Design and synthesis of potent macrocyclic renin inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.10.140

Two types of P1-P3-linked macrocyclic renin inhibitors containing the hydroxyethylene isostere (HE) scaffold just outside the macrocyclic ring have been synthesized. An aromatic or aliphatic substituent (P3sp) was introduced in the macrocyclic ring aiming

Full text of DOI:10.1016/j.bmcl.2010.10.140

Bioorganic & Medicinal Chemistry Letters 21 (2011) 358–362
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and synthesis of potent macrocyclic renin inhibitors
⇑
Christian Sund , Oscar Belda, Daniel Wiktelius, Christer Sahlberg, Lotta Vrang, Susanne Sedig,
Elizabeth Hamelink, Ian Henderson, Tatiana Agback, Katarina Jansson, Neera Borkakoti,
Dean Derbyshire, Anders Eneroth, Bertil Samuelsson
Medivir AB, PO Box 1086, SE-14122 Huddinge, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Two types of P1–P3-linked macrocyclic renin inhibitors containing the hydroxyethylene isostere (HE)
scaffold just outside the macrocyclic ring have been synthesized. An aromatic or aliphatic substituent
(P3sp) was introduced in the macrocyclic ring aiming at the S3 subpocket (S3sp) in order to optimize
the potency. A 5–6-fold improvement in both the Ki and the human plasma renin activity (HPRA)IC50
was observed when moving from the starting linear peptidomimetic compound 1 to the most potent
macrocycle 42 (Ki = 3.3 nM and HPRA IC50 = 7 nM). Truncation of the prime side of 42 led to 8–10-fold
loss of inhibitory activity in macrocycle 43 (Ki = 34 nM and HPRA IC50 = 56 nM). All macrocycles were epi-
meric mixtures in regard to the P3sp substituent and X-ray crystallographic data of the representative
renin macrocycle 43 complex showed that only the S-isomer buried the substituent into the S3sp. Inhib-
itory selectivity over cathepsin D (Cat-D) and BACE-1 was also investigated for all the macrocycles and
showed that truncation of the prime side increased selectivity of inhibition in favor of renin.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 22 September 2010
Revised 29 October 2010
Accepted 31 October 2010
Available online 5 November 2010
Keywords:
Renin
Aspartyl protease
Macrocycle
Antihypertensive
Peptidomimetic
Cathepsin D
BACE-1
S2
The renin-angiotensin-aldosterone system (RAAS) plays a key
role in the regulation of blood pressure and in the maintenance
of sodium and volume homeostasis.1 Inappropriate activation of
the RAAS, as seen in disease states such as diabetes, is important
in hypertension-induced cardiovascular disease and chronic kid-
ney disease.2,3 The aspartyl protease renin catalyzes the first and
also rate-limiting cleavage of angiotensinogen in the RAAS and
has long been recognized as a prominent target for antihyperten-
sive therapy.4 Since the 1980s a number of generations of linear
peptidomimetic renin inhibitors have been developed by pharma-
ceutical companies,5–7 but these compounds were hampered by
high molecular weight and poor oral bioavailability. However, this
development finally resulted in the linear nonpeptidomimetic ali-
skiren as an acceptable compromise between potency and drug-
metabolism-pharmacokinetic (DMPK) properties.8
O
S1'
S
N
O
OH
O
O
H
N
H
N
H
N
S3
N
H
O
O
O
S3'
S3sp
S2'
1
Ki = 21 nM; HPRA IC50 = 38 nM
Cat-D Ki = 3.3 nM;
S1
BACE-1 Ki = 30 nM
The linear peptidomimetic compound 1 (Fig. 1), which had ear-
lier been synthesized and tested in our laboratory, showed potent
renin inhibitory activity (Ki = 21 nM and HPRA IC50 = 38 nM), but
characteristically suffered from high MW, low stability in human
O
N
S
O
OH
H
H
N
X = CO,
CH2CH2
Y = NH,
CH2
N
R2
liver microsomes (HLM) (Clint ꢀ260
lL/min/mg) and low perme-
ability (Caco-2, papp <0.4 ꢁ 10ꢂ6 cm/s). Furthermore, compound 1
had poor selectivity over Cat-D (Ki = 3.3 nM) and BACE-1
(IC50 = 30 nM). One possible way to favorably alter the DMPK prop-
erties of a flexible linear compound is to limit the number of
X
O
O
R2 = Val benzylamide,
O
Y
methyl, isobutyl
R1
R1 = Me, Ph, 4-MeOPh,
MeOCH2CH2CH2,
MeOCH2CH2O
⇑
Corresponding author. Tel.: +46 8 54683142; fax: +46 8 54683199.
E-mail address: christian.sund@medivir.se (C. Sund).
Figure 1. Development of lead compound 1 to the target macrocycles.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.10.140

C. Sund et al. / Bioorg. Med. Chem. Lett. 21 (2011) 358–362
359
rotational bonds by rigidifying the compound.9 This may be
HO2C
CO2t-But
MeO2C
CO2Me
achieved by macrocyclization10,11 and a number of research groups
have employed various chemical strategies for macrocyclizations
of linear peptidomimetic structures by bridging different P-
moieties. Some common methods that have been employed are
peptide coupling,12,13 metathesis,14–19 macrolactonization,20 palla-
dium coupling,20 reductive amination21 and [3 + 2] cycloaddition
(click chemistry).22,23
i, ii, iii
O
O
N
N
S
S
O
O
14
13
R3
CO2H
In our present work with renin inhibitors, we decided to con-
nect the P1 and P3 moieties in 1 (Fig. 1), either by peptide cou-
plings or metathesis, with the intention of further improving the
renin inhibitory activity and establishing selectivity over Cat-D
and BACE-1 and also to alter the DMPK properties in a favorable
way. We also wanted to reduce the molecular weight by truncating
the prime side of the molecules. Computational modeling indicated
that 15–16-membered macrocycles would have a suitable fit in the
active site of renin as for 1 and that substituents at the newly
formed benzylic position in the macrocycle would favorably aim
into the renin S3sp. This positioning of a suitable substituent into
the S3sp was earlier shown to be an important feature for excellent
inhibitory activity of aliskiren against renin.8
Schemes 1–3 display the synthesis of the key building blocks for
the construction of the macrocycles, while Scheme 4 shows the syn-
thesis of the final target macrocycles. For the functionalization at
the 3-position of the P1 benzylic moiety, to be used for the amido
linked macrocycles (41–46), 3-cyanobenzylalcohol was conve-
niently converted in four-steps to the O, N-protected intermediates
2 (R = Me), 3 (R = Ph) and 4 (R = 4-MeOPh), by the addition of aryl or
O
N
S
O
1525
R3 = -CH2CH=CH2 (~40%)
-CH=CHCH3 (~60%)
Scheme 3. Reagents and conditions: (i) NaOH, H2O, MeOH, THF, rt, 80%; (ii)
t-butOH, EDAC, DMAP, DMF, rt, 46%; (iii) NaOH, H2O, MeOH, THF, rt, 85%.
alkyl Grignard reagents to the cyano group followed by reduction
with LiAlH4 and N-protection with Boc2O (Scheme 1). These inter-
mediates were then each treated with acid (80% acetic acid) and
the generated benzylic alcohol was then converted to the corre-
sponding bromide (Ph3P, CBr4) to give 3-functionalized benzylbro-
mides 6 (R = Me), 7 (R = Ph) and 8 (R = 4-MeOPh). Similarly,
3-cyanobenzylalcohol was conveniently converted in four-steps
to the O, N-protected intermediate 5 by addition of the O,C-
bis-Mg reagent, followed by reduction and N-protection and
methylation of the generated 3-hydroxy group by MeI and Ag2O
(Scheme 1). Acidic deprotection and bromination in the usual
way gave the benzyl bromide 9.
For the 3-functionalisation of the P1 benzylic moiety, to be used
for macrocyclization through metathesis (macrocycles 47, 48), 1,3-
bis-hydroxymethylbenzene was monosilylated and then oxidized
to the aldehyde 10, which was reacted with vinyl magnesium bro-
mide, followed by alkylation of the resulting secondary alcohol
with 2-methoxyethyl bromide to give intermediate 11. This com-
pound was deprotected by fluoride ion and the resulting benzylic
alcohol was brominated in the usual way to give the 3-functional-
ized benzyl bromide 12 (Scheme 2).
i, ii
R
N
OH
OMMTr
HN
BOC
2: R = Me
3: R = Ph
4: R = 4-MeOPh
5: R = MeO(CH2)3
iii, iv
R
Br
HN
BOC
The benzoic acid moiety harboring the P2 sulfonamide group
needed to be modified for engagement in macrocyclization
(Scheme 3). The methylsulfonamido dimethylester 13, which was
prepared according to published procedure,24 was converted in
three-steps (33%) to the mono t-butylester mono carboxylic acid
derivative 14, which was used for macrocyclizations through pep-
tide couplings giving the amido linked macrocycles 41–46. The
benzoic acid derivative 1525 (Scheme 3) provided the olefinic han-
dle in the intermediate 40 necessary for the metathesis reaction
leading to the macrocyclic compounds 47 and 48.
6: R = Me
7: R = Ph
8: R = 4-MeOPh
9: R = MeO(CH2)3
Scheme 1. Reagents and conditions: (i) MMTrCl, pyridine, rt, 98%; (ii) Method A (for
2–4): RMgBr, ether, reflux, then LiAlH4, THF, reflux, then Boc2O, EtOAc, rt, 77–91% in
three-steps; Method B (for 5): ClMg(CH2)3OMgBr, THF, reflux, then LiAlH4, THF,
reflux, then Boc2O, EtOAc, rt, 60% in three-steps; MeI, Ag2O, reflux, 52%; (iii)
80%AcOH, rt, 92–97%; (iv) Ph3P, CBr4, DCM, rt, 58–89%.
The synthesis of macrocycles 41–48 is depicted in Scheme 4.
Starting by regioselective monobenzylations of the chirally pure
dihydroxylactone 1626 by the 3-functionalized benzyl bromides
6–9 and 12 gave the benzylethers 17–21 in 59–70% yields. The sec-
ondary hydroxyl group was converted into the azido group with
inverted configuration either by triflation followed by reaction
with NaN3 (Method A, worked for 17–19 but sluggishly for 20
and 21) or by a Mitsunobu type reaction (Method B, for 20, 21) with
yields of all azides 22–26 in the range of 60–96%. The lactone
function of these compounds was opened either by a reaction with
(2S)-2-amino-N-benzyl-3-methyl-butanamide, with isobutyl
amine or methyl amine to give the open chained azido alcohols
(57–95% yields), which were reduced to the corresponding amino
alcohols, either by hydrogenation with Lindlar catalyst to give 27
(95%), 28 (88%), 29 (95%), 30 (99%), 31 (99%) and 32 (78%), or by tri-
phenylphosphine to give 33 (84%). These crude amino alcohols
i, ii
iii, iv
CHO
OH
OH
OTBDPS
10
v, vi
O
O
Br
O
OTBDPS
O
12
11
Scheme 2. Reagents and conditions: (i) TBDPSiCl, DIPEA, DCM, rt, 90%; (ii) Dess-
Martin periodane, DCM, rt, 79%; (iii) CH2@CHMgBr, THF, rt, 74%; (iv) NaH,
MeOCH2CH2Br, TBAI, THF, rt, 73%; (v) TBAF, THF, rt, 86%; (vi) Ph3P, CBr4, DCM, rt,
76%.

360
C. Sund et al. / Bioorg. Med. Chem. Lett. 21 (2011) 358–362
3-(R1)-BnO
3-(R1)-BnO
HO
HO
HO
OH
H
N
N3
O
O
O
O
O
O
H2N
iii, iv
R2
ii
i
H
H
H
O
OBn-(R1)-3
16
17: R1 = a (68%)
18: R1 = b (70%)
19: R1 = c (70%)
20: R1 = d (70%)
21: R1 = e (70%)
22: R1 = a (60%)
23: R1 = b (63%)
24: R1 = c (76%)
25: R1 = d (96%)
26: R1 = e (83%)
27: R1 = a, R2 = f (95%)
28: R1 = b, R2 = f (88%)
29: R1 = b, R2 = i-But (95%)
30: R1 = b, R2 = Me (99%)
31: R1 = c, R2 = i-But (99%)
31: R1 = d, R2 = i-But (78%)
33: R1 = e, R2 = i-But (84%)
O
O
S
S
N
O
O
N
OH
OH
H
N
H
N
H
N
H
N
v
vi, vii
R2
R3
R2
X
O
O
O
O
OBn-(R1)-3
O
Y
34: R1 = a, R2 = f , R3 = -CO2t-But (63%)
35: R1 = b, R2 = f, R3 = -CO2t-But (48%)
36: R1 = b, R2 = i-But , R3 = -CO2t-But (56%)
37: R1 = b, R2 = Me, R3 = -CO2t-But (50%)
38: R1 = c, R2 = i-But , R3 = -CO2t-But (75%)
39: R1 = d, R2 = i-But , R3 = -CO2t-But (40%)
R1
41: R1 = Me, R2 = f , X = CO, Y = NH (26%)
42: R1 = Ph, R2 = f , X = CO, Y = NH (28%)
43: R1 = Ph, R2 = i-But, X = CO, Y = NH (25%)
44: R1 = Ph, R2 = Me, X = CO, Y = NH (43%)
40: R1 = e, R2 = i-But , R3 = -CH2CH=CH2
&
-CH=CHCH3 (~40:60 mix) (81%)
45: R1 = 4-MeOPh, R2 = i-But, X = CO, Y = NH (7%)
46: R1 = -(CH2)3OMe, R2 = i-But, X = CO, Y = NH (44%)
47: R1 = -O(CH2)2OMe, R2 = i-But, X = CO, Y = NH (15%)
48: R1 = -O(CH2)2OMe, R2 = i-But, X = CH2, Y = CH2CH2 (17%)
a: -CH(Me)NHBoc; b: -CH(Ph)NHBoc; c: -CH(4-MeOPh)NHBoc;
d: -CH((CH2)3OMe)NHBoc; e: -CH(O(CH2)2OMe)CH=CH2;
f: -CH((S)-i-Prop)CONHBn
Scheme 4. Reagents and conditions: (i) 6–9,12, Bu2SnO, toluene, reflux; (ii) Method A (for 17–19): Tf2O, pyridine, DCM, 0 °C, then NaN3, DMF, 70 °C; Method B (for 20,21):
Ph3P, DIAD, DPPA, THF, 0 °C–rt; (iii) Method A (for NH2CH((S)-isopr)CONHBn): 2-hydroxypyridine, DIPEA, DMF, 70 °C, (57–63%); Method B (for isobutylamine): neat, 70 °C,
(57–95%); Method C (for methylamine): 40% aqMeNH2, 70 °C, (84%); (iv) Method A (for azides derived from 22–25): Pd/CaCO3, H2 (1 atm), EtOH, rt; Method B (for azide derived
from 26): Ph3P, MeOH, H2O, rt; (v) 14 or 15, DCC, pentafluorphenol, rt; (vi) Method A (for 34–37, 39): TFA, DCM, rt, (crude); Method B (for 38): 100% HCO2H, dioxane, rt,
(crude); (vii) Method A (for 34–39): HATU, DIPEA, DMF, rt, 0.001 M substr. concn; Method B (for 40): H–G-II catalyst, DCE, reflux, then H2 (1 atm), Pd/C, EtOH, rt.
were then coupled with the benzoic acid derivative 14 (for 27–32)
or with benzoic acid derivative 15 (for 33), through a first in situ
activation of the carboxylic acid function with DCC and pentafluor-
phenol followed by mixing the resulting pentafluorphenylester
with the respective amino compounds (27–33), to give the respec-
tive benzamido derivatives 34 (63%), 35 (48%), 36 (56%), 37 (50%),
38 (75%), 39 (40%) and 40 (81%). The Boc and the t-butyl groups
were then removed, either with trifluoracetic acid (TFA) (34–37,
39) or with 100% formic acid (HCO2H) (38) and the crude amino
acids obtained after evaporations were each dissolved in DMF to
high dilution (0.001 M) and treated with the coupling agent HATU
to give after HPLC purification macrocyclic compounds 41 (26%),
42 (28%), 43 (25%), 44 (43%), 45 (7%) and 46 (44%). Intermediate
40 was actually a mixture of two different propene isomers (allyl
and 1-propenyl) and was subjected to metathesis reaction with
Hoveyda–Grubbs second generation catalyst (H–G-II catalyst) un-
der high dilution conditions to give a corresponding mixture of
the unsaturated macrocyclic intermediates. This mixture was sub-
jected to hydrogenation on palladium charcoal to give the final
macrocycles 47 (15%, 15-membered) and 48 (17%, 16-membered),
after HPLC separation.
All synthesized inhibitors were screened against renin, Cat-D
and BACE-1 to determine the respective Ki or IC50 values (Table 1,
Fig. 3). The macrocycles were all 15-membered, except for 48,
which was 16-membered. The macrocycles were epimeric mix-
tures at the position of the P3sp substituent in the ring suggesting
that the renin potencies reported herein could be improved with
diastereomerically pure compounds having the correct stereo-
chemistry for fit into the S3sp. Attempts were made to chromato-
graphically separate the diastereomers, both among the
intermediates 34–40 and the final compounds 41–48, but these at-
tempts were unsuccessful. However, X-ray crystallography data
from the renin macrocycle 43 complex with 2.0 Å resolution
showed that only the isomer of 43 with S stereochemistry at the
benzylic position turned the phenyl group into the S3sp (PDB-
code: 3OWN, Fig. 2). We consider this orientation of the P3sp
group to be a contributing factor for the renin potency seen in most
of these macrocycles. This is balanced against binding interactions
Table 1
Renin, cathepsin D and BACE-1 inhibition data. (Fig. 3)
Compd
X
Y
R1
R2
Renin Kia (nM)
Cathepsin D Ki (nM)
BACE-1 IC50 (nM)
1
21
3.3
30
41
42
44
43
45
46
48
47
C@O
C@O
C@O
C@O
C@O
C@O
(CH2CH2)
CH2
NH
NH
NH
NH
NH
NH
CH2
CH2
Me
Ph
Ph
Ph
ValBnamide
ValBnamide
Methyl
Isobutyl
Isobutyl
Isobutyl
Isobutyl
Isobutyl
94
3.3 (7.0)
340
34 (56)
130
450
13
50
240
0.75
1700
200
760
460
>10000
3700
3100
1900
>10000
>10000
4-MeOPh
MeO(CH2)3
MeO(CH2)2O
MeO(CH2)2O
940
>5000
>5000
>5000
a
In brackets: HPRA IC50 (nM).

C. Sund et al. / Bioorg. Med. Chem. Lett. 21 (2011) 358–362
361
During this investigation we observed that truncation of the
prime side significantly weakened the BACE-1 activity, and in some
cases abolished it (Table 1, Fig. 3). Interestingly, the renin/BACE-1
selectivity ratio decreases 43 ? 45 ? 46, which seems to hint at
BACE-1 being more prone to accept straight chain aliphatic linkers
into its S3sp, as part of the explanation for improved binding to
BACE-1, while the opposite holds true for renin.
The second class of macrocycles represented by 47 and 48
(Table 1, Fig. 3) had only poor or no inhibitory activity against
renin, Cat-D and BACE-1. The more flexible macrocycle 48 still
allowed for sub micromolar potency in case of renin. As shown
in 47 and 48, increased lipophilicity in the macrocyclic ring, facing
the S3 region, together with limited interactions on the prime side,
was not well tolerated by any of these three aspartyl proteases.
In terms of DMPK a modest twofold improvement of the HLM
stability was observed for 42 (Clint ꢀ110
lL/min/mg) over 1
lL/min/mg) and the permeability was still low despite
(Clint ꢀ260
Figure 2. Superimposed X-ray structures of the R (magenta) and S (green) isomers
of 43 bound to renin. 2.0 Å resolution. (PDB-code: 3OWN).
a decrease in rotational bonds (42, Caco-2, papp <0.4 ꢁ 10ꢂ6 cm/s).
The permeability value for the prime side truncated 43 remained
basically the same as for 42 despite the decrease in molecular
weight.
P2
O
In order to gain some insights into the P-glycoprotein (Pgp)-
efflux of these macrocycles, permeability assays with the MDCK
wild type (wt) and human Pgp-enriched MDCK cells (MDR-1)27
were performed on the representative 42 and 43 and the BA/AB
ratios were assessed. Unfortunately, both MDCK cell types gener-
ated papp-values in the lower range of 0.1 ꢂ 2.0 ꢁ 10ꢂ6 cm/s. This
is in line with the results from the earlier Caco-2 assays and indi-
cates that these macrocycles have too low intrinsic permeability
to be able to generate reliable BA/AB ratios from both MDCK cell
types (42, wt = 2.3, MDR-1 = 12.0; 43, wt = 2.0, MDR-1 = 10.0).
However, judging from these ratios, macrocycles 42 and 43 may
be Pgp-substrates. For comparison, analogous MDCK assays were
also run on aliskiren as a reference (BA/AB ratio: wt = 0.7; MDR-
1 = 1.5). This compound gave also very low papp-values (<1), thus
again raising concern about the reliability of the BA/AB ratios.
Nevertheless, the small difference we obtained between the wt
and MDR-1 BA/AB ratios might indicate that aliskiren is not a
Pgp-substrate, which would be in contrast to earlier work indicat-
ing that aliskiren is a Pgp-substrate, based on in vitro Pgp ATPase
S
P1'
O
N
OH
H
N
H
N
R2
P2'-P3'
X
O
O
O
P3
Y
R1
P3sp
P1
Figure 3.
in other parts of the ligand-active site complex, giving thus the net
potency reflected in the measured Ki values. We find it plausible
that this S-orientation seen for 43 is also important for activity
for the rest of the macrocycles in this series.
Another explanation of the difference in activity between 41
and 42 (Table 1, Fig. 3) is that the possibility that the methyl group
is not spacious enough for filling the S3sp, but the phenyl group is.
Unfortunately, also the Cat-D activity followed the same trend, 42
having the highest potency towards this anti-target (Ki = 0.75 nM).
Enzymes of this class are known to have flexibility in the S3 region
and the sub pocket of Cat-D would be expected to expand in a sim-
ilar manner to that seen in BACE-1 and renin when challenged with
the larger P3sp groups, such as a phenyl. These enzymes have dif-
ferences in subsites other than S3 and S3sp, which could influence
the overall binding of our macrocycles and the selectivity ratios ob-
served. Furthermore, since isomeric mixtures were tested herein,
some of the activity may be attributed to the isomer which does
not have the R1 group in the S3sp.
In order to address the issues with selectivity and permeability
some prime side truncated compounds were prepared. A fivefold
selectivity over Cat-D was observed in 44 (renin Ki = 340 nM;
Cat-D Ki = 1700 nM), where the prime side Val-benzyl amide has
been replaced by a methyl group, but with a 100-fold penalty on
renin potency compared to 42 (Table 1, Fig. 3). The corresponding
penalty for Cat-D was over 2000-fold, indicating that ligand bind-
ing on the prime side is particularly crucial for Cat-D in this series
of ligands. By replacing the NH–methyl group with the more lipo-
philic NH–isobutyl group, which may have the possibility to reach
into the S20 pocket, both the renin and Cat-D potencies were recov-
ered with about 10-fold improvement compared to 44 (43, renin
Ki = 34 nM; Cat-D Ki = 200 nM) and with marginally higher renin/
Cat-D selectivity ratio.
activity assays28
.
The described synthetic route provided two types of macrocy-
clic hydroxyethylene isosteres (HE) and the route gave possibility
for smooth decoration of the macrocyclic ring with different sub-
stituents. In total 8 macrocyclic renin inhibitors were synthesized.
The most potent inhibitor 42 exhibited a renin Ki value of 3.3 nM.
There was no selectivity over Cat-D in this case, but a 75-fold selec-
tivity over BACE-1 was recorded. A modest sixfold selectivity of
inhibition of renin over Cat-D was achieved with the prime side
truncated compound 43 followed by a fivefold selectivity for 44.
Based on results from crystallography, we judge that the S-config-
uration of the P3sp group in our macrocycles is important for
inhibitory activity against renin, but is also important for Cat-D,
thus creating low or modest selectivity ratios. This configuration
of the P3sp group also plays a role in BACE-1, but is seemingly less
significant when judging from the activity data.
The measurements of HLM values of the most renin potent
examples, 42 and 43, showed that macrocyclization gave metabol-
ically more stable compounds compared to the starting linear com-
pound 1, but no improvement of permeability (Caco-2) was
achieved. The assessment of the BA/AB ratios for representative
42 and 43 from MDCK wt/MDCK MDR-1 assays implies that these
macrocycles may be Pgp-substrates while aliskiren under same
conditions may not be. However, bearing in mind the low intrinsic
permeability of 42, 43 and aliskiren this conclusion is to be treated
with caution.

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C. Sund et al. / Bioorg. Med. Chem. Lett. 21 (2011) 358–362
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Bioorg. Med. Chem. 2006, 14, 2197.
optimizations are needed for these types of macrocyclic com-
pounds in order to further improve pharmacokinetic properties
and in particular renin/Cat-D inhibitory selectivity ratios, while
sustaining and or improving on the already good nanomolar renin
potencies.
Acknowledgments
19. Lerchner, A.; Machauer, R.; Betschart, C.; Veenstra, S.; Rueegger, H.; McCarthy,
C.; Tintelnot-Blomley, M.; Jaton, A.-L.; Rabe, S.; Desrayaud, S.; Enz, A.;
Staufenbiel, M.; Paganetti, P.; Rondeau, J.-M.; Neumann, U. Bioorg. Med.
Chem. Lett. 2010, 20, 603.
20. Moore, K. P.; Zhu, H.; Rajapakse, H. A.; McGaughey, G. B.; Colussi, D.; Price, E.
A.; Sankaranarayanan, S.; Simon, A. J.; Pudvah, N. T.; Hochmann, J. H.; Allison,
T.; Munshi, S. K.; Graham, S. L.; Vacca, J. P.; Nantermet, P. G. Bioorg. Med. Chem.
Lett. 2007, 17, 5831.
We thank Britt-Louise Sahlberg, Veronica Werlinder, Annelie
Lindqvist and Emma Ulander for excellent technical work in carry-
ing out crucial HLM, Caco-2 and MDCK assays.
References and notes
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