Synthesis and Comparative Inotropic Effects of Several Isoquinoline Alkaloids

Article abstract of DOI:10.1007/s11094-020-02148-4

Compounds 3a [1-(3′,4′-methylenedioxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] and 3b [1-(6′-bromo-3′,4′-dimethoxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] demonstrated dose-dependent (5-75 μM) negative inotropic effects. Compound 5 [1,3-bis-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin- 1-yl)propane] demonstrated a two-phase inotropic effect. The experimental results and a literature analysis suggested that the negative inotropic effects of the tested compounds (3a, 3b, 5) could be due to their influences on the [Ca²⁺]_i concentration through blocking of cardiomyocyte Na⁺- and Ca²⁺-channels. The positive inotropic effect of free base 5 could be related to modulation of cardiomyocyte muscarinic receptor activity.

Full text of DOI:10.1007/s11094-020-02148-4

DOI 10.1007/s11094-020-02148-4
Pharmaceutical Chemistry Journal, Vol. 54, No. 1, April, 2020 (Russian Original Vol. 54, No. 1, January, 2020)
SYNTHESIS AND COMPARATIVE INOTROPIC EFFECTS
OF SEVERAL ISOQUINOLINE ALKALOIDS
Sh. S. Khushmatov,1 I. Z. Zhumaev,1 Sh. N. Zhurakulov,2
A. Sh. Saidov,3,* and V. I. Vinogradova2
Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 54, No. 1, pp. 9 – 13, January, 2020.
Original article submitted March 24, 2015.
Compounds 3a [1-(3¢,4¢-methylenedioxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] and 3b
[1-(6¢-bromo-3¢,4¢-dimethoxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] demonstrated dose-de-
pendent (5-75 mM) negative inotropic effects. Compound 5 [1,3-bis-(6,7-dimethoxy-1,2,3,4-tetrahydroisoqui-
nolin-1-yl)propane] demonstrated a two-phase inotropic effect. The experimental results and a literature anal-
ysis suggested that the negative inotropic effects of the tested compounds (3a, 3b, 5) could be due to their influ-
ences on the [Ca2+]i concentration through blocking of cardiomyocyte Na+- and Ca2+-channels. The positive
inotropic effect of free base 5 could be related to modulation of cardiomyocyte muscarinic receptor activity.
Keywords: papillary muscle, positive inotropic effect, isoquinoline alkaloids.
Natural isoquinolines and many of their derivatives pos-
sess broad spectra of pharmacological activity [1 – 8].
Biotesting of several isoquinoline derivatives revealed that
they had physiological effects on the cardiovascular system
[9 – 15]. Therefore, the synthesis of new isoquinoline deriva-
tives (Scheme 1) and the study of their mechanism of
cardiotropic action on the contractile activity of rat papillary
thesized compounds were confirmed using IR and PMR
spectroscopy.
EXPERIMENTAL CHEMICAL PART
PMR spectra were recorded on Tesla BS-567A
(100 MHz) and Varian UNITY-400+ spectrometers (CDCl
3
and DMSO-d solvents, HMDS internal standard). R values
6
f
muscle are highly interesting.
were determined on LS 5/40 silica gel plates with elution by
The target compounds were prepared using Pictet–
CHCl —MeOH (4:1). Melting points of all synthesized com-
3
Spengler and Bischler–Napieralski reactions. The amine
component was homoveratrylamine (1), condensation of
which with aldehydes 2a and 2b gave Schiff bases that
formed isoquinolines (3a and 3b) after cyclization in
pounds were determined on a Boetius melting-point appara-
tus.
General method for preparing substituted 1-aryltet-
rahydroisoquinolines. A solution of 3,4-dimethoxyphenyl-
ethylamine (1, 1.66 g, 0.009 mol) in C H (30 mL) was
CF COOH [16]. The reaction of 1 with glutaric acid fol-
3
6
6
lowed by Bischler—Napieralski cyclization of the diamide
(4) and reduction of the 3,4-dihydroisoquinoline synthesized
bis-tetrahydroisoquinoline 5 [17]. The structures of the syn-
treated with a substituted benzaldehyde (2, 0.009 mol),
refluxed with a Dean—Stark trap until H O evolution ceased
2
(1 – 2 h), cooled, and made basic to pH 9 – 10 using
NH OH. The amine was exhaustively extracted by CHCl .
4
3
1
A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of
1-(3¢,4¢-Methylenedioxyphenyl)-6,7-dimethoxy-1,2,3,4-
tetrahydroisoquinoline (3a), C H O N, was prepared
the Republic of Uzbekistan, 83 Kh. Abdullaev St., Tashkent, 100125,
Uzbekistan; e-mail: Khushmatov Sh. S@bk.ru
18 19
4
2
S. Yu. Yunusov Institute of the Chemistry of Plant Substances, Academy
from the amine (1.66 g, 0.009 mol) and 3,4-methylenedioxy-
benzaldehyde (1.37 g, 0.009 mol). Yield 2.06 (72%), mp
254 – 257°C, Me CO, R 0.5. PMR (400 MHz, CDCl ), d,
of Sciences of the Republic of Uzbekistan, Kh. Abdullaev St., Tashkent,
100170, Uzbekistan; e-mail: j.sherzod.78@mail.ru
3
A. Navoi Samarkand State University, Samarkand, 140104 Uzbekistan.
2
f
3
*
e-mail: a-saidov85@mail.ru
ppm: 2.66 (1H, dt, J 4.7, 15.9 Hz, H -4), 2.85 (1H, ddd, J 4.6,
a
7
0091-150X/20/5401-0007 © 2020 Springer Science+Business Media, LLC

8
Sh. S. Khushmatov et al.
Scheme 1
O
H
C
H3CO
H3CO
R1
H3CO
H3CO
H+
NH
+
NH2
R3
R1
R2
2a, b
1
3a, b
R3
+
a: R1=H; R2 =R3 =OCH2O;
b: R1=Br; R2 =R3=OCH3
R2
O
O
H
C
(CH2)3 C
H
H3CO
H3CO
H3CO
OCH3
NH
(CH2)3
1. POCl3
HN
NH
2. NaBH4
C (CH2)3
C
H3CO
OCH3
O
O
OCH3
OCH3
HN
4
5
8.4, 12.1 Hz, H -4), 2.96 (1H, ddd, J 5.4, 8.4, 15.8 Hz, H -3),
3.57 (4H, t, J 7.5 Hz, H-3.3¢); 3.84 (6H, s, OCH ); 3.85 (6H,
e
a
3
3.15 (1H, dt, J 5.2, 12.1 Hz, H -3), 3.61* (3H, s, OCH -7),
s, OCH ); 6.62 (2H, s, H-8.8¢); 7.00 (2H, s, H-5.5¢).
e
3
3
3.80* (3H, s, OCH -6), 4.90 (1H, s, H-1), 5.87 (2H, dd, J 1.4,
1,3-bis-(6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinolin-
1-yl)propane (5). Yield 5.84% (0.33 g), C H N O , mp
3
2.3 Hz, 3¢-OCH O-4¢), 6.20 (1H, s, H-8), 6.55 (1H, s, H-5),
25 34
2
4
2
99 – 101°C (Me CO), R 0.35. IR spectrum, n, cm– 1: 3378,
6.64 (1H, d, J 1.4 Hz, H-2¢), 6.67 (1H, dd, J 1.5, 7.9 Hz,
H-6¢), 6.69 (1H, d, J 7.9 Hz, H-5¢). 13C NMR spectrum, d,
2
f
2917, 1612, 1520, 1468, 1257, 1223. PMR spectrum
(400 MHz, CDCl , d, ppm: 1.57 (4H, q, J 7.4, H-1¢,2¢); 1.83
ppm: 29.51 (C-4), 42.09 (C-3), 56.05 (6-OCH ), 56.12
3
3
(2H, m, CH ), 2.63 (4H, dt, J 6 Hz, H-4.4¢); 3.86 (2H, dd, J 3.5,
(7-OCH ), 61.42 (C-1), 101.16 (C-7¢), 108.06 (C-5¢), 109.35
2
3
8.5 Hz, H-1, 1¢); 6.50 (2H, s, H-8, 8¢); 6.55 (2H, s, H-5, 5¢).
(C-2¢), 111.17 (C-8), 111.64 (C-5), 122.39 (C-6¢), 127.85
(C-1¢), 130.14 (C-8a), 139.24 (C-4a), 146.99 (C-6), 147.29
(C-7), 147.87 (C-3¢), 147.91 (C-4¢).
EXPERIMENTAL BIOLOGICAL PART
N,N¢-(3,4-Dimethoxy-b-phenylethyl)glutardiamide
(4), C H N O . A mixture of 1 (5 g, 0.027 mol) and glu-
The experiments were conducted according to the Coun-
cil of International Organizations for Medical Sciences
(CIOMS) International Guiding Principles for Biomedical
Research Involving Animals of 1985. Experiments were per-
formed on prepared papillary muscle that was isolated from
the right cardiac ventricle of mature laboratory white rate
(150 – 200 g) and placed into a special chamber perfused
with Krebs—Henseleit buffer (pH 7.4). The solutions were
oxygenated with carbogen (O 95%, CO 5%) at 35 ± 0.5°C.
25 34
2
6
taric acid (2 g, 0.011 mol) was dissolved in MeOH (5 mL).
Then, the salt was heated at 178°C on an oil bath for 2 h. The
reaction mixture was dissolved in CHCl (100 mL) and
3
treated with HCl solution (3%), NaOH solution (2%), and
H O until neutral. The CHCl was distilled off. The solid was
2
3
crystallized from Me CO to afford crystals that were filtered
2
off. Yield 79% (5 g), mp 132 – 135°C (Me CO), R 0.76. IR
2
f
2
2
spectrum (KBr), n, cm–1: 3290 (NH), 2931 (Ar-CH), 1638
Prepared muscle was clamped in the experimental chamber
with one end connected to the rod of an F30 stress sensor
(Germany). The muscle was stimulated using Pt electrodes
and an ESL-2 stimulator (Russia) with rectangular pulses at
0.5 – 3 Hz for 5 – 10 ms at amplitude 20% greater than
threshold. The muscle was stabilized for 60 min, after which
the length at which it developed the maximal isometric stress
(N-C=O), 1591, 1551, 1519 (Ar-H). PMR spectrum
(400 MHz, CDCl , d, ppm: 1.82 (2H, t, J 6.9 Hz, H-2¢); 2.10
3
(4H, t, J 7 Hz, H-1¢,3¢); 2.70 (4H, t, J 7 Hz, H-a); 3.41 (4H,
q, J 6.2 Hz, H-b); 5.69 (2H, t, NH); 6.64 (2H, d, J 2 Hz, H-2);
6.66 (2H, dd, J 2 Hz, 8.6, H-6); 6.74 (2H, d, J 8.6 Hz, H-5).
1,3-bis-(6,7-Dimethoxy-3,4-dihydroisoquinolin-1-yl)p
(L ) was found. All experiments were performed under
max
ropane. A mixture of diamide 4 (0.5 g, 0.6 mmol) in POCl
3
these conditions. The stress sensor signal was fed into an am-
plifier (TAM-A, Hugo Sachs Elektronik, Germany) and re-
corded using a TZ 4620 recorder (Czech Rep.). Results were
statistically processed using the OriginPro 7.5 statistical pro-
gram suite (OriginLab Corp., USA). The paired Student
(1.5 mL) was refluxed on a water bath for 6 h to afford the
dihydroisoquinoline (0.4 g, 87%). C H N O . PMR spec-
25 32
2
4
trum (400 MHz, CDCl , d, ppm: 2.02 (2H, q, J 7.2 Hz, CH );
3
2
2.57 (4H, t, J 7.3 Hz, 2CH ); 2.81 (4H, t, J 7.5 Hz, H-4, 4¢);
2

Synthesis and Comparative Inotropic Effects
9
a
3a
1-(3,4-methylenedioxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline
Control
5 mM
10 mM
25 mM
75 mM
3
2
1
0
20 min
0
5
10
Time, min
b
3a
3b
100
80
60
40
20
0
*
*
**
**
*
**
**
**
0
25
50
75
Concentration, mM
Fig. 1. Negative inotropic effects of alkaloids 3a [1-(3¢,4¢-methylenedioxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] and 3b
[1-(6¢-bromo-3¢,4¢-dimethoxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] on contractile activity of rat heart papillary muscle: nega-
tive trace of contractions of papillary muscle at stimulation frequency 0.5 Hz (a); concentration-dependent inotropic effect of studied alkaloids
(b ). Along the ordinate, muscle contraction force expressed in percent of maximal; along the abscissa, solution concentration of 3a and 3b.
*
**
p < 0.05; p < 0.01 (n = 3 – 5).
t-criterion was used to find the statistical significance of
changes before and after administration of the alkaloid. Dif-
ferences were considered statistically significant for p < 0.05
and 0.01.
of these compounds decrease [Ca2+] by inhibiting its entry
i
into cardiomyocytes from the extracellular milieu; others, by
modifying Ca2+-transporter systems of intracellular Ca2+-de-
pots. Therefore, it could be proposed that the NIE of the
studied alkaloids was due to reduction of [Ca2+] by modify-
The experimental results showed that isoquinoline alka-
loids 3a and 3b had dose-dependent (5 – 75 mM) effects on
the contractile activity of rat papillary muscle starting at
5 mM. Compounds 3a and 3b suppressed the contraction
force by 12.6 ± 2.8 and 14.2 ± 3.4%, respectively, as com-
pared to the control (n = 3 – 5). The degrees of suppression
reached maxima at 75 mM of 83.5 ± 6.6 and 92.4 ± 5.4%, re-
spectively, as compared to the control (Fig. 1). Also, com-
pound 5 affected specifically the contractile activity of rat
heart papillary muscle. Compound 5 at all used stimulation
frequencies (0.1 – 3 Hz) and a concentration of 75 mM ini-
tially increased the muscle contraction force by 27.3 ± 4.7%
relative to the control.
i
ing Ca2+ transport through the sarcolemma. Data indicating
that the NIE of isoquinoline alkaloids is related to blocking
of Na+-, K+-, and Ca2+-channels of cardiomyocytes were
published. For example, the isoquinoline alkaloid dauricine,
which possesses significant antiarrhythmic activity, blocks
Na+-, K+-, and Ca2+-channels of cardiomyocytes and in-
creases the duration of the myocardium action potential.
Modulation of the duration of the refractory myocardium ac-
tion potential resulting from modification of ion channels
was found experimentally to underly the antiarrhythmic ac-
tivity of several isoquinoline derivatives demonstrating NIEs
[18]. Research on several isoquinolone alkaloids, in particu-
lar berberine, found that they blocked L-type and T-type
Ca2+-channels of cardiomyocytes [19] whereas others, e.g.,
cycleanine, blocked only myocardium L-type Ca2+-channels
and smooth-muscle cells of isolated rabbit aorta [20]. Several
studies found that isoquinolone alkaloids such as berberine
blocked L-type and T-type cardiomyocyte Ca2+-channels
[19] whereas cycleanine blocked more effectively myocar-
dium Ca2+-channels and isolated rabbit aorta smooth muscle
The positive inotropic effect (PIE) of 5 changed to nega-
tive (NIE) after 1 – 1.5 min of incubation. The contraction
force decreased by 85.4 ± 7.1% as compared to the control
(p < 0.05) (Fig. 2).
Under these conditions, the EC (concentration causing
50
50% suppression of contraction force) for 5 was 24.6 mM.
Reduction of the intracellular [Ca2+] in cardiomyocytes is
i
one reason for NIEs of most pharmacological agents. Several

10
Sh. S. Khushmatov et al.
a
5 [1,3-bis-(6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinolin-1-yl)propane]
10 mM
25 mM
75 mM
Control
3
2
1
0
PIE
NIE
0
5
10
Time, min
b
5 [1,3-bis-(6,7-Dimethoxy-1,2,3,4-
150
tetrahydroisoquinolin-1-yl)propane]
*
100
50
*
*
*
0
0
5
10 15
Time, min
20
25
Fig. 2. Two-phase inotropic effect of 5 [1,3-bis-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-1-yl)propane] on contractile activity of rat heart
papillary muscle: original trace of contractions of papillary muscle at stimulation frequency 1 Hz (a); time-dependent two-phase inotropic effect
of 5 (b). Along the ordinate, muscle contraction force expressed in percent of maximal; along the abscissa, concentration incubation time, min.
*
p < 0.05 vs. the control (n = 4).
cells, in contrast with nifedipine, which blocked potential-
dependent L-type Ca2+-channels [20].
alkaloid BIIA (3-benzylamino-5,6-dihydro-8,9-dimethoxy-
imidazo[5,1-a]isoquinoline hydrochloride) and was associ-
ated with blocking of cardiomyocyte Na+/K+-ATPase
activity without influencing cardiomyocyte a and b-adreno-
receptors [22]. BIIA (5 – 100 mM) competed with the cardiac
glycoside ouabain for blocking of cardiomyocyte Na+/K+-
ATPase activity. The antiarrhythmic effect of this alkaloid
may be related to its influence on the duration of the cardio-
myocyte action potential [23]. The antiarrhythmic activity of
the isoquinoline alkaloid tetradrine was demonstrated to be
due to blocking of Ca2+-channels via modulation of cardio-
myocyte muscarinic receptor (MR) activity [13]. Therefore,
we surmised that the PIE caused by 5 might be due to its in-
fluence on cardiomyocyte MR functioning. The influence of
atropine, a MR blocker, on the effects caused by 5 was stud-
ied to check this hypothesis. The experiments demonstrated
that the PIE of 5 decreased significantly if MRs were
blocked by atropine (5 mM).
Thus, the NIEs of 3a, 3b, and 5 could be assumed to be
due to their influence on [Ca2+] via blocking of cardio-
i
myocyte Na+-, K+-, and Ca2+-channels, which determined
their contractile activity. Synthetic isoquinoline-alkaloid de-
rivatives CSH109 and CSH118 increased dose-dependently
rat myocardium contraction force with the latter also increas-
ing the myocardium action potential duration. The PIE of
CSH109 was proposed to be related to increased [Ca2+] via
in
activation of cardiomyocyte b-adrenoreceptors [21]. b-Adre-
nergic stimulation is known to have a PIE on mammal
myocardium that is caused, among others, by an increase of
cardiomyocyte current ICa2+ . Activation of cardiomyocyte
L
b-adrenoreceptors is related to the b-receptor of transmem-
brane adenylate cyclase that stimulates G -protein, thereby
s
increasing cAMP. In turn, cAMP activates protein kinase A,
which phosphorylates cellular proteins, including L-type
Ca2+-channels. Phosphorylation of Ca2+-channels increases
cAMP-dependent activation through G-protein with
stimulation of cardiomyocyte MRs is known to occur with
phosphorylation of cardiomyocyte enzyme systems that reg-
ulate contraction [23]. Thus, the Ca2+-sensitivity of
myofilaments is increased by phosphorylation of myosin so
that the contraction force increases (PIE) [24].
intracellular current ICa2+ , which increases Ca2+ release
L
from sarcoplasmic reticulum by ryanodine receptors (RyR)
and increases myocardium contractions (PIE). Therefore, the
role of cardiomyocyte b-adrenoreceptors on the PIE of 5 was
studied in the next series of experiments.
It is noteworthy that the PIE of the tested alkaloid did not
change if the b-adrenoreceptor blocker propranolol (10 mM)
was used. Previously, a PIE was reported for the isoquinoline
A comparison of the present results with the literature
suggested that the PIE of free base 5 and its effect on
cardiomyocyte MR activity were consistent.

Synthesis and Comparative Inotropic Effects
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