitors (Fig. 2).

nitrostyrenes were synthesized using known methods if not

available commercially. All products were identiﬁed with

help of nuclear magnetic resonance (NMR) spectra, infrared

(IR), Mass Spectroscopy (MS) and melting points. Melting

points were determined on a Buchi B-545 melting point

apparatus. ¹H NMR spectra were recorded on 300 MHz

spectrometer in CDCl₃and DMSO-d₆. MS were measured on

Agilent 5975 MSD. The IR spectra were recorded on “Perkin

Elmer FTIR Spectrometer-Spectrum RX1”. Solids were

recorded as KBr pallets and liquids as thin ﬁlm or CHCl₃

solution. Column chromatography was performed on silica

gel (SiO₂: 60–120 mesh). Porcine pancreatic α-amylase and

rat intestinal acetone powder were procured from Sigma

Aldrich Inc., (St Louis, MO). Substrate: p-Nitro phenyl-α-^D-

glucopyranoside (PNPG) was procured from Sigma Aldrich

Inc. 3,5-Dinitrosalicylic acid (DNSA) was obtained from

Himedia Laboratory, Mumbai. Starch was purchased from

Sisco Research Laboratories, (Mumbai, India). Acarbose was

obtained from Bayer Medical Co. (Germany). All other

chemicals and solvents used are of analytical grade.

Materials and methods

General consideration

Different substituents of aliphatic amines, aldehydes, and

various reagents were commercially available. Analogs of

R

O

Chemistry

R₂

In the present work, the target compounds 1–28 were syn-

thesized utilizing the reaction sequence as shown in

Schemes 1 and 2. Nitrostyrenes (3a–i) were prepared from

corresponding aromatic aldehydes and nitromethane

according to the literature procedure. All pyrrole derivatives

N

H₃C

R₁

Fig. 2 Common structural scaffold of designed pyrrole molecules (6–33)

Scheme 1 Synthetic route for

the synthesis of pyrrole

derivatives (1–25), Reagents and

conditions: a NaOH solution,

methanol, target temperature

0–10 °C, stirring 30 min.; HCl b

DIB, EtOH, reﬂux, 4 h

Med Chem Res

(Na₂SO₄). The solvent was evaporated under reduced

pressure to give crude product. The pure product (74%) was

obtained after silica gel column chromatography (2%

EtOAc–Hexane).

General procedure to synthesize N-formyl or N-acylpyrroles

(26–28)

Pyrrole derivative was synthesized using above procedure

utilizing ammonia instead of amine followed by acylation as

described herein. Pyrrole derivative (1.08 mmol) and formic

or acetic acid (2 mmol) were added to a suspension of 2 M

aq. sodium dichloroiodate (NaICl₂) (0.26 mmol), carbon

(0.13 g) and oxone® (1.08 mmol) in water (10 mL) and

mixture was stirred at reﬂux temperature for 3 h. Upon

completion of reaction, the mixture was ﬁltered to remove

carbon. The ﬁltrate was extracted with ethyl acetate (2 × 10

mL) and organic layer was dried over anhydrous sodium

sulphate(Na₂SO₄). The solvent was evaporated and crude

residue was puriﬁed by column chromatography to yield

pure product.

Scheme 2 Synthetic route for the synthesis of N-acyl pyrrole deri-

vatives (26–28), Reagents and conditions: b DIB, EtOH, reﬂux, 4 h.

c Acetic acid/formic acid, aq. NaICl₂, carbon, oxone®, reﬂux, 3 h

(1–28) were prepared using our novel methodology with

good yields (Jadhav et al. 2013).

General procedure to synthesize nitrostyrenes (3a–i)

To a RBF kept in a freezing mixture of ice and salt, are

placed 1 mmol each of nitromethane and benzaldehyde, and

10 mL of methyl alcohol. In another ﬂask, a chilled solution

of sodium hydroxide (5.25 mmol) in equal volume of water

was prepared. This solution was diluted with 20 mL ice-

water and poured into funnel and added slowly to stirred

reaction mixture keeping temperature between 10 and

15 °C. A bulky white precipitate was formed and little

methyl alcohol was poured if stirring became difﬁcult. After

15 min of stirring, 100 mL of ice water was added and kept

in separating funnel. In a beaker, 2:3 Hydrochloric acid

solutions were prepared and reaction mixture was added at

such a rate that the stream just fails to break into drops. As

soon as the alkaline solution comes in contact with acid, a

pale yellow crystalline mass separated out. After separating

cloudy liquid layer by decantation, the crude product was

ﬁltered by suction and washed with water until free from

chlorides. The crude product (78%) was recrystallized using

ethanol to yield pure nitrostyrene.

Biological activity

Invitro antidiabetic evaluation

Assay for α-amylase inhibitory activity α-Amylase activ-

ity was performed according to the chromogenic method

(Ali et al. 2006) with some modiﬁcations. In a micro-

centrifuge tube, 100 µL of sample solution in Buffer or

DMSO and 500 µL of 1% w/v soluble potato starch solution

in 20 mM sodium phosphate buffer pH 6.9 containing 6.7

mM sodium chloride were incubated at 25 °C for 10 min.

The reaction was initiated by addition of 100 µL of enzyme

solution (0.5 mg/mL in 0.02 M sodium phosphate buffer) to

each tube and reaction mixtures were incubated at 25 °C for

another 10 min. The reaction was stopped with 200 µL of

DNSA color reagent [1 g of 3, 5-dinitrosalicylic acid

(96 mM), 30 g of sodium potassium tartarate and 20 mL of

2 N sodium hydroxide to a ﬁnal volume of 100 mL in dis-

tilled water] and reaction mixture was transferred to a hot

water bath maintained at 85–90 °C for 5 min. After cooling

to room temperature, the 50 µL reaction mixtures were

taken in 96-well plate and then diluted by adding 200 µL of

distilled water. The absorbance was measured at 540 nm

(Shimadzu UV-160 spectrophotometer, Kyoto, Japan). For

each concentration, blank incubations were prepared by

replacing the enzyme solution with 100 µL in distilled water

at the start of the reaction. Control incubations, representing

100% enzyme activity were conducted in a similar manner,

replacing sample with 100 µL DMSO. All the tests were run

in triplicate. The α-amylase inhibitory activity was expres-

sed as IC₅₀values.

General procedure to synthesize pyrrole derivatives (1–25)

The mixture of amine (2 mmol), nitrostyrene (1 mmol), and

1,3-dicarbonyl compound (1.2 mmol) in ethanol (10 mL)

was stirred vigorously at room temperature for 10 min. DIB

(1 mmol) was added slowly, then the mixture was reﬂuxed

for 4 h. After the completion of the reaction (monitored by

thin layer chromatography the solvent was evaporated

under the vacuum. The resulted residue was diluted with

water (10 mL) and extracted with ethyl acetate (3 × 10 mL).

The organic layer was separated and washed successively

with 10% sodium bicarbonate (2 × 10 mL), water (2 × 15

mL), and ﬁnally dried over anhydrous sodium sulfate

Med Chem Res

Assay for α -glucosidase inhibitory activity α- glucosidase

activity was performed according to the method (Khan et al.

2014) with some modiﬁcations. Brieﬂy, 50 µL of sample

solution in DMSO or buffer and same amount of α-

glucosidase (EC 3.2.1.20) solution (1.0 U/mL) in 0.1 M

phosphate buffer (pH 6.9) was incubated in 96-well plates at

25 °C for 10 min. The reaction was initiated by adding 50

µL of substrate [5 mM PNPG] solution in 0.1 M phosphate

buffer (pH 6.9). The reaction mixtures were again incubated

at 25 °C for 20 min. The reaction was stopped by adding

80 µL 0.4 M sodium carbonate and α-glucosidase activity

was determined by monitoring the p-Nitro phenol released

from PNPG and the absorbance was recorded at 405 nm in

microplate reader (Shimadzu UV-160 spectrophotometer,

Kyoto, Japan). The α-glucosidase inhibitory activity was

expressed as IC₅₀values.

The model was generated using prime module. The model

was reﬁned with the reﬁnement procedure of Prime.

Model evaluation

The required models would be generated after performing

homology modeling with prime. The 3-D structure of

Q6P7A9 was validated with the programs PROCHECK.

These programs generated Ramachandran plots of the

amino acid residues in the allowed region (Ramachandran

et al. 1963).

Active site analysis

The IC₅₀values (inhibitor concentration at which 50%

inhibition of the enzyme activity occurs) of the synthesized

compounds were determined by performing the assay as

above with varying concentrations of each compound from

0.05, 0.1, 0.25, 0.5, and 1 µmol/mL. Acarbose was used as a

positive control. The data was expressed as mean standard

deviation (SD) of results of three replicate readings (n = 3).

The IC₅₀values were calculated from plots inhibitor

concentration vs. percentage inhibition curves using the

formula:

Binding sites of the target protein were predicted using

sitemap. (Active site prediction tool). The α-glucosidase

active site was then characterized sitemap module (version

6.3, Schrödinger, LLC, NY) installed on redhat Linux

workstation. The ﬁrst stage of a Sitemap calculation is to

locate the sites. A site is deﬁned by a set of site points on a

grid that are either contiguous or bridged by short gaps in

solvent-exposed regions. The site-ﬁnding algorithm begins

by placing a 1-Å grid of possible site points around the

entire protein or around a placeholder species, such as a

ligand.

Absorbance_controlꢀ Absorbance_test

% inhibition ¼

ꢁ 100

Absorbance_control

Molecular docking

The docking studies were performed using Glide module

(version 6.3, Schrödinger, LLC, NY) installed on redhat

Linux workstation. Docking consists of ﬁve steps protein

preparation, ligand preparation, receptor grid generation,

actual docking procedure and ﬁnally viewing the docking

results using the pose-viewer.

Computational method

Homology model development

The crystal structure of α-glucosidase has not been pub-

lished yet. Homology modeling is a theoretical method that

is used to predict the structure of a sequence with an

accuracy that is comparable to the best results achieved

experimentally. The modeled protein quality is extremely

dependent on the identity between the target template and

Query template proteins. The sequence of uninfected alpha

glucosidase enzyme of homo sapiens species was not

available on uni-prot protein database. So, the sequence of

rat Q6P7A9 was collected from the Uni-Prot Protein

Database. A similarity search for Q6P7A9 protein in the

Protein Data Bank (http://www.rcsb.org) was performed

using the BLAST server. The protein similarity search

identiﬁed a very similar protein structure belonging to the

N-terminal Maltase-Glucoamylase in human (PDB ID:

3L4V), which has sequence identity with Q6P7A9 rat, so

this structure was used as a template to generate the model.

Protein preparation

Protein preparation was performed by using Protein Pre-

paration Wizard of Maestro software. α-amylase (PDB ID-

1OSE at resolution 2.3 Å) was taken and treated to add

missing hydrogens, assign proper bond orders, treat metal

(i.e., breaking bonds to metal and correct the formal charge

on metal and neighboring atoms), and to delete water

molecules that are more than 5 Å from the heterogeneous

groups. The H bonds were optimized using sample orien-

tations. All the polar hydrogens were displayed. Finally, the

protein structure was minimized to the default root mean

square deviation value of 0.30 Å. The inhibitor structure

was minimized using OPLS-2005 force ﬁeld.

Med Chem Res

Ligand preparation

assignment of speciﬁc structural motifs that contribute sig-

niﬁcantly to binding afﬁnity, and expanded sampling

algorithms required by scoring function improvement

(Glide 2014). Therefore, XP mode were used for molecular

docking of α-amylase and α-glucosidase inhibitors.

Ligand preparation was accomplished on all the molecules

using Ligprep module to clean the structure (Lig prep

2014).

Receptor grid generation

Characterization data

Receptor was deﬁned and the cocrystallized ligand was

differentiated from the active site of receptor chain B. The

atoms were scaled by van der Waals radii of 1.0 Å with the

partial atomic charge less than 0.25 default. The active site

was deﬁned as an enclosing box at the centroid of the

workspace ligand as selected in the receptor folder. The

ligands similar in size to the workspace ligand were allowed

to dock into the active site. No constraints either positional,

H bonding or hydrophobic were deﬁned (Glide 2014).

Compound 1

(1-[2-methyl-1-(1-methylethyl)-4-phenyl-1H-pyrrol-3-yl]

ethanone): (light brown solid) mp 114–117 °C; IR (KBr)

ν_max3064, 3022, 1641, 1512, 1400, 1222 cm⁻¹; H NMR

1

(CDCl₃, 400 MHz): δ = 1.63 (6H, d, H-1′), 2.41 (3H, s, H-

2′), 2.52 (3H, s, H-3″′), 4.67–4.81 (1H, m, H-1′), 6.49 (1H,

s, H-5), 7.41–7.53 (5H, m, H-2″-H-6″) ppm; ¹³C NMR

(CDCl₃, 100 MHz) δ (ppm): 197.3 (C, COPyrrol), 163.4 (C,

C-4″) 139.19 (C,C-2), 134.8 (C, C-1″), 130.1 (CH, C-2″),

129.6 (CH, C-3″)126.3 (C, C-4), 123.4 (CH, C-5″), 110.5

(CH, C-6″), 109.7 (CH, C-5), 59.8 (CH₃, COPyrrol) 30.3

(CH, CH(CH₃)₂), 25.6(CH₃, C-1′) 12.1(CH₃, C-1′); HRMS

m/z (pos): 241.3333 C₁₆H₁₉NO (calcd. 241.3333); Anal.

calcd. for C₁₆H₁₉NO found 241.02.

Ligand docking

Ligand docking was performed using OPLS-2005 force

ﬁeld. The receptor grid deﬁned in the receptor grid gen-

eration folder was selected for the docking of ligands pre-

pared using Ligprep. Flexible docking was performed using

the Extra Precision (XP) feature of Glide module. The van

der Waals radii was scaled using a default scaling factor of

0.80 and default partial cutoff charge of 0.15 to decrease the

penalties for close contacts. The core pattern comparison

and similarity mode were not used since our aim was to

study the binding of ligands to the active site. The con-

straints to deﬁned ligand–receptor interactions were not set.

The structure output form was set to pose viewer ﬁle so as

to view the output of the resulting docking studies from

pose-viewer (Glide 2014).

Compound 2

1-(1-butyl-2-methyl-4-phenyl-1H-pyrrol-3-yl)ethanone:

(brown solid); mp 111–114 °C; IR (KBr) ν_max3025, 1651,

1539, 1278, 1148, 1039 cm⁻^{1 1}H NMR (CDCl₃, 400

;

MHz): δ = 0.90 (3H, t, H-4′), 1.31 (2H, m, H-3′), 1.74 (2H,

m, H-2′), 2.49 (3H, s, H-2), 2.59 (3H, s, H-3″′), 4.16 (2H, t,

H-1′), 6.41 (1H, s, H-5), 7.43–7.58 (5H, m, H-2″-H-6″)

ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm): 199.2 (C,

COPyrrol), 163.4 (C, C-4″) 139.4 (CH, C-2), 138.7 (C, C-

1″), 131.4 (CH, C-2″), 130.2 (CH, C-3″), 129.6 (C, C-4),

126.4 (CH, C-5″), 125.9 (CH, C-6″), 122.7 (C, C-4), 109.5

(C, C-3), 108.9 (CH, C-5), 51.2 (CH₂, C-1′) 36.8 (CH₂, C-

2′), 29.6 (CH₂, C-3′), 21.0 (CH₂, C-4′), 14.5 (CH₃, C-2);

HRMS m/z (pos): 255.3505 C₁₇H₂₁NO(calcd. 255.33);

Anal. calcd. for C₁₇H₂₁NO found 255.31.

Viewing docking results

It was done using pose-viewer. The H bonds and bad and

ugly van der Waals contacts to the receptor were visualized

using default settings to analyze the binding modes of the

ligands to receptor.

The constraints to deﬁned ligand–receptor interactions

were not set. The ﬁnal ligand binding poses were ranked

according to a computed model score that encompasses the

grid score, proprietary GLIDE score, and the internal energy

strain. The structure output format was set to pose-viewer

ﬁle so as to view the output of the resulting docking studies

from pose-viewer. The score function of Glide, or Glide

score, a modiﬁed and expanded version of ChemScore, was

used for binding afﬁnity prediction and ligand ranking. The

docking can be on the level of either standard (SP) or XP.

The improvement of XP over SP includes the addition of

large desolvation penalties to both ligand and protein,

Compound 3

1-(1-Isobutyl-2-methyl-4-phenyl-1H-pyrrol-3-yl)-1-etha-

none: (brown solid) mp 109–112 °C; IR (KBr) ν_max3057,

3028, 1651, 1504, 1404, 1222 cm⁻¹; ¹H NMR (CDCl₃, 400

MHz): δ = 0.92 (6H, d, J = 6.8 Hz, H-2′), 2.05 (1H, m, H-

2′), 2.47 (3H, s, H-2), 2.50 (3H, s, H-3″′), 4.03 (2H, d, H-

1″), 6.35 (1H, s, H-5), 7.41–7.52 (5H, m, H-2″-H-6″) ppm;

¹³C NMR (CDCl₃, 100 MHz) δ (ppm): 196.7 (C, COPy-

rrol), 163.4 (C, C-4″) 138.2 (CH, C-2), 133.5 (C, C-1″),

107.0 (CH, C-2″), 124.2 (CH, C-3″), 127.2 (C, C-4), 126.4

(CH, C-5″), 125.9 (CH, C-6″), 108.2 (C, C-3), 108.9 (CH,

Med Chem Res

C-5), 59.2 (CH₂, C-1′), 30.2 (C, C-2′), 21.4 (CH₃, C-2′),

11.9 (CH₃, C-2′); HRMS m/z (pos): 255.3502 C₁₇H₂₁NO

(calcd. 255.35); Anal. calcd. for C₁₇H₂₁NO found 255.65.

Compound 7

1-[4-(4-ﬂuorophenyl)-2-methyl-1-(2-methylpropyl)-1H-pyr-

rol-3-yl]ethanone: (brown solid) mp 102–105 °C; IR (KBr)

1

Compound 4

ν_max: 3035, 1652, 1541, 1278, 1151, 1041 cm⁻¹; H NMR

(CDCl₃, 400 MHz): δ = 0.91 (6H, d, H-2′), 2.07 (1H, m, H-

2′), 2.48 (3H, s, H-3″′), 2.51 (3H, s, H-2), 4.08 (2H, d, H-

1″), 6.31 (1H, s, H-5), 7.30–7.38 (4H, m, H-2″-H-6″)

ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm): 197.2 (C,

COPyrrol), 162.4 (C, C-4″), 138.8 (CH, C-2), 131.4 (C, C-

1″), 130.2 (CH, C-2″), 129.7 (CH, C-3″), 126.4 (C, C-4),

125.9 (CH, C-5″) 122.9 (CH, C-6″), 109.5 (C, C-3), 108.9

(CH, C-5), 55.2 (CH₂, C-1′), 29.4 (C, C-2′), 21.2 (CH₃, C-

2′), 14.5 (CH₃, C-2′); HRMS m/z (pos): 273.3444

C₁₇H₂₀FNO (calcd. 273.34); Anal. calcd. C₁₇H₂₀FNO

found 273.14.

1-[2-methyl-4-(4-methylphenyl)-1-(2-methylpropyl)-1H-

pyrrol-3-yl] ethanone: (brown solid) mp 110–113 °C; IR

(KBr) ν_max: 3057, 3029, 1648, 1509, 1404, 1222 cm⁻¹; H

1

NMR (CDCl₃, 400 MHz): δ = 0.96 (6H, d, H-2′), 2.05 (1H,

m, H-2′), 2.17 (3H, s, H-4″), 2.61 (3H, s, H-2), 2.50 (3H, s,

H-3″′), 4.51(2H, d, H-1″), 6.43 (1H, s, H-5), 7.29–7.33 (4H,

m, H-2″-H-6″) ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm):

195.3 (C, COPyrrol), 169.4 (C, C-4″), 136.7 (CH, C-2),

132.5 (C, C-1″), 127.6 (CH, C-2″), 121.4 (CH, C-3″), 127.2

(C, C-4), 126.4 (CH, C-5″), 110.8 (C, C-3), 109.5 (CH, C-

5), 59.9 (CH₂, C-1′), 30.7 (C, C-2′), 21.4(CH₃,-Ph), 11.1

(CH₃, C-2′); HRMS m/z (pos): 269.3760 C₁₈H₂₃NO

(calcd.269.38); Anal. calcd. C₁₈H₂₃NO found 269.58.

Compound 8

Compound 5

1-[4-(4-bromophenyl)-2-methyl-1-(2-methylpropyl)-1H-

pyrrol-3-yl]ethanone: (dark brown solid) mp 115–118 °C;

1-[4-(4-methoxyphenyl)-2-methyl-1-(2-methylpropyl)-1H-

IR (KBr) ν_max: 3062, 3024, 1651, 1504, 1408, 1223 cm⁻¹

;

pyrrol-3-yl] ethanone: (light brown solid) mp 108–111 °C;

¹H NMR (CDCl₃, 400 MHz): δ = 0.91 (6H, d, H-2′), 2.05

(1H, m, H-2′), 2.47 (3H, s, H-3″′), 2.51(3H, s, H-2), 4.03

(2H, d, H-1″), 6.32 (1H, s, H-5), 7.53–7.66 (4H, m, H-2″-H-

6″) ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm): 198.8 (C,

COPyrrol), 168.4 (C, C-4″), 135.4 (CH, C-2), 130.1(C, C-

1″), 130.2 (CH, C-2″), 129.7 (CH, C-3″), 126.3 (C, C-4),

125.9 (CH, C-5″), 121.6 (CH, C-6″), 109.4 (C, C-3), 108.5

(CH, C-5), 59.9 (CH₂, C-1′), 30.1(C, C-2′), 20.6 (CH₃, C-

2′), 12.1 (CH₃, C-2′); HRMS m/z (pos): 334.2451

C₁₇H₂₀BrNO (calcd. 334.25); Anal. calcd. C₁₇H₂₀BrNO

found 334.21.

IR (KBr) ν_max: 3059, 3025, 1653, 1511, 1401, 1212 cm⁻¹

;

¹H NMR (CDCl₃, 400 MHz): δ = 0.93 (6H, d, H-2′), 21.63

(1H, m, H-2′), 2.36 (3H, s, H-4″), 2.57 (3H, s, H-2), 3.84

(3H, s, H-3″′), 4.55 (2H, d, H-1″), 6.77 (1H, s, H-5),

7.05–7.33 (4H, m, H-2″-H-6″) ppm; ¹³C NMR (CDCl₃, 100

MHz) δ (ppm): 189.8 (C, COPyrrol), 163.3 (C, C-4″), 142.4

(CH, C-2), 132.4 (C, C-1″), 130.9 (CH, C-2″), 121.4 (CH,

C-3″), 127.2 (C, C-4), 126.4 (CH, C-5″), 117.6 (CH, C-6″),

109.9 (C, C-3), 108.2 (CH, C-5), 59.6 (CH₃, OPh), 57.4

(CH₂, C-1′), 30.1(C, C-2′), 21.6 (CH₃, C-2′), 11.2 (CH₃, C-

2′); HRMS m/z (pos): 285.380 C₁₈H₂₃NO₂(calcd. 285.38);

Anal.calcd. C₁₈H₂₃NO₂found 285.24.

Compound 9

Compound 6

1-[4-(2-bromophenyl)-2-methyl-1-(2-methylpropyl)-1H-

1-[4-(4-chlorophenyl)-2-methyl-1-(2-methylpropyl)-1H-

pyrrol-3-yl]ethanone: (dark brown solid) mp 118–121 °C;

pyrrol-3- yl]ethanone: (brown solid), mp 111–114 °C; IR

IR (KBr) ν_max: 3052, 3029, 1650, 1503, 1416, 1228 cm⁻¹

;

(KBr) ν_max: 3063, 3031, 1641, 1512, 1400, 1221 cm⁻¹; H

¹H NMR (400 MHz, CDCl₃): δ = 0.88 (6H, d, H-2′), 2.03

(1H, m, H-2′), 2.44 (3H, s, H-3″′), 2.50 (3H, s, H-2), 4.00

(2H, d, H-1″), 6.30 (1H, s, H-5), 7.33–7.66 (4H, m, H-2″-H-

6″) ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm): 198.5 (C,

COPyrrol), 168.4 (C, C-4″), 138.7 (CH, C-2), 136.6 (C, C-

1″), 130.3 (CH, C-2″), 129.7 (CH, C-3″), 126.4 (C, C-4),

123.4 (CH, C-5″) 121.6 (C, C-6″), 109.5 (C, C-3), 108.8

(CH, C-5), 60.3 (CH₂, C-1′), 30.3 (C, C-2′), 20.2 (CH₃, C-

2′), 13.6 (CH₃, C-2′); HRMS m/z (pos): 334.2544

C₁₇H₂₀BrNO (calcd. 334.25); Anal. calcd. C₁₇H₂₀BrNO

found 334.25.

1

NMR (CDCl₃, 400 MHz): δ = 0.94 (6H, d, H-2′), 2.04 (1H,

m, H-2′), 2.53 (3H, s, H-3″′), 2.59 (3H, s, H-2), 4.01 (2H, d,

H-1″), 6.42 (1H, s, H-5), 7.59–7.86 (4H, m, H-2″-H-6″)

ppm; ¹³C NMR (CDCl₃,100 MHz) δ (ppm): 198.5 (C,

COPyrrol), 162.3 (C, C-4″), 137.4 (CH, C-2), 132.4 (C, C-

1″), 130.9 (CH, C-2″), 126.4 (CH, C-3″), 127.2 (C, C-4),

126.4 (CH, C-5″) 117.6 (CH,C-6″), 109.9 (C, C-3), 108.2

(CH, C-5), 56.4 (CH₂, C-1′), 29.7 (C, C-2′), 21.1 (CH₃, C-

2′), 11.5 (CH₃, C-2′); HRMS m/z (pos): 289.7880

C₁₇H₂₀ClNO (calcd. 289.79); Anal. calcd. C₁₇H₂₀ClNO

found 289.6.

Med Chem Res

Compound 10

Compound 13

1-[2-methyl-1-(2-methylpropyl)-4-(4-nitrophenyl)-1H-pyr-

1-[2-methyl-1-(3-methylbutyl)-4-(4-methylphenyl)-1H-pyr-

rol-3-yl]ethanone: (yellow solid) mp 112–115 °C; IR (KBr)

rol-3-yl] ethanone: (light brown solid) mp 108–111 °C; IR

1

ν_max: 3025, 1649, 1541, 1279, 1149, 1048 cm⁻¹; H NMR

(KBr) ν_max: 3029, 2933, 2826, 1684, 1529, 1123 cm⁻¹; H

(400 MHz, CDCl₃): δ = 0.92 (6H, d, H-2′), 2.07 (1H, m, H-

2′), 2.49 (3H, s, H-3″′), 2.62 (3H, s, H-2), 4.03 (2H, d, H-

1″), 7.31 (1H, s, H-5), 7.80–8.38 (4H, m, H-2″-H-6″) ppm;

¹³C NMR (CDCl₃,100 MHz) δ (ppm): 197.8 (C, COPyrrol),

149.6 (C, C-6″), 148.1 (C,C-1″), 135.1 (C, C-2), 130.1 (CH,

C-2″), 129.0 (CH, C-3″), 124.2 (CH, C-4″), 125.9 (CH, C-

5″) 122.9 (C, C-4), 109.9 (C, C-3), 108.3 (CH, C-5), 59.5

(CH₂, C-1′), 30.8 (C, C-2′), 20.6 (CH₃, C-2′), 14.5 (CH₃, C-

2′); HRMS m/z (pos): 300.3501 C₁₇H₂₀N₂O₃(calcd.

300.35); Anal. calcd. C₁₇H₂₀N₂O₃found 300.35.

NMR (400 MHz, CDCl₃): δ = 0.89 (6H, d, H-3′), 1.62(1H,

m, H-3′), 1.62 (1H, m, H-3′), 1.73 (2H, q, H-2′), 2.17 (3H, s,

H-3″′), 2.31 (3H, s, H-4″), 2.46 (3H, s, H-2), 3.80 (2H, t, H-

1″), 6.09 (1H, s, H-5), 7.29–7.33 (5H, m, H-2″-H-6″) ppm;

¹³C NMR (CDCl₃,100 MHz) δ (ppm): 195.0 (C, COPyrrol),

163.6 (C, C-6″), 136.2 (C, C-1″), 133.4 (C, C-2), 130.3

(CH, C-2″), 126.8 (CH, C-3″), 126.3 (CH, C-4″), 126.1

(CH, C-5″) 123.2 (C, C-4), 110.4 (C, C-3), 109.2 (CH, C-5),

56.0 (CH₂, C-1′), 40.9 (CH₂, C-2′), 30.9 (CH, C-3′), 25.1

(CH₃, C-3′), 21.3 (CH₃, –ph, C-4″) 11.0 (CH₃, C-2′);

HRMS m/z (pos): 283.4111 C₁₉H₂₅NO (calcd. 283.41);

Anal. calcd. C₁₉H₂₅NO found 283.36.

Compound 11

1-[4-(3,4-dimethoxyphenyl)-2-methyl-1-(2-methylpropyl)-

Compound 14

1H-pyrrol-3-yl]ethanone: (light brown solid) mp 104–107 °C;

IR (KBr) ν_max: 3045, 3025, 1647, 1522, 1409, 1211 cm⁻¹

;

1-[2-methyl-1-(3-methylbutyl)-4-(4-nitrophenyl)-1H-pyrrol-

3-yl] ethanone: (yellowish brown solid) mp 103–106 °C; IR

(KBr) ν_max: 3039, 2922, 2854, 1699, 1528,1270, 1154,

1120 cm⁻¹; ¹H NMR (400 MHz, CDCl₃): δ = 0.91 (6H, d,

H-3′), 1.64 (1H, m, H-3′), 1.79 (2H, q, H-2′), 2.46 (3H, s,

H-3″′), 4.29 (2H, q, H-2′), 6.38 (1H, s, H-5), 7.80–8.31 (5H,

m, H-2″-H-6″) ppm; ¹³C NMR (CDCl₃,100 MHz) δ (ppm):

197.8 (C, COPyrrol), 149.4 (C, C-6″), 145.4 (C, C-1″),

132.1 (C, C-2), 129.3 (CH, C-2″), 124.3 (CH, C-3″), 109.8

(C, C-3), 108.1 (CH, C-5), 60.2 (CH₂, C-1′), 30.3 (CH₂, C-

2′), 26.3 (CH, C-3′), 20.6 (CH₃, C-3′), 22.3 (CH₃, C-3′),

21.0 (CH₃, –ph, C-4″), 12.1 (CH₃, C-2′); HRMS m/z (pos):

314.3887 C₁₈H₂₂N₂O₃(calcd. 314.39); Anal. calcd.

C₁₈H₂₂N₂O₃found 314.27.

¹H NMR (CDCl₃, 400 MHz): δ = 0.90 (6H, d, H-2′), 2.08

(1H, m, H-2′), 2.47 (3H, s, H-3″′), 2.53 (3H, s, H-2), 3.83

(6H, s, OCH₃H-3″,H-4″), 4.03 (2H, d, H-1″), 6.13 (1H, s,

H-5), 6.93 (2H, m, H-2″,H-5″) 7.24 (1H, H-6″) ppm; ¹³C

NMR (CDCl₃,100 MHz) δ (ppm): 198.4 (C, COPyrrol),

161.0 (C, C-4″) 136.8 (C, C-3″), 131.6 (C, C-1″), 131.2

(C, C-2), 122.6 (CH, C-2″), 129.0 (CH, C-6″), 119.5

(CH, C-5″), 112.3 (C, C-4), 109.5 (C, C-3), 108.4 (CH,

C-5), 59.6 (CH₂, C-1′), 57.9 (C, C-3″, C-4″), 29.8 (CH₃, C-

2′), 11.2 (CH₃, C-2′); HRMS m/z (pos): 315.4000

C₁₉H₂₅NO₃(calcd. 315.40); Anal. calcd. C₁₉H₂₅NO₃found

315.40.

Compound 12

Compound 15

1-(1-Isopentyl-2-methyl-4-phenyl-1H-pyrrol-3-yl)-1-etha-

none: (yellowish brown solid) mp 118–121 °C; IR (KBr)

1-[4-(4-bromophenyl)-2-methyl-1-(3-methylbutyl)-1H-pyr-

1

ν_max: 3029, 1648, 1531, 1278, 1148, 1039 cm⁻¹; H NMR

rol-3-yl]ethanone: (yellowish brown solid) mp106–109 °C;

(400 MHz, CDCl₃): δ = 0.95 (6H, d, H-3′), 1.62 (1H, m, H-

3′), 1.73 (2H, q, H-2′), 2.49 (3H, s, H-3″′), 2.52 (3H, s, H-

2), 4.18 (2H, t, H-1″), 6.42 (1H, s, H-5), 7.43–7.56 (5H, m,

H-2″-H-6″) ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm):

199.3 (C, COPyrrol), 143.7 (C, C-6″), 167.1 (C, C-1″),

135.9 (C, C-2), 130.1 (CH, C-2″), 129.0 (CH, C-3″), 126.3

(CH, C-4″), 126.1 (CH, C-5″) 123.2 (C, C-4), 107.0 (C, C-

3), 104.2 (CH, C-5), 58.8 (CH₂, C-1′), 43.0 (CH₂, C-2′),

30.2 (CH, C-3′), 25.1 (CH₃, C-3′), 11.9 (CH₃, C-2′); HRMS

m/z (pos): 269.3788 C₁₈H₂₃NO (calcd. 269.38); Anal.

calcd. C₁₈H₂₃NO found 269.38.

IR (KBr) ν_max: 3039, 2922, 2815, 1699, 1528, 1120 cm⁻¹

;

¹H NMR (400 MHz, CDCl₃): δ = 0.92 (6H, d, H-2′), 1.61

(1H, m, H-2′), 1.70 (2H, q, H-2′), 2.51 (3H, s, H-3″′), 2.61

(3H, s, H-2), 4.11(2H, d, H-1″), 6.41 (1H, s, H-5),

7.51–7.61 (5H, m, H-2″-H-6″) ppm; ¹³C NMR (CDCl₃, 100

MHz) δ (ppm): 201.2 (C, COPyrrol), 139.1(C, C-2), 138.7

(CH, C-2″), 130.3 (CH, C-3″), 126.3 (CH, C-4″), 123.2

(CH, C-5″) 121.6 (C, C-4), 110.8 (C, C-3), 109.8 (CH, C-5),

60.8 (CH₂, C-1′), 30.1 (C, C-2′), 20.6 (CH₃, C-2′), 12.1

(CH₃, C-2′); HRMS m/z (pos): 348.2705 C₁₈H₂₂BrNO

(calcd. 348.27); Anal. calcd. C₁₈H₂₂BrNO found 348.29.

Med Chem Res

Compound 16

IR (KBr) ν_max: 3045, 3021, 2924, 2824, 1699, 1645, 1535,

1

1408, 1122 cm⁻¹; H NMR (400 MHz, CDCl₃): δ = 0.92

1-(1-tert-butyl-2-methyl-4-phenyl-1H-pyrrol-3-yl)

etha-

(6H, d, H-2′), 1.31 (3H, t, H-2′), 2.10 (1H, m, H-1′) 2.39

(3H, s, H-3″′), 3.83 (3H, s, H-2), 4.08 (2H, d, H-1″), 6.28

(1H, s, H-5), 7.39–7.46 (4H, m, H-2″-H-3″, H-5″-H-6″)

ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm): 164.4 (C,

COPyrrol), 159.6 (C, C-4″), 137.1 (C, C-1″), 132.5 (C, C-

2), 131.7 (CH, C-3″), 129.0 (CH, C-2″), 124.2 (CH, C-6″),

126.9 (CH, C-5″) 115.9 (C, C-4), 109.9 (C, C-3), 108.3

(CH, C-5), 61.3 (CH₂, OPY), 59.5 (CH₂, C-1′), 55.2 (CH₃,

OCH₃), 30.1 (CH₃, OCH₂, C-2), 20.6 (CH, C-2′), 15.3

(CH₃, C-2′), 12.1 (CH₃, C-2′); HRMS m/z (pos): 315.4000

C₁₉H₂₅NO₃(calcd. 315.40); Anal. calcd. C₁₉H₂₅NO₃found

315.40.

none: (brown solid Table) mp 115–118 °C; IR (KBr) ν_max

:

1

3025, 1647, 1524, 1278, 1150, 1036 cm⁻¹; H NMR (400

MHz, CDCl₃): δ = 1.6 (9H, s, H-1′), 2.47 (3H, s, H-2), 2.53

(3H, s, H-3″′), 7.43–7.53 (5H,m, H-2″-H-6″) ppm; ¹³C

NMR (CDCl₃,100 MHz) δ (ppm): 197.8 (C, COPyrrol),

139.4 (C, C-6″), 148.1 (C, C-1″), 136.5 (C, C-2), 129.4

(CH, C-2″), 126.0 (CH, C-3″), 124.2 (CH, C-4″), 125.9

(CH, C-5″), 122.9 (C,C-4), 109.9 (C, C-3), 108.3 (CH, C-

5), 69.4 (CH₂, C-1′), 32.2 (C, C-2′), 29.3 (CH₃, C-2′), 12.4

(CH₃, C-2′); HRMS m/z (pos): 255.1622 C₁₇H₂₁NO (calcd.

255.162); Anal. calcd. C₁₇H₂₁NO found 255.15.

Compound 17

Compound 20

1-[2-methyl-1-(2-methylbutyl)-4-phenyl-1H-pyrrol-3-yl]

ethanone: (yellowish brown solid) mp 109–111 °C; IR

Ethyl 4-(4-ﬂuorophenyl)-2-methyl-1-(2-methylpropyl)-1H-

pyrrole-3-carboxylate: (light brown solid) mp 94–97 °C; IR

1

(KBr) ν_max: 3019, 1649, 1536, 1274, 1147, 1037 cm⁻¹; H

NMR (400 MHz, CDCl₃): δ = 0.91 (3H, t, H-4′), 0.96 (3H,

d, H-2′), 1.55 (2H, m, H-3′), 1.70 (1H, m, H-2′), 2.49 (3H, s,

H-3″′), 2.50 (3H, s, H-2), 3.94 (2H, d, H-1″), 6.32 (1H, s, H-

5), 7.40–7.54 (5H, m, H-2″-H-6″) ppm; ¹³C NMR (CDCl₃,

100 MHz) δ (ppm): 199.9 (C, COPyrrol), 139.7 (C, C-6″),

135.1 (C, C-2), 130.1 (CH, C-2″), 129.0 (CH, C-3″), 126.3

(CH, C-4″), 126.1(CH, C-5″) 123.2 (C, C-4), 107.0 (C, C-

3), 104.2 (CH, C-5), 59.6 (CH₂, C-1′), 41.1 (C, C-2′), 30.2

(CH₃, C-2′), 11.9 (CH₃, C-2′); HRMS m/z (pos): 269.3890

C₁₈H₂₃NO (calcd. 269.389); Anal. calcd. C₁₈H₂₃NO found

269.384.

1

(KBr) ν_max: 3031, 2924, 2824, 1699, 1535, 1122 cm⁻¹; H

NMR (400 MHz, CDCl₃): δ = 0.95 (6H, d, H-2′), 1.26 (3H,

t, H-2′), 2.12 (1H, m, H-1′) 2.44 (3H, s, H-3″′), 4.12 (2H, d,

H-1″), 6.63 (1H, s, H-5), 7.30–7.39 (4H, m, H-2″-H-3″,

H-5″-H-6″) ppm; ¹³C NMR (CDCl₃,100 MHz) δ (ppm):

160.7 (C, COPyrrol), 148.8 (C, C-4″), 137.1 (C, C-1″),

133.5 (C, C-2), 131.7 (CH, C-3″), 130.3 (CH, C-2″), 124.2

(CH, C-6″), 126.4 (CH, C-5″), 115.2 (C, C-4), 111.4 (C, C-

3), 108.3 (CH, C-5), 65.2 (CH₂,OPY), 64.5 (CH₂, C-1′),

29.96 (CH₃, OCH₂, C-2), 22.8 (CH,C-2′), 14.5 (CH₃, C-2′)

10.92 (CH₃, C-2′); HRMS m/z (pos): 303.3666

C₁₈H₂₂FNO₂(calcd. 303.37); Anal. calcd. C₁₈H₂₂FNO₂

found 303.29.

Compound 18

Ethyl 2-methyl-1-(2-methylpropyl)-4-phenyl-1H-pyrrole-3-

carboxylate: (light brown solid) mp 97–100 °C; IR (KBr)

1

ν_max: 3030, 2924, 2824, 1693, 1529, 1122 cm⁻¹; H NMR

Compound 21

(400 MHz, CDCl₃): δ = 0.85 (6H, d, H-2′), 1.29 (3H, t, H-

2), 2.05 (1H, m, H-2′), 2.46 (3H, s, H-3″′), 4.23 (2H, d, H-

1″), 6.46 (1H, s, H-5), 7.49–7.56 (5H, m, H-2″-H-6″) ppm;

¹³C NMR (CDCl₃, 100 MHz) δ (ppm): 156.3 (C, C-2′),

139.8 (C, C-6″), 137.6 (C, C-1″), 132.3 (C, C-2), 130.2

(CH, C-2″), 129.1 (CH, C-3″), 126.6 (CH, C-4″), 124.9

(CH, C-5″) 112.4 (C, C-4), 109.9 (C, C-3), 108.7 (CH, C-5),

61.7 (CH₃, C-2), 60.2 (CH₂, C-1′), 35.2 (CH₃, OCH₂, C-2),

30.0 (CH, C-2′), 20.8(CH₃, C-2′), 11.1 (CH₃, C-2′); HRMS

m/z (pos): 285.3602 C₁₈H₂₃NO₂(calcd. 285.36); Anal.

calcd. C₁₈H₂₃NO₂found 285.20.

Ethyl4-(4-bromophenyl)-2-methyl-1-(2-methylpropyl)-1H-

pyrrole-3- carboxylate: (dark brown solid), mp 98–101 °C;

IR (KBr) ν_max: 3038, 2920, 2814, 1701, 1531, 1124 cm⁻¹

;

¹H NMR (400 MHz, CDCl₃): δ = 0.94 (6H, d, H-2′), 1.26

(3H, t, H-2′), 2.02 (1H, m H-1′), 2.45 (3H, s, H-3″′), 4.00

(2H, d, H-1″), 6.27 (1H, s, H-5), 7.50–7.69 (4H, m, H-2″-H-

3″,H-5″-H-6″) ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm):

165.8 (C, COPyrrol), 139.4 (C, C-4″), 135.1 (C, C-1″),

133.5 (C, C-2), 130.1 (CH, C-3″), 130.3 (CH, C-2″), 124.2

(CH, C-6″), 121.1 (CH, C-5″) 115.2 (C, C-4), 111.4 (C, C-

3), 108.3 (CH, C-5), 61.2 (CH₂, OPY), 59.8 (CH₂, C-1′),

30.4 (CH₃, OCH₂, C-2), 20.2 (CH, C-2′), 14.7 (CH₃, C-2′)

12.1 (CH₃, C-2′); HRMS m/z (pos): 364.2800

C₁₈H₂₂BrNO₂(calcd. 364.25); Anal. calcd. C₁₈H₂₂BrNO₂

found 364.25.

Compound 19

Ethyl 4-(4-methoxyphenyl)-2-methyl-1-(2-methylpropyl)-1H-

pyrrole-3-carboxylate: (light brown solid) mp 94–97 °C;

Med Chem Res

Compound 22

Compound 25

Ethyl2-methyl-1-(2-methylpropyl)-4-(4-nitrophenyl)-1H-

pyrrole-3-carboxylate: (light brown solid), mp 98–101 °C;

IR (KBr) ν_max: 3030, 2928, 2854, 1695, 1530, 1271, 1150,

1127 cm⁻¹; ¹H NMR (400 MHz, CDCl₃): δ = 0.95 (6H, d,

H-2′), 1.32 (3H, t, H-2), 2.05 (1H, m, H-1′), 2.44 (3H, s, H-

3″′), 4.17 (2H, t, H-1″), 4.36 (2H, q, H-2), 6.37 (1H, s, H-5),

7.80–8.31 (4H, m, H-2″-H-6″) ppm; ¹³C NMR (CDCl₃, 100

MHz) δ (ppm): 168.8 (C, COPyrrol), 159.6 (C, C-4″), 137.1

(C, C-1″), 133.5 (C, C-2), 131.7 (CH, C-3″), 130.3 (CH, C-

2″), 124.2 (CH, C-6″), 126.4 (CH, C-5″) 115.2 (C, C-4),

111.4 (C, C-3), 108.3 (CH, C-5), 61.2 (CH₂, OPY), 59.5

(CH₂, C-1′), 30.1 (CH₃, OCH₂, C-2), 20.6 (CH, C-2′), 14.7

(CH₃, C-2′) 12.1 (CH₃, C-2′); HRMS m/z (pos): 330.3666

C₁₈H₂₂N₂O₄(calcd. 330.37); Anal. calcd. C₁₈H₂₂N₂O₄-

found 330.35.

Ethyl 2-methyl-1-(3-methylbutyl)-4-(4-nitrophenyl)-1H-pyr-

role-3-carboxylate: (yellowish brown solid) mp 96–99 °C;

IR (KBr) ν_max: 3031, 2928, 2844, 1690, 1533,1277, 1149,

1127 cm⁻¹; ¹H NMR (400 MHz, CDCl₃): δ = 0.91 (6H, d,

H-2′), 1.61 (1H, m, H-3′), 1.73 (2H, q, H-2′), 2.49 (3H, s,

H-3″′), 4.17 (2H, t, H-1″), 4.30 (2H, q, H-2), 6.32 (1H, s, H-

5), 7.83–8.25 (4H, m, H-2″-H-3″,H-5″-H-6″) ppm; ¹³C

NMR (CDCl₃, 100 MHz) δ (ppm): 165.1 (C, COPyrrol),

149.8 (C, C-4″), 135.8 (C, C-1″), 135.3 (C, C-2), 131.7

(CH, C-3″), 130.3 (CH, C-2″), 124.2 (CH, C-6″), 126.1

(CH, C-5″) 115.6 (C, C-4), 110.1 (C, C-3), 108.4 (CH, C-5),

60.9 (CH₂, OPY), 49.6 (CH₂, C-1′), 30.3 (CH₃, OCH₂, C-

2), 26.1 (CH, C-2′), 20.2 (CH, C-3′), 14.6 (CH₃, C-3′) 12.1

(CH₃, C-3′); HRMS m/z (pos): 344.4111 C₁₉H₂₄N₂O₄

(calcd. 344.41); Anal. calcd. C₁₉H₂₄N₂O₄found 334.21.

Compound 26

Compound 23

3-acetyl-2-methyl-4-phenyl-1H-pyrrole-1-carbaldehyde:

Ethyl 2-methyl-1-(3-methylbutyl)-4-phenyl-1H-pyrrole-3-

(light brown solid) mp113–116 °C; IR (KBr) ν_max: 3056,

carboxylate: (light brown solid) mp 95–98 °C; IR (KBr)

2923, 1664, 1650, 1537, 1390, 1295 cm⁻^{1 1}H NMR

;

1

ν_max: 3029, 2931, 2828, 1683, 1524, 1119 cm⁻¹; H NMR

(CDCl₃, 400 MHz): δ = 2.14 (3H, s, H-2), 2.50 (3H, s, H-

4″), 6.90 (1H, s, H-5), 7.43–7.58 (5H, m, H-2″-H-6″), 8.25

(1H, s, H-1′) ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm):

198.6 (C, COPyrrol), 161.3 (C, CO, C-1′), 138.4 (C, C-6″),

135.2 (C, C-1″), 133.4 (C, C-2), 129.4 (CH, C-2″), 126.8

(CH, C-3″), 125.1 (C, C-4″), 126.1 (CH, C-5″) 121.2 (C, C-

4), 117.8 (C, C-3), 108.2 (CH, C-5), 29.3 (CH₃, C-2) 10.6

(CH₃, C-4″) HRMS m/z (pos): 227.2555 C₁₄H₁₃NO₂(calcd.

227.25); Anal. calcd. C₁₄H₁₃NO₂found 227.14.

(400 MHz, CDCl₃): δ = 0.86 (6H, d, H-2′), 1.31 (3H, t, H-

2), 1.62 (1H, m, H-3′), 2.40 (3H, s, H-3″′), 3.86 (2H, t, H-

1′), 4.37 (2H, q, H-2) 6.38 (1H, s, H-5), 7.44–7.51 (5H, m,

H-2″-H-6″) ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm):

162.3 (C, COPyrrol), 147.2 (CH, C-4″), 134.7 (C, C-1″),

136.7 (C, C-2), 131.7 (CH, C-3″), 130.3 (CH, C-2″), 124.2

(CH, C-6″), 125.4 (CH, C-5″) 121.3 (C, C-4), 111.8 (C, C-

3), 109.5 (CH, C-5), 61.2 (CH₂, OPY), 58.3 (CH₂, C-1′),

27.8 (CH₃, OCH₂, C-2), 20.1 (CH, C-2′), 13.9 (CH₃, C-3′)

11.9 (CH₃, C-3′); HRMS m/z (pos): 299.4000 C₁₉H₂₅NO₂

(calcd. 299.40); Anal. calcd. C₁₉H₂₅NO₂found 299.46.

Compound 27

Ethyl

ylate: (yellowish brown solid) mp 107–110 °C; IR (KBr)

ν_max: 3046, 3074, 1648, 1551, 1439 cm^{−1 1}H NMR

1-formyl-2-methyl-4-phenyl-1H-pyrrole-3-carbox-

Compound 24

;

Ethyl4-(4-ﬂuorophenyl)-2-methyl-1-(3-methylbutyl)-1H-

pyrrole-3-carboxylate: (light brown solid) mp 91–94 °C; IR

(CDCl₃, 400 MHz): δ = 1.29 (3H, t, H-2), 2.14 (3H, s, H-3″

′), 4.31 (2H, q, H-2), 7.05 (1H, s, H-5), 7.41–7.48 (5H, m,

H-2″-H-6″), 8.25 (1H, s, H-1′) ppm; ¹³C NMR (CDCl₃,100

MHz) δ (ppm): 197.2 (C, COPyrrol), 168.2 (C, CO, C-1′),

140.1 (C, C-1″), 130.6 (C, C-2), 129.5 (CH, C-2″), 118.9

(C, C-4), 114.2 (C, C-3), 107.1 (CH, C-5), 30.2 (CH₃, C-2),

25.5 (CH₃, C-3″′), 11.2 (CH₂, C-2); HRMS: m/z (pos):

257.2602 C₁₅H₁₅NO₃(calcd. 257.26); Anal. calcd.

C₁₅H₁₅NO₃found 257.30.

1

(KBr) ν_max: 3030, 2928, 2844, 1691, 1533, 1127 cm⁻¹; H

NMR (400 MHz, CDCl₃): δ = 0.95 (6H, d, H-2′), 1.29 (3H,

t, H-2), 1.62 (1H, m, H-3′), 1.80 (2H, q, H-2′), 2.40 (3H, s,

H-3″′), 3.80 (2H, t, H-1″), 4.18 (2H, q, H-2), 6.38 (1H, s, H-

5), 7.30–7.39 (4H, m, H-2″-H-3″,H-5″-H-6″) ppm; ¹³C

NMR (CDCl₃,100 MHz) δ (ppm): 163.5 (C, COPyrrol),

158.5 (C, C-4″), 140.8 (C, C-1″), 133.5 (C, C-2), 131.7

(CH, C-3″), 130.3 (CH, C-2″), 124.2 (CH, C-6″), 126.1

(CH, C-5″) 115.6 (C, C-4), 110.4 (C, C-3), 108.4 (CH, C-5),

64.9 (CH₂, OPY), 57.3 (CH₂, C-1′), 27.9 (CH, C-2′), 20.0

(CH, C-3′), 13.9 (CH₃, C-3′) 11.9 (CH₃, C-3′); HRMS m/z

(pos): 317.4000 C₁₉H₂₄FNO₂(calcd. 317.40); Anal. calcd.

C₁₉H₂₄FNO₂found 317.29.

Compound 28

1-(1-acetyl-2-methyl-4-phenyl-1H-pyrrol-3-yl) ethanone:

(yellowish brown solid) mp 112–115 °C; IR (KBr) ν_max

:

3042, 3080, 1659, 1554, 1432 cm⁻¹; ¹H NMR (CDCl₃, 400

Med Chem Res

Table 2 In vitro α-amylase and

α-glucosidase activity of novel

pyrrole hybrids

Compound no.

R

R₁

R₂

IC₅₀

α-Amylase

µmol/mL

α-Glucosidase

µmol/mL

1

–H

–CH(CH₃)₂

–CH₃

1.658 0.41

1.91 0.90

0.430 0.82

0.965 0.14

0.981 0.63

1.725 2.44

0.365 0.58

1.765 0.26

2.872 0.299

>3.293

1.781 0.33

3.132 0.07

0.861 0.35

1.447 0.37

3.118 0.28

2.380 0.10

0.804 0.18

2.572 0.07

2.872 0.29

>3.32

2

–H

–(CH₂)₃–CH₃

3

–H

–CH₂–CH(CH₃)₂

–(CH₂)₂–CH(CH₃)₂

–(CH₂₎₂–CH(CH₃)₂

–C(CH₃)₃

4

4-CH₃

4-OCH₃

4-Cl

5

6

7

4-F

8

4-Br

9

2-Br

10

11

12

13

14

15

16

17

4-NO₂

3,4-diOCH₃

–H

1.014 0.25

0.408 0.11

1.023 0.317

>3.180

2.758 0.12

0.779 0.259

1.41 0.28

>3.180

4-CH₃

4-NO₂

–-Br

1.837 0.20

3.916

2.813 0.05

>3.916

–H

-H

–CH₂–CH(CH₃)

1.521 0.55

1.707 0.11

CH₂CH₃

18

–H

–CH₂–CH(CH₃)₂

–(CH₂₎₂–CH(CH₃)₂

–CHO

–OC₂H₅

–CH₃

0.456 0.42

1.014 0.66

0.396 0.131

1.729 0.16

2.996 0.30

1.068 0.16

0.378 0.22

2.903

0.840 0.17

2.948 0.06

1.285 0.16

>2.745

19

4-OCH₃

4-F

20

21

4-Br

4-NO₂

–H

22

>3.026

23

0.901 0.23

1.354 0.09

>2.903

24

4-F

25

4-NO₂

–H

26

4.13 0.08

3.459 0.27

4.144

4.40 0.44

3.80 0.15

4.144

27

–H

–CHO

–OC₂H₅

–CH₃

28

–H

–C=O(CH₃)

Standard

Acarbose

0.154 0.03

0.3 0.046

MHz): δ = 2.17 (3H, s, H-2), 2.49 (3H, s, H-3″′), 2.68 (3H,

s, H-1′), 6.98 (1H, s, H-5), 7.41–7.50 (5H, m, H-2″-H-6″)

ppm; ¹³C NMR (CDCl₃, 100 MHz) δ (ppm): 198.6 (C,

COPyrrol), 161.3 (C, CO, C-1′), 138.4 (C, C-6″), 135.2

(C, C-1″), 133.4 (C, C-2), 129.4 (CH, C-2″), 126.8 (CH, C-

3″), 125.1 (C, C-4″), 126.1 (CH, C-5″) 121.2 (C, C-4),

117.8 (C, C-3), 108.2 (CH, C-5), 59.8 (CH₃, C-1′), 29.3

(CH₃, C-2), 10.6 (CH₃, C-4″) HRMS: m/z (pos): 241.2788

C₁₅H₁₅NO₂(calcd. 241.28); Anal. calcd. C₁₅H₁₅NO₂found

241.36.

and MS). IR (KBr) spectrum of synthesized compounds

showed C=O absorption band for ketone and ester group at

1700–1675 cm^-1and 1740–1695 cm⁻¹respectively and

C–O stretching vibrations for ester group at 1300–1000

cm⁻¹. The ¹HNMR spectrum showed singlet for CH₃–C=O

group at 2.5–3.0 ppm. The ¹³C NMR spectrum showed

C=O of methyl ketone and ester at 196 and 164.9 ppm,

respectively.

The IC₅₀values of all synthesized pyrrole derivatives are

as shown in (Table 2). The pyrrole derivatives showed a

good range of anti-diabetic activity for both α-amylase and

α-glucosidase inhibition assays. As expected, aliphatic

amines resembled to branched amino acids (Table 2, Entry

3, 7, 12, and 18) showed good IC₅₀values. To conﬁrm the

importance of derivatives of branched amino acid, pyrroles

containing other amines such as n-butylamine[–NH

Results and discussion

The structures of all the synthesized compounds were

conﬁrmed from spectral data (IR, ¹H NMR,¹³C NMR,

Med Chem Res

Fig. 3 It shows the alignment

between target (Q6P7A9) and

template sequence (3L4V)

obtained from PRIME. The

asterisk showed the identity of

amino acids present in two

protein sequences

(CH₂)₃CH₃],

t-butylamine[–NHC(CH₃)₃],

N-Formyl

Loop reﬁnement

[–NHCHO], and N-acetyl [–NHCOCH₃] pyrroles were

synthesized and evaluated for enzyme assays. These

molecules (Table 2, Entry 2, 16, 26–28) did not show any

enzyme inhibitory activity. Many pyrrole derivatives con-

taining different substituents on the aromatic ring at 4-

position of pyrrole were synthesized and evaluated. It was

observed that the aromatic ring with no functional group

attached, and aromatic ring with small functional groups

like –CH₃, –F (Table 2, Entry 4, 7, and 13) had well to

excellent activity. The larger groups such as –Br and –NO₂

(Table 2, Entry 8–10, 14–15) showed very low or no anti-

diabetic activity. Amongst the synthesized molecules, 7 and

12 were the most active inhibitors for α-amylase and α-

glucosidase. Ester group attached at 3-position of pyrrole

ring (Table 2, Entry 18) instead of ketone, slightly

decreased the activity. This position can be utilized further

for lead optimization. Aliphatic amines resembling bran-

ched amino acids are important for the anti-diabetic activity

and it was considered as part of pyrrole pharmacophore for

synthesis of new chemical entities.

This above homology model was imported to the maestro

panel of the Schrodinger software. Where it was examined

through the Ramachandran plot and the loops with outlier

residues were reﬁned using the “reﬁne loops” tool with the

“extended medium-serial-loop sampling” procedure of the

prime module of Schrodinger software package.

Evaluation of model

Geometric validation of the modeled 3D structure of

Q6P7A9 was performed using PROCHECK by calculating

the Ramachandran plot (Fig. 4). Based on the theory ori-

ginally proposed by Ramachandran (1963) the plot repre-

sents the distribution of the phi and psi angles for the amino

acid residues. For the present study, the percentage of phi

and psi angles that occur in the most favored region was 95,

3% in the allowed region, 2% in the generously allowed

region, whereas this percentage was 0.0% for the residues

located in the disallowed regions. These results revealed

that the majority of the amino acids are in a phi–psi dis-

tribution, and the model is reliable and of good quality

which is parallel to the report proposed by Singh et al.

(2007). So, the quality of Ramachandran plots is acceptable

and the stereo chemical quality of the model was found to

be satisfactory.

Homology modeling

Sequence alignment between target and template

Homology modeling produced high quality structural

models when the target and template are closely related.

Protein structure modeling was undertaken in this present

work. The main criteria in homology modeling were

template selection and sequence alignment between the

target and the template. In this respect, in the present

study, the BLAST searching result showed that, the

sequence identity between the target Q6P7A9 and the

template human 3L4V is 59% which allowed for rather

straight forward sequence alignment (Fig. 3) and model

was generated.

Active site analysis

A required number of active sites were generated after

performing sitemap. The best ranked sitemap was subjected

for grid generation in molecular docking study.

Molecular docking

The docking studies were carried out to explore the inter-

action mechanism between inhibitors and the receptor. The

score function of Glide, gives highest binding afﬁnity

Med Chem Res

Fig. 4 Ramachandran plot of

Q6P7A9 protein obtained from

PROCHECK

prediction as well as molecule ranking. The all molecule

along with their Glide docking score has been listed in

Table 1.

deciphers that the oxygen of carboxylic group showed the H

bond interaction with Hip 305 (Fig. 5a, 5b). The pyrrole

ring of the molecule 3 occupied the cavity made by the

residues namely Glu63, Trp58, Trp59, Leu165, and Val 163

while the phenyl ring itself occupied the cavity formed by

the residues Leu162, Hie101, Glu233, Ala198, Ash197, and

Arg195 (Fig. 5b).

Molecular docking on α-amylase (PDB ID-1OSE)

To validate the docking protocol, co-crystallized ligand was

re-docked into the active site of α-amylase with a root mean

squared deviation of 0.321 A°. All molecules were docked

into the active site of α-amylase, and they have shown a

similar binding pattern as that of the co-crystallized ligand.

The binding site analysis of most docked molecule 3 clearly

Molecular docking on α-glucosidase (homology model)

The all molecules showed best interaction with the active

sites of Q6P7A9 (Lys 348) which was predicted by sitemap

Med Chem Res

Fig. 6 a 3D binding pose view of molecule 3 (G-gray colored surface

area of active site of α-glucosidase). b 2D binding pose view of

molecule 3

Fig. 5 a 3D binding pose view of molecule 3 (G-gray colored sur-

face area of active site of α-amylase). b 2D binding pose view of

molecule 3

percentage human oral absorption for compounds ranged

from 85.8 to 100%.

(Fig. 6a). The binding site analysis of most docked mole-

cule 3 clearly deciphers that the oxygen of carboxylic group

showed the H bond interaction with Lys 348 (Fig. 6a, b).

The pyrrole ring of the molecule 3 occupied the cavity made

by the residues namely Glu 857, Leu729, Ser855, Gly856,

Trp823, and Trp766 while the phenyl ring itself occupied

the cavity formed by the residues Glh730, Val740, ser739,

Gln743, and Tyr766. (Fig. 6b).

All these pharmacokinetic parameters within the accep-

table range deﬁned for human use see in Table 1, thereby

indicating their potential as drug-like molecule.

We were studied 28 compounds from that most active

and least active molecules are mentioned in Table 1.

Conclusion

The present work focused on design, synthesis and

screening α-amylase and α-glucosidase inhibitory activity

of novel pyrrole derivatives in a quest to ﬁnd low cost,

potent anti-diabetic molecule with no or minimum side

effects. A library of 28 pyrrole derivatives has been syn-

thesized using molecular hybridization concept utilizing our

own novel, simple multicomponent direct route for pyrrole

synthesis. Among all molecules evaluated for α-amylase

and α-glucosidase inhibitory activity four pyrrole deriva-

tives (3, 7, 12, 18) gave promising results (Table 3).

Thus, homology protein model of α-glucosidase and

docking studies as well as QikProp pharmacokinetic ana-

lysis presented in this paper is hoped to be a primer towards

the development of various novel α-amylase and α-

QikProp pharmacokinetic prediction

QikProp pharmacokinetic predicted parameters give infor-

mation about molecular weight, partition coefﬁcient

(QPlogPo/w), stars, % oral absorption values and Lipinski’s

properties (Rule of Five) and apparent Caco-2 cell perme-

ability (QPPCaco) in nm/sec. For the 28 molecules, the

partition coefﬁcient (QPlogPo/w) for the estimation of

absorption and distribution of drug within the body ranged

between –2.0 and 6.5.

Caco-2 cell permeability (QPPCaco), a key factor gov-

erning drug metabolism and its access to biological mem-

brane, ranged from 128.256 to 1470.581. overall, the

Med Chem Res

Table 3 Docking score of α-amylase and α-glucosidase inhibitors

Compliance with ethical standards

Compound no.

Docking score

Conﬂict of interest The authors declare that they have no competing

interests

α-Amylase

α-Glucosidase

1

−4.321

−5.639

−7.995

−6.396

−5.369

−7.52

−3.254

−5.236

−8.236

−6.36

2

3

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Article Doi

Design, synthesis and molecular docking study of novel pyrrole-based α-amylase and α-glucosidase inhibitors

DOI: 10.1007/s00044-017-1965-z

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Full text of DOI:10.1007/s00044-017-1965-z

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