Tryptophan and thiosemicarbazide derivatives: Design, synthesis, and biological evaluation as potential β-D-galactosidase and β-D-glucosidase inhibitors

Article abstract of DOI:10.1007/s00044-014-1314-4

Glycosidases, including β-D-galactosidase and β-D-glucosidase, are involved in a range of metabolic disorders, such as cancer, viral or bacterial infections, and diabetes. Previously, we scanned the pharmacophoric space of these enzymes and had a self-consistent and predictive quantitative structure-activity relationship that was used to identify several β-D-galactosidase and β-D-glucosidase inhibitors via in silico search of structural databases. Guided by the preceding modeling efforts, synthesis of a series of tryptophan and thiosemicarbazide derivatives as β-D-galactosidase and β-D-glucosidase inhibitors that match the generated pharmacophores followed by in vitro bioassay was carried out. Synthesized compounds 3c (37 % inhibition at 100 μM) and 4d (49 % inhibition at 100 μM) exhibited the best inhibitory bioactivities against β-D-galactosidase and β-D-glucosidase, respectively. They can serve as a promising lead compounds for the development of potential glycosidase inhibitors.

Full text of DOI:10.1007/s00044-014-1314-4

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-014-1314-4
ORIGINAL RESEARCH
Tryptophan and thiosemicarbazide derivatives: design, synthesis,
and biological evaluation as potential b-D-galactosidase
and b-D-glucosidase inhibitors
•
Reema Abu Khalaf Ahmed Mutanabbi Abdula
•
•
Mohammad S. Mubarak Mutasem O. Taha
Received: 23 April 2014 / Accepted: 9 December 2014
Ó Springer Science+Business Media New York 2014
Abstract Glycosidases, including b-D-galactosidase and
b-D-glucosidase, are involved in a range of metabolic dis-
orders, such as cancer, viral or bacterial infections, and
diabetes. Previously, we scanned the pharmacophoric space
of these enzymes and had a self-consistent and predictive
quantitative structure–activity relationship that was used to
identify several b-D-galactosidase and b-D-glucosidase
inhibitors via in silico search of structural databases. Gui-
ded by the preceding modeling efforts, synthesis of a series
of tryptophan and thiosemicarbazide derivatives as b-D-
galactosidase and b-D-glucosidase inhibitors that match the
generated pharmacophores followed by in vitro bioassay
was carried out. Synthesized compounds 3c (37 % inhibi-
tion at 100 lM) and 4d (49 % inhibition at 100 lM)
exhibited the best inhibitory bioactivities against b-D-
galactosidase and b-D-glucosidase, respectively. They can
serve as a promising lead compounds for the development
of potential glycosidase inhibitors.
Keywords Glycosidase ꢀ b-D-Galactosidase ꢀ
b-D-Glucosidase ꢀ Pharmacophore ꢀ QSAR ꢀ
Thiosemicarbazide ꢀ Tryptophan
Introduction
Glycosidases are common enzymes in living organisms
(Scofield et al., 1995a, b). They catalyze the hydrolysis of
glycosidic bonds in carbohydrates, and glycoconjugates
resulting in low-molecular weight monosaccharides and
oligosaccharides.
The mechanism by which a-glucosidases cleave the
glycosidic bond of carbohydrates involves the participation
of two carboxylic acid-containing amino acids in the cat-
alytic site, acting either as an acid or a base, with gener-
ation of a positive-charged oxonium–carbenium ion
transition state. This charge buildup is accompanied by
pseudo-axial orientation of the CO bond to be broken and
concomitant distortion of the pyranose ring out of its chair
conformation (Campo et al., 2013).
Glycosidases, including b-D-galactosidase and b-D-glu-
cosidase, are involved in a variety of metabolic disorders
and diseases such as diabetes, viral or bacterial infections,
and cancer. Consequently, the inhibition of glycosidases
has many potential applications, e.g., antidiabetic, antiviral
(HIV, influenza), and anticancer agents (Gunasekaran
et al., 2014; Jenkinson et al., 2013; Gerber-Lemairer and
Juillerat-Jeanneret, 2006; Lillelund et al., 2002; Markad
et al., 2006; Merrer et al., 2000; Robina and Vogel, 2005;
Shitara et al., 1999).
R. Abu Khalaf (&)
Department of Pharmacy, Faculty of Pharmacy, Al-Zaytoonah
University of Jordan, Amman, Jordan
e-mail: rima_abu_khalaf@yahoo.com;
reema.abukhalaf@zuj.edu.jo
A. M. Abdula
Department of Chemistry, College of Science, Al-Mustansiriyah
University, Baghdad, Iraq
M. S. Mubarak
Department of Chemistry, Faculty of Science, The University of
Jordan, Amman, Jordan
Recently, the great concern in the chemistry, biochem-
istry, and pharmacology of glycosidase inhibitors has lead
to many types of natural and synthetic glycosidase inhibi-
tors (Asano et al., 2000; Asano, 2003; Berecibar et al.,
M. O. Taha
Department of Pharmaceutical Sciences, Faculty of Pharmacy,
The University of Jordan, Amman, Jordan
123

Med Chem Res
1999; Kim et al., 2006; Li et al., 2006; Pandey et al.,
2006). Synthetic enantiomers of natural iminosugars are
frequently powerful glycosidase inhibitors (d’Alonzo et al.,
2009; Macchi et al., 2010). Natural and synthetic imino-
sugars comprise a major family of glycosidase inhibitors
(Lee et al., 2012; Filipa et al., 2011; Amit et al., 2011;
Asano, 2009).
compound toward achieving more potent inhibitory ana-
logs against both enzymes.
Materials and methods
General methods
Previously reported glycosidase inhibitors were sugar
mimics (azasugars and carbasugars) and their analogs; how-
ever, no efforts were made to discover new scaffolds of better
pharmacokinetic profiles, chemical stabilities, and higher
potencies (Wang et al., 2013; Kooij et al., 2013; Asano et al.,
2000; Asano, 2003; Berecibar etal., 1999; Kim etal., 2006; Li
et al., 2006; Pandey et al., 2006).
Melting points were measured using Gallenkampf melting
1
point apparatus and are uncorrected. H-NMR (300 MHz)
and 13C-NMR (75 MHz) spectra were collected on a Varian
Oxford NMR300 spectrometer. The samples were dissolved in
DMSO-d6 or CDCl3. Mass spectrometry was performed using
LC Mass Bruker Apex-IV mass spectrometer utilizing an
electrospray interface.
Synthetic a-glucosidase inhibitors are in general envi-
sioned to mimic the distorted conformation of the transition
state, as observed for natural glucosidase substrates. The
potency and specificity of glucosidase inhibitors are directly
associated to their capacity to mimic the enzyme transition
state, being their inherent conformational (shape and
structural) and electrostatic (charge) properties of great
relevance for binding into the enzyme active site (Campo
et al., 2013).
Analytical thin-layer chromatography (TLC) was car-
ried out using pre-coated aluminum plates and visualized
by UV light (at 254 and/or 360 nm). Elemental analysis
was performed using EuroVector elemental analyzer.
Chemicals and solvents were purchased from corre-
sponding companies (Sigma-Aldrich, Riedel-de Haen,
Fluka, BDH Laboratory Supplies and Promega Corporation)
and were used in the experimentation without further
purification.
Lately, we explored the pharmacophoric space of b-D-
galactosidase (Abdula et al., 2011) and b-D-glucosidase
(Abu Khalaf et al., 2011) inhibitors via CATALYST-
HYPOGEN, followed by employing the classical quanti-
tative structure–activity relationship (QSAR) analysis to
search for the best combination of orthogonal pharmaco-
phores and other structural descriptors capable of
explaining bioactivity variation across the training list. The
optimal shape-complemented pharmacophores were then
used as 3D search queries to screen several available vir-
tual molecular databases for new b-D-galactosidase and
b-D-glucosidase inhibitors (Abdula et al., 2011; Abu
Khalaf et al., 2011).
General procedure for synthesis of (S)-methyl N-
(arylcarbonyl)tryptophanoate (3a–d)
A solution of N,N0-carbonyldiimidazole (CDI) (0.9 g,
5.6 mmol) in dry DMF (10 mL) was added to a solution of
the desired carboxylic acid 1 (indol-3-acetic acid, 2-pyra-
zinecarboxylic acid, 3-nitrobenzoic acid or 3-chloroben-
zoic acid) (5.5 mmol) in dry DMF (3 mL) under N2. After
stirring for 15 min, a solution of L-tryptophan methyl ester
hydrochloride 2 (1.37 g, 5.4 mmol) and triethyl amine
(1 mL) in dry DMF (4 mL) was added. The solution was
stirred overnight under N2 gas, most of DMF was evapo-
rated under reduced pressure, and the residue was treated
with water and kept in the freezer for 1 h. The solution was
then filtrated off to afford 3a–d in a good yield (Kotake
et al., 1995). The prepared compounds were recrystallized
from ethanol.
In our attempts to discover new inhibitors for b-D-
galactosidase and b-D-glucosidase enzymes, this part of
research includes the synthesis of a series of tryptophan
and thiosemicarbazide derivatives that match the generated
pharmacophores followed by in vitro bioassay to determine
their inhibitory activity against the corresponding enzyme.
Pharmacophore models developed for b-D-glucosidase
(three models) and b-D-galactosidase (five models) inhibi-
tors were employed to screen our in house built structural
database of natural compounds (contains 3,000 com-
pounds) (Abdula et al., 2011; Abu Khalaf et al., 2011). One
of the captured hits, 4a (Fig. 1), displayed mediocre
inhibitory potential against b-D-glucosidase. The fact that
this compound combines easy synthetic accessibility and
tight mapping against all pharmacophore models, i.e., those
of b-D-glucosidase and b-D-galactosidase (Figs. 2, 3),
prompted us to attempt chemical optimization of this lead
(S)-Methyl N-(1H-indole-3-acetyl)tryptophanoate (3a)
(68 %): mp. 170–172 °C; 1H-NMR (300 MHz, DMSO-d6)
d 3.00–3.17 (m, 2H, CH2–CH), 3.51 (s, 2H, CH2–C=O),
3.53 (s, 3H, O–CH3), 4.47–4.54 (m, 1H, CH2–CH),
6.87–7.08 (m, 6H, CH indole), 7.28–7.2 (m, 4H, CH
indole), 8.31 (d, J = 7.55 Hz, 1H, NH amide), 10.78 (s,
1H, NH indole), 10.82 ppm (s, 1H, NH indole); 13C-NMR
(75 MHz, DMSO-d6) d 27.6 (CH2–CH), 32.7 (CH2–C=O),
52.2 (CH3), 53.7 (CH2–CH), 109.0, 109.9 (2C-Indole),
123

Med Chem Res
111.7, 111.9, 118.5, 118.8, 118.9, 119.2, 121.4, 121.5,
124.1, 124.2 (10CH Indole), 127.6, 127.7, 136.5, 136.6
(4C Indole), 171.3, 173.0 ppm (2C=O); HRMS (ESI)
m/z [M?Na]? 398.1497 (C22H21N3O3Na requires
398.1481); Anal. calcd for C22H21N3O3: C 70.38, H 5.64,
N 11.19, found: C 69.98, H 5.89, N 11.42.
O
O
O
OH
O
O
N
NH
N
H
NH
H
N
H
N
H
4a
3a
O
O
O
OH
O
O
N
N
N
H
N
H
N
H
N
N
H
N
4b
3b
O
O
OH
O
O
O
N
H
N
H
NO2
NO2
N
H
N
H
4c
3c
O
O
OH
O
O
O
N
H
N
H
Cl
Cl
N
N
H
H
4d
3d
O
OH
O
O
O
O
O
O
Cl
Cl
Cl
Cl
N
N
H
N
N
H
H
H
7a
6a
Fig. 1 Chemical structures of the synthesized compounds 3a–d, 4a–d, 6a–c, and 7a–c
123

Med Chem Res
HO
O
O
O
O
O
O
O
N
N
H
N
H
N
N
N
H
N
H
N
N
N
N
N
7b
6b
6c
HO
O
O
O
O
O
O
O
O2N
NO2
O2N
NO2
N
N
H
N
H
N
H
H
7c
Fig. 1 continued
(S)-Methyl N-(pyrazin-2-ylcarbonyl)tryptophanoate (3b)
127.6 (C indole), 129.8, 133.5 (2CH, Ar–CH), 135.5(C Ar),
136.2 (C indole), 148.2 (C Ar), 164.6, 172.0 ppm (2C=O);
HRMS (ESI) m/z [M?Na]? 390.1073 (C19H17N3O5Na
requires 390.1066); Anal. calcd for C19H17N3O5: C 62.12,
H 4.66, N 11.1, found: C 61.94, H 4.86, N 11.77.
1
(48 %): mp. 115–118 °C; H-NMR (300 MHz, CDCl3) d
3.43 (d, J = 5.65 Hz, 2H, CH2–CH), 3.69 (s, 3H, O–CH3),
5.09–5.16 (m, 1H, CH2–CH), 7.02–7.07 (m, 2H, CH
indole), 7.12 (m, 1H, CH indole), 7.32 (d, J = 7.32 Hz,
1H, CH indole), 7.53 (d, J = 7.91 Hz, 1H, CH indole),
8.21 (brs, 1H, NH indole), 8.30 (d, J = 8.10 Hz, 1H, NH
amide), 8.43 (dd, J = 1.47, 2.43 Hz, 1H, CH pyrazine),
8.70 (d, J = 2.43 Hz, 1H, CH pyrazine), 9.36 ppm (d,
J = 1.47 Hz, 1H, CH pyrazine); 13C-NMR (75 MHz,
CDCl3) d 28.0 (CH2), 52.6 (CH3), 53.0 (CH2–CH), 110.0
(C indole), 111.3, 118.7, 119.7, 122.3, 122.8 (5CH indole),
127.5, 136.2 (2C indole), 142.7 (CH pyrazine), 143.1
(C pyrazine), 145.4, 147.4 (2CH pyrazine), 162.8 (C=O),
172.0 ppm (C=O); HRMS (ESI) m/z [M?Na]? 347.1118
(C17H16N4O3Na requires 347.1120); Anal. calcd for
C17H16N4O3: C 62.95, H 4.97, N 17.27, found: C 62.96, H
5.20, N 17.42.
(S)-Methyl N-(3-chlorobenzoyl)tryptophanoate (3d)
1
(62 %): mp. 126–129 °C; H-NMR (300 MHz, CDCl3) d
3.42–3.1 (m, 2H, CH2–CH), 3.71 (s, 3H, O–CH3),
5.10–5.12 (m, 1H, CH2–CH), 6.65 (d, J = 7.61 Hz, 1H,
NH amide), 6.97 (d, J = 2.24 Hz, 1H, CH indole),
7.06–7.21 (m, 2H, CH indole), 7.28 (d, J = 7.85 Hz, 1H,
CH indole), 7.34 (d, J = 8.12 Hz, 1H, CH indole), 7.43
(m, 1H, CH Ar), 7.48–7.54 (m, 2H, CH Ar), 7.65 (t,
J = 1.70 Hz, 1H, CH Ar), 8.29 ppm (s, 1H, NH indole);
13C-NMR (75 MHz, CDCl3) d 27.6 (CH2), 52.6 (CH3),
53.6 (CH2–CH), 109.9 (C indole), 111.5, 118.6, 119.9,
122.5, 122.9 (5CH indole), 125.2, 127.5 (2CH Ar), 127.7
(C indole), 129.9, 131.8 (2CH Ar), 134.8, 135.6 (2C Ar),
136.2 (C indole), 165.7, 172.3 ppm (2C=O); HRMS (ESI)
m/z [M?Na]? 379.0833 (C19H17ClN2O3Na requires
379.0825); Anal. calcd for C19H17ClN2O3: C 63.96, H
4.80, N 7.85, found: C 63.68, H 5.04, N 7.48.
(S)-Methyl N-(3-nitrobenzoyl)tryptophanoate (3c)
1
(33 %): mp. 130–132 °C; H-NMR (300 MHz, CDCl3) d
3.2–3.48 (m, 2H, CH2–CH), 3.75 (s, 3H, O–CH3),
5.12–5.17 (m, 1H, CH2–CH), 6.72 (d, J = 7.57 Hz, 1H,
NH amide), 7.01 (d, J = 2.38 Hz, 1H, CH indole), 7.08 (m,
1H, CH indole), 7.18 (m, 1H, CH indole), 7.36 (d,
J = 8.12 Hz, 1H, CH indole), 7.52–7.58 (m, 2H, CH
indole, CH Ar), 7.97 (m, 1H, CH Ar), 8.17 (brs, 1H, NH
indole), 8.30 (m, 1H, CH Ar), 8.2 ppm (t, J = 1.9 Hz, 1H,
CH Ar); 13C-NMR (75 MHz, CDCl3) d 27.5 (CH2), 52.7
(CH3), 53.8 (CH2–CH), 109.8 (C indole), 111.5, 118.4,
120.1, 122.2, 122.6 (5CH indole), 122.8, 126.3 (2CH Ar),
General procedure for synthesis of (S)-N-
(arylcarbonyl)tryptophan (4a–d)
The titled derivatives were synthesized by similar proce-
dure described by Kotake et al. (1995). Compounds 3a–
d (5.5 mmol) were dissolved in 5 % NaOH (40 mL) and
stirred overnight; the solution was acidified with diluted
HCl, and the precipitate that formed was collected by
123

Med Chem Res
a
b
O
OH
O
N
H
NH
N
H
c
d
Fig. 2 In-silico discovered hit 4a mapping a GluHypo10/1, b Glu-
Hypo4/4, c GluHypo9/4 (hydrogen bond acceptor as green vectored
spheres, hydrophobic features as blue spheres, ring aromatic as
orange vectored spheres, hydrogen bond donor as violet vectored
spheres), and d chemical structure of hit 4a (Color figure online)
filtration, washed with distilled water, dried in vacuum, and
purified by plate chromatography using (ethyl acetate:
hexane, 80:20) to obtain compounds 4a–d.
indole), 8.14 (d, J = 7.8 Hz, 1H, NH amide), 10.78 (s,1H,
NH indole), 10.81 (s,1H, NH indole), 12.61 ppm (bs, 1H,
OH); 13C-NMR (75 MHz, DMSO-d6) d 27.7 (CH2–CH),
32.7 (CH2–C=O), 53.5 (CH2–CH), 109.1, 110.3
(2C indole), 111.7, 111.9, 118.6, 118.7, 118.9, 119.2, 121.3,
121.4, 124.1, 124.2 (10CH indole), 127.6 (2C indole),
136.5, 136.6 (2C indole), 171.1, 174.0 ppm (2C=O); HRMS
(ESI) m/z [M?Na]? 384.1336 (C21H19N3O3Na requires
384.1324); Anal. calcd for C21H19N3O3: C 69.79, H 5.30, N
11.63, found: C 69.38, H 5.43, N 11.54.
(S)-N-(1H-Indole-3-acetyl)tryptophan (4a)
(22 %): mp. 183–185 °C; 1H-NMR (300 MHz, DMSO-d6)
d 2.96–3.17 (m, 2H, CH2–CH), 3.49 (s, 2H, CH2–C=O),
4.42–4.49 (m, 1H CH2–CH), 6.84–7.06 (m, 6H, CH indole),
7.26–7.37 (m, 3H, CH indole), 7.47 (d, J = 7.8 Hz, 1H, CH
123

Med Chem Res
b
a
d
c
O
OH
O
N
H
NH
N
H
e
f
Fig. 3 In-silico discovered hit 4a mapping a GalHypo3/1, b GalHyp-
o8/1, c GalHypo10/1, d GalHypo4/5, e GalHypo5/5 (hydrogen bond
acceptor as green vectored spheres, hydrophobic features as blue
spheres, ring aromatic as orange vectored spheres, hydrogen bond
donor as violet vectored spheres), and f Chemical structure of hit 4a
(Color figure online)
123

Med Chem Res
(S)-N-(Pyrazin-2-ylcarbonyl)tryptophan (4b)
1C indole), 165.4 (C=O), 173.9 ppm (C–OH); HRMS (ESI)
m/z [M?Na]? 365.0678 (C18H15ClN2O3Na requires
365.0669); Anal. calcd for C18H15ClN2O3: C 63.07, H 4.41,
N 8.17, found: C 62.66, H 4.62, N 7.73.
(55 %): mp. 117–120 °C; 1H-NMR (300 MHz, DMSO-d6)
d 3.32–3.34 (d, J = 6.11 Hz, 2H, CH2–CH), 4.72–4.79 (m,
1H, CH2–CH), 6.88 (m, 1H, CH indole), 7.01 (m, 1H, CH
indole), 7.12 (d, J = 2.2 Hz, 1H, CH indole), 7.29 (d,
J = 8.1 Hz, 1H, CH indole), 7.49 (d, J = 7.8 Hz, 1H, CH
indole), 8.66 (dd, J = 2.1, 1.46 Hz, 1H, CH pyrazine), 8.70
(d, J = 7.99 Hz, 1H, NH amide), 8.83 (d, J = 2.1 Hz, 1H,
CH pyrazine), 9.14 (d, J = 1.46 Hz, 1H, CH pyrazine),
10.83 (s, 1H, NH indole), 13.02 ppm (brs, 1H, OH); 13C-
NMR (75 MHz, DMSO-d6) d 27.1 (CH2), 53.5 (CH2–CH),
110.0 (C indole), 111.9, 118.8, 118.9, 121.5, 124.2 (5CH
indole), 127.8, 136.6 (2C indole), 143.8, 143.9 (2CH pyr-
azine), 145.5 (C pyrazine), 148.3 (CH pyrazine), 163.0
(C=O), 173.3 ppm (C–OH); HRMS (ESI) m/z [M?Na]?
333.0974 (C16H14N4O3Na requires 333.0964); Anal. calcd
for C16H14N4O3: C 61.93, H 4.55, N 18.06, found: C 61.59,
H 4.65, N 17.83.
General procedure for synthesis of (S)-ethyl N,N0-
bis(arylcarbonyl)lysinoate (6a–c)
The title compounds were synthesized using the same pro-
cedure employed for the synthesis of compounds 3a–c. L-
Lysine ethyl ester dihydrochloride 5 (6.8 g, 2.75 mmol) and
the desired carboxylic acid 1 (3-chlorobenzoic acid, 2-pyr-
azinecarboxylic acid and 3-nitrobenzoic acid) were used to
obtain compounds 6a–c. The synthesized compounds were
purified by preparative TLC using ethyl actate: ethanol
(80:20).
(S)-Ethyl N,N0-bis(chlorobenzoyl)lysinoate (6a)
(63 %): mp. 90–93 °C; 1H-NMR (300 MHz, CDCl3) d
1.30 (t, J = 7.1 Hz, 3H, CH3–CH2), 1.46–2.00 (m, 6H,
CH2–CH2–CH2–CH), 3.1–3.50 (m, 2H, NH–CH2), 4.24 (q,
J = 7.1 Hz, 2H, CH3–CH2), 4.74–4.78 (m, 1H, CH2–CH–
NH), 6.57 (brs, 1H, NH–CH2), 6.99 (d, J = 7.5 Hz, 1H,
CH–NH), 7.27–7.37 (m, 2H, CH Ar), 7.42–7.46 (m, 2H,
CH Ar), 7.62 (m, 1H, CH Ar), 7.66 (m, 1H, CH Ar), 7.76
(t, J = 1.8 Hz, 1H, CH Ar), 7.79 ppm (t, J = 1.8 Hz, 1H,
CH Ar); 13C-NMR (75 MHz, CDCl3) d 14.2 (CH3), 22.5,
28.6, 32.2, 39.4 (4CH2, CH2–CH2–CH2–CH2), 52.4 (CH–
NH), 61.8 (CH2–CH3), 125.1, 125.2, 127.4, 127.6, 129.8,
129.9, 131.4, 131.9 (8CH, CH Ar), 134.7, 134.8, 135.6,
136.3 (4C, C Ar), 166.3, 166.7 (2C=O amide), 172.5 ppm
(C=O ester); HRMS (ESI) m/z [M?Na]? 473.1005
(C22H24Cl2N2O4Na requires 473.1011) .
(S)-N-(3-Nitrobenzoyl)tryptophan (4c)
(62 %): mp. 170–173 °C; 1H-NMR (300 MHz, DMSO-d6)
d 3.15–3.35 (m, 2H, CH2–CH), 4.63–4.71 (m, 1H, CH2–
CH), 6.87–7.04 (m, 2H, CH indole), 7.18 (d, J = 2.1 Hz,
1H, CH indole), 7.29 (d, J = 7.9 Hz, 1H, CH indole), 7.58
(d, J = 7.7 Hz, 1H, CH indole), 7.75 (t, J = 7.9 Hz, 1H,
CH Ar), 8.22 (d, J = 7.67 Hz, 1H, CH Ar), 8.32–8.39 (m,
1H, CH Ar), 8.64 (s, 1H, CH Ar), 9.10 (d, J = 7.8 Hz, 1H,
NH amide), 10.79 (s, 1H, NH indole), 12.09 ppm (brs, 1H,
OH); 13C-NMR (75 MHz, DMSO-d6) d 27.2 (CH2–CH),
54.6 (CH2–CH), 110.9 (C indole), 111.9, 118.7, 118.9,
121.5, 122.6 (5CH indole), 124.0, 126.5 (2CH Ar), 127.7
(C indole), 130.6, 134.3 (2CH Ar), 135.9, 136.6 (2C indole
and Ar), 148.0 (C Ar), 164.7 (C=O), 173.9 ppm (C–OH);
HRMS (ESI) m/z [M?Na]? 376.0936 (C18H15N3O5Na
requires 376.0909); Anal. calcd for C18H15N3O5: C 61.19,
H 4.28, N 11.89, found: C 61.38, H 4.46, N 11.95.
(S)-Ethyl N,N0-bis(pyrazin-2-ylcarbonyl)lysinoate (6b)
(43 %): mp. 95–97 °C; 1H-NMR (300 MHz, CDCl3) d 1.27
(t, J = 7.1 Hz, 3H, CH3–CH2), 1.2–2.02 (m, 6H, CH2–CH2–
CH2–CH), 3.43–3.50 (m, 2H, NH–CH2), 4.22 (q, J = 7.1 Hz,
2H, CH3–CH2), 4.75–4.83 (m, 1H, CH2–CH–NH), 7.81 (brs,
1H, NH–CH2), 8.26 (d, J = 8.3 Hz, 1H, CH–NH), 8.47 (dd,
J = 2.4, 1.5 Hz, 1H, CH pyrazine), 8.54(dd, J = 2.4, 1.5 Hz,
1H, CH pyrazine), 8.71 (d, J = 2.4 Hz, 1H, CH pyrazine),
8.74 (d, J = 2.4 Hz, 1H, CH pyrazine), 9.35–9.36 ppm (m,
2H, CH pyrazine); 13C-NMR (75 MHz, CDCl3) d 14.2 (CH3),
22.7, 29.1, 32.3, 39.1 (4CH2, CH2–CH2–CH2–CH2), 52.1
(CH–NH), 61.8 (CH2–CH3), 142.5, 142.8 (2CH pyrazine),
143.1 (2C pyrazine), 144.4, 145.5, 147.3, 147.5 (4CH pyra-
zine), 162.9, 163.0 (2C amide), 171.9 ppm (C ester); HRMS
(ESI) m/z [M?Na]? 409.1629 (C18H22N6O4Na requires
409.1600); Anal. calcd for C18H22N6O4: C 55.95, H 5.74, N
21.75, found: C 56.39, H 5.42, N 21.61.
(S)-N-(3-Chlorobenzoyl)tryptophan (4d)
(72 %): mp. 155–157 °C; 1H-NMR (300 MHz, DMSO-d6) d
3.12–3.31 (m, 2H, CH2–CH), 4.59–4.64 (m, 1H, CH2–CH),
6.92–7.05 (m, 2H, CH indole), 7.16 (d, J = 2.24 Hz, 1H, CH
indole), 7.29 (d, J = 7.92 Hz, 1H, CH indole), 7.2 (t,
J = 7.86 Hz, 1H, CH Ar), 7.55–7.58 (m, 2H, CH Ar and CH
indole), 7.73–7.75 (m, 1H, CH Ar), 7.83 (t, J = 1.75 Hz, 1H,
CH Ar), 8.81 (d, J = 7.89 Hz, 1H, NH amide), 10.79 (s, 1H,
NH indole), 12.76 ppm (brs, 1H, OH); 13C-NMR (75 MHz,
DMSO-d6) d 27.1 (CH2–CH), 54.3 (CH2–CH), 110.9
(C indole), 111.9, 118.6, 118.8, 121.5, 124.0 (5CH indole),
126.5 (CH Ar), 127.6 (C indole), 127.7 (CH Ar), 130.8 (CH
Ar), 131.7 (CH Ar), 133.6, 136.4, 136.6 (3C, 2C Ar and
123

Med Chem Res
(S)-Ethyl N,N0-bis(3-nitrobenzoyl)lysinoate (6c). (50 %):
CH pyrazine), 9.12 (d, J = 1.5 Hz, 1H, CH pyrazine),
12.81 ppm (brs, OH); 13C-NMR (75 MHz, DMSO-d6) d
23.4, 29.1, 30.8, 38.9 (4CH2, CH2–CH2–CH2–CH2), 52.6
(CH–NH), 143.7, 143.8, 143.9, 144.0 (4CH, CH pyrazine),
145.7, 146.4 (2C, C pyrazine), 147.8, 148.2 (2CH, CH
pyrazine), 163.2, 163.3 (2C=O amide), 173.6 ppm (C–
1
mp. 128–130 °C; H-NMR (300 MHz, CDCl3) d 1.29 (t,
J = 7.1 Hz, 3H, CH3–CH2), 1.48–2.04 (m, 6H, CH2–CH2–
CH2–CH), 3.47–3.55 (m, 2H, NH–CH2), 4.24 (q,
J = 7.1 Hz, 2H, CH3–CH2), 4.77–4.80 (m, 1H, CH2–CH–
NH), 6.75 (brs, 1H, NH–CH2), 7.16 (d, J = 7.5 Hz, 1H, CH–
NH), 7.54–7.62 (m, 2H, CH Ar), 8.10–8.14 (m, 2H, CH Ar),
8.27–8.34 (m, 2H, CH Ar), 8.56 (t, J = 1.7 Hz, 1H, CH Ar),
8.60 ppm (t, J = 1.8 Hz, 1H, CH Ar); 13C-NMR (75 MHz,
CDCl3) d 14.2 (CH3), 22.6, 28.6, 32.1, 39.6 (4CH2–, CH2–
CH2–CH2–CH2), 52.6 (CH2–CH), 62.0 (CH2–CH3), 121.9,
122.3, 126.0, 126.4, 129.7, 129.8, 133.1, 133.2 (8CH, CH
Ar), 135.4, 136.1, 148.1, 148.2 (4C, C Ar), 165.3, 165.6
(2C=O amide), 172.3 ppm (C=O ester); HRMS (ESI) m/
z [M?Na]? 495.1490 (C22H24N4O8Na requires 495.1492).
OH);
HRMS
(ESI)
m/z
[M?Na]?
381.1327
(C16H18N6O4Na requires 381.1287); Anal. calcd for
C16H18N6O4: C 53.63, H 5.06, N 23.2, found: C 53.98, H
5.35, N 23.91.
(S)-N,N0-Bis(3-nitrobenzoyl)lysine (7c)
(63 %): mp. 148–150 °C; 1H-NMR (300 MHz, DMSO-d6)
d 1.32–1.2 (m, 2H, CH2–CH2–CH2–CH), 1.38–1.53 (m,
2H, CH2–CH2–CH2–CH), 1.75–1.82 (m, 2H, CH2–CH2–
CH2–CH), 3.20–3.30 (m, 2H, NH–CH2), 4.21–4.32 (m, 1H,
CH–NH), 7.64–7.71 (m, 2H, CH Ar), 8.23–8.31 (m, 4H,
CH Ar), 8.58–8.59 (m, 2H, CH Ar), 8.72 (d, J = 7.3 Hz,
1H, CH–NH), 8.94 ppm (t, J = 5.2 Hz, 1H, NH–CH2);
13C-NMR (75 MHz, DMSO-d6) d 23.6, 29.1, 31.5, 39.6
(4CH2, CH2–CH2–CH2–CH2), 54.5 (CH–NH), 122.40,
122.43 (2CH, CH Ar), 126.1 (2CH, CH Ar), 130.5 (2CH,
CH Ar), 134.1(2CH. CH Ar), 136.5 (2C, C Ar), 148.15,
148.18 (2C Ar), 164.0, 164.3 (2C=O amide), 175.1 ppm
(C–OH); HRMS (ESI) m/z [M?Na]? 467.1204
(C20H20N4O8Na 467.1179); Anal. calcd for C20H20N4O8: C
54.05, H 4.54, N 12.61, found: C 54.08, H 4.81, N 12.25.
General procedure for synthesis of (S)-N,N0-
bis(arylcarbonyl)lysine (7a–c)
Compounds 6a–c (5.5 mmol) were dissolved in 5 % NaOH
(40 mL) and stirred overnight; the solution was acidified
with diluted HCl, and the precipitate that formed was
collected by filtration, washed with distilled water, dried in
vacuum, and purified by plate chromatography using (ethyl
acetate: hexane, 80:20) to obtain compounds 7a–c.
(S)-N,N0-Bis(3-chlorobenzoyl)lysine (7a)
(63 %): mp. 141–143 °C; 1H-NMR (300 MHz, DMSO-d6)
d 1.37–1.52 (m, 4H, CH2–CH2–CH2–CH), 1.74–1.84 (m,
2H, CH2–CH2–CH2–CH), 3.19–3.25 (m, 2H, NH–CH2),
4.29–4.33 (m, 1H, CH–NH), 7.40–7.49 (m, 2H, CH Ar),
7.52–7.60 (m, 2H, CH Ar), 7.72–7.82 (m, 3H, CH Ar), 7.89
(t, J = 1.7 Hz, 1H, CH Ar), 8.55 (t, J = 5.5 Hz, 1H, NH–
CH2), 8.69 (d, J = 7.6 Hz, 1H, CH–NH–C=O), 12.59 ppm
(s, 1H, OH); 13C-NMR (75 MHz, DMSO-d6) d 23.8, 29.1,
30.6, 39.5 (4CH2, CH2–CH2–CH2–CH2), 53.2 (CH–NH),
126.4, 126.8, 127.4, 127.7, 130.7, 130.8, 131.3, 131.7
(8CH, CH Ar), 133.6 (2C, C Ar), 136.4, 137.1 (2C, C Ar),
165.2, 165.7 (2C=O amide), 174.1 ppm (C–OH); HRMS
(ESI) m/z [M?Na]? 446.0713 (C20H20Cl2N2O4Na requires
446.0698); Anal. calcd for C20H20Cl2N2O4: C 56.75, H
4.76, N 6.62, found: C 57.15, H 5.04, N 6.91.
General procedure for synthesis of ethyl ester derivatives
8a and 8b
Indol-3-acetic acid or 2-pyrazinecarboxylic acid (5.5 mmol)
were heated under reflux for 3 h in 90 mL ethanol and
15 mL concentrated H2SO4. The solution was neutralized
with saturated Na2CO3 solution and filtered. The volume
was reduced in vacuum and extracted with four 30 mL
aliquots of dichloromethane. The combined fractions were
washed with 10 mL of water and dried over anhydrous
MgSO4. The dichloromethane was removed using vacuum
to yield the ethyl carboxylate derivatives, 8a mp. 1–2 °C
(Lit. 1–2 °C, Vlaovic et al., 1990) or 8b mp. 46–47 °C (Lit.
48–49 °C, Yoshino et al., 2006) which crystallized on
cooling.
(S)-N,N0-Bis(pyrazin-2-ylcarbonyl)lysine (7b)
Ethyl 2-(1H-indol-3-yl)acetate (8a)
(67 %): mp. 227–230 °C; 1H-NMR (300 MHz, DMSO-d6)
d 1.29–1.37 (m, 2H, CH2–CH2–CH2–CH), 1.48–1.54 (m,
2H, CH2–CH2–CH2–CH), 1.82–1.90 (m, 2H, CH2–CH2–
CH2–CH), 3.22–3.28 (m, 2H, NH–CH2), 4.38–4.2 (m, 1H,
CH–NH), 8.64 (dd, J = 2.3,1.5 Hz, 1H, CH pyrazine),
8.69 (dd, J = 2.3, 1.5 Hz, 1H, CH pyrazine), 8.79–8.91 (m,
4H, 2CH pyrazine, 2NH amide), 9.10 (d, J = 1.5 Hz, 1H,
(78 %): mp. 1–2 °C; 1H-NMR (300 MHz, DMSO-d6) d 1.17
(t, J = 7.1 Hz, 3H, CH2–CH3), 3.75 (s, 2H, CH2C=O), 4.08
(q, J = 7.1 Hz, 2H, CH2–CH3), 7.02(m, 1H, CHindole), 7.13
(m, 1H, CH indole), 7.27 (d, J = 1.8 Hz, 1H, CH indole),
7.39–7.42 (m, 1H, CH indole), 7.54 (d, J = 7.8 Hz, 1H, CH
indole), 10.97 ppm (s, 1H, NH indole); 13C-NMR (75 MHz,
123

Med Chem Res
DMSO-d6) d 14.6 (CH2–CH3), 31.4 (CH2–CH3), 60.6
(CH2C=O), 107.6 (C indole), 111.9, 119.0, 119.1, 121.6,
124.5 (5CH indole), 127.7, 136.7 (2C indole), 172.1 ppm
(C=O ester).
alkylisothiocyanate 10 (isothiocyanatomethane, isothiocy-
anatobenzene, 1-isothiocyanato-4-methoxybenzene, 1-isoth-
iocyanatonaphthalene, 1-isothiocyanato-4-nitrobenzene) was
added. The mixture was refluxed for 3 h. The solid product,
obtained on cooling, was washed with distilled water and
recrystallized from ethanol to obtain compounds 11a–h (Ilyin
et al., 2007).
Ethyl pyrazine-2-carboxylate (8b)
(81 %): mp. 46–47 °C; 1H-NMR (300 MHz, CDCl3) d 1.39
(t, J = 7.1 Hz, 3H, CH2–CH3), 4.2 (q, J = 7.1 Hz, 2H,
CH2–CH3), 8.67 (dd, J = 2.34, 1.4 Hz, 1H, CH pyrazine),
8.70 (d, J = 2.4 Hz, 1H, CH pyrazine), 9.25 ppm (d,
J = 1.4 Hz, 1H, CH pyrazine); 13C-NMR (75 MHz, CDCl3)
d 14.2 (CH2CH3), 62.4 (CH2CH3), 143.6 (C pyrazine),
145.4, 146.3, 147.6 (3CH pyrazine), 164.0 ppm (C=O ester).
N-Methyl-2-(pyrazine-2-carbonyl)
hydrazinecarbothioamide (11a)
(95 %): mp. 217–219 °C; 1H-NMR (300 MHz, DMSO-d6) d
2.46 (d, J = 4.3 Hz, 3H, NH–CH3), 7.95 (brs, 1H, NH–CH3),
8.72 (dd, J = 2.3, 1.3 Hz, 1H, CH pyrazine), 8.86 (d,
J = 2.3 Hz, 1H, CH pyrazine), 9.14 (d, J = 1.3 Hz, 1H, CH
pyrazine), 9.40 (brs, 1H, NH–NH–C=S), 10.69 ppm (brs,
NH–NH–C=S, 1H); 13C-NMR (75 MHz, DMSO-d6) d 31.4
(NH–CH3), 143.9, 144.3 (2CH pyrazine), 146.1 (C pyrazine),
148.2 (CH pyrazine), 163.2 (C=O amide), 182.4 ppm (C=S);
HRMS(ESI)m/z[M?Na]? 234.0418(C7H9N5OSNarequires
234.0425); Anal. calcd for C7H9N5OS: C 39.80, H 4.29, N
33.15, S 15.18, found: C 39.59, H 4.58, N 33.46, S 14.87.
General procedure for synthesis of acid hydrazides 9a
and 9b
A mixture of the ester derivative 8a or 8b (5.5 mmol) and
hydrazine hydrate (11 mmol) in 50 mL of ethanol was
heated under reflux for 6 h. The reaction mixture was left
overnight at room temperature, and the solid which sepa-
rated was collected by filtration. The solid was then washed
with ethanol, dried, and recrystallized from ethanol
(Yoshino et al., 2006; Vlaovic et al., 1990).
N-(4-Methoxyphenyl)-2-(pyrazine-2-carbonyl)hydrazine
carbothioamide (11b)
2-(1H-Indol-3-yl)acetohydrazide (9a)
(95 %): mp. 187–189 °C; 1H-NMR (300 MHz, DMSO-d6)
d 3.70 (s, 3H, OCH3), 6.85 (d, J = 8.5 Hz, 2H, CH Ar),
7.24 (d, J = 8.5 Hz, 2H, CH Ar), 8.73 (brs, 1H, CH pyr-
azine), 8.86 (d, J = 1.3 Hz, 1H, CH pyrazine), 9.17 (s, 1H,
CH pyrazine), 9.58 (s, 1H, NH–(C=S)–NH), 9.71 (brs, 1H,
NH–NH–C=S), 10.84 ppm (s, 1H, NH–NH–C=S); 13C-
NMR (75 MHz, DMSO-d6) d 55.7 (OCH3), 113.7 (2CH
Ar), 127.7 (2CH Ar), 132.5 (C Ar), 143.9, 144.3 (2CH
pyrazine), 145.2 (C pyrazine), 148.1 (CH pyrazine), 157.2
(C Ar), 163.0 (C=O), 181.5 ppm (C=S); HRMS (ESI) m/
z [M?Na]? 326.0690 (C13H13N5O2SNa 326.0688); Anal.
calcd for C13H13N5O2S: C 51.47, H 4.32, N 23.09, S 10.57,
found: C 51.85, H 4.58, N 23.42, S 10.19.
(90 %): mp. 142–143 °C; 1H-NMR (300 MHz, DMSO-d6)
d 3.41 (s, 2H, CH2C=O), 4.16 (brs, 2H, NH–NH2), 6.93 (m,
1H, CH indole), 7.02 (m, 1H, CH indole), 7.14 (d,
J = 2.3 Hz, 1H, CH indole), 7.30 (d, J = 8.0 Hz, 1H, CH
indole), 7.53 (d, J = 7.8 Hz, 1H, CH indole), 9.09 (s, 1H,
NH), 10.82 ppm (s, 1H, NH); 13C-NMR (75 MHz, DMSO-
d6) d 31.2 (CH2–C=O), 109.3 (C indole), 111.7, 118.7,
119.2, 121.4, 124.2 (5CH indole), 127.7, 136.5 (2C indole),
172.1 ppm (C=O amide).
Pyrazine-2-carbohydrazide (9b)
(95 %): mp. 181–183 °C; 1H-NMR (300 MHz, DMSO-d6)
d 4.61 (brs, 2H, NH–NH2), 8.66 (dd, J = 2.3, 1.5 Hz, 1H,
CH pyrazine), 8.80 (d, J = 2.3 Hz, 1H, CH pyrazine), 9.09
(d, J = 1.5 Hz, 1H, CH pyrazine), 10.10 ppm (brs, 1H,
NH–NH2); 13C-NMR (75 MHz, DMSO-d6) d 143.7, 143.9
(2CH pyrazine), 145.4 (C pyrazine), 147.7 (CH pyrazine),
161.9 ppm (C=O amide).
N-Phenyl-2-(pyrazine-2-
carbonyl)hydrazinecarbothioamide (11c)
(82 %): mp. 178–180 °C; 1H-NMR (300 MHz, DMSO-d6)
d 7.09–7.14 (m, 1H, CH Ar), 7.26–7.31 (m, 2H, CH Ar),
7.38–7.41 (m, 2H, CH Ar), 8.74 (dd, J = 1.9, 0.9 Hz, 1H,
CH pyrazine), 8.87 (d, J = 1.9 Hz, 1H, CH pyrazine), 9.17
(s, 1H, CH pyrazine), 9.69 (s, 1H, NH–(C=S)–NH), 9.82 (s,
1H, NH–(C=S)–NH), 10.89 ppm (s, 1H, NH–NH–C=S);
13C-NMR (75 MHz, DMSO-d6) d 125.5 (2CH Ar), 127.0
(CH Ar), 128.5 (2CH Ar), 139.6 (C Ar), 143.9, 145.3 (2CH
pyrazine), 146.0 (C pyrazine), 148.2 (CH pyrazine), 163.0
General procedure for synthesis of thiosemicarbazide
derivatives (11a–h)
To a solution of 5.5 mmol of substituted acid hydrazides 9a or
9b in 30 mL of ethanol, 5.5 mmol of the appropriate aryl or
123

Med Chem Res
(C=O amide), 181.3 ppm (C=S); HRMS (ESI) m/
z [M?Na]? 296.0590 (C12H11N5OSNa requires 296.0582);
Anal. calcd for C12H11N5OS: C 52.73, H 4.06, N 25.62, S
11.73, found: C 53.11, H 4.49, N 25.87, S 12.34.
(C=O), 182.8 ppm (C=S); HRMS (ESI) m/z [M?Na]?
285.0779 (C12H14N4OSNa requires 285.0786).
2-(2-(1H-Indol-3-yl)acetyl)-N-(4-
methoxyphenyl)hydrazinecarbothioamide (11f)
N-(Naphthalen-1-yl)-2-(pyrazine-2-carbonyl)
hydrazinecarbothioamide (11d)
(78 %): mp. 188–190 °C; 1H-NMR (300 MHz, DMSO-d6) d
3.57 (s, 2H, CH2–C=O), 3.71 (s, 3H, OCH3), 6.86 (d,
J = 8.3 Hz, 2H, CH Ar), 6.91–7.03 (m, 2H, CH indole),
7.21–7.23 (m, 3H, 2CH Ar, CH indole), 7.30 (d, J = 8.1 Hz,
1H, CH indole), 7.55 (d, J = 7.8 Hz, 1H, CH indole), 9.35
(s, 1H, NH–(C=S)–NH), 9.48 (s, 1H, NH–(C=S)–NH), 10.02
(s, 1H, NH–NH–C=S), 10.86 ppm (s, 1H, NH indole); 13C-
NMR (75 MHz, DMSO-d6) d 31.2 (CH2–C=O), 55.7
(OCH3), 108.5 (C indole), 111.8 (CH indole), 113.8 (2 CH
Ar), 118.8, 119.8, 121.5, 124.5 (4CH indole), 127.5 (2CH
Ar), 127.8 (C indole), 132.4 (C Ar), 136.5 (C indole), 157.2
(C Ar), 170.9 (C=O), 181.7 ppm (C=S); HRMS (ESI) m/
z [M?Na]? 377.1065 (C18H18N4O2SNa requires 377.1048).
1
(77 %): mp. 173–175 °C; H-NMR (300 MHz, DMSO-d6) d
7.37–8.04 (m, 7H, CH Ar), 8.75 (d, J = 1.2 Hz, 1H, CH pyra-
zine), 8.86 (d, J = 1.2 Hz, 1H, CH pyrazine), 9.24 (s, 1H, CH
pyrazine), 9.94 (s, 1H, NH–(C=S)–NH), 9.98 (s, 1H, NH–
(C=S)–NH), 11.13 ppm (s, 1H, NH–NH–C=S); 13C-NMR
(75 MHz, DMSO-d6)d124.6, 125.9, 126.4, 126.5, 126.9, 127.4,
128.0 (7CH Ar), 131.2, 134.2, 136.2 (3C Ar), 143.8, 145.4 (2CH
pyrazine), 146.3 (C pyrazine), 148.1 (CH pyrazine), 163.6 (C=O
amide), 182.9 ppm (C=S); HRMS (ESI) m/z [M?Na]?
346.0739 (C16H13N5OSNa requires 346.0739); Anal. calcd for
C16H13N5OS: C 59.43, H 4.05, N 21.66, S 9.92, found: C 58.98,
H 4.29, N 21.82, S 10.32.
2-(2-(1H-Indol-3-yl)acetyl)-N-(4-nitrophenyl)
2-(2-(1H-Indol-3-yl)acetyl)-N-
hydrazinecarbothioamide (11g)
methylhydrazinecarbothioamide (11e)
(68 %): mp. 185–187 °C; 1H-NMR (300 MHz, DMSO-d6) d
(ppm): 3.61 (s, 2H, CH2–C=O), 6.91–7.05 (m, 2H, CH
indole), 7.23 (brs, 1H, CH indole), 7.31 (d, J = 8.1 Hz, 1H,
CH indole), 7.58 (d, J = 7.8 Hz, 1H, CH indole), 7.85 (d,
J = 8.9 Hz, 2H, CH Ar), 8.18 (d, J = 8.9 Hz, 2H, CH Ar),
9.85 (brs, 1H, NH–(C=S)–NH), 10.08 (brs, 1H, NH–(C=S)–
NH), 10.12 (brs, 1H, NH–NH–C=S), 10.88 ppm (s, 1H, NH
indole); 13C-NMR (75 MHz, DMSO-d6) d 31.2 (CH2–C=O),
108.3 (C indole), 111.8, 118.8, 119.3, 121.5 (4CH indole),
124.3 (2CH Ar), 124.5 (CH indole), 125.2 (2 CH Ar), 127.7
(77 %): mp. 196–198 °C; 1H-NMR (300 MHz, DMSO-d6) d
2.84 (d, J = 3.9 Hz, 3H, NH–CH3), 3.2 (s, 2H, CH2–C=O),
6.92–7.06 (m, 2H, CH indole), 7.19 (brs, 1H, CH indole), 7.31
(d, J = 8.0 Hz, 1H, CH indole), 7.53 (d, J = 7.8 Hz, 1H, CH
indole), 7.85 (brs, 1H, NH–(C=S)–NH), 9.18 (s, 1H, NH–
(C=S)–NH), 9.82 (s, 1H, NH–NH–C=S), 10.85 ppm (s, 1H,
NH indole); 13C-NMR (75 MHz, DMSO-d6) d 31.1 (CH2–
C=O), 31.4 (NH–CH3), 108.0 (C indole), 111.8, 118.8, 119.3,
121.5, 124.4 (5CH indole), 127.8, 136.5 (2C indole), 171.0
Scheme 1 Synthesis of (S)-
methyl N-
(arylcarbonyl)tryptophanoate
(3) and (S)-N-
(arylcarbonyl)tryptophan (4).
Carboxylic acid 1: indol-3-
acetic acid,
2-pyrazinecarboxylic acid,
3-nitrobenzoic acid, or
3-chlorobenzoic acid
O
O
O
O
O
HCl
N
H
NH2
O
R
CDI, TEA
DMF
+
R
OH
N
H
N
H
1
2
3
O
NaOH
5%
OH
O
N
H
R
N
H
4
123

Med Chem Res
Scheme 2 Synthesis of (S)-
ethyl N,N0-
O
bis(arylcarbonyl)lysinoate (6)
and (S)-N,N0-
O
R
O
O
NH
CDI, TEA
DMF
bis(arylcarbonyl)lysine (7)
derivatives. Carboxylic acid 1:
3-chlorobenzoic acid,
2-pyrazinecarboxylic acid, or
3-nitrobenzoic acid
O
+
R
OH
H2N
NH2
1
5
O
6
H
N
NaOH
O
R
O
HO
O
R
O
NH
NH
7
R
Scheme 3 Synthesis of
thiosemicarbazide (11) and 1H-
1,2,4-triazole-5(4H)-thione (12)
derivatives. Carboxylic acid 1:
2-pyrazinecarboxylic acid or
indol-3-acetic acid.
O
O
O
NH2NH2.H2O
EtOH
H2SO4
EtOH
NH2
R
N
H
R
O
R
OH
9
1
8
Isothiocyanate 10:
10
R1NCS
EtOH
isothiocyanatomethane,
isothiocyanatobenzene,
1-isothiocyanato-4-
methoxybenzene,
1-isothiocyanatonaphthalene, or
1-isothiocyanato-4-nitrobenzene
R1
N
R
O
S
S
R
NaOH
HN
R1
N
H
N
H
N
NH
11
12
Table 1 b-D-Glucosidase
inhibitory activity of the
synthesized compounds and
their corresponding fit values
against b-D-glucosidase binding
hypotheses
Fit values againsta
GluHypo4/4
No.b
GluHypo10/1
GluHypo9/4
In vitro % inhibitionc
3a
3b
3c
3d
4a
4b
4c
4d
6a
6b
6c
7a
7b
7c
9.494
8.911
9.981
9.822
10.353
9.061
9.968
9.932
10.027
4.418
11.030
11.033
5.099
11.174
2.697
–
8.029
4.593
7.02
7
NI
6
–
0.625
3.431
–
8.377
8.276
3.959
8.357
8.275
8.784
5.622
8.110
8.965
1.500
7.608
21
15
11
20
49
NI
NI
4
–
0.674
2.164
–
NI no inhibition
a
Synthesized compounds
5.358
3.667
–
b
Best-fit values against each
binding hypothesis
9
NI
NI
c
% inhibition at 100 lM
inhibitor concentration
4.759
123

Med Chem Res
Table 2 b-D-Galactosidase
inhibitory activity of the
synthesized compounds and
their corresponding fit values
against b-D-galactosidase
binding hypotheses
Fit values againsta
No.b
GalHypo3/1
GalHypo8/1
GalHypo10/1
GalHypo4/5
GalHypo5/5
In vitro %
inhibitionc
3a
10.187
5.782
7.186
7.041
8.810
10.194
9.488
7.597
–
11.232
11.409
11.395
11.325
11.553
11.032
11.288
10.075
2.522
9.214
8.781
6.943
8.683
10.439
11.287
11.05
–
10.630
10.432
10.627
10.486
10.782
12.413
5.239
10.185
–
14.826
14.335
15.029
14.594
14.654
17.390
15.872
15.691
6.956
16.421
15.555
16.648
15.767
16.901
16.834
16.753
17.296
6.085
3.019
9.424
7.416
–
NI
NI
37
23
NI
NI
NI
NI
10
28
16
19
NI
NI
NI
21
NI
NI
3b
3c
3d
4a
6a
6b
6c
11a
11b
11c
11d
11e
11f
11g
11h
12b
12c
6.753
2.962
6.22
10.043
6.992
8.365
8.329
9.306
9.087
8.041
6.051
6.606
5.53
3.531
10.221
16.964
13.52
7.535
7.524
7.707
8.72
NI no inhibition
a
Synthesized compounds
–
14.022
16.188
7.269
11.918
–
b
Best-fit values against each
binding hypothesis
–
5.503
6.28
c
% inhibition at 100 lM
inhibitor concentration
–
2.191
8.31
a
b
O
O
O
N
H
Cl
N
H
c
Fig. 4 Synthesized compound 3d mapping a GluHypo10/1, b Glu-
Hypo4/4 (hydrogen bond acceptor as green vectored spheres,
hydrophobic features as blue spheres, ring aromatic as orange
vectored spheres, hydrogen bond donor as violet vectored spheres),
and c Chemical structure of compound 3d (Color figure online)
123

Med Chem Res
a
b
O
OH
O
N
H
Cl
N
H
c
Fig. 5 Synthesized compound 4d mapping a GluHypo10/1, b Glu-
Hypo4/4 (hydrogen bond acceptor as green vectored spheres,
hydrophobic features as blue spheres, ring aromatic as orange
vectored spheres, hydrogen bond donor as violet vectored spheres),
and c chemical structure of compound 4d (Color figure online)
General procedure for synthesis of 1H-1,2,4-triazole-
5(4H)-thione derivatives (12a–f)
(C indole), 136.5 (C indole), 143.0, 146.2 (2C Ar), 171.2
(C=O), 181.0 ppm (C=S); HRMS (ESI) m/z [M?Na]?
392.0819 (C17H15N5O3SNa requires 392.0793).
A solution of the thiosemicarbazide derivative 11a, 11c–f,
or 11h (5.5 mmol) in 5 % sodium hydroxide solution
(100 mL) was heated under reflux for 4 h. After cooling to
room temperature, concentrated hydrochloric acid was
added. The precipitate was filtered and washed several
times with distilled water (Ilyin et al., 2007). The titled
compounds were recrystallized from ethanol.
2-(2-(1H-Indol-3-yl)acetyl)-N-(naphthalen-1-
yl)hydrazinecarbothioamide (11h)
(77 %): mp. 197–199 °C; 1H-NMR (300 MHz, DMSO-d6) d
3.63 (s, 2H, CH2–C=O), 6.94–7.07 (m, 2H, CH indole), 7.25
(d, J = 1.8 Hz, 1H, CH indole), 7.35 (d, J = 8.1 Hz, 1H, CH
indole), 7.37–7.52 (m, 4H, CH Ar), 7.59 (d, J = 7.8 Hz, 1H,
CH indole), 7.82–7.92 (m, 3H, CH Ar), 9.66 (s, 1H, NH–
(C=S)–NH), 9.85 (s, 1H, NH–(C=S)–NH), 10.20 (s, 1H, NH–
NH–C=S), 10.88 ppm (s, 1H, NH indole); 13C-NMR
(75 MHz, DMSO-d6) d 31.2 (CH2–C=O), 108.5 (C indole),
111.8, 118.7, 119.4, 121.5, 124.3, 124.4, 125.9, 126.4, 126.5,
126.9, 127.4 (11CH indole and Ar), 127.8 (C indole), 128.4
(CH Ar), 131.2, 134.2, 136.1, 136.5 (4C indole and Ar), 171.2
(C=O amide), 183.1 ppm (C=S); HRMS (ESI) m/z [M?Na]?
397.1109 (C21H18N4OSNa requires 397.1099).
4-Methyl-3-(pyrazin-2-yl)-1H-1,2,4-triazole-5(4H)-thione
(12a)
(93 %): mp. 255–258 °C; 1H-NMR (300 MHz, DMSO-d6)
d 3.76 (s, 3H, N–CH3), 8.77 (m, 2H, CH pyrazine), 9.14 (s,
1H, CH pyrazine), 14.21 ppm (s, 1H, NH); 13C-NMR
(75 MHz, DMSO-d6) d 32.9 (N–CH3), 142.5 (C pyrazine),
144.2, 145.5, 146.0 (3CH pyrazine), 147.7 (C triazole),
169.2 ppm (C=S); HRMS (ESI) m/z [M?H]? 194.0506
(C7H8N5S requires 194.0500).
123

Med Chem Res
a
b
c
d
O
O
O
N
H
NO2
N
H
e
f
Fig. 6 Synthesized compound 3c mapping a GalHypo3/1, b GalHyp-
o8/1, c GalHypo10/1, d GalHypo4/5, e GalHypo5/5 (hydrogen bond
acceptor as green vectored spheres, hydrophobic features as blue
spheres, ring aromatic as orange vectored spheres, hydrogen bond
donor as violet vectored spheres), and f chemical structure of
compound 3c (Color figure online)
123

Med Chem Res
a
b
c
d
O
O
O
N
H
Cl
N
H
e
f
Fig. 7 Synthesized compound 3d mapping a GalHypo3/1, b GalHyp-
o8/1, c GalHypo10/1, d GalHypo4/5, e GalHypo5/5 (hydrogen bond
acceptor as green vectored spheres, hydrophobic features as blue
spheres, ring aromatic as orange vectored spheres, hydrogen bond
donor as violet vectored spheres), and f chemical structure of
compound 3d (Color figure online)
123

Med Chem Res
O
N
O
S
O
S
N
NH
NH
N
HN NH
N
HN NH
11b
11a
O
S
N
O
S
N
NH
NH
NH
HN
N
HN NH
N
11c
11d
O
O
S
O
S
NH
NH
NH
HN
HN NH
N
N
H
H
11f
11e
NO2
O
S
NH
O
S
HN NH
NH
HN NH
N
H
N
H
11h
11g
Fig. 8 Chemical structures of the synthesized thiosemicarbazide derivatives 11a–h
4-Phenyl-3-(pyrazin-2-yl)-1H-1,2,4-triazole-5(4H)-thione
8.41 (dd, J = 2.5, 1.3 Hz, 1H, CH pyrazine), 8.62 (d,
J = 2.5 Hz, 1H, CH pyrazine), 8.99 (d, J = 1.3 Hz, 1H,
CH pyrazine), 14.40 ppm (s, 1H, NH); 13C-NMR (75 MHz,
DMSO-d6) d 128.9 (2CH Ar), 129.4 (2CH Ar), 129.5 (CH
Ar), 135.2 (C Ar), 141.8 (C pyrazine), 143.3, 145.0, 146.1
(12b)
(60 %): mp. 297–300 °C; 1H-NMR (300 MHz, DMSO-d6)
d 7.30–7.32 (m, 2H, CH Ar), 7.41–8.43 (m, 3H, CH Ar),
123

Med Chem Res
a
b
O
S
N
NH
N
HN NH
c
Fig. 9 Synthesized compound 11a mapping a GalHypo4/5, b GalHypo4/5 (hydrogen bond acceptor as green vectored spheres, hydrophobic
features as blue spheres, hydrogen bond donor as violet vectored spheres), and c chemical structure of compound 11a (Color figure online)
(3CH pyrazine), 147.9 (C triazole), 169.9 ppm (C=S);
HRMS (ESI) m/z [M?H]? 256.0671 (C12H10N5S requires
256.0657).
indole), 10.99 (s, 1H, NH indole), 13.49 ppm (s, 1H, NH
triazole); 13C-NMR (75 MHz, DMSO-d6) d 22.4 (CH2),
30.3 (CH3), 107.3 (C indole), 112.1, 118.8, 119.2, 121.8,
124.6 (5CH indole), 127.2, 136.8 (2C indole), 152.1
(C triazole), 167.0 ppm (C=S); HRMS (ESI) m/z [M?H]?
245.0856 (C12H13N4S requires 245.0861).
4-(Naphthalen-1-yl)-3-(pyrazin-2-yl)-1H-1,2,4-triazole-
5(4H)-thione (12c)
(64 %): mp. 265–267 °C; 1H-NMR (300 MHz, DMSO-d6)
d 7.34–7.59 (m, 5H, CH Ar), 7.99–8.05 (m, 2H, CH Ar),
8.13 (dd, J = 1.9, 1.1 Hz, 1H, CH pyrazine), 8.50 (d,
J = 1.9 Hz, 1H, CH pyrazine), 9.06 (brs, 1H, CH pyra-
zine), 14.56 ppm (s, 1H, NH triazole); 13C-NMR (75 MHz,
DMSO-d6) d 122.9, 126.0, 126.9 (3CH Ar), 127.8 (2CH
Ar), 128.8 (CH Ar), 130.0 (C Ar), 130.3 (CH Ar), 131.9
(C Ar), 134.1 (C pyrazine), 141.5 (C Ar), 143.2 (CH pyr-
azine), 145.5, 146.0 (2CH pyrazine), 148.4 (C triazole),
170.6 ppm (C=S); HRMS (ESI) m/z [M?H]? 306.0833
(C16H12N5S requires 306.0813).
3-((1H-Indol-3-yl)methyl)-4-(4-methoxyphenyl)-1H-1,2,4-
triazole-5(4H)-thione (12e)
(86 %): mp. 268–270 °C; 1H-NMR (300 MHz, DMSO-d6) d
3.77 (s, 3H, OCH3), 3.89 (s, 2H, CH2), 6.67 (brs, 1H, CH
indole), 6.89–7.13 (m, 6H, CH Ar), 7.28 (t, J = 8.6 Hz, 2H,
CH Ar), 10.81 (s, 1H, NH indole), 13.64 ppm (s, 1H, NH
triazole); 13C-NMR (75 MHz, DMSO-d6) d 22.7 (CH2), 55.9
(OCH3), 107.3 (C indole), 111.9 (CH indole), 114.8 (2CH
Ar), 118.6, 119.0, 121.6, 124.2 (4CH indole), 126.8
(C indole), 127.1 (C Ar), 129.9 (2CH Ar), 136.5 (C indole),
152.2 (C triazole), 160.1 (C Ar), 168.0 ppm (C=S); HRMS
(ESI) m/z [M?Na]? 359.0957 (C18H16N4OSNa requires
359.0943).
3-((1H-Indol-3-yl)methyl)-4-methyl-1H-1,2,4-triazole-
5(4H)-thione (12d)
(86 %): mp. 265–267 °C; 1H-NMR (300 MHz, DMSO-d6)
d 3.53 (s, 3H, N–CH3), 4.13 (s, 2H, CH2), 6.93 (t,
J = 7.4 Hz, 1H, CH indole), 7.05 (t, J = 7.4 Hz, 1H, CH
indole), 7.26 (d, J = 1.7 Hz, 1H, CH indole), 7.33 (d,
J = 8.1 Hz, 1H, CH indole), 7.2 (d, J = 7.9 Hz, 1H, CH
3-((1H-Indol-3-yl)methyl)-4-(naphthalen-1-yl)-1H-1,2,4-
triazole-5(4H)-thione (12f)
(91 %): mp. 247–250 °C; 1H-NMR (300 MHz, DMSO-d6)
d 3.76 (s, 2H, CH2), 6.41 (d, J = 1.6 Hz, 1H, CH Ar),
123

Med Chem Res
a
b
c
d
O
N
O
S
NH
N
HN NH
e
Fig. 10 Synthesized compound 11b mapping a GalHypo3/1, b Gal-
Hypo8/1, c GalHypo10/1, d GalHypo4/5 (hydrogen bond acceptor as
green vectored spheres, hydrophobic features as blue spheres, ring
aromatic as orange vectored spheres, hydrogen bond donor as violet
vectored spheres), and e chemical structure of compound 11b (Color
figure online)
6.83–6.99 (m, 3H, CH Ar), 7.14–7.59 (m, 6H, CH Ar), 7.98
(d, J = 8.2 Hz, 1H, CH Ar), 8.06 (d, J = 8.2 Hz, 1H, CH
Ar), 10.60 (s, 1H, NH indole), 13.84 ppm (s, 1H, NH tri-
azole); 13C-NMR (75 MHz, DMSO-d6) d 22.7 (CH2),
106.9 (C indole), 111.8, 118.4, 118.9, 121.5 (4CH indole),
122.3 (CH Ar), 124.1 (CH indole), 125.9 (CH Ar), 126.9
(C indole), 127.0, 127.5, 127.7, 128.7 (4CH Ar), 129.7
(C Ar), 130.5 (C Ar), 130.6 (CH Ar), 134.2 (C Ar), 136.5
123

Med Chem Res
b-D-galactosidase) were added to the reaction mixtures, and
the concentration of released p-nitorphenol was monitored
at 405 nm every minute within 5-min period. Substrate
concentrations were selected to approximate Km values for
each enzyme. The percentage inhibition was determined
from the residual activity for each compound by comparing
the glycosidase activity with and without the synthesized
compound (Abdula et al., 2011; Abu Khalaf et al., 2011).
S
NH
N
N
N
S
N
N
N
N
NH
N
12a
12b
S
Results and discussion
N
NH
Chemistry
N
S
NH
N
N
N
Initially, 4a was prepared by coupling L-tryptophan methyl
hydrochloride with indole-3-acetic acid to form 3a (Fig. 1),
employing N,N0-carbonyl diimidazole (CDI) as coupling
reagent. Subsequently, basic hydrolysis followed by acid-
ification afforded 4a.
N
H
N
12c
12d
The optimization process preceded by exploring differ-
ent heterocyclic substitutes to the indole wings of 4a and
3a. The fact that 4a and 3a exhibited electron-rich indole
acetic amide moieties prompted us to explore electron-
deficient heterocyclic equivalents of variable hydrophilic/
hydrophobic properties as exemplified in 3b (pyrazine
amide), 3c (m-nitrobenzoic amide), 3d (m-chlorobenzoic
amide), 4b (pyrazine amide), 4c (m-nitrobenzoic amide),
and 4d (m-chlorobenzoic amide).
O
S
N
S
N
NH
N
NH
The synthesis of (S)-Methyl N-(arylcarbonyl)tryptop-
hanoate (3a–d) was achieved by the activation of carbox-
ylic acid 1 (indol-3-acetic acid, 2-pyrazinecarboxylic acid,
3-nitrobenzoic acid and 3-chlorobenzoic acid) with a 1:1
equivalent of N,N0-carbonyldiimidazole in dry DMF under
N2 gas. After stirring for 15 min, a solution of L-tryptophan
methyl ester hydrochloride and triethyl amine in dry DMF
was added; the mixture was stirred overnight; excess DMF
was evaporated, and the residue was placed in the refrig-
erator, then the solid product was filtrated and recrystal-
lized from the appropriate solvent (Scheme 1).
N
N
H
N
H
12e
12f
Fig. 11 Chemical structures of the synthesized 1H-1,2,4-triazole-
5(4H)-thione derivatives 12a–f
(C indole), 152.6 (C triazole), 168.9 ppm (C=S); HRMS
(ESI) m/z [M?H]? 357.1196 (C21H17N4S requires
357.1174).
Scheme 1 shows the synthesis of (S)-N-(arylcarbon-
yl)tryptophan (4a–d) via base-promoted hydrolysis (5 %
NaOH) of their corresponding esters followed by acidifi-
cation with diluted HCl.
In vitro glycosidase inhibition assay
The same procedure employed for the preparation of
compounds 3a–d was used to prepare (S)-ethyl N,N0-bis
(arylcarbonyl)lysinoate (6a–c) as can be seen in Scheme 2.
As was mentioned in the synthesis of 4a–d, the base
hydrolysis of compounds 6a–c followed by acidification with
HCl gives (S)-N,N0-bis(arylcarbonyl)lysine (7a–c) (Scheme 2).
For the synthesis of thiosemicarbazide derivatives (11a–
h), ethyl 2-(1H-indol-3-yl)acetate 8a and ethyl pyrazine-2-
carboxylate 8b were synthesized from corresponding acids
(2-pyrazinecarboxylic acid and indol-3-acetic acid) and
The inhibitory potentials of the synthesized compounds
against b-D-glucosidase and b-D-galactosidase were eval-
uated using spectrophotometric assay of the released
p-nitrophenol. The enzyme solutions of b-D-glucosidase
(0.16 U) or b-D-galactosidase (0.25 U) were pre-incubated
with 100 lM of each particular synthesized compound for
1 h at 25 °C. The final concentration of DMSO did not
exceed 1.0 %. Subsequently, the corresponding substrate
solutions (1.3 mM for b-D-glucosidase and 0.4 mM for
123

Med Chem Res
a
b
S
N
N
N
NH
N
c
Fig. 12 Synthesized compound 12c mapping a GalHypo4/5, b GalHypo5/5 (hydrogen bond acceptor as green vectored spheres, hydrophobic
features as blue spheres, hydrogen bond donor as violet vectored spheres), and c chemical structure of compound 12c (Color figure online)
used as starting material for the acid hydrazide production
(9a, 9b) (Scheme 3). The reaction between acid hydrazide
9 and corresponding isothiocyanate 10 in ethanol yielded
thiosemicarbazide derivatives 11a–h in good yield
(Scheme 3).
b-D-galactosidase. Unfortunately, these analogs showed
reduced anti-glycosidase bioactivities, suggesting particu-
lar significance of the tryptophan moiety for glycosidase
inhibition. Figure 4 shows how compound 3d (% inhibition
of 21 at 100 lM) maps GluHypo10/1 and GluHypo4/4,
while Fig. 5 depicts how compound 4d matches GluHyp-
o10/1 and GluHypo4/4. Figures 6 and 7 illustrate how the
most potent synthesized b-D-galactosidase inhibitors, 3c
and 3d, respectively, map all b-D-galactosidase inhibitor
pharmacophores. Tables 1 and 2 give the fit values of the
synthesized derivatives and the actual affinities against
b-D-glucosidase and b-D-galactosidase inhibitor pharma-
cophores, respectively.
Scheme 3 shows the synthesis of triazole derivatives
1H-1,2,4-triazole-5(4H)-thione (12a–f) through the cycli-
zation of the corresponding thiosemicarbazide derivatives
in aqueous sodium hydroxide solution (5 %).
Biological evaluation
The fact that 4d (% inhibition of 49 at 100 lM) and 3c (%
inhibition of 37 at 100 lM) exhibited the best inhibitory
bioactivities against b-D-glucosidase and b-D-galactosi-
dase, respectively (Tables 1, 2) prompted us to keep elec-
tron-deficient heterocyclic substituents at the amide side
and explore electron-deficient, hydrophilic/hydrophobic
replacements for tryptophan moiety as exemplified in
compounds 6a, 6b, 6c, 7a, 7b, and 7c (Fig. 1). Addition-
ally, these analogs should provide information about
the influence of the length of the aliphatic linker on
the inhibitory action against b-D-glucosidase and
The generated b-D-galactosidase inhibitor pharmaco-
phore models were assessed against a group of syntheti-
cally facile thiosemicarbazide derivatives of which
compound 11a (Fig. 8) illustrated moderate fit values
against 3 out of the 5 developed b-D-galactosidase inhibitor
pharmacophore models (Fig. 9; Table 2). The fact that this
compound exhibited mediocre anti-b-D-galactosidase
activity (% inhibition of 10 at 100 lM) prompted us to
explore its chemical neighborhood toward more potent
inhibitors. The exploration process proceeded via assessing
123

Med Chem Res
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a variety of side chains substituents: electron-rich versus
electron-poor, bulky versus lean, or aliphatic versus aro-
matic. Compound 11b achieved the best results by both
fitting all 5 b-D-galactosidase pharmacophore models and
achieving the best in vitro inhibitory properties against b-D-
galactosidase (% inhibition of 28 at 100 lM). Figure 10
shows how 11b maps b-D-galactosidase inhibitor pharma-
cophore models. This supports the inference of direct
relationship between pharmacophore mapping and inhibi-
tory bioactivity.
The fact that the corresponding 1H-1,2,4-triazole-5(4H)-
thione cyclization derivatives 12b and 12c (Fig. 11) dis-
played good fit properties against b-D-galactosidase inhib-
itor pharmacophore models prompted us to explore the
inhibitory potential of these analogs. Figure 12 shows how
the synthesized compound 12c maps GalHypo4/5 and
GalHypo5/5. Other 1,2,4-triazolin-3-thione product that do
not match b-D-galactosidase inhibitor pharmacophore
models exhibit no activity.
Although our newly synthesized compounds are of
lower potency than some published b-D-galactosidase and
b-D-glucosidase inhibitors, these derivatives are charac-
terized by their novel scaffold that can serve as promising
leads for further optimization.
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Protective effect of p-methoxycinnamic acid, an active phenolic
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Jenkinson SF, Best D, Saville AW, Mui J, Martinez RF, Nakagawa S,
Conclusions
Synthetic investigation of a series of b-D-glucosidase and
b-D-galactosidase inhibitors was successfully achieved.
Tryptophan analogs, thiosemicarbazide derivatives, and
their corresponding 1H-1,2,4-triazol-5(4H)-thione deriva-
tives were synthesized and biologically evaluated. Synthe-
sized compounds 3c (% inhibition of 37 at 100 lM) and 4d
(% inhibition of 49 at 100 lM) exhibited the best inhibitory
bioactivities against b-D-galactosidase and b-D-glucosidase,
respectively. They can serve as a promising lead compounds
for the development of potential glycosidase inhibitors.
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