PAMs 6 and 7, which are devoid of adverse effects.
provide derivatives 12 as mixtures of diastereomers. Finally,
1
5
As briefly detailed in the initial disclosure of 7, we
scaffold-hopped from the prototypical 6,6-fused ring system
of 2 to a novel benzomorpholine core (as in 7) wherein we
either a copper-mediated coupling with heterocycles, or a
Suzuki coupling protocol, produced the putative M PAMs 13
1
in 35-86% yield. To facilitate more rapid SAR, we initially
screened analogs 13 as racemates, and used the racemic
3
simultaneously increased sp character while bringing the
Lewis basic oxygen of the quinolone into the 6,6-ring system.
These modifications of the core also created a new sterogenic
center, which, in the case of 7, the (R)-enantiomer displayed
enantiopreference. Here, we will detail the synthesis, SAR,
and DMPK profiles of a multi-dimensional optimization
campaign within the benzomorpholine series that ultimately
led to the discovery of 7, an M PAM with a balance of
1
overall properties as a new in vivo tool compound, free from
adverse effect liability.
version of 7, 14 (VU0484043, M EC = 0.92 M, pEC =
1
50
50
6.10±0.13, ACh Max 77±7; M -M EC s >30 M) as a
2
5
50
1
5
reference compound.
Initial SAR around 14 with analogs 15-20 showed overall
‘flat’ SAR in terms of M PAM potency, but significant
1
5
1
impact on physiochemical and DMPK properties. Of the
structural changes in Figure 2, introduction of a quaternary
carbon at the chiral center, as in 16, led to a diminution in
potency (M EC50 = 7.3 M, 61% ACh Max); however, all
1
other modifications were within 2- to 3-fold of 14. A major
finding was that the des-oxy tetrahydroisoquinoline analog 15
was essentially equipotent to 14, suggesting that the key
a
1
Scheme 1. Synthesis of M PAM analogs 13.
7
-14
intramolecular hydrogen bond (IMHB) of PAMs 4-7 may
not be a key tenet in this new series (however, this will be
1
6
disclosed in a subsequent publication). Other changes,
represented by 17-20, while active as M PAMs, negatively
impacted plasma protein binding (f <0.001) and/or decreased
CNS penetration (brain/plasma K s <0.05) relative to 14 (f
.11, rat K = 0.17, mouse K = 0.7).
Based on these data, we next explored the ‘fluorine walk’,
a strategy that has been highly successful in allosteric
modulator optimization, particularly for other M PAM
This exercise led to intriguing SAR (Figure 3)
1
u
p
u
=
0
p
p
1
1
7,18
scaffolds.
relative to 14. While incorporation of a fluorine atom at the 5-
positon (21) led to an approximate 3-fold decrease in activity
(
7
M
1
PAM EC50 = 3.2 M, pEC50 = 5.51±0.12, ACh Max
6±2), installation at the 6-position (22) led to a ~3-fold
increase in M PAM potency (M PAM EC = 0.32 M,
a
Reagents and conditions: (a) substituted 2-aminophenols, CH
3
CN, K
2
CO
CN, 80 C, 66-74%;
, HATU, DIEA, DMF, rt,
6-80%; (e) Het-NH, (1S,2S)-N ,N -dimethylcyclohexane-1,2-diamine, CuI,
PO , dioxane, rt, 35-50%, or Ar(Het)-B(OH) , 5 mol% Pd(PPh
THF:H
3
,
o
o
6
(
6
K
0 C, 52-80%; (b) 4-bromoAr(Het)bromide, K
2 3 3
CO , CH
1
1
50
c) KOH, THF/H O (2:1), rt, 95-98%; (d) HN R
2
2 3
pEC50 = 6.51±0.08, ACh Max 88±1). Further movement to
the 7-position (23) led to a diminution in potency (M PAM
EC50 = 2.2 M, pEC50 = 5.66±0.03, ACh Max 80±2). An
almost 7-fold increase in M PAM potency (M PAM EC50
0.14 M, pEC = 6.85±0.06, ACh Max 89±1) was realized by
incorporation of a single fluorine atom at the 8-position (24).
Moreover, the rat CNS penetration was improved, relative to
14 (K = 0.17), with K s ranging from 0.3 to 0.4. Despite the
1
2
1
3
4
2
3 4
) ,
o
2
O, 45 C, 54-86%.
1
1
=
The synthesis of diverse analogs 13 was straightforward
50
and starting materials were readily available from commercial
1
5
sources. Ethyl 2,3-dibromopropanoate 8 was condensed with
various substituted 2-aminophenols to provide the racemic
heterocyclic cores 9 in 52-80% yields. Alkylation with
substituted 4-bromo benzyl bromides or the analogous
heterocyclic congeners proceeded smoothly delivering 10 in
p
p
improvement in M PAM potency and modest gains in CNS
penetration, incorporation of a single
1
Figure 2. Initial SAR around 7, surveying multiple dimensions with analogs
of 13, M PAMs 15-20.
1
yields ranging from 66-74%. A quantitative hydrolysis of the
ester gave 11, which then underwent a HATU-mediated
amide coupling with diverse primary and secondary amines to
Figure 3. Impact of the ‘fluorine walk’ around the benzomorpholine core of