(D)- and (L)-cyclohexenyl-G, a new class of antiviral agents: Synthesis, conformational analysis, molecular modeling, and biological activity

Article abstract of DOI:10.1081/NCN-100002360

(D)- and (L)-cyclohexeneyl-G were synthesized enantioselectively starting from (R)-carvone. Both show potent and selective anti-herpesvirus activity (HSV-1, HSV-2, VZV, CMV). Molecular modeling demonstrates that both isomers are bound in the active site o

Full text of DOI:10.1081/NCN-100002360

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(D)- AND (L)-CYCLOHEXENYL-G, A NEW CLASS OF
ANTIVIRAL AGENTS: SYNTHESIS, CONFORMATIONAL
ANALYSIS, MOLECULAR MODELING, AND BIOLOGICAL
ACTIVITY
J. Wang a , M. Froeyen a , C. Hendrix a , C. Andrei a , R. Snoeck a , E. Lescrinier a , E. De
Clercq a & P. Herdewijn b
a Rega Institute for Medical Research, Katholieke Universiteit Leuven,
Minderbroedersstraat 10, Leuven, B-3000, Belgium
b Rega Institute for Medical Research, Katholieke Universiteit Leuven,
Minderbroedersstraat 10, Leuven, B-3000, Belgium
Version of record first published: 07 Feb 2007.
To cite this article: J. Wang, M. Froeyen, C. Hendrix, C. Andrei, R. Snoeck, E. Lescrinier, E. De Clercq & P. Herdewijn
(2001): (D)- AND (L)-CYCLOHEXENYL-G, A NEW CLASS OF ANTIVIRAL AGENTS: SYNTHESIS, CONFORMATIONAL ANALYSIS,
MOLECULAR MODELING, AND BIOLOGICAL ACTIVITY, Nucleosides, Nucleotides and Nucleic Acids, 20:4-7, 727-730
To link to this article: http://dx.doi.org/10.1081/NCN-100002360
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NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS, 20(4–7), 727–730 (2001)
(D)- AND (L)-CYCLOHEXENYL-G, A NEW CLASS
OF ANTIVIRAL AGENTS: SYNTHESIS,
CONFORMATIONAL ANALYSIS, MOLECULAR
MODELING, AND BIOLOGICAL ACTIVITY
J. Wang, M. Froeyen, C. Hendrix, C. Andrei, R. Snoeck,
E. Lescrinier, E. De Clercq, and P. Herdewijn∗
Rega Institute for Medical Research, Katholieke Universiteit Leuven,
Minderbroedersstraat 10, B-3000 Leuven, Belgium
ABSTRACT
(D)- and (L)-cyclohexeneyl-G were synthesized enantioselectively starting
from (R)-carvone. Both show potent and selective anti-herpesvirus activity
(HSV-1, HSV-2, VZV, CMV). Molecular modeling demonstrates that both iso-
mers are bound in the active site of HSV-1 thymidine kinase in a high-energy
conformation with the base moiety orienting in an equatorial position. It is be-
lieved that the flexibility of the cyclohexene ring is essential for their antivirial
activity.
The development of novel nucleoside analogues as potential antiviral agents
continues to attract considerable attention. Better understanding of the structure-
activity relationship has provided information and criteria for a more rational design
of new drugs. Based on our previous studies, it has been claimed that the conforma-
tional behavior of a nucleoside plays an important role in its biological activity. For
example, the hexitol nucleosides, which show antiviral activity, in solution as well
as in the solid state adopt a 3ꢀ-endo conformation (northern type) with the base moi-
ety in an axial position. Co-crystallization of an antiviral anhydrohexitol nucleoside
with herpes simplex virus (HSV) type 1 thymidine kinase showed a conformational
inversion when the nucleoside analogue was bound in the active site (i.e. 2ꢀ-endo
∗Corresponding author.
727
ꢁ
C
Copyright 2001 by Marcel Dekker, Inc.
www.dekker.com

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WANG ET AL.
HO
G
G
HO
HO
HO
(L)-1
(D)-1
Scheme 1.
conformation with an equatorial base moiety) (1). This suggests that nucleosides
can undergo conformational alteration during binding to herpesvirus thymidine ki-
nase. This led us to assume that the conformational flexibility is important for the
antiviral activity of a nucleoside.
Cyclohexene nucleosides are a class of six-membered carbocyclic nucleosides
in which a double bond replaces the ring oxygen atom of a natural nucleoside. The
resultingπ → σC∗1ꢀ−N interactionmimicstheanomericeffectofanaturalnucleoside
and considerably reduces the energy difference among the different conformers.
These nucleosides are therefore conformationally more flexible to meet different
enzymatic requirements.
The enantioselective synthesis of both (D)- and (L)-cyclohexene guanines 1,
using R-(−)-carvone as starting material, is shown in Scheme 1 (2–4). Carvone was
convertedintointermediate3a,baccordingtothereportedprocedure(5). Depending
on the nature of the protection groups R1–R4, intermediate 3 allows for the synthesis
of both (D)-1 and (L)-1.
For the synthesis of (L)-1, the two free hydroxyl groups of 3a were protected
as a benzoate, the TBS group (R2) was chemoselectively removed by treatment
with 1 equiv. of TBAF, and the generated alcohol was converted into mesylate 4.
Removal of the remaining TBS group and eliminative oxidation gave rise to enone
5. Reduction using NaBH4 in the presence of CeCl3 · 7H2O afforded the α-enol 6
ready for base moiety introduction. Treatment of 6 with 2-amino-6-chloropurine
under Mitsunobu reaction conditions and conversion of the resulting 6-chloropurine
compound into the guanine derivative gave (L)-1, after final deprotection under
basic conditions.
The synthesis of (D)-1 was carried out in a similar way. Enone 8 was obtained
by mesylation of 3b and deprotection of the Bn group, followed by oxidative elim-
ination. Selective reduction and introduction of the base moiety was carried out ac-
cording to the same procedure as used for (L)-1. Conversion of the 6-chloroguanine
into guanine using TFA/H2O (3:1) resulted in simultaneous deprotection of the two
TBS groups, affording directly (D)-1.
Both enantiomers show potent and selective anti-herpesvirus activity (HSV-
1, HSV-2, VZV, CMV) (3). The activity spectrum of both compounds is very
similar. They display the same activity against HSV-1 and HSV-2. Against VZV
and CMV the potency of (L)-1 is two-fold lower than that of (D)-1. They are as
active as acyclovir and brivudin against HSV-1 and their activity is similar to that of

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(D)- AND (L)-CYCLOHEXENYL-G
729
2
O
R-(-)-carvone
ref 3
R3O
3a R1=R3=H
R2=R4=TBS
3b R1=R2=TBS
R3=H, R4=Bn
OR4
R1O
R2O
1. Bz2O, DMAP, 98%
MsCl, Et3N, CH2Cl2, 92%
2. TBAF(1eq), THF, 74%
3. MsCl, Et3N, CH2Cl2, 98%
Ms O
BzO
OBn
OTBS
TBSO
BzO
TBSO
MsO
7
4
1.Pd-C(10%), HCOONH4,
MeOH, 76%
2. MnO2, CH2Cl2, 48%;
1. TBAF, THF, 86%
2. PDC, CH2Cl2, 68%
47% recovery of 7
BzO
O
TBSO
TBSO
O
BzO
5
8
NaBH4, CeCl3.7H2O, 75%
NaBH4, CeCl3.7H2O, 91%
BzO
TBSO
TBSO
BzO
OH
OH
6
9
1. 2-amino-6-chloropurine,
DEAD, PPh3, dioxane
2. TFA/H2O (3:1), 58% from 6
1. 2-amino-6-chloropurine,
DEAD, PPh3, dioxane
2. TFA/H2O (3:1), 46% from 9
3. NH3/MeOH, 80 C, 2d, 73%
(D)-1
(L)-1

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WANG ET AL.
acyclovir against HSV-2. (D)-1 shows the same potency against CMV as ganci-
clovir. (D)-1 as well as (L)-1 didn’t show toxicity in four different cell lines (HeLa,
Vero, E6Sm, HEL).
Both compounds showed a reduced antiviral activity when evaluated against
TK− strains of HSV-1. This suggests that intracellular phosphorylation in the virus-
infected cells is an important step for the enzymatic activation of these two nucle-
osides. Molecular modeling of (D)-1 and (L)-1 in complex with HSV-1 thymidine
kinase showed that both compounds were bound in the active site in a high-energy
conformation (2H3 with pseudo-equatorial orientation of the base moiety in the
syn conformation). This is in agreement with our previous observation that HSV-1
thymidine kinase may induce a conformational change of the nucleoside upon
binding. The amino acids involved in binding of both isomers are the same, but
their interaction energy is slightly different, mainly due to the hydrogen bonding
interaction difference between the secondary hydroxyl group of the nucleosides
with Glu-225. This energy difference might be relevant to their different biological
activity.
Structural analysis demonstrates that the cyclohexene system is very flexible.
This flexibility may be an important conformational characteristic explaining the
potent antiviral activity of these cyclohexenyl nucleosides.
REFERENCES
1. Ostrowski, T.; Wroblowski, B.; Busson, R.; Rozenski, J.; De Clercq, E.; Bennett, M.S.;
Champness, J.N.; Summers, W.C.; Sanderson, M.R.; Herdewijn, P. J. Med. Chem. 1998,
41, 4343–4353.
2. Wang, J.; Herdewijn, P. Helv. Chim. Acta 2000 (in press).
3. Wang, J.; Froeyen, M.; Hendrix, C.; Andrei, G.; Snoeck, R.; De Clercq, E.; Herdewijn,
P. J. Med. Chem. 2000, 43 (4), 736–745.
4. Wang, J.; Herdewijn, P. J. Org. Chem. 1999, 64 (21), 7820–7827.
5. Wang, J.; Busson, R.; Blaton, N.; Rozenski, J.; Herdewijn, P. J. Org. Chem. 1998, 63
(9), 3051–3058.

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