Highly potent activity of isopulegol-derived substituted octahydro-2H-chromen-4-ols against influenza A and B viruses

Article abstract of DOI:10.1016/j.bmcl.2018.04.057

A set of (?)-isopulegol derived octahydro-2H-chromen-4-ols was synthesized and evaluated in vitro for antiviral activity against panel of reference influenza virus strains differing in subtype, origin (human or avian) and drug resistance. Compound (4R)-11

Full text of DOI:10.1016/j.bmcl.2018.04.057

Bioorganic & Medicinal Chemistry Letters xxx (2018) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Highly potent activity of isopulegol-derived substituted octahydro-2H-
chromen-4-ols against influenza A and B viruses
Irina V. Ilyina a,b, Vladimir V. Zarubaev c, Irina N. Lavrentieva c, Anna A. Shtro d, Iana L. Esaulkova e,
Dina V. Korchagina a, Sophia S. Borisevich f, Konstantin P. Volcho a,b, , Nariman F. Salakhutdinov a,b
⇑
a Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Lavrentjev av.9, 630090 Novosibirsk, Russian Federation
b Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russian Federation
c Pasteur Institute of Epidemiology and Microbiology, 14 Mira str., 197101 St. Petersburg, Russian Federation
d Department of Pre-clinical trials, Influenza Research Institute, 15/17 Prof. Popova St., 197376 St. Petersburg, Russian Federation
e Saint Petersburg State University, 7/9 Universitetskaya nab., 199034 St. Petersburg, Russian Federation
f Laboratory of chemical physics, Ufa Chemistry Institute of the Ufa Federal Research Center, 71 Octyabrya pr., 450054 Ufa, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
A set of (ꢀ)-isopulegol derived octahydro-2H-chromen-4-ols was synthesized and evaluated in vitro for
antiviral activity against panel of reference influenza virus strains differing in subtype, origin (human or
avian) and drug resistance. Compound (4R)-11a produced via one-pot synthesis by interaction between
(ꢀ)-isopulegol and acetone was found to exhibit an outstanding activity against a number of H1N1 and
H2N2 influenza virus strains with selectivity index more than 1500. (4R)-11a was shown to be most
potent at early stages of viral cycle. Good correlation between anti-viral activity and calculated binding
energy to hemagglutinin TBHQ active site was demonstrated.
Received 14 March 2018
Revised 19 April 2018
Accepted 23 April 2018
Available online xxxx
Keywords:
Influenza
Antiviral
Ó 2018 Elsevier Ltd. All rights reserved.
Monoterpene
Chromene
Montmorillonite K10
Development of novel drugs for therapy and prevention of viral
infections remains a first-level priority problem of modern phar-
macology and medicinal chemistry. Influenza is the most common
human infectious disease, with 9% of the world population (20% in
USA alone) affected annually.1 The influenza virus causes recurrent
epidemic outbreaks characterized by mass morbidity and high
mortality rates associated with influenza complications.2 Along-
side vaccination, chemotherapy is the key method to prevent and
treat viral diseases, especially during the pandemics when a new
virus spreads much faster than the practical medicine can produce
vaccine and immunize the epidemically significant population
cohort.
The high variability of the influenza virus allows it to become
resistant to the few currently used anti-influenza drugs (neu-
raminidase inhibitors (oseltamivir and zanamivir) and M2 channel
blockers (amantadine and rimantadine).3 The development of
drug-resistant influenza virus mutants can be prevented by using
a combination of two or more agents with different mechanisms
of action.4 Hence, it is necessary to search for novel anti-influenza
agents belonging to new structural types, including those whose
targets and mechanisms of action differ from the currently used
ones.
Natural compounds, including monoterpenoids that are compo-
nents of natural essential oils exhibiting antiviral activity, are a
promising source of novel anti-influenza agents.5,6 For example,
(+)-a
-pinene-derived compounds pinanamine (Fig. 1)7 and its
derivative 18 were found to be more active than amantadine with
respect to influenza A M2 channel inhibition. Several imines based
on natural (+)-camphor were shown to be promising antiviral
agents. Thus, camphecene (Fig. 1) exhibits a high level and a broad
range of inhibiting activity against influenza viruses including
viruses A of H1N1, H3N2 and H5N2 subtypes and influenza B.9,10
Its activity is supposed to be based on inhibition of viral hemagglu-
tinin.13 Substituted 1-norbornylamine 2 (Fig. 1) synthesized from
( )-camphor also exhibited high activity against influenza virus
A.11
⇑
Corresponding author at: Novosibirsk Institute of Organic Chemistry, Siberian
Branch of the Russian Academy of Sciences, Lavrentjev av.9, 630090 Novosibirsk,
Russian Federation.
Interesting group of compounds exhibiting activity against the
influenza virus H1N1 was derived from monoterpenoid diol 3
(Fig. 1), which is synthesized from a monoterpenoid (ꢀ)-verbenone
E-mail address: volcho@nioch.nsc.ru (K.P. Volcho).
https://doi.org/10.1016/j.bmcl.2018.04.057
0960-894X/Ó 2018 Elsevier Ltd. All rights reserved.
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2
I.V. Ilyina et al. / Bioorganic & Medicinal Chemistry Letters xxx (2018) xxx–xxx
(usually aldehydes) in the presence of various catalysts, including
montmorillonite clays,18–22 zeolites and mesoporous materi-
als,23,24 Lewis acids,20 and iodine25 (Scheme 1). (R)-Citronellal 920
can also be used as a starting compound as it is converted to
(ꢀ)-isopulegol 7 during the reaction. However, compound 9 is
more expensive that isopulegol
7 and the catalyst Sc(OTf)3
employed in this reaction is also quite expensive. Based on these
findings, we selected (ꢀ)-isopulegol 7 as a starting agent to synthe-
size compounds with the octahydro-2H-chromene framework;
montmorillonite clay, which is most often used for these processes,
was chosen as a catalyst.
We started our research with studying the reaction between
(ꢀ)-isopulegol 7 and acetone 10a (Scheme 2). Iodine in dichloro-
methane was previously used to catalyze this reaction;25 the only
diastereomer (4S)-11a, which was mistakenly assigned by
authors25 as (4R)-11a (for details, see Suppl. data), was produced
with 49% yield.
We used K10 montmorillonite clay as a catalyst. The reaction
was carried out in the absence of solvent at room temperature
for 1 h; i.e., under the conditions used previously when studying
the interaction between alcohol 7 and hetaryl aldehydes.18 As a
result, the heterocyclic compounds (4R)- and (4S)-11a (Scheme 2)
with the octahydro-2H-chromene framework (a mixture of two
isomers with respect to the relative position of the methyl and
hydroxyl groups at the C(4) position) were obtained with the total
yield of 21% (the (4R)/(4S) ratio being equal to 9:1). In addition,
other three compounds were formed during the reaction; accord-
ing to the GC-MS data, they are the products of dehydration of
chromenes 11a (m/z = 194) and apparently contain a double bond
(12–14) similar to what was observed in the reactions between
(ꢀ)-isopulegol 7 and hetaryl aldehydes.18 The total yield of the
dehydration products was 23%.
We managed to isolate individual compounds (4R)-11a and
(4S)-11a, while the isomeric compounds 12–14 could not be sepa-
rated by column chromatography with SiO2 adsorbent used for
product separation. Hence, both diastereomers were produced
using K10 clay to catalyze the reaction between isopulegol 7 and
acetone for further research on their biological activity.
We have attempted to select reaction conditions that would
reduce the contents of 12–14 and increase the yield of 11a. Ear-
lier,19 H+-K10 montmorillonite clay produced by treating K10 clay
with 1 M HCl was successfully applied for Prins cyclization reac-
tions of isopulegol with aldehydes. We found that when using
H+-K10 montmorillonite clay to catalyze the reaction between
(ꢀ)-isopulegol 7 and acetone 10a and conducting the reaction at
room temperature for 2.5 h, the total yield of 11a increased from
21% to 57% (the (4R)/(4S) ratio being equal to 3:1), while the total
yield of 12–14 was 24%.
Fig. 1. Structure of monoterpene-derived compounds with anti-influenza activity.
in three stages.12 Thus, anti-influenza activity was observed for
mononicotinate 4,13 compound 5 with the hexahydro-2H-chro-
mene framework synthesized via interaction between monoter-
penoid 3 and p-chlorobenzaldehyde in the presence of K10 clay,
and fluorine-containing compound 6 produced using BF3 * Et2O
as a catalyst and a reagent.14 Compound 6 seems to be the most
promising one among these compounds combining high antiviral
potency (IC50 = 5 mM) and low cytotoxicity with the selectivity
index SI (the ratio of the 50% cytotoxic concentration to the 50%
inhibitory concentration) value of 55.
2-(5-Bromothiophen-2-yl)octahydro-2H-chromen-4-ol
8
(SI
value of 25) synthesized via interaction between monoterpenoid
(ꢀ)-isopulegol 7 and 5-bromothiophene-2-carbaldehyde (Fig. 1)
has recently been shown to exhibit antiviral activity.15 Although
chromenes derived from compound 7 had a less pronounced
anti-influenza activity than compounds synthesized from diol 3,
it is preferential from a practical perspective to search for novel
antiviral compounds among polyhydro-2H-chromenes synthesized
from (ꢀ)-isopulegol 7 rather than from diol 3. The reason is that
(ꢀ)-isopulegol 7 is a commercially available compound, while 3
is produced via multi-stage synthesis.12 Furthermore, (ꢀ)-isopule-
gol 7 shows higher activity in reacting with carbonyl compounds
than monoterpenoid 3 does; heterocyclic compounds with the
octahydro-2H-chromene framework are the only products in these
reactions, while the interaction between compound 3 and aldehy-
des often yields complex reaction mixtures.16,17
Based on these results, all the subsequent reactions between
(ꢀ)-isopulegol 7 and ketones were carried out using H+-K10 clay
at room temperature for 2 h, with the catalyst quantity varied in
Since the products obtained via interaction between isopulegol
7 and aldehydes exhibited only moderate antiviral activity, the aim
of this study was to search for novel anti-influenza agents with the
octahydro-2H-chromene framework synthesized via interaction
between isopulegol 7 and ketones.
The key method for stereoselective synthesis of chiral com-
pounds with the octahydro-2H-chromene framework is the inter-
Scheme 1. Synthesis of chiral compounds with octahydro-2H-chromene
action between (ꢀ)-isopulegol
7
and carbonyl compounds
framework.
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I.V. Ilyina et al. / Bioorganic & Medicinal Chemistry Letters xxx (2018) xxx–xxx
3
Scheme 2. Synthesis of 11a–c, 16, 17a–d.
order to achieve the complete conversion of alcohol 7 and optimal
yields of the target octahydro-2H-chromenols 11. Only symmetri-
cal aliphatic ketones, both cyclic and acyclic, were used to avoid
formation of the isomers with respect to position 2 among the
products (Scheme 2).
formed the reactions between (ꢀ)-isopulegol 7 and aldehydes
carrying the linear and cyclic aliphatic substituents, namely,
butyraldehyde 22a and cyclohexanecarbaldehyde 22b (Scheme 3).
The reactions were conducted in the presence of K10 montmoril-
lonite clay for 1 and 1.5 h, respectively. Unlike the reactions
between alcohol 7 and ketones, the interaction with aldehydes
was characterized by higher yields and was not accompanied by
formation of dehydration products. The individual (4R)- and (4S)-
isomers of 23a and 23b carrying a single substituent at the C(2)
position were isolated by column chromatography.
A set of target compounds with the octahydro-2H-chromene
framework has been synthesized in this study, making it possible
to investigate their antiviral activities.
For biological testing, we used reference laboratory strain of
H1N1 subtype (A/Puerto Rico/8/34) at the first step. The antiviral
activity of the synthesized compounds was studied using the tech-
nique described recently.29
Cytotoxicity of the compounds was evaluated in MDCK cells as
described previously.29,30 The selectivity index was calculated for
each derivative based on the data obtained. The compounds with
SI = 10 and higher were considered as active.
The results of an in vitro study of cytotoxic and antiviral proper-
ties of the resulting compounds against H1N1 (A/Puerto Rico/8/34)
virus are summarized in Table 1.
One can see from the data summarized in Table 1 that the (4R)-
isomer of 11a, which was synthesized via interaction between (ꢀ)-
isopulegol 7 and acetone 10a, exhibited high antiviral activity (IC50
7.5 mM), which, in combination with its low cytotoxicity, resulted
in a very high selectivity index (SI) for (4R)-11a (SI = 189). The
selectivity indices of the reference drugs, rimantadine and rib-
avirin, were 4 and 48, respectively.
It turned out that the yields of octahydro-2H-chromenols 11
decrease substantially with increasing length of the carbon back-
bone in ketones. It is important to mention that in the reactions
with ketones 10b and 10c, (4R)-isomers were formed almost exclu-
sively, with only trace amounts of (4S)-isomers detected. The yield
of (4R)-11b derived from 3-pentanone 10b was 28%, while the
yield of (4R)-11c derived from 4-heptanone 10c was 19%.
The relative and absolute configurations of monoterpenoids and
their derivatives are well known to be capable of exerting a deci-
sive influence on their biological activity.26,27 In order to study
the effect of configuration of the type of ring conjugation, octahy-
dro-2H-chromenol 16 (42% yield, the (4R)/(4S) ratio being equal to
1:1) was synthesized via the reaction between acetone and
neoisopulegol 15 (the stereoisomer of alcohol 7 with respect to
configuration of the carbon atom connected to the hydroxy group)
(Scheme 2). The (4R)- and (4S)-isomers of 16 were not separated.
We have also made an attempt to synthesize fluorine-contain-
ing chromenes via the reaction between alcohol 7 and acetone
10a in the presence of BF3 * Et2O-H2O using the procedure28 that
has previously been successfully employed to conduct the reac-
tions between p-menthane terpenoids and aldehydes. However,
(4R)-11a is the only product formed under these conditions with
a 36% yield.
Compounds 17a–d containing a spirocyclic substituent were
synthesized via interaction between (ꢀ)-isopulegol 7 and cyclic
ketones 18a–d (Scheme 2). It should be mentioned that the total
yield of 17a–d decreased with increasing ring size in ketones; for-
mation of the (4S)-isomer was observed only in the reaction
between alcohol 7 and cyclopentanone 18a; in all other cases the
reactions were stereospecific leading to formation (4R)-isomer
only. Similar to the reactions with acyclic ketones, the interaction
between alcohol 7 and cyclic ketones gave rise to a significant
amount of dehydration products 19–21. We did not manage to
considerably reduce their contents as well as increase the yields
of 17a–d by varying reaction conditions.
It was found that the relative arrangement of the methyl and
hydroxy groups with respect to C(4) had a decisive effect on
In order to study the need for presence of two aliphatic sub-
stituents at the C(2) position of the chromene framework, we per-
Scheme 3. Synthesis of compounds 23a,b.
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I.V. Ilyina et al. / Bioorganic & Medicinal Chemistry Letters xxx (2018) xxx–xxx
Table 1
Antiviral activity against H1N1 (A/Puerto Rico/8/34) influenza virus and cytotoxicity of compounds 11a–c, 16, 17a–d, 23a–b.
a,d
b,d
Structure
CC50
,
mM
IC50
,
mM
SIc
(4R)-11a
>1415.1
7.5 1.1
189
(4S)-11a
816.0 52.3
72.2 5.9
70.8 6.1
17.0 1.4
12
16
4
(4R)-11b
(4R)-11c
187.9 14.3
130.6 8.4
19.6 2.2
45.5 6.9
10
3
(4R)-17a
(4R)-17b
(4R)-17c
810.0 52.3
626.9 48.8
210.5 14.8
8.4 1.1
96
34
3
18.3 2.5
82.7 10.1
(4R)-17d
378.6 29.8
>117.9
3
(4R)-23a
(4R)-23b
>1327.4
>1327.4
1
2
24.2 1.7
12.4 1.5
Rimantadine
Ribavirin
318.9 14.9
>2130
72 8.3
4
48
44
5
a
b
c
CC50 is the median cytotoxic concentration; i.e., the concentration causing 50% cell death.
IC50 is the 50% inhibiting concentration; i.e., the concentration causing a 50% decrease in virus replication.
SI is the selectivity index, which is the CC50/IC50 ratio.
CC500s and IC500s are given as mean SD of three replicates.
d
biological properties of compound 11a. Thus, the minor (4S)-iso-
mer of 11a was significantly less active and exhibited a higher
cytotoxicity than the (4R)-11a isomer, which reduced the selectiv-
ity index down to 12. Furthermore, the way the rings in octahydro-
2H-chromenols are conjugated was also important. Thus, com-
pound 16 differing from 11a by the fact that the rings in it are
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I.V. Ilyina et al. / Bioorganic & Medicinal Chemistry Letters xxx (2018) xxx–xxx
5
Table 2
Antiviral activity of (4R)-11a against influenza viruses.
b,c
Strain
Subtype
Origin
Drug resistancea
IC50
SId
A/Puerto Rico/8/34
A/California/07/09
A/Vladivostok/02/09
A/Singapore/1/57
H1N1
H1N1pdm09
H1N1
H2N2
H3N2
H5N2
H7N3
Yamagata-like
Human
Human
Human
Human
Human
Avian
Am
Am
Os
–
–
–
7.5 1.1
0.9 0.2
>1415.1
0.9 0.3
189
1570
1
1570
1
9
2
83
A/Aichi/2/68
>1415.1
A/mallard/Pennsylvania/10218/84
A/mallard/Netherlands/12/00
B/Florida/04/06
160.4 20.1
613.2 42.5
17.0 2.2
Avian
Human
–
Am
a
b
c
‘‘Am” – amantadine/rimantadine, ‘‘Os” – oseltamivir, ‘‘ꢀ” – susceptible to both adamantanes and Os.
IC50 is the 50% inhibiting concentration; i.e., the concentration causing a 50% decrease in virus replication.
CC50 data are given as mean SD of three replicates.
d
SI is the selectivity index, which is the CC50/IC50 ratio.
cis-conjugated instead of trans-conjugation in 11a, exhibited a
lower antiviral activity and was much more toxic than 11a.
The findings demonstrate that the carbon backbone length and
ring size in substituents at the C(2) position have a significant
effect responsible for the antiviral activity in the synthesized
octahydro-2H-chromenols: antiviral activity decreases, while cyto-
toxicity simultaneously increases for longer substituent length /
ring size. Thus, among the compounds (4R)-11a–c derived from
linear ketones, the highest activity was exhibited by (4R)-11a syn-
thesized from acetone 10a (SI = 189). Octahydro-2H-chromenol
(4R)-11b derived from 3-pentanone 10b possessed a moderate
activity, with SI = 10, whereas compound (R)-11c derived from 4-
heptanone 10c demonstrated very low selectivity index (SI = 3)
with respect to the influenza virus strain used.
Among the compounds (4R)-17a–d with a spirocyclic frame-
work, significant antiviral activity in combination with low cyto-
toxicity was observed for (4R)-17a (IC50 = 8.4 mM, SI = 96)
synthesized from cyclopentanone 18a. An increase in ring size at
the C(2) position of the chromene framework when proceeding
from (4R)-17a to (4R)-17b derived from cyclohexanone 18b results
in reduction of antiviral activity (IC50 = 18.3 mM, SI = 34). The
remaining compounds (4R)-17c,d synthesized via the reactions
between (ꢀ)-isopulegol 7 and ketones with a larger ring size
exhibited smaller anti-influenza activity and were much more
cytotoxic.
neuraminidase (N1), A/Puerto Rico/8/34 and A/California/07/09.
Similarly, it effectively inhibited the virus A/Singapore/1/57 but
appeared ineffective against A/Aichi/2/68, although they both have
the same type of neuraminidase, N2. The target of (4R)-11a, there-
fore, should not be identified as M2 or NA, suggesting a novel, pre-
viously unexplored, mechanism of influenza-inhibiting action.
Based on the data presented, the anti-influenza activity of the
compounds may depend on the type of hemagglutinin (HA). It
was shown previously that all influenza virus hemagglutinins can
be divided into two major groups.31 Among the influenza A viruses
tested, viruses of H1, H2 and H5 subtypes belong to the group 1,
while viruses of H3 and H7 subtypes belong to the group 2. With
two exceptions (A/Vladivostok/02/09 and A/mallard/Pennsylva-
nia/10218/84 viruses), the range of activity of (4R)-11a corre-
sponds to subdivision of HAs into groups. Indeed, it is effective
against viruses of H1 and H2 subtypes (group 1) and ineffective
against those of subtypes H3 and H7 (group 2).
In addition, (4R)-11a appeared to be effective against influenza
B virus. This suggests that it may either bind to similar sites of HAs
of influenza A and influenza B viruses or use another protein of
viral or cellular origin as a target. Further experiments should be
definitely performed to completely characterize the range of activ-
ity and target(s) of the compounds belonging to this class.
To further study the mode of activity of (4R)-11a we performed
time-of-addition experiments where the compound was added to
the replicating virus at different time points corresponding to dif-
ferent stages of viral life cycle. As presented in Fig. 2, the com-
pound was most effective in suppressing the viral replication
when administered at early stages of the viral cycle (0–2 h post
infection). This additionally confirms that the activity of (4R)-11a
may be directed to viral hemagglutinin which is essential at early
stages of viral cycle, namely for viral attachment to cell surface and
membrane fusion.
The number of aliphatic substituents at the C(2) position is
another factor having an apparent effect on biological properties
of octahydro-2H-chromenols. Thus, (4R)-23b synthesized via inter-
action between cyclohexanecarbaldehyde 22b and isopulegol 7
exhibited a moderate antiviral activity in combination with high
cytotoxicity, resulting in very low selectivity index, while (4R)-
23a derived from butyraldehyde 22a showed no antiviral activity
at all. Hence, two substituents need to be present at the C(2) posi-
tion in octahydrochromenols such as 11 and 17 to ensure the
emergence of antiviral activity.
Activity against other types of influenza virus, including viruses
of A and B types, of human and avian origin and differing in their
susceptibility to antivirals, was tested for (4R)-11a, which exhib-
ited the highest activity against type A virus (A/Puerto Rico/8/34
(H1N1) strain) (Table 2).
The results demonstrate that (4R)-11a possesses an activity
against a wide range of influenza viruses independently of their
resistance or susceptibility to rimantadine. Thus, it exhibits the
equally high levels of activity against both rimantadine-resistant
and rimantadine-sensitive strains A/California/07/09 and A/Singa-
pore/1/57. Nevertheless, it appeared inactive against three other
rimantadine-sensitive strains A/Vladivostok/02/09, A/Aichi/2/68
and A/mallard/Pennsylvania/10218/84. Moreover, it did not inhibit
the oseltamivir-resistant strain A/Vladivostok/02/09 but was
highly effective against other viruses with the same subtype of
Fig. 2. Activity of (4R)-11a against influenza virus A/Puerto Rico/8/34 (H1N1)
according to time-of-addition experiment.
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I.V. Ilyina et al. / Bioorganic & Medicinal Chemistry Letters xxx (2018) xxx–xxx
Based on the results of biological studies, hemagglutinin (HA)
may be proposed as a possible molecular target for compound
(4R)-11a.
We have carried out the docking of the most active compounds
((4R)-11a, (4S)- 11a, 16, (4R) -11b, (4R)-11c, (4R)-17a, (4R)-23b
and (4R)-17c) into the two possible binding sites of H1 hemagglu-
tinin (PDB code: 1RU7).32–34 The first active site is located at the
interface between two monomer of HA trimer and known as bind-
ing site of tert-butylhydroquinone (TBQH) well-known inhibitor of
HA.30 The second active site was found using SiteMap35 application
by Small-Molecule Drug Discovery Suite 2017–3 in the field central
helix coil of HA (Fig. 3).
a
We compared the results of molecular docking procedure and
biological test. Although the binding energy was higher for the sec-
ond active site, good correlation between experimental data and
theoretical calculations was observed for the TBHQ binding site
only (Fig. 4).
Molecular docking demonstrated that lead compound (4R)-11a
forms some supramolecular interactions in the TBHQ active site
between ligand and a number of amino acids including H-bond
Fig. 3. The visualization of the docking results: a – secondary structures of HA; b – the location of (4R)-11a in the TBHQ binding site; c – the location of (4R)-11a in the central
helix coil of HA: hydrophobic space is shown yellow; H-bonds are presented as yellow dotted lines; negative interactions between ligand and some amino acids are shown
a
as orange dotted line.
Fig. 4. Comparison of results of biological tests and theoretical calculations: a – correlation between IC50 values and the results of docking of the active compounds in the first
binding site (TBQH site); b – absence of correlation between experimental and theoretical data in the case the docking procedure into the second binding site.
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I.V. Ilyina et al. / Bioorganic & Medicinal Chemistry Letters xxx (2018) xxx–xxx
7
with Arg554 and hydrophobic interactions with Leu598 and
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In conclusion, we have synthesized a set of compounds with the
octahydro-2H-chromene framework, including the spirocyclic
derivatives, from monoterpenoid (ꢀ)-isopulegol 7 and aliphatic
ketones in one preparative stage. The yield of the target products
is shown to decrease with increasing length of aliphatic sub-
stituents or size of the aliphatic cycles. Evaluation of activity of
the resulting compounds against influenza virus A/Puerto
Rico/8/34 (H1N1) demonstrated that high activity is exhibited by
chromenes (4R)-11a (IC50 7.5
lM, SI 189) and (4R)-17a (IC50 8.4
lM, SI 96) synthesized using acetone and cyclopentanone, respec-
tively, as a carbonyl component. The configuration of substituents
at the C(4) position and the type of ring conjugation in the frame-
work was shown to have a crucial effect on anti-influenza activity
of 11a.
Activity against other influenza virus strains (including viruses
of A and B types, of human and avian origin and differing in their
susceptibility to antivirals) was tested for (4R)-11a, which had
exhibited potent activity and low cytotoxicity. (4R)-11a exhibited
the highest activity against H1N1 (A/California/07/09) and H2N2
(A/Singapore/1/57) influenza virus strains (IC50 0.9
excellent selectivity index exceeding 1500. (4R)-11a also appeared
active against influenza B virus (IC50 17.0 M, SI 83). It was demon-
lM), with an
l
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early stages of viral cycle (0–2 h post infection). According to these
findings, we can suggest that it may either bind to similar sites of
hemagglutinins of influenza A and influenza B viruses or use
another protein of viral or cellular origin as a target. Clear correla-
tion between anti-viral activity and calculated binding energy to
hemagglutinin TBHQ active site was demonstrated.
Hence, the novel type of monoterpenoid derivatives with a
highly potent activity against influenza virus has been detected.
Although the exact target and mechanisms of activity of (4R)-11a
are still to be identified, our data could serve as a basis for rational
approach to further development of monoterpene-based low-
molecular antivirals with new mechanism of action.
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This work was supported by Russian Science Foundation (grant
15-13-00017). Authors would like to acknowledge the Multi-
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A. Supplementary data
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Supplementary data associated with this article can be found, in
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These data include MOL files and InChiKeys of the most important
compounds described in this article.
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Please cite this article in press as: Ilyina I.V., et al. Bioorg. Med. Chem. Lett. (2018), https://doi.org/10.1016/j.bmcl.2018.04.057