Synthesis and biological evaluation of the first N-alkyl cage dimeric 4- aryl-1,4-dihydropyridines as novel nonpeptidic HIV-1 protease inhibitors

Article abstract of DOI:10.1021/jm991115k

A first series of novel NH and N-alkyl-substituted cage dimeric 4-aryl- 1,4-dihydropyridines 3a-f has been synthesized and evaluated as HIV-1 protease inhibitors in in vitro assays. While the NH and N-methyl derivatives 3a,b,e,f were almost inactive with

Full text of DOI:10.1021/jm991115k

J . Med. Chem. 1999, 42, 4729-4732
4729
Syn th esis a n d Biologica l Eva lu a tion of th e F ir st N-Alk yl Ca ge Dim er ic
4
-Ar yl-1,4-d ih yd r op yr id in es a s Novel Non p ep tid ic HIV-1 P r otea se In h ibitor s
,
†
†
‡
Andreas Hilgeroth,* Michael Wiese, and Andreas Billich
Department of Pharmacy, Martin-Luther-University Halle-Wittenberg, Wolfgang-Langenbeck-Strasse 4,
D-06120 Halle, Germany, and Department of Antiretroviral Therapy, Novartis Forschungsinstitut GmbH,
Brunnerstrasse 59, A-1235 Vienna, Austria
Received J uly 7, 1999
A first series of novel NH and N-alkyl-substituted cage dimeric 4-aryl-1,4-dihydropyridines
3
a -f has been synthesized and evaluated as HIV-1 protease inhibitors in in vitro assays. While
the NH and N-methyl derivatives 3a ,b,e,f were almost inactive with IC50 values of about 200
µM, the N-Benzyl compounds exhibited stronger activity with an IC50 value of 16.2 µM for the
presently best compound 3c. The type of HIV-1 protease inhibition of these novel inhibitors
was characterized as competitive. With the increase of observed activity from NH and N-methyl
derivatives to N-benzyl compounds, respectively, the binding mode may correspond to that of
cyclic and azacyclic ureas showing hydrophobic interactions of the four aromatic residues to
the S1/S1′ and S2/S2′ regions of HIV-1 protease.
In tr od u ction
Since the discovery of HIV-1 protease (PR) as a novel
target enzyme for the development of HIV-1 protease
inhibitors (PI), certain peptidic PIs have been estab-
lished in HIV therapy combined with nucleoside ana-
logues or reverse transcriptase inhibitors.1-3 Neverthe-
less, numerous resistances against the present PIs have
4
been described. The early problems of peptidic PIs, poor
oral bioavailability and severe side effects caused by the
1
necessarily high doses of the inhibitors, strengthened
the development of nonpeptidic PIs that promised better
bioavailability. However, the most potent inhibitors of
the first series of cyclic ureas, DMP 323 and DMP 450
(
Figure 1), were disappointing in clinical trials with
5
unsatisfying bioavailabilities. The introduction of cer-
tain aromatic substituents meanwhile led to derivatives
with Ki values in the lower nanomolar and picomolar
6
ranges. The azacyclic urea A-98881, a highly potent
F igu r e 1. Structures of cyclic and azacyclic ureas DMP 323,
DMP 450, and A-98881, respectively, and the general structure
of cage dimeric target compounds (with chosen N-benzyl
substitution) I discussed in the text.
inhibitor, is currently being investigated in clinical
7
trials. 4-Hydroxycoumarins have been discovered as a
8
nonpeptidic class of PIs with better oral bioavailability.
Motivated by the present situation that demands
innovative lead structures for PIs, we designed N-alkyl-
substituted cage dimeric 4-aryl-1,4-dihydropyridines I
with functional groups that are similar to those of cyclic
and azacyclic ureas as potential PR inhibitors. Recently
we demonstrated by molecular modeling certain con-
formities in the molecular properties of A-98881 and our
cage dimeric target structure I, which pointed to a
similar binding mode in the active site cavity of PR as
Ch em istr y
Cage dimers 2a ,c (Scheme 1) have been synthesized
either by solid-state photodimerization reaction of mon-
1
0
omeric 4-phenyl-1,4-dihydropyridine (1a ) in nearly
quantitative yields or by solution dimerization reaction
of the corresponding monomeric derivative 1c, which
itself was produced by cyclocondensation reaction of
benzaldehyde, ethyl propiolate, and benzylamine in
9
11
was found for A-98881. Requiring only a few reaction
acetic acid.
steps, the following facile synthesis represents a less
expensive alternative for the development of novel
nonpeptidic PIs. Several of them have been evaluated
regarding their PI activity and the type of inhibition of
PR in an in vitro system.
Reduction of the ester groups in the cage compounds
2a -d (Scheme 2) to the alcoholic target structures 3a -d
succeeded in excellent yields of about 90% under
optimized conditions at -8 °C without any observed
dimer fragmentation using lithium aluminum hydride
(LiAlH4) in dry THF.
†
The NH alcohols 3e,f could not be obtained from
Martin-Luther-University Halle-Wittenberg.
Novartis Forschungsinstitut GmbH.
‡
12
2e,f
by direct ester reduction because the primary
1
0.1021/jm991115k CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/07/1999

4
730 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 22
Brief Articles
Sch em e 1a
Sch em e 2a
a
Reagents and conditions: (i) LiAlH4, THF, -8 °C.
Sch em e 3a
a
Reagents and conditions: (i) hν, solid state, Ultra-Vitalux
lamp; (ii) hν, MeOH/THF, Ultra-Vitalux lamp.
proton abstraction led to spontaneous dimer fragmenta-
tion into the corresponding monomeric adducts. How-
ever, compounds 3e,f (Scheme 3) could be synthesized
by N-acylation of 2e,f with benzyl chloroformate at room
temperature in THF to 4e,f, followed by selective ester
group reduction with calcium borohydride at room
temperature in THF to 5e,f and finally hydrogenolytical
cleavage of the benzylcarbamate moiety.
Biologica l Activity a s P R In h ibitor s
The in vitro inhibitory activities of the synthesized
cage dimers 3a -f against PR have been evaluated as
described.1
3-15
Saquinavir has been used as reference
a
compound. Due to the poor solubilities of the derivatives
a ,b,d -f, their IC50 values could not be determined
Reagents and conditions: (i) BzlOCOCl, THF, rt; (ii) Ca(BH4)2,
THF, rt; (iii) H2, Pd/C, THF.
3
directly. They were estimated based on triple inhibitory
determinations at 1 µM (3d ) or 50 µM (for the other
compounds) by simultaneous analysis of all dose-
response data assuming parallel dose-response curves
according to eq 1 using Scientist.16 The Hill coefficient
Ta ble 1. HIV-1 Protease Inhibition of Cage Dimers 3a -f
compd
IC50 (µM)
262
195
16.1 ( 1.04
33
227
209
Ki (µM)
nda
nd
7.8 ( 1
nd
3
3
3
3
a
b
c
d
ν
1
3e
nd
nd
)
(1)
3
f
(
C-IjXIC50,j)
ν0
1 + 10
a
nd, not determined.
of the dose-response curve for 3c was found to be 1 and
was therefore fixed to this value. IC50 values are given
in Table 1. The determination of Ki followed ref 15.
Considering the binding mode suggested by us for the
cage compound 3d based on a molecular modeling
8
study, this great difference in activities from NH and
N-methyl substitution to N-benzyl substitution can be
explained presuming a necessary binding of the inhibi-
tors for high inhibitory activity to both hydrophobic
regions S1/S1′ and S2/S2′ of PR as has been shown for
the aromatic residues of cyclic and azacyclic ureas.5
In the case of NH and N-methyl substitutions, respec-
tively, binding to S2/S2′ is not possible as the N-
substituents do not reach these regions.
Resu lts a n d Discu ssion
Within the small series of investigated target struc-
tures 3a -f, the IC50 values of the N-methyl and NH
derivatives (3a ,b and 3e,f) of about 200 µM are com-
parable to those of the first C2-symmetric inhibitor
A-7470217 or pepstatin A with IC50 > 200 µM proving,
those compounds almost inactive. The introduction of
the N-benzyl substituents mainly increases inhibitory
activity up to 16.2 µM for 3c as the most active
compound (cf. Table 1).
,7
18
To characterize the type of inhibition, the best inhibi-
tor of this first series of N-alkyl derivatives 3c has been
selected. The Lineweaver-Burk plot for 3c obviously

Brief Articles
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 22 4731
stirring: 1H NMR (CDCl
3
) δ 1.17 (t, 7 Hz, 6H), 4.08 (q, 7 Hz,
H), 4.46 (s, 2H), 4.91 (s, 1H), 7.09-7.73 (m, 12H); ESI-MS
4
+
m/z 392 (M + H ). Anal. (C24
4
H25NO ) C, H, N.
Tetr am eth yl 3,9-Dim eth yl-6,12-diph en yl-3,9-diazah exa-
cyclo[6.4.0.02 .0 .0 ]dodecan e-1,5,7,11-tetr acar boxylate
.7
4.11 5.10
(
2a ). Crystalline 1a (1.0 g, 1.74 mmol) with a layer thickness
1
1
of 1 mm was irradiated as recently described. After 6 days
the reaction product was dissolved in boiling toluene from
which 0.90 g (90%) of 2a crystallized on cooling: H NMR
1
(
7
CDCl
.22 (m, 10H); ESI-MS m/z 597 (M + Na ). Anal. (C32
C, H, N.
Tetr aeth yl 3,9-Diben zyl-6,12-diph en yl-3,9-diazah exacy-
3
) δ 3.10 (s, 6H), 3.52 (s, 12H), 4.11 (4H), 4.16 (2H), 7.10-
+
34 2 4
H N O )
clo[6.4.0.02 .0 .0 ]d od eca n e-1,5,7,11-tetr a ca r boxyla te
.7
4.11 5.10
(
2c). 1c (0.40 g, 0.51 mmol) was dissolved in 40 mL of
methanol/THF under stirring. The solution was irradiated in
a quartz flask with an Ultra-Vitalux lamp from a distance of
6
0 cm for about 4 weeks. During the irradiation compound 2c
crystallized from the solution finally yielding 0.28 g (70%) as
white crystals: 1H NMR (CDCl
) δ 0.96 (t, 7.0 Hz, 12H), 3.96
q, 7.0 Hz, 8H), 4.26 (s, 4H), 4.27 (s, 2H), 7.05-7.31 (m, 24H);
3
(
+
ESI-MS m/z 783 (M + H ). Anal. (C48
50 2 8
H N O ) C, H, N.
Rep r esen ta tive P r oced u r e for th e Ester Red u ction of
Com p ou n d s 2a -d t o Alcoh ols 3a -d : 1,5,7,11-Tet r a h y-
d r oxym eth yl-3,9-d im eth yl-6,12-d ip h en yl-3,9-d ia za h exa -
cyclo[6.4.0.02 .0 .0 ]d od eca n e (3a ). 2a (0.04 g, 0.7 mmol)
.7
4.11 5.10
was dissolved in dry THF and the solution was cooled to -8
°
C. Then a solution of lithium aluminum hydride (1.4 mL, 1.4
mmol) in THF (1 M) was added. After 2 h the reaction mixture
was hydrolyzed with 2 mL of a solution of potassuim hydroxide
(20%) at 0 °C. The water layer was then extracted with 100
mL of chloroform three times. The combined extracts were
dried over sodium sulfate. On reducing the extraction volume
the crude compound 3a crystallized and was recrystallized
from methanol/water yielding 0.28 g (88%) of pure 3a as white
F igu r e 2. (a) Lineweaver-Burk plot for inhibitor 3c. The
substrate concentration was varied in the range of 15-500 µM.
Measurements were conducted in the absence or presence of
inhibitor 3c at a fixed concentration of 15 µM. From linear
fits of the data the parameters Vmax and Km/ app were calculated
powder: 1H NMR (DMSO-d
dd, after D
O addition d, 10.6 Hz, 4.9 Hz, 4H), 3.59 (s, 2H), 4.30 (t, 4.9
Hz, 4H, exchangeable), 7.07-7.81 (m, 10H); ESI-MS m/z 463
) δ 2.73 (s, 4H), 2.76 (s, 6H), 3.04
6
(
2
O addition d, 10.6 Hz, 4.9 Hz, 4H), 3.19 (dd, after
D
2
with Vmax [µM/min] ) 37 and K
ited reaction and Vmax [µM/min] ) 46 and Kapp [µM] ) 670,
respectively, for the inhibited reaction. The determined K
value of 7.0 µM corresponds well to the one given in Table 1.
b) Simultaneous analysis of both dose-response curves by
nonlinear regression analysis yielded values of 44.0 ((2.4) µM/
min for Vmax, K ) 240 ((28) µM and K ) 9.55 ((1.03) µM.
m
[µM] ) 214 for the uninhib-
+
(
M + H ). Anal. (C28
H
34
N
2
O
4
‚1.5H
2
O) C, H, N.
i
1,5,7,11-Tet r a h yd r oxym et h yl-3,9-d im et h yl-6,12-bis(4-
2
.7 4.11 5.10
(
m et h oxyp h en yl)-3,9-d ia za h exa cyclo[6.4.0.0 .0 .0 ]-
1
d od eca n e (3b): yield 0.029 g (89%); H NMR (DMSO-d
2.69 (s, 4H), 2.74 (s, 6H), 3.02 (dd, after D O addition d, 10.4
Hz, 4.6 Hz, 4H), 3.18 (dd, after D O addition d, 10.4 Hz, 4.6
6
) δ
m
i
2
2
Hz, 4H), 3.52 (s, 2H), 3.70 (s, 6H), 4.24 (t, 4.6 Hz, 4H,
shows that 3c is a competitive inhibitor of PR with a
decrease of Km and a nearly unchanged Vmax for the
substrate hydrolysis of the inhibited reaction compared
to the uninhibited one as demonstrated in Figure 2.
Comparing the inhibitory activity to the first repre-
sentatives in the class of 4-hydroxycoumarins (Warfarin)
+
exchangeable), 6.68-7.70 (m, 8H); ESI-MS m/z 523 (M + H ).
Anal. (C30
H
38
N
2
O
6
2
‚0.5H O) C, H, N.
3
,9-Diben zyl-1,5,7,11-tetr a h yd r oxym eth yl-6,12-d ip h en -
2.7 4.11 5.10
yl-3,9-diazah exacyclo[6.4.0.0 .0 .0 ]dodecan e (3c): yield
0.029 g (92%); H NMR (DMSO-d ) δ 2.95 (s, 4H), 3.06 (dd,
after D O addition d, 10.5 Hz, 4.4 Hz, 4H), 3.16 (dd, after D
addition d, 10.5 Hz, 4.4 Hz, 4H), 3.66 (s, 2H), 4.13 (s, 4H), 4.41
t, 4.4 Hz, 4H, exchangeable), 7.03-7.79 (m, 20H); ESI-MS m/z
1
6
2
2
O
8
8
with an IC50 ∼ 30 µM and phenprocoumon (Ki ) 1 µM)
(
6
the cage dimers developed by us having a Ki value of
+
15 (M + H ). Anal. (C40
H
42
N
2
O
4
‚0.5H
2
O) C, H, N.
7
-9 µM and an IC50 of 16.1 µM for 3c can actually be
3
,9-Dib en zyl-1,5,7,11-t et r a h yd r oxym et h yl-6,12-b is(4-
classified as an innovative, promising new class of
nonpeptidic PIs.
2
.7 4.11 5.10
m et h oxyp h en yl)-3,9-d ia za h exa cyclo[6.4.0.0 .0 .0 ]-
d od eca n e (3d ): yield 0.027 g (87%); H NMR (DMSO-d
.92 (s, 4H), 3.06 (dd, after D
H), 3.20 (dd, after D
1
6
) δ
O addition d, 10.5 Hz, 4.0 Hz,
O addition d, 10.5 Hz, 4.0 Hz, 4H), 3.60
2
4
2
Exp er im en ta l Section
2
Gen er a l. Commercial reagents were used without further
purification. H NMR (400 or 500 MHz) spectra were recorded
(s, 2H), 3.70 (s, 6H), 4.11 (s, 4H), 4.43 (t, 4.4 Hz, 4H,
exchangeable), 6.49-7.67 (m, 18H); FD-MS m/z 675 (M ). Anal.
) C, H, N.
1
+
using tetramethylsilane as internal standard. TLC was per-
formed on E. Merck 5554 silica gel plates. Mass spectra were
measured with an AMD 402 mass spectrometer. Elemental
analysis was performed using a Leco CHNS-932 apparatus.
The synthesis of compounds 2b,d was recently reported; see
ref 11.
46 2 6
(C42H N O
Rep r esen ta tive P r oced u r e for th e Hyd r ogen olytica l
Clea va ge of N-Ben zyloxyca r bon yl Su bstitu en ts in Com -
p ou n d s 5e,f t o NH Der iva t ives 3e,f: 1,5,7,11-Tet r a h y-
2
.7
d r oxym eth yl-6,12-d ip h en yl-3,9-d ia za h exa cyclo[6.4.0.0
0
.
4
.11 5.10
.0 ]d od eca n e (3e). Compound 5e (0.04 g, 0.05 mmol)
Dieth yl 1-Ben zyl-1,4-d ih yd r o-4-p h en ylp yr id in e-3,5-d i-
ca r boxyla te (1c). Ethyl propiolate (1.96 g, 20 mmol), ben-
zaldehyde (1.06 g, 10 mmol), and benzylamine (1.07 g, 10
mmol) were heated in 1 mL of glacial acetic acid on a steam
bath for 15 min. The reaction mixture was then poured into
ice-water from which 2.8 g (72%) of 1c crystallized on
was dissolved im 25 mL of THF. After the addition of Pd/C
(10%) (20 mg, 0.02 mmol) the suspension was shaken under
hydrogen atmosphere for 1 week. Then the solution was
filtered and the residue was washed several times with warm
methanol. The methanolic extracts were evaporated to dry-
ness. The remaining white powder was recrystallized from

4
732 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 22
Brief Articles
methanol/water yielding 0.017 g (69%) of 3e: 1H NMR (DMSO-
(2) Hilgeroth, A. New Nucleoside Analogues for the Therapy of Viral
Diseases - An Overview. Pharm. uns. Zeit 1998, 27, 111-116.
d
6
) δ 2.91 (s, 4H), 2.94 (dd, after D O addition d, 10.4 Hz, 4.9
Hz, 4H), 3.17 (dd, after D O addition d, 10.4 Hz, 4.9 Hz, 4H),
.30 (s, 2H), 4.11 (t, 4.9 Hz, 4H, exchangeable), 7.09-8.32 (m,
0H); NH signals were covered by the water signal of DMSO;
2
(
(
(
3) Stellbrink, H.-J . Chemotherapy of HIV-1 Infection. Dt. A¨ rztebl.
2
1
997, 94, 2497-2503.
3
1
4) Ridky, T.; Leis, J . Development of drug resistance to HIV-1
protease inhibitors. J . Biol. Chem. 1995, 270, 29621-29623.
5) De Lucca, G. V.; Lam, Y. S. De novo design, discovery and
development of cyclic urea HIV protease inhibitors. Drugs Future
1998, 23, 987-994.
+
ESI-MS m/z 435 (M + H ). Anal. (C26
H
30
N
2
O
4
‚2H
2
O) C, H, N.
1
,5,7,11-T e t r a h y d r o x y m e t h y l-6,12-b is (4-m e t h o x y -
2
.7 4.11 5.10
p h en yl)-3,9-d ia za h exa cyclo[6.4.0.0 .0 .0 ]d od eca n e
1
(
3f): yield 0.017 g (65%); H NMR (DMSO-d
6
) δ 2.97 (s, br,
(6) Wilkerson, W. W.; Akamike, E.; Cheatham, W. W.; Hollis, A.
Y.; Collins, R. D.; De Lucca, I.; Lam, P. Y. S.; Ru, Y. HIV Protease
Inhibitory Bis-benzamide Cyclic Ureas: A Quantitative Struc-
ture-Activity Relationship Analysis. J . Med. Chem. 1996, 39,
4
H), 3.28 (d, br, 15 Hz, 4H), 3.56 (s, br, 2H), 3.58 (d, br, 15
Hz, 4H), 3.73 (s, 6H), 3.75 (s, 2H), 4.62, 4.71 (2 × s, br, 4H,
+
exchangeable), 6.72-7.14 (m, 8H); ESI-MS m/z 495 (M + H ).
4
299-4312.
Anal. (C28
34 2 6
H N O ) C, H, N.
(
7) Sham, H. L.; Zhao, Ch.; Stewart, K. D.; Betebener, D. A.; Lin,
Sh; Park, Ch. H.; Kong, X.-P.; Rosenbrook, W.; Herrin, J r. Th.;
Madigan, D.; Vasavanonda, S.; Lyons, N.; Molla, A.; Saldivar,
A.; Marsh, K. C.; McDonald, E.; Wideburg, N. E.; Denissen, J .
F.; Robins, T.; Kempf, D. J .; Plattner, J . J .; Norbeck, D. W. Novel,
Picomolar Inhibitor of Human Immunodeficiency Virus Type 1.
J . Med. Chem. 1996, 39, 392-397.
8) Thaisrivongs, S.; Tomich, P. K.; Watenpaugh, K. D.; Chong, K.-
T.; Howe, W. J .; Yang, Ch.-P.; Strohbach, J . W.; Turner, St. R.;
McGrath, J . P.; Bohanon, M. J .; Lynn, J . C.; Mulichak, A. M.;
Spinelli, P. A.; Hinshaw, R. R.; Pagano, K. F.; Moon, J . B.;
Ruwart, M. J .; Wilkinson, K. F.; Rush, B. D.; Zipp, G. L.; Dalga,
R. J .; Schwende, F. J .; Howard, G. M.; Pabury, G. E.; Toth, L.
N.; Zhao, Z.; Koeplinger, K. A.; Kakuk, Th. J .; Cole, S. L.; Zaya,
R. M.; Piper, R. C.; J effrey, P. Structure-Based Design of HIV
Protease Inhibitors: 4-Hydroxycoumarins and 4-Hydroxy-2-
pyrones as nonpeptidic Inhibitors. J . Med. Chem. 1994, 37,
Gen er al P r ocedu r e for N-Acylation of NH Cage Dim er s
2
e,f w ith Ben zyl Ch lor ofor m a te to 4e,f: Tetr a m eth yl 3,9-
Diben zyloxyca r bon yl-6,12-d ip h en yl-3,9-d ia za h exa cyclo-
2
.7 4.11 5.10
[
6.4.0.0 .0 .0 ]dodecan e-1,5,7,11-tetr acar boxylate (4e).
Compound 2e (0.04 g, 0.07 mmol) was dissolved in 40 mL of
THF at 40 °C. Under stirring benzyl chloroformate (0.119 g,
(
0
.7 mol) was added to the solution at room temperature and
stirring continued overnight. Then the solution volume was
reduced by evaporation in vacuo compound 4e precipitated
1
with a yield of 0.053 g (89%): H NMR (CDCl
3
) δ 3.57, 3.55,
3
4
4
.46 (3 × s, br, 24 H of two rotamers), 3.81 (s, 4H), 5.27 (s, br,
H), 5.33 (s, br, 4H), 5.66, 5.56 (2 × s, br, 8H), 6.87-7.33 (m,
+
0H); ESI-MS m/z 837 (M + Na ). Anal. (C46
42 2
H N O12) C, H,
N.
Tetr a m eth yl 3,9-d iben zyloxyca r bon yl-6,12-bis(4-m eth -
3
200-3204.
2
.7 4.11 5.10
oxyph en yl)-3,9-diazah exacyclo[6.4.0.0 .0 .0 ]dodecan e-
1
(
9) Hilgeroth, A.; Fleischer, R.; Wiese, M.; Heinemann, F. W.
Comparison of HIV-1 protease inhibitor azacyclic urea A-98881
with cage-dimeric N-benzyl-4-(4-methoxyphenyl)-1,4-dihydro-
pyridine as representative of a novel class of HIV 1 protease
inhibitors: A molecular modeling study. J . Comput.-Aided Mol.
Des. 1999, 13, 233-242.
1
,5,7,11-tetr a ca r boxyla te (4f): yield 0.047 g (85%); H NMR
(
3
CDCl
3
) δ 3.41, 3.46 (2 × s, 24H), 3.51, 3.53, 3.65 (3 × s, 12H),
.71 (s, 4H), 3.26 (s, br, 4H), 5.32 (s, br, 4H), 5.50, 5.59 (2 × s,
+
br, 8H), 6.48-7.34 (m, 36H); ESI-MS m/z 913 (M + K ). Anal.
(C
48
H
46
N
2
O
14) C, H, N.
(
10) Chennat, U.; Eisner, U. A Novel Synthesis of 1,4-Dihydropy-
ridines. J . Chem. Soc., Perkin Trans. 1 1975, 10, 926-927.
11) Hilgeroth, A.; Baumeister, U.; Heinemann, F. W. Novel Solid-
State Synthesis of Polyfunctionalized 3,9-Diazatetraasteranes.
Eur. J . Org. Chem. 1998, 2, 1213-1218.
Gen er a l P r oced u r e for th e Ester Red u ction of Ca ge
Com p ou n d s 4e,f t o Alcoh olic Der iva t ives 5e,f: 3,9-Di-
b en zyloxyca r b on yl-1,5,7,11-t et r a h yd r oxym et h yl-6,12-
(
2
.7
4.11
5.10
d ip h e n yl-3,9-d ia za h e xa cyclo[6.4.0.0 .0
ca n e (5e). Compound 4e (0.04 g, 0.05 mmol) was dissolved in
5 mL of a suspension of 0.027 g (0.5 mmol) of freshly prepared
.0
]d od e -
(12) Hilgeroth, A.; Heinemann, F. W. Novel solid-state synthesis of
dimeric 4-aryl-1,4-dihydropyridines. J . Heterocycl. Chem. 1998,
35, 359-364.
2
1
9
calcium borohydride in THF. The mixture was stirred for
about 4 weeks at room temperature. Then 2.5 mL of ice-water
was added at 0 °C and the excess of calcium borohydride was
hydrolyzed by the dropwise addition of hydrochloric acid (10%).
The solution was kept stirring for 1 h at 0 °C and then
extracted with 100 mL of chloroform three times. After drying
over sodium sulfate for 30 min the solution was filtered. After
evaporation to dryness in vacuo the residue was recrystallized
(
13) Enzymatic activity of PR was measured by following the cleavage
of the substrate H-Lys-Ala-Arg-Val-Leu-p-nitrophenylalanine-
14
15
Glu-Ala-Nle-NH
2
as described previously.
(
14) Richards, A.; D.; Phylip, L. H.; Farmeries, W. G.; Scaborough,
P. E.; Alvarez, A.; Dunn, B. M.; Hirel, Ph.-H.; Konvalinka, J .;
Strop, P.; Pavlickova, L.; Kosta, V. Sensitive, Soluble Chromoge-
nic Substrates for HIV-1 Proteinase. J . Biol. Chem. 1990, 265,
7
733-7736.
(
15) Scholz, D.; Billich, A.; Charpiot, B.; Ettmayer, P.; Lehr, P.;
Rosenwirth, B.; Schreiner, E.; Gstach, H. Inhibitors of HIV-1
Proteinase Containing Heterosubstituted 4-Amino-3-hydroxy-
from methanol/water yielding 0.031 g (89%) of 5e as a white
1
powder: H NMR (DMSO-d
(
6
) δ 3.02-3.07 (m, 12H), 3.41-3.44
m, 8H), 4.40, 4.44, 4.50 (3 × s, 8H), 4.63, 4.66, 4.69, 4.71 (4 ×
5
-phenylpentanoic Acid: Synthesis, Enzyme Inhibition, and
t, 13 Hz, 8H, exchangeable), 5.11 (d, 13.0 Hz, 4H), 5.28 (d,
Antiviral Activity. J . Med. Chem. 1994, 37, 3079-3089.
+
1
3.0 Hz, 4H), 6.88-7.39 (m, 40H); ESI-MS m/z 741 (M + K ).
Anal. (C42 ) C, H, N.
,9-Diben zyloxyca r bon yl-1,5,7,11-tetr a h ydr oxym eth yl-
,1 2 -b i s ( 4 -m e t h o x y p h e n y l ) -3 ,9 -d i a z a h e x a c y c l o -
(16) Scientist, V. 2; MicroMath, Salt Lake City, UT 84121. Schaper,
K. J .; Emig, P.; Engel, J .; Fleischhauer, I.; Kutscher, B.;
Samitier, M. Dose Response Relationship, Biotest Intercorrela-
tions, QSAR and the Saving of Animal Experiments. In QSAR
and Molecular Modeling Concepts, Computational Tool and
Biological Applications; Sanz, F., Giraldo, F., Manaut, F., Eds.;
Prous Science: Barcelona, 1995; pp 73-76.
42 2 8
H N O
3
6
[
2
.7 4.11 5.10
1
6.4.0.0 .0 .0 ]d od eca n e (5f): yield 0.032 g (93%); H
NMR (DMSO-d ) δ 3.00 (s, 4H), 3.01-3.06 (m, 8H), 3.50-3.51
6
(
m, 8H), 3.68 (s, 12H), 4.40, 4.42, 4.47 (3 × s, 8H), 4.57, 4.61,
(
17) Erickson, J .; Neidhart, D. J .; VanDrie, J .; Kempf, D. J .; Wang,
X. Ch.; Norbeck, D. W.; Plattner, J . J .; Rittenhouse, J . W.; Turon,
M.; Wideburg, N.; Kohlenbrenner, W. E.; Simmer, R.; Helfrich,
R.; Paul, D. A.; Knigge, M. Design, Activity, and 2.8 Å Crystal
4
4
8
.63, 4.65 (4 × t, 2.0 Hz, 8H, exchangeable), 5.09 (d, 13.2 Hz,
H), 5.30 (d, 13.2 Hz, 4H), 6.42-7.39 (m, 36H); ESI-MS m/z
+
01 (M + K ). Anal. (C44
46 2
H N O10) C, H, N.
2
Structure of a C Symmetric Inhibitor Complexed to HIV-1
Protease. Science 1990, 249, 527-533.
Ack n ow led gm en t. Andreas Hilgeroth is grateful for
the support of his work by the German Pharmaceutical
Society (DPhG).
(
18) Seelmeier, S.; Schmidt, H.; Turk, V.; v. d. Helm, K. Human
immunodeficiency virus has an aspartic-type protease that can
be inhibited by pepstatin A. Proc. Natl. Acad. Sci. U.S.A. 1988,
8
5, 6612-6616.
(
19) Daluge, S.; Vince, R. Synthesis of Carbocyclic Aminonucleosides.
Refer en ces
J . Org. Chem. 1978, 43, 2311-2320.
(
1) Hilgeroth, A. HIV-1 Protease Inhibitors - An Overview. Pharm.
uns. Zeit 1998, 27, 22-25.
J M991115K