Anti-AIDS agents. Part 62: Anti-HIV activity of 2′-substituted 4-methyl-3′,4′-di-O-(-)-camphanoyl-(+)-cis-khellactone (4-methyl DCK) analogs

Article abstract of DOI:10.1016/j.bmcl.2004.09.032

Four 4-methyl-3′,4′-di-O-(-)-camphanoyl-(+)-cis-khellactone (4-methyl DCK) analogs (7a-d) with different alkyl substituents at the 2′-position were synthesized and evaluated for inhibition of HIV-1 replication in H9 lymphocytes. 2′-Methyl-2′-ethyl-4-methyl DCK (7b) was more potent (EC₅₀ = 0.22 μM, TI > 175) than the other three compounds (7a, 7c, and 7d), but significantly less potent than 4-methyl DCK (2, EC₅₀ = 0.0059 μM, TI > 6600). Four 4-methyl-3′,4′- di-O-(-)-camphanoyl-(+)-cis-khellactone (4-methyl DCK) analogs (7a-d) with different alkyl substituents at the 2′-position were synthesized and evaluated for inhibition of HIV-1 replication in H9 lymphocytes. 2′-Methyl-2′-ethyl-4-methyl DCK (7b) was more potent (EC ₅₀ = 0.22 μM, TI > 175) than the other three compounds (7a, 7c, and 7d), but significantly less potent than 4-methyl DCK (2, EC₅₀ = 0.0059 μM, TI > 6600). The bioassay results indicated that the 2′-substituents had a strong effect on the anti-HIV activity, and gem-dimethyl substitution at the 2′-position was greatly preferable to larger alkyl substituents or hydrogen atoms.

Full text of DOI:10.1016/j.bmcl.2004.09.032

Bioorganic & Medicinal Chemistry Letters 14 (2004) 5855–5857
0
Anti-AIDS agents. Part 62: Anti-HIV activity of 2 -substituted
0
0
4
-methyl-3 ,4 -di-O-(ꢀ)-camphanoyl-(+)-cis-khellactone
I
(4-methylDCK) ana ol gs
a
a
a,
b
b
Qian Zhang, Ying Chen, Peng Xia, Yi Xia, Zheng-Yu Yang, Donglei Yu,
b
*
b
Susan L. Morris-Natschke and Kuo-Hsiung Lee
b,
*
a
Department of Medicinal Chemistry, School of Pharmacy, Fudan University, Shanghai 200032, China
Natural Products Laboratory, School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599-7360, USA
b
Received 13 August 2004; accepted 15 September 2004
Available online 12 October 2004
0
0
Abstract—Four 4-methyl-3 ,4 -di-O-(ꢀ)-camphanoyl-(+)-cis-khellactone (4-methyl DCK) analogs (7a–d) with different alkyl sub-
0
0
0
stituents at the 2 -position were synthesized and evaluated for inhibition of HIV-1 replication in H9 lymphocytes. 2 -Methyl-2 -
ethyl-4-methyl DCK( 7b) was more potent (EC50 = 0.22lM, TI > 175) than the other three compounds (7a, 7c, and 7d), but signif-
icantly less potent than 4-methyl DCK( 2, EC50 = 0.0059lM, TI > 6600). The bioassay results indicated that the 2 -substituents had
a strong effect on the anti-HIV activity, and gem-dimethyl substitution at the 2 -position was greatly preferable to larger alkyl sub-
0
0
stituents or hydrogen atoms.
ꢀ
2004 Elsevier Ltd. All rights reserved.
1. Introduction
will be helpful in exploring interactions with the viral
target and the mechanism of DCKanalogs.
0
0
3
was discovered as a potent anti-HIV agent with an
,4 -Di-O-(ꢀ)-camphanoyl-(+)-cis-khellactone (DCK, 1)
6
,7
In recent structure modifications, two new series of 4-
methyl DCK( 2) analogs were synthesized based on the
concept of bioisosterism, namely, by replacing the ring
oxygen atom of DCKwith a sulfur atom. The bioassay
ꢀ
4
EC50 value of 2.56 · 10 lM and a therapeutic index
5
(
TI) of 1.37 · 10 in H9 lymphocytic cells in our previ-
2
ous research. Further research studies indicated that
-methyl DCK, 4-methyl DCK, and 5-methyl DCK
were much more potent than DCKand AZT in the same
0
3
results suggested that the 2 -substituents might have a
significant effect on the anti-HIV activity. This finding
prompted us to synthesize additional DCKanalogs with
different substituents at the 2 -position and examine the
relationship with anti-HIV activity (Fig. 1).
ꢀ
5
assay with EC and TI values ranging from 5.25 · 10
to 2.39 · 10 lM and 2.15 · 10 to 3.97 · 10 , respec-
5
0
ꢀ
7
6
8
0
3
,4
tively. A preliminary mechanistic study showed that
the DCKanalog 3-hydroxymethyl-4-methyl DCK
inhibits HIV reverse transcriptase (RT), but has a novel
mechanism of action compared to current anti-HIV/
AIDS drugs. More recent studies indicated that DCK
analogs act at a point in the virus life cycle immediately
following the target for AZT and nevirapine, which are
O
O
O
O
O
O
5
RT inhibitors. Additional mechanism of action studies
are ongoing; therefore, further structure modification
O
O
O
O
O
O
O
O
O
O
O
O
O
O
q
See Ref. 1.
O
O
*
Corresponding authors. Tel.: +86 21 54237563 (P.X.); tel.: +1 919
62 0066; fax: +1 919 966 3893 (K.-H.L.); e-mail addresses:
pxia@shmu.edu.cn; khlee@unc.edu
1
2
9
Figure 1. Structures of 1 and 2.
0
960-894X/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.09.032

5856
Q. Zhang et al. / Bioorg. Med. Chem. Lett. 14 (2004) 5855–5857
2
. Chemistry
O
OH
X
i
ii
R
R
C
CH
C
CH
R
R'
R'
R'
The propargyl ethers 4a–d were synthesized via the
reaction of 4-methyl-7-hydroxycoumarin with 3-bromo-
prop-1-yne, 3-chloro-3-methylpent-1-yne, 3-chloro-3-
ethylpent-1-yne, or 3-chloro-3-methylhex-1-yne, respec-
tively, in the presence of K CO and KI by refluxing
a: R=R'=H; b: R=CH
3
2
, R'=C H
5
; c: R=CH
3
, R'=C
3
H
7
; d: R=R'=C H ;
2 5
Scheme 2. Reagents and conditions: (i) t-BuOK, acetylene gas, THF,
ꢁC, >99%; (ii) PBr or SOCl , rt, 40–50%.
0
3
2
2
3
in acetone or heating in DMF at 80–90ꢁC (Scheme 1).
The propargyl bromides were obtained from the halo-
genation of corresponding propargyl alcohols, which
were prepared by ethynylation of different carbonyl
compounds (Scheme 2). Thermo ring closure of 4a–d
by refluxing in N,N-dimethylaniline or heating in
DMF at 80–90ꢁC afforded 5a–d. Compounds 5b and
Table 1. Anti-HIV activity of DCKanalogs in acutely infected H9
*
lymphocytes
a
b
c
TI
Compound
IC50 (lM)
EC50 (lM)
7
7
7
7
a
b
c
>41.1
>38.4
>37.6
>37.6
6.9
>6.0
>175
>5.9
>13.2
0.22
6.4
5
c are racemic mixtures.
d
2.84
d
8
DCK( 1)
-Me DCK( 2)
AZT
>16.1
>38.9
1872
0.049
0.0059
0.048
>328
>6600
39,000
Asymmetric dihydroxylation of 5a–d followed by acyl-
ation with (S)-camphanic chloride gave the desired 4-
methyl DCKanalogs with different alkyl substituents
d
4
0
9
*
at the 2 -position (7a–d) (Scheme 1).
This assay was performed by Panacos, Inc. The general procedure
5
was described previously.
Concentration that inhibits uninfected H9 cell growth by 50%.
Concentration that inhibits viral replication by 50%.
a
b
c
3
. Results and discussion
TI = therapeutic index IC50/EC50
.
d
ꢀ4
EC50 and TI for DCKand 4-methyl DCKwere 2.56 · 10 lM,
Table 1 shows the inhibitory activities against HIV-1
replication of compounds 7a–d together with DCK, 4-
methyl DCK, and AZT as reference compounds. 4-
Methyl DCK( 2), which has gem-dimethyl substitution
at the 2 -position, was the most potent compound with
an EC50 value of 0.0059lM and a therapeutic index
(TI) of >6600 in H9 lymphocytic cells. Replacing just
0
one 2 -methyl group with an ethyl group resulted in a
dramatic decrease of anti-HIV activity. 2 -Methyl-2 -
ethyl-4-methyl DCK( 7b) was ca. 10 -fold less active
ꢀ6
5
7
1
screenings and publication.
.83 · 10 lM, and 1.37 · 10 , 6.89 · 10 , respectively, in previous
2
0
0
0
0
2 -propyl-4-methyl DCK( 7c) and 2 ,2 -diethyl-4-methyl
DCK( 7d) were ca. 30- and 10-fold less potent, respec-
tively, than 7b. The 2 -unsubstituted compound, 2 ,2 -di-
hydro-4-methyl DCK( 7a), showed weak potency,
similar to 7c.
0
0
0
0
0
2
0
than 4-methyl DCK( 2). When the 2 -substituents be-
0
Based on these findings, we speculate that the space
0
came bulkier, the activity decreased further. 2 -Methyl-
around the 2 -position is very tight when a DCKanalog
i
ii
O
O
O
O
O
O
HO
O
O
R
R
R'
R'
3
4
5
a: R=R'=H
a: R=R'=H
b: R=CH , R'=C
c: R=CH , R'=C
d: R=R'=C
b: R=CH , R'=C H
3
3
2
H
5
7
3
2
5
7
c: R=CH
3
, R'=C
3
H
3
H
d: R=R'=C H
H
2 5
2
5
iii
O
iv
O
O
O
R'' =
O
O
O
R
O
O
R
R'
OH
R'
OR''
OH
OR''
6
7
a: R=R'=H
a: R=R'=H
b: R=CH , R'=C H
b: R=CH , R'=C H
3
2
3
5
7
3
2
5
7
c: R=CH , R'=C H
c: R=CH , R'=C H
3 3
3
d: R=R'=C H
d: R=R'=C H
2 5
2
5
0
0
Scheme 1. Reagents and conditions: (i) 3-bromoprop-1-yne (R = R = H), 3-chloro-3-methylpent-1-yne (R = CH
3
, R = C
, KI in acetone reflux or in DMF at
, (DHQ) -PHAL, K CO , 75–98%; (iv) (S)-
2 5
H ), 3-chloro-3-
0
0
methylhex-1-yne (R = CH
0–90ꢁC, 32–95%; (ii) diethylaniline, reflux, or DMF 80–90ꢁC, 11–85%; (iii) K
camphanic chloride, DMAP/CH Cl , 80–88%.
3
, R = C
3
H
7
), and 3-chloro-3-ethylpent-1-yne (R = R = C
2
H
5
2 3
), respectively, K CO
8
2
OsO
2
(OH) , K Fe(CN)
4
3
6
2
2
3
2
2

Q. Zhang et al. / Bioorg. Med. Chem. Lett. 14 (2004) 5855–5857
5857
binds with its target enzyme. Thus, there is a space
requirement at this position for optimal anti-HIV activ-
Wang, Z. M.; Xu, D.; Zhang, X. L. J. Org. Chem. 1992, 57,
768.
9. Physical and spectral data for 7a–d:
2
0
ity. To date, two methyl groups at the 2 -position are
preferred to other alkyl substituents for enhanced anti-
HIV activity in the DCKseries. Synthesis of analogs
0
0
0
0
2
,2 -Dihydro-4-methyl-3 ,4 -di-O-(ꢀ)-camphanoyl-(+)-cis-
3
1
khellactone (7a) mp: 170ꢁC (dec); H NMR (CDCl
,
4
2
4
3
00MHz) d 0.85–1.12 (18H, m, camphanoyl CH ), 1.64–
0
with other 2 -functional groups and mechanism studies
of this compound series are under investigation.
.60 (2H · 4, m, camphanoyl CH ), 2.48 (3H, s, CH -4),
.31 (2H, m, CH
0
2
3
0
2
-2 ), 6.13 (1H, d, J = 6.0Hz, H-3), 5.51
0
(1H, m, H-3 ), 6.80 (1H, m, H-4 ), 6.88 (1H, d, J = 8.9Hz,
H-6), 7.55 (1H, d, J = 8.9Hz, H-5); MS m/z (%): 608 (M ,
+
+
Acknowledgements
3.65), 427 ([Mꢀcamphanoyl] , 3.35), 411 ([MꢀOꢀcampha-
+
noyl] , 2.17); HR-MS: calcd for C33
36
H O11 608.22577,
This research was supported by grants from the
National Natural Science Foundation of China (No.
found: 608.22521.
0
0
0
0
2
-Ethyl-2 ,4-dimethyl-3 ,4 -di-O-(ꢀ)-camphanoyl-(+)-cis-
3
1
khellactone (7b) mp: 166ꢁC (dec); H NMR (CDCl
,
and
2
0272010) and Research Foundation for University
PhD Project of China Education Ministry (No.
0020246069) awarded to P. Xia, and Grant AI-33066
4
CH
00MHz) d 0.85–1.12 (m, 21H, camphanoyl CH
3
0
0
2
CH -2 ), 1.38–2.52 (m, 13H, camphanoyl CH
3
2
, CH
3
-2
2
0
and CH CH -2 ), 2.39 (3H, s, CH -4), 6.10 (1H, d,
2
3
3
from the National Institute of Allergies and Infectious
Diseases awarded to K. H. Lee.
0
J = 5.3Hz, H-3), 5.46–5.55 (1H, m, H-3 ), 6.64–6.83 (1H,
0
m, H-4 ), 6.85 (1H, d, J = 8.8Hz, H-6), 7.53 (1H, d,
J = 8.8Hz, H-5); MS m/z (%): 650 (M , 5.41), 453
+
+
(
[MꢀOꢀcamphanoyl] , 5.40); HR-MS: calcd for
References and notes
36 42 11
C H O 650.27271, found 650.27216.
2
khellactone (7c) mp: 140ꢁC (dec); H NMR (CDCl ,
400MHz) d 0.88–1.13 (21H, m, camphanoyl CH
0
0
0
0
-Propyl-2 ,4-dimethyl-3 ,4 -di-O-(ꢀ)-camphanoyl-(+)-cis-
3
1
1
. For Part 61, see: Zhu, X. K.; Guan, J.; Xiao, Z.; Cosentino,
L. M.; Lee, K. H. Bioorg. Med. Chem. 2004, 12, 4267.
. Huang, L.; Kashiwada, Y.; Cosentino, L. M.; Fan, S.;
Chen, C. H.; McPhail, A. T.; Fujioka, T.; Mihashi, K.; Lee,
K . H.J. Med. Chem. 1994, 37, 3947.
3
and
0
2
CH
2
CH
0
2
CH
3
-2 ), 1.40–2.52 (15H, m, camphanoyl CH
0
2
,
CH -2 and CH CH CH -2 ), 2.39 (3H, s, CH -4), 6.11
3
3
2
2
3
0
(1H, d, J = 5.5Hz, H-3), 5.43–5.53 (1H, m, H-3 ), 6.65–6.82
0
3
4
5
6
. Xie, L.; Takeuchi, Y.; Cosentino, L. M.; Lee, K. H. J. Med.
Chem. 1999, 42, 2662.
. Yu, D.; Suzuki, M.; Xie, L.; Morris-Natschke, S. L.; Lee,
K . H.Med. Res. Rev. 2003, 23, 322.
. Xie, L.; Yu, D.; Wild, C.; Allaway, G.; Turpin, J.; Smith, P.
C.; Lee, K. H. J. Med. Chem. 2004, 47, 756.
. Chen, Y.; Zhang, Q.; Zhang, B.; Xia, P.; Xia, Y.; Yang, Z.
Y.; Kilgore, N.; Wild, C.; Morris-Natschke, S. L.; Lee, K.
H. Bioorg. Med. Chem., in press.
(1H, m, H-4 ), 6.84 (1H, d, J = 8.9Hz, H-6), 7.53 (1H, d,
J = 8.9Hz, H-5); MS m/z (%): 664 (M , 3.65), 467
+
+
([MꢀOꢀcamphanoyl] , 2.33); HR-MS: calcd for C H O
37
44 11
664.28837, found 664.28781.
2 ,2 -Diethyl-4-methyl-3 ,4 -di-O-(ꢀ)-camphanoyl-(+)-cis-
0
0
0
0
1
khellactone (7d) mp: 150ꢁC (dec); H NMR (CDCl ,
3
500MHz) d 0.93–1.13 (24H, m, camphanoyl CH and
3
0
2 · CH
2
CH
3
-2 ), 1.56–2.51 (12H, m, camphanoyl CH
2
and
-4), 6.10 (1H, d,
0
2 -CH
2
CH · 2), 2.39 (3H, s, CH
J = 6.3Hz, H-3), 5.60–5.62 (1H, m, H-3 ), 6.68–6.77 (1H,
m, H-4 ), 6.86 (1H, d, J = 9.0Hz, H-6), 7.53 (1H, d,
J = 9.0Hz, H-5); MS m/z (%): 664 (M , 3.65), 467
3
3
0
7
. Xia, P.; Yin, Z. J.; Chen, Y.; Zhang, Q.; Zhang, B. N.; Xia,
Y.; Yang, Z. Y.; Kilgore, N.; Wild, C.; Morris-Natschke, S.
L.; Lee, K. H. Bioorg. Med. Chem. Lett. 2004, 14, 3341.
. Sharpless, K. B.; Amberg, W.; Bennani, Y. L.; Crispino, G.
A.; Hartung, J.; Jeong, K. S.; Kwong, H. L.; Morikawa, K.;
0
+
+
8
([MꢀOꢀcamphanoyl] , 5.20); HR-MS: calcd for
C H O 664.28837, found 664.28960.
7
3
44 11