Discovery of potent azaindazole leucine-rich repeat kinase 2 (LRRK2) inhibitors possessing a key intramolecular hydrogen bond – Part 2

Article abstract of DOI:10.1016/j.bmcl.2018.10.017

The discovery of disease-modifying therapies for Parkinson's Disease (PD) represents a critical need in neurodegenerative medicine. Genetic mutations in LRRK2 are risk factors for the development of PD, and some of these mutations have been linked to incr

Full text of DOI:10.1016/j.bmcl.2018.10.017

Accepted Manuscript
Discovery of potent azaindazole leucine-rich repeat kinase 2 (LRRK2) inhibi-
tors possessing a key intramolecular hydrogen bond — Part 2
Daniel G.M. Shore, Zachary K. Sweeney, Alan Beresford, Bryan K. Chan,
Huifen Chen, Jason Drummond, Andrew Gill, Tracy Kleinheinz, Xingrong Liu,
Andrew D. Medhurst, Edward G. McIver, John G. Moffat, Haitao Zhu, Anthony
A. Estrada
PII:
S0960-894X(18)30807-2
https://doi.org/10.1016/j.bmcl.2018.10.017
BMCL 26076
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
16 August 2018
8 October 2018
12 October 2018
Please cite this article as: Shore, D.G.M., Sweeney, Z.K., Beresford, A., Chan, B.K., Chen, H., Drummond, J., Gill,
A., Kleinheinz, T., Liu, X., Medhurst, A.D., McIver, E.G., Moffat, J.G., Zhu, H., Estrada, A.A., Discovery of potent
azaindazole leucine-rich repeat kinase 2 (LRRK2) inhibitors possessing a key intramolecular hydrogen bond —
Part 2, Bioorganic & Medicinal Chemistry Letters (2018), doi: https://doi.org/10.1016/j.bmcl.2018.10.017
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Discovery of potent azaindazole leucine-rich
repeat kinase 2 (LRRK2) inhibitors
possessing a key intramolecular hydrogen
bond — Part 2
Daniel G. M. Shore, Zachary K. Sweeney, Alan Beresford, Bryan K. Chan, Huifen Chen, Jason Drummond,
Andrew Gill, Tracy Kleinheinz, Xingrong Liu, Andrew D. Medhurst, Edward G. McIver, John G. Moffat,
Haitao Zhu, and Anthony A. Estrada

Discovery of potent azaindazole leucine-rich repeat kinase 2
(LRRK2) inhibitors possessing a key intramolecular
hydrogen bond — Part 2
Daniel G. M. Shore a,1, Zachary K. Sweeney a,2, Alan Beresford b, Bryan K. Chan a, Huifen Chen a, Jason
Drummond c, Andrew Gill d, Tracy Kleinheinz c, Xingrong Liu e, Andrew D. Medhurst d, Edward G. McIver f,
John G. Moffat c, Haitao Zhu g, and Anthony A. Estrada a,†
a Department of Discovery Chemistry, Genentech, Inc., 1 DNA Way, South San Francisco, CA 94080, USA
b Department of Drug Metabolism and Pharmacokinetics, BioFocus, Chesterford Research Park, Saffron
Walden, Essex CB10 1XL, UK
c Department of Biochemical and Cellular Pharmacology, Genentech, Inc., 1 DNA Way, South San Francisco,
CA 94080, USA
d Department of Biochemical and Cellular Pharmacology, BioFocus, Chesterford Research Park, Saffron
Walden, Essex CB10 1XL, UK
e Department of Drug Metabolism and Pharmacokinetics, Genentech, Inc., 1 DNA Way, South San Francisco,
CA 94080, USA
f LifeArc, Accelerator Building, Open Innovation Campus, Stevenage SG1 2FX, UK
g Department of Neuroscience, Genentech, Inc., 1 DNA Way, South San Francisco, CA 94080, USA
RECEIVED DATE
Abstract: The discovery of disease-modifying therapies for Parkinson’s Disease (PD) represents a critical
need in neurodegenerative medicine. Genetic mutations in LRRK2 are risk factors for the development of PD,
and some of these mutations have been linked to increased LRRK2 kinase activity and neuronal toxicity in
cellular and animal models. As such, research towards brain-permeable kinase inhibitors of LRRK2 has
received much attention. In the course of a program to identify structurally diverse inhibitors of LRRK2

kinase activity, a 5-azaindazole series was optimized for potency, metabolic stability and brain penetration. A
key design element involved the incorporation of an intramolecular hydrogen bond to increase permeability
and potency against LRRK2. This communication will outline the structure-activity relationships of this
matched pair series including the challenge of obtaining a desirable balance between metabolic stability and
brain penetration.
Keywords: LRRK2; Kinase inhibitor; Azaindazole; Parkinson’s disease; Brain penetration

Mutations in the LRRK2 gene were first linked to familial Parkinson’s disease (PD) more than a decade
ago.[1] The most prevalent of these missense mutations, G2019S, has been shown to increase LRRK2 kinase
activity in both biochemical and cellular assays.[2] Additionally, LRRK2 mutation carriers possess
phenotypes that are indistinguishable from idiopathic PD.[3] Consequently, many research groups are
pursuing LRRK2 kinase inhibitors as potential disease-modifying or neuroprotective therapies for both familial
and sporadic cases of PD.[4],[5]
Our group previously reported the discovery of highly potent, selective, and brain-penetrant LRRK2
small molecule inhibitors such as anilino-aminopyrimidine GNE-7915 (1)Error! Bookmark not defined.d
and aminopyrazole GNE-0877 (2)Error! Bookmark not defined.f (Figure 1). These highly optimized
compounds were evaluated in preclinical efficacy and safety studies to assess the consequences of prolonged in
vivo LRRK2 kinase inhibition. In this communication, we describe the identification of structurally
differentiated azaindazole LRRK2 inhibitors,[6] and highlight the use of intramolecular hydrogen bonding in
the optimization of LRRK2 binding affinity. We also discuss the challenges associated with achieving in vivo
brain penetration with the azaindazole N-H hinge-binding motif, and our attempts to improve membrane
permeability
through
incorporation
of
intramolecular
hydrogen
bonding.[7]
Figure 1. Previously described aminopyridine-based LRRK2 inhibitors
Profiles of azaindazole LRRK2 inhibitors, obtained from LifeArc (formerly MRC Technology), are
shown in Table 1.Error! Bookmark not defined.b,[8] Small molecule inhibitors 3 and 4 were extensively profiled at
Genentech and were confirmed to have good biochemical LRRK2 potency (182 nM and 44 nM, respectively).
As such, they represented efficient starting points (3: LE = 0.56, LLE = 5.3, LELP = 2.7; 4: LE = 0.61, LLE =
5.4, LELP = 3.1)[9],[10] requiring kinase selectivity[11] and LRRK2 cellular potency optimization. DMPK

profiling of azaindazoles 3 and 4 demonstrated reasonable in vitro and in vivo metabolic stability and no P-gp-
mediated efflux as measured by a MDCK-MDR1 assay (NIH cell line) using a compound concentration of 5
µM. We also knew from inherited SAR that 4-alkoxy-substituted azaindazole inhibitors such as 4 were several
fold more potent than the corresponding 4-amino analogues, (cf. compound 3).Error! Bookmark not
defined.b
Table 1. MRCT azaindazole profiles
Cmpd
Structure
cLogP, TPSAa
LRRK2 Kib
(nM)
pLRRK2c IC50
(nM)
LM Clhep
MDR1e P-gp
ERf
Rat Cl (mL
min-1 kg-1)h
(mL min-1 kg-1)d
human / rat
(B-A/A-B)g
1.5, 62
182
44
426
301
135
24
5.5 / 19
6.0 / 21
9.2 / 35
14 / 49
1.1
0.9
1.5
3.4
25
3
4
5
6
1.7, 60
34
2.1, 88
27
117
69
2.5, 85
4.2
aTopological polar surface area
bBiochemical assay
cCellular assay; all biochemical and cellular assay results represent the arithmetic mean of a minimum of two determinations, and these assays generally produced
results within 3-fold of the reported mean
dLiver microsome predicted hepatic clearance
eMDCK-MDR1 human P-gp transfected cell line
fEfflux ratio
gBasolateral-to-apical/apical-to-basolateral
hCompounds dosed IV (1 mg/kg or 0.5 mg/kg) as a 40-60% PEG400 solution in H2O
With a goal to increase the potency and kinase selectivity of this series, we turned to a LRRK2
homology model that has been previously described by our group.Error! Bookmark not defined.c Figure 2a
shows the proposed binding mode of 4 in the ATP binding site of LRRK2 overlaid with GNE-7915 (1).
Previous studies have shown that the front pocket region of the LRRK2 binding site, occupied by a phenyl ring
in 1, is a shallow and hydrophobic pocket optimally suited for flat aryl or heteroaryl rings. Appropriate
substitution of the front pocket ring (methoxy substituent in 1) typically yields high levels of kinase selectivity
due to an invoked steric clash with residues such as Phe or Tyr (cf. Y931 of JAK2), which exist in

approximately 300 kinases.Error! Bookmark not defined.c The modeled overlay (Figure 2a) supports our
hypothesis that the modest kinase selectivity of 4 is due to the lack of an offensive interaction with Y931 of
JAK2 (L1949 in LRRK2). We hypothesized that increased LRRK2 potency and selectivity of 4 versus off-
target kinases, such as JAK2, would be improved with substituted 5- and 6-membered heteroaryl rings at the 3-
position of the indazole. Figure 2b illustrates the proposed clash between 3-(2-morpholinopyridine) 6 and
Y931 (yellow) of JAK2.
Figure 2. a) Overlay of docking models of GNE-7915 (1) (cyan) and 4 (magenta) in the ATP binding site of a LRRK2 homology model with LRRK2 binding site
residues (green) and Y931 of JAK2 (yellow). Predicted intermolecular hydrogen bonds are shown as yellow dashed lines. b) Predicted binding mode of 6 (salmon) in
the ATP binding site of a LRRK2 homology model with LRRK2 binding site residues (green) and Y931 of JAK2 (yellow). Predicted intermolecular hydrogen bonds
are shown as yellow dashed lines.
Morpholino substituted LifeArc compounds 5 and 6 with appropriately substituted 6-membered
heteroaryl rings in the front pocket region are indeed potent and selective LRRK2 inhibitors (Table 1).Error!
Bookmark not defined.b Compound 6 demonstrates a JAK2/LRRK2 biochemical selectivity index of 882x
and in a representative panel of 70 kinases at 1 μM (237-fold over LRRK2 Ki), 6 only inhibited 2 off-target
kinases at greater than 50% inhibition (MELK at 60% and TTK at 86%). The greater potency of 6 compared
to 5 reproduces the previous observation that 4-alkoxyazaindazoles are generally more potent than the
corresponding 4-aminoazaindazoles, possibly because the N-H of 5 causes the 3-aryl ring to be rotated slightly
out of plane. Unfortunately, inhibitor 6 was cleared greater than liver blood flow in rat and appeared to be a
modest P-gp substrate. Examination of the overall profiles for azaindoles 5 and 6 suggested that cLogP and

TPSA would need to be carefully modulated to appropriately balance metabolic stability and brain
permeability.
Initial efforts focused on preparing close-in analogs of 4-alkoxyazaindazole 6 with 5- and 6-membered
front pocket heterocycles (7–10, Table 2) engineered with increasing polarity compared to the more lipophilic
compound 6. Compound 7, isomeric to 6 showed a marked decrease in potency with no improvement in
metabolic stability. While an increase in metabolic stability was achieved with pyrazole 8, the accompanying
efflux ratio was unacceptable for sufficient brain penetration. Unsubstituted pyrazole 9 showed modest
potency, possibly due to a co-planar confirmation encouraged by intramolecular hydrogen bonding between
the pyrazole N-H and the alkoxy oxygen. Interestingly, 1,2,4-triazole 10 showed a sharp reduction in potency
compared to pyrazoles 8 and 9.

Table 2. 3-Heteroaryl substituted 5-azaindazoles
Cmpd
Structure
cLogP, TPSAa
LRRK2 Kib
(nM)
pLRRK2c IC50
(nM)
LM Clhep
MDR1e P-gp
ERf
Rat Cl (mL
min-1 kg-1)h
(mL min-1 kg-1)d
human / rat
(B-A/A-B)g
7
2.7, 85
147
21
n.d. i
14 / 48
2.0 / 22
10 / 14
5.1 / 8.9
n.d. i
n.d. i
8
1.9, 98
13
80
30
2.1, 88
44
n.d. i
n.d.i
n.d. i
n.d.i
n.d. i
n.d.i
9
2.5, 101
4600
10
aTopological polar surface area
bBiochemical assay
cCellular assay; all biochemical and cellular assay results represent the arithmetic mean of a minimum of two determinations, and these assays generally produced
results within 3-fold of the reported mean
dLiver microsome predicted hepatic clearance
eMDCK-MDR1 human P-gp transfected cell line
fEfflux ratio
gBasolateral-to-apical/apical-to-basolateral
hCompounds dosed IV (0.5 mg/kg) as a 40-80% PEG400 solution in H2O or 50-60% NMP solution in H2O
iNot determined
Quantum mechanical torsional scans[12] suggest that the dominant low-energy conformation of
compound 10 is that shown in Figure 3 with a potential intramolecular hydrogen bond between the ether
oxygen and the triazole N-H, and this conformation should be well accommodated in the flat front pocket
binding site of LRRK2. However, this conformation of 10 also presents a lone pair towards a carbonyl oxygen
on the protein backbone. We rationalized that the significant decrease in potency was due to disfavourable
lone pair repulsion between a nitrogen on the 1,3,4-triazole moiety and a carbonyl oxygen on the protein
backbone. This hypothesis also explains the diminished potency of compound 7 due to a similar disfavourable
lone pair repulsion with the protein back bone.

Figure 3. Lowest energy conformation of compound 8 with postulated
intramolecular hydrogen bond and proposed repulsion with protein backbone
Figure 4. 4-aminoazaindazole is postulated to preserve the intramolecular
hydrogen bond with a front pocket triazole while presenting an N-H to form
putative favourable interactions with the protein backbone
Using this hypothesis, we postulated that a compound without this disfavourable interaction between
the protein backbone and the inhibitor could result in improved potency. An intramolecular hydrogen bond
between a nitrogen of the depicted triazole and the polar N-H of a 4-aminoazaindazole (Figure 4) could serve
to favour the preferred flat conformation as well as provide a potential point of interaction between the
inhibitor and the protein backbone through the triazole N-H. This could serve to rescue the potency of the 4-
aminoazaindazole series compounds which were typically less potent than their 4-alkoxyazaindazole matched
molecular pairs as shown in Table 1. In addition, the invoked intramolecular hydrogen bonding should mask
the polarity, effectively neutralizing one hydrogen bond donor and acceptor, such that intrinsic permeability is
improved and P-gp efflux may be reduced.Error! Bookmark not defined.,[13]
3-heterocyclic-4-amino-5-azaindazoles which were capable of making an intramolecular hydrogen
bond were designed and synthesized. Gratifyingly, compound 11 (Table 3) showed excellent biochemical (7.8
nM) and cellular potency (35 nM) representing a biochemical potency gain of 600-fold compared to the direct
ether matched molecular pair 10. Triazole 11 also demonstrated good in vitro microsomal stability and a
moderate in vivo rat clearance of 36 mL min-1 kg-1. However, despite the masked polarity, compound 11
suffered from P-gp efflux (MDR1-MDCK efflux ratio of 21).
In an attempt to alleviate permeability concerns, several approaches were applied to decrease the
polarity of the series. Compounds 12–17 (Table 3) exemplify employed strategies including the removal of

hydrogen bond donors and the reduction of polar surface area. It should be noted that substituting at the
azaindazole N-H was not an option as this was a key hinge-binding element. Methylating the free N-H of the
1,3,4-triazole (12), resulted in an expected significant potency loss, likely due to steric clash with the protein
backbone. Removal of one hydrogen bond donor through substitution with a 1,2,3-triazole (13) maintained
desirable potency suggesting a C-H can potentially mimic the proposed interaction between the N-H of the
triazole in 11 and the protein in some cases. However, P-gp mediated efflux was still significant. Pyrazoles 14
and 15, with TPSA values of 80 and 71 respectively, demonstrated high levels of LRRK2 potency. However
MDR1 efflux ratios were still unacceptable for brain penetration. Additionally, as polarity was reduced in an
attempt to decrease MDR1 efflux, liver microsome stability predictably worsened (e.g. human LM Cl = 19 mL
min-1 kg-1 for pyrazole 15). This exemplifies the crucial balance that exists with this azaindazole series
between permeability and stability. Notably, when regioisomeric pyrazole 16 was synthesized, potency was
greatly reduced. This result serves as more evidence to the requirement of an intramolecular hydrogen bond
for excellent LRRK2 potency using the 4-aminoazaindazole core since clearly no intramolecular hydrogen
bonding can occur with this compound and significant out of plane torsion of the front pocket pyrazole is
likely.

Table 3. 3-Heteroaryl substituted 4-amino-5-azaindazoles
Cmpd
Structure
cLogP, TPSAa
1.6, 104
1.4, 84
LRRK2 Kib
(nM)
pLRRK2c IC50
(nM)
LM Clhep
MDR1e P-gp
ERf
Rat Cl (mL
min-1 kg-1)h
(mL min-1 kg-1)d
human / rat
(B-A/A-B)g
7.8
35
7.0 / 11
17 / 42
10 / 31
15 / 29
19 / 47
10 / 29
15 / 27
13 / 23
21
n.d.i
23
10
4
35
11
151
1.2
n.d.i
n.d.i
n.d.i
n.d.i
n.d.i
n.d.i
22
12
1.4, 93
49
13
2.2, 80
0.5
4.5
n.d.i
n.d.i
41
14
2.7, 71
3.5
15
2.1, 80
3900
3.1
11
3.6
1.4
16
2.0, 75
17
2.1, 88
4.1
24
18
18
aTopological polar surface area
bBiochemical assay
cCellular assay; all biochemical and cellular assay results represent the arithmetic mean of a minimum of two determinations, and these assays generally produced
results within 3-fold of the reported mean
dLiver microsome predicted hepatic clearance
eMDCK-MDR1 human P-gp transfected cell line
fEfflux ratio
gBasolateral-to-apical/apical-to-basolateral
hCompounds dosed IV (0.5 mg/kg) as a 40-80% PEG400 solution in H2O or 50-60% NMP solution in H2O
iNot determined
As we were unable to successfully incorporate the desired balance of potency, metabolic stability, and
brain permeability with 4-aminoazaindazoles with 5-membered ring front-pocket heterocycles, 6-membered
heterocycles capable of intramolecular hydrogen bonding were also synthesized. Compound 17 with a front-
pocket pyridine was found to have excellent potency, although a modest P-gp liability still existed.

Trifluoropyrimidine 18 possessed excellent biochemical and cellular potency, in vitro stability, and lacked
MDR1 efflux. Compounds 17 and 18 show considerably improved potency over compound 5 (Table 1),
(which cannot participate in intramolecular hydrogen bonding,) and also greatly improved in vivo metabolic
stability. Excellent selectivity of 18 was observed against JAK2 (1000-fold) as well as against the broader
kinome, inhibiting only three other kinases at >50% at 1 µM in a 74-kinase panel.[14] When 18 was analyzed
in vivo, it distinguished itself from other azaindazoles by demonstrating moderate rat clearance (18 mL·min-1
kg-1),[15] good rat oral bioavailability (62 %),[16] and total and unbound brain to plasma ratios of 1.0 and 0.22
respectively.[17]
Compounds 8, 10–18 were synthesized as described in Schemes 1–3.[18] Tertiary alcohol 8 was
synthesized via a Suzuki reaction with 4-pyrazole boronic acid pinacol ester followed by alkylation with
isobutylene oxide under basic conditions and deprotection of the trityl group with TFA and triethylsilane in
dichloromethane. 1,3,4-triazoles 10–12 were synthesized starting from the appropriate PMB-protected 3-
iodoazaindazole using a two-step, one-pot protocol involving a carbonylative C-N coupling with isopropyl
amidine forming intermediate 22 followed by condensation of hydrazine[19] and subsequent PMB
deprotection with triflic acid. Pyridine 17 and trifluoropyrimidine 18 were synthesized from the same starting
material via a palladium-catalyzed stannylation to form stannane 23 followed by a Stille coupling and acidic
PMB-deprotection.
1,2,3-triazole 13 was synthesized through a four-step sequence starting from the appropriate 1-trityl-
protected azaindazole. A Sonogashira reaction with TMS-acetylene followed by methanolysis yielded the
terminal alkyne 25. A 1,3-dipolar cycloaddition of this terminal alkyne with sodium azide and in situ
alkylation yielded the desired 1-isopropyl-1,2,3-triazole as a single regioisomer, which was converted to the
final product through acidic trityl-deprotection. Pyrazole 14 was synthesized from the same trityl-protected
azaindazole and pyrazole 15 was synthesized analogously. A Heck reaction with ethyl vinyl ketone yielded the
α,β-unsaturated ketone 26. This was condensed with hydrazine under microwave heating and oxidized with
DDQ to give the N-H pyrazole, which was methylated and deprotected to give the final compound. It should
be noted that methylation occurs selectively at the desired position, suggesting that the other pyrazole nitrogen
is unavailable for alkylation due to intramolecular hydrogen-bonding. Lastly, to synthesize weakly potent

pyrazole isomer 16, α,β-unsaturated ketone 26 was cyclized with methyl hydrazine under microwave heating,
oxidized and deprotected as per pyrazole 14.
Scheme 1. Reagents and conditions: (a) Pd(AmPhos)2Cl2, 4-pyrazole boronic
acid pinacol ester, KOAc, Na2CO3, CH3CN/H2O, 150 °C, 90 min. (b)
Isobutylene oxide, Cs2CO3, DMF, 80 °C, 2 h. (c) TFA, Et3SiH, DCM, rt, 2 h.
Scheme 2. Reagents and conditions: (a) Isopropylamidine hydrochloride,
Pd(OAc)2, XantPhos, Et3N, CO atm, DMF, 80 °C, 2 h. (b) Hydrazine
hydrate, HOAc, rt, 1 h. (c) TfOH, DCM, rt, 15 min. (d) Hexamethylditin,
Pd(dppf)Cl2, PhMe, 140 °C, 30 min. (e) 2-bromopyridine, Pd(PPh3)4, CuI,
LiCl, THF, 100 °C, 30 min. (f) TFA, DCM, 150 °C, 2.5 h. (g) 4-bromo-6-
trifluoromethylpyrimidine, Pd(PPh3)4, CuI, LiCl, THF, 100 °C, 30 min.
Scheme 3. Reagents and conditions: (a) TMSCCH, Pd(PPh3)2Cl2, CuI, Et3N,
CH3CN, rt, 2 h. (b) K2CO3, MeOH, rt, 1 h. (c) Isopropyliodide, NaN3, CuI,
5:1 H2O : tBuOH, 100 °C, 16 h. (d) TFA, Et3SiH, DCM, rt, 15 min. (e) Ethyl
i
vinyl ketone, Pd(P(o-tol)3)2Cl2, Pr2NEt, DMF, 90 °C, 3 h. (f) Hydrazine
hydrate, DMF, 180 °C, 10 min. (g) DDQ, DCM, rt, 16 h. (h) Cs2CO3, MeI,
DMF, 60 °C, 2 h. (i) TFA, Et3SiH, DCM, rt, 15 min. (j) Methyl hydrazine,
DMF, 180 °C, 10 min.

In conclusion, we have presented a series of potent 3-heteroaryl-4-amino-5-azaindazole-based LRRK2
inhibitors. Optimal LRRK2 potency was contingent on the ability to invoke an intramolecular hydrogen bond
between the 3-heteroaryl and 4-amino groups forming a 7-membered ring with no steric or electronic repulsion
near the protein backbone. Though the balance of brain penetration and metabolic stability was a challenge
within the hinge-binding azaindazole series, trifluoropyrimidine 18 showed excellent potency, and moderate in
vivo rat clearance and brain penetration. Inhibitor 18 should contribute to the growing diversity of reported
LRRK2 in vivo tool compounds and assist with exploring the diverse and emerging roles of LRRK2 function
in preclinical studies.
Acknowledgements
The authors thank our Analytical, Bioanalytical, NMR, DMPK, Biochemical Pharmacology and Safety
Assessment colleagues for their contributions.
Supplementary material
Supplementary data associated with this article can be found, in the online version, at http://xxxx
References and notes
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[17] AUC ratio; compound 16 was dosed IV (0.5 mg/kg) as a 60% NMP solution in H2O.

[18] Compounds 5 and 6 were synthesized as described previously, see ref. Error! Bookmark not defined.
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Highlights



A series of potent azaindazole inhibitors of LRRK2 was discovered
A putative intramolecular hydrogen bond was crucial for LRRK2 potency of 4-aminoazaindazole compounds
Careful optimization of polarity and conformation was necessary to ensure potency, metabolic stability and
brain permeability

Compound 18 showed excellent LRRK2 potency, and moderate in vivo rat clearance and brain penetration