Journal of Computer-Aided Molecular Design
could save researchers a lot of time [19]. It was a power-
prior to experimental analysis, and allowed the transforma-
tion of existing compounds. The Ludi algorithm worked in
three steps. Firstly, it calculated interaction sites, which were
discrete positions in space that was suitable to form hydro-
gen bonds or fll hydrophobic pockets. Then, the molecu-
lar fragments were ftted onto the interaction sites. Finally,
some or all of the ftted fragments was connected to a single
molecule.
to evaluate the toxicity of the compounds in the Toxicity
Prediction (TOPKAT) module. Promising compounds thus
were obtained for the further studies.
Flexible docking
Molecular docking was one of the most frequently used
methods in drug design, which was used to investigate inter-
action patterns of target protein with its inhibitors [26]. In
the process of docking, the conformations of the protein side
chain and ligand molecular were fexible.
In our study, De novo design method [20] by Ludi algo-
rithm was used to design novel inhibitors. Firstly, De novo
library generation protocol was used to generate fragments
library for De novo design. Secondly, De novo receptor
protocol in Discovery Studio v3.5 was used to defne the
binding site of a receptor. Scafold A and scafold B were
derived from computational Fragment-based drug design
in allosteric sites. Thirdly, the De novo link protocol used
“Ludi algorithm” to add linkers between the defned scaf-
folds A and scafold B in the binding site of a receptor. The
placed linker parts were scored using Ludi energy estima-
tion, and then the fnal scafolds C library was established.
Accordingly, each scafold C was made up of scafold A
and scafold B and linkers, respectively. Fourthly, the pro-
tocol of De novo evolution could develop whole molecule
in the binding site environment of the receptor based on the
scafold C. The Ludi algorithm was used to add appropriate
fragments to scafold C, and then produced a collection of
whole molecules with higher scores. The evolution mode
was set to full evolution, which allowed the scafold C to link
up to a maximum of three fragments. Finally, 24 top-ranked
molecules were selected for the following ADMET analysis.
During the process of core docking, the 1st step, protein
was prepared by the clean protein protocol in DS v3.5. The
2nd step was to calculate protein conformation using Chi-
Flex [27] (CHARMm) by changing the side chain conforma-
tion. The 3rd step, the preparation ligand protocol was used
to prepare ligand for pharmacophore generation, including
removing duplicates, enumerating isomers tautomers, gen-
erating 3D conformation, and generating possible states by
ionization at target pH 7.0 2.0. The 4th step was to defne
the binding site. There were two ways to defne the binding
pocket: the frst was to defne binding site from key residue
in the structure of the receptor; the second was to calculate a
binding site from a selected ligand. In our study, the bind site
was defned applying the second method. In the docking pro-
cess, the residues Arg111, Phe113 Glu250, Leu254, Glu257,
Pro491, and Glu495 were used to generate active site for
SHP2 and Arg109, Glu247, Ser250, Gln254, Gln485 and
Gln489 for SHP1. The 5th step was to optimize the selected
protein side chains using the ChiRotor [27] in the presence
of a rigid ligand. In 6th step, ligands were fexibly docked
to the binding sphere of diverse receptor conformations by
the LibDock program. The last step was to optimize the fnal
ligand using CDOCKER program [28]. Prior to the docking
analysis, the docking model was validated by the re-dock
method. When all steps were fnished, the compounds were
docked into the receptor pockets.
Lipinski’s flter and ADMET analysis
During virtual screening in early drug discovery, the
ADMET descriptors of DS v3.5 could be used for estimat-
ing crucial physicochemical and biological properties for
large numbers of candidate drug compounds. The ADMET
(absorption, distribution, metabolism, excretion, and tox-
icity) properties of each compounds were calculated to
assess the good pharmacokinetics of a drug in the human
body using the ‘ADMET Descriptors’ calculation of DS
v3.5. Some important ADMET descriptors were calcu-
lated, including human intestinal absorption (HIA) [21],
2D6 inhibition hepatotoxicity [24]. Hence, attrition could
be reduced in drug discovery and development by fltering
the ADMET characteristics of the gained compounds. The
property analyses for carcinogenicity, aerobic biodegrada-
icity, and ocular and skin irritancy [25] were considered
Chemistry
All the reagents were purchased from commercial suppliers
and were used without further purifcation unless otherwise
indicated. All the reactions were monitored by thin-layer
chromatography (TLC) on silica gel precoated F254 Merck
plates, and spots were examined under UV light (254 nm).
All column chromatography was performed using 200–300
mesh silica gel. 1H-NMR and 13C-NMR spectra were taken
on a Bruker Avance 300-MHz NMR Spectrometer at 300 K
with TMS as the internal standard, and CDCl3 and DMSO-
d6 were used as solvents, the values of the chemical shifts
(δ) were expressed in parts per million (ppm), and coupling
constants (J) were expressed in hertz (Hz). MS spectra
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