Design of a novel pyrrolidine scaffold utilized in the discovery of potent and selective human β3 adrenergic receptor agonists

Article abstract of DOI:10.1016/j.bmcl.2010.12.087

A novel class of human β₃-adrenergic receptor agonists was designed in effort to improve selectivity and metabolic stability versus previous disclosed β₃-AR agonists. As observed, many of the β₃-AR agonists seem to need th

Full text of DOI:10.1016/j.bmcl.2010.12.087

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1865–1870
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design of a novel pyrrolidine scaffold utilized in the discovery of potent
and selective human b3 adrenergic receptor agonists
⇑
Gregori J. Morriello , Harvey R. Wendt, Alka Bansal, Jerry Di Salvo, Scott Feighner, Jiafang He,
Amanda L. Hurley, Donna L. Hreniuk, Gino M. Salituro, Marat Vijay Reddy, Sheila M. Galloway,
Katherine K. McGettigan, George Laws, Crystal McKnight, George A. Doss, Nancy N. Tsou, Regina M. Black,
Judy Morris, Richard G. Ball, Anthony T. Sanfiz, Eric Streckfuss, Mary Struthers, Scott D. Edmondson
Merck Research Laboratories, Rahway, NJ 07065, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel class of human b3-adrenergic receptor agonists was designed in effort to improve selectivity and
metabolic stability versus previous disclosed b3-AR agonists. As observed, many of the b3-AR agonists seem
to need the acyclic ethanolamine core for agonist activity. We have synthesized derivatives that constrained
this moiety by introduction of a pyrrolidine. This unique modification maintains human b3 functional
potency with improved selectivity versus ancillary targets and also eliminates the possibility of the same
oxidative metabolites formed from cleavage of the N–C bond of the ethanolamine. Compound 39 exhibited
excellent functional b3 agonist potency across species with good pharmacokinetic properties in rat, dog, and
rhesus monkeys. Early de-risking of this novel pyrrolidine core (44) via full AMES study supports further
research into various new b3-AR agonists containing the pyrrolidine moiety.
Received 9 November 2010
Revised 14 December 2010
Accepted 16 December 2010
Available online 25 December 2010
Keywords:
b3 Adrenergic receptor agonist
Pyrrolidine scaffold
Ó 2011 Elsevier Ltd. All rights reserved.
OH
The b3-adrenergic receptor (b3-AR), also referred to as ADRB3, is
present mainly in adipose tissue and is involved in the regulation
of lipolysis and thermogenesis.1,2 Consequently, b3-AR agonists
were extensively explored in the 1980’s and 1990’s for treatment
of obesity and type 2 diabetes.3 However, recent studies have
shown that b3-AR’s are not only expressed in adipocytes but also
in the bladder detrusor muscle and the lining of the gastrointesti-
nal tract.4,5 As a result, new therapeutic applications of b3-AR ago-
nists for the treatment of overactive bladder (OAB) and irritable
bowel syndrome (IBS) have recently been explored.6,7 Multiple
companies have reported b3-AR agonists over the past few decades,
which has led to innovative ideas in the attempt to discover struc-
turally unique b3-AR agonists in this crowded competitive arena
(Fig. 1).8
H
OH
N
NH2
S
H
N
O
N
N
NH
S
O
N
H
O
Astellas, mirabegron9
Ph III for OAB, POC in 2Q2005
N
F3C
S
Merck, (L-796,568)10
OH
H
Me
OH
N
O
O
H
CO2H
CO2H
N
Me
Me
HO
O
CO2H
Cl
Lederle
(CL-316423)11
Me
Kissei/BI, ritobegron12
We present a recent discovery of a new pyrrolidine variation of
the secondary amine moiety that appears as a conserved core of
many reported b3-AR agonists (Fig. 2). This modification affords
analogs that maintain good potency and selectivity at the human
b3-AR while unlocking new prospects for research that could lead
to a drug candidate.
In the late 1990’s, Merck reported a series of potent and selec-
tive sulfonamide derived human b3-AR agonists for the possible
treatment for obesity.13 Clinical candidate L-796,568 was discov-
ered which possessed good functional human b3-AR agonist
Figure 1. Examples of b3-AR agonists (conserved acyclic ethanolamine pharmaco-
phore in red). See above-mentioned references for further information.
OH
H
OH
H
N
N
R
R
N
N
H
H
Figure 2. Pyrrolidine derived scaffold (blue highlights modification to acyclic
ethanolamine).
potency and ꢀ1000-fold selectivity over b1 and b2 adrenergic
⇑
Corresponding author.
E-mail address: greg_morriello@merck.com (G.J. Morriello).
receptors. In preclinical species, however, L-796,568 exhibited
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.12.087

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G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1865–1870
moderate oral bioavailabilities in rats and dogs and low oral bio-
availability in rhesus.14 To identify possible metabolic pathways
which may be causing the high clearance and moderate oral bio-
availability in rats, studies to determine oxidative metabolism in
rat liver microsomes were performed.15 These studies revealed
that the majority of metabolites were derived from cleavage of
the central C–N bond from the ethanolamine which ultimately
led to identification of a carboxylic acid metabolite and a primary
amine metabolite (Fig. 3). This oxidative metabolism may be a
contributing factor to the high clearance and moderate oral
bioavailability seen in rats. Moreover, the released metabolites
may have untoward biological effects in animals. Blockade or mod-
ification of this metabolic pathway may therefore improve the
pharmacokinetic profiles of acyclic b3-AR agonists and prevent
formation of metabolites such as those observed from L-796,568.
Previous reports have described the effects of simple substitu-
ents at either of the two carbons adjacent to the secondary
amine,11,12 and we sought to understand the effects of substituents
on both sides of the amine. We therefore synthesized sulfonamide
4 (as a mixture of four diastereomers) which is a close analog of 3
(Fig. 4).16 Unfortunately, the introduction of methyl substituents
onto each of the carbons adjacent to the secondary amine resulted
in a complete loss of b3-AR activity which may be attributed to ste-
ric interactions between the two methyl substituents that induce a
rotational conformation not favored by the b3-AR.
simultaneously modulating the metabolic pathways observed with
L-796,568. Observation of molecular models suggested that a five-
membered ring may best mimic the conformations of the acyclic
ethanolamine. Consequently, chemistry was developed to synthe-
size a pyrrolidine core. Initially, the stereochemistry of the disubsti-
tuted pyrrolidine ring would need to be investigated to determine
the preferred stereoisomer for b3-AR agonist activity. A cross
metathesis synthetic route using two substituted vinyl intermedi-
ates would afford the foundation from which all isomers could be
obtained using a common synthetic sequence.
The synthesis of four distinct vinyl stereoisomer precursors be-
gan by treating commercially available 3-chlorobenzaldehyde (5)
with vinyl magnesium bromide to afford vinyl alcohol 6 (Scheme
1). Protection of the hydroxyl group was accomplished with tert-
butyl, dimethyl silyl chloride in the presence of triethylamine.
Aldehyde 7 was obtained by oxidative cleavage of the vinyl group
with ozone and subsequent reduction of the ozonide using tri-
phenylphosphine. After formation of sulfinimide 817 treatment
with vinyl magnesium bromide afforded sulfinamide 9 as a mix-
ture of all four diastereomers which were separated using silica
gel column chromatography. Protecting group manipulation was
then carried out on all four isomers to afford the N-Boc-protected
compounds 10–13 which were then poised to undergo the desired
cross metathesis reaction.
Preparation of the second vinyl intermediate is shown in
Scheme 2. Intermediate 15 was obtained upon treatment of com-
mercially available methyl (4-aminophenyl) acetate (14) with ben-
zyl chloroformate followed by ester saponification with 5.0 N
lithium hydroxide. The carboxylic acid was then converted to
the Weinreb amide18 (16) using standard EDC coupling with
N,O-methylhydroxylamine. After purification via silica gel flash
column chromatography, the Weinreb amide was then treated
with vinyl magnesium bromide to afford the vinyl ketone 17.
Cross metathesis19 could now be accomplished between olefins
10–13 and 17 (Scheme 3). Diastereomers 10–13 were each cross-
coupled with vinyl ketone 17 by mixing the two intermediates in
the presence of a stoichiometric amount of Zhan I catalyst20 under
dilute conditions (0.05 M). Intermediates 18–21 were next
converted to the pyrrolidine rings using a catalytic hydrogenation
reaction which accomplished five separate reactions in a single pot.
Careful tracking of the reaction using LC–MS allowed the sequence
of reactions to be identified. Initially, the reduction of the double-
bond occurs with 90% conversion after 30 min under 50 PSI hydro-
gen. Next, removal of the chloride and Cbz protecting groups was
observed, followed by formation of the cyclic imine from the ring
closure of the ketone with the free amine. Finally, the rate-limiting
step in this reaction appears to be the hydrogenation of the imine
to form the pyrrolidine ring. The protection of the amines with
tert-butyl-dicarbonate is the final reaction step to afford the four
separate cis/trans (3:1 ratio) pyrrolidine diastereomers 26–29 (as
shown in Scheme 3).
If this hypothesis is correct, it is possible that restricting the
rotation of the acyclic ethanolamine may result in
a favo-
rable conformation for b3-AR agonist functional activity while
oxidative cleavage (57%)
OH
H
N
O
S
N
N
H
O
oxidative
N
CF3
cleavage to amine (25%)
S
N-oxidation (2%)
Major metabolites identified:
HO
O
S
O
H2N
O
O
N
S
O
N
H
H
N
CF3
N
CF3
S
1
S
2
Pharmacokinetics
Rat
62
8.1
23
Dog
20
14
12
0.64
27
Rhesus
19
9
6.2
0.04
4
Clp(ml/min/kg):
t1/2 (h):
Vd (L/kg):
PO AUCN (μM•hr/mpk): 0.07
F (%)
17
The pyrrolidine scaffolds were now available for synthesis of
b3-AR agonists. We first targeted a sulfonamide analogous to
L-796,568. Sulfonyl chloride 3021 was reacted with each of the four
diastereomers followed by simultaneous deprotection of the amine
and hydroxyl groups using 4 N HCl in dioxane with 10% (v/v) water
to furnish 31–34.
Figure 3. Metabolism of L-796,568 observed in rats.15
OH
OH
H
H
N
N
The acyclic compound (3) is also shown to allow comparisons to
the pyrrolidine analogs (Table 1). The four diastereomers vary
greatly in hb3-AR agonist potency and hb1/hb2-AR selectivity.
Not surprisingly, analogs with the undesired (S)-hydroxyl
stereochemistry were 100-fold less potent than the (R)-hydroxyl
diastereomers. On the other hand, the two analogs with the (R)-hy-
droxyl stereochemistry both exhibited good potency in the hb3-AR
agonist functional assay. Compound 31 was optimal and exhibited
similar functional activity as acyclic analog 3. Since 31 was a 3:1
CH3 CH3
NH
S
NH
O
O
S
O
O
N
N
S
F3C
F3C
S
3
4
inactive
human ED50: 11 nM
Figure 4. Di-methyl substituted analog 4.

G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1865–1870
1867
O
OTBS
OH
d
b, c
a
O
Cl
Cl
CH2
Cl
H
5
7
6
OTBS
OTBS
H
Separation of
e
Cl
N
Cl
N
f, g
all four isomers
S
S
done on silica gel
columns.
O
O
CH2
8
9
OTBS
OTBS
OTBS
OTBS
H
H
H
H
S
R
S
N
Cl
Cl
N
R
N
Cl
N
Cl
Cbz
Cbz
Cbz
Cbz
S
R
S
R
CH2
CH2
CH2
CH2
isomer 4
isomer 3
12
isomer 2
11
isomer 1
13
10
Scheme 1. Synthesis of ethanolamine intermediates.16 aReagents and conditions: (a) 1.6 M vinylmagnesium bromide in THF, THF (0–25 °C) 16 h (82%); (b) TBSCl, imidazole,
DCM (68%); (c) ozone, DCM (À78 °C) followed by PPh3 (À78 °C to 25 °C) overnight (71%); (d) S-(À)-2-methyl-2-sulfinimide, copper sulfate, DCM, overnight (72%);
(e) vinylmagnesium bromide, THF (0 to 25 °C), 5 h (88% total yield); (f) 4 N HCl in dioxane (quantitative); (g) benzyl chloroformate, TEA, DCM (63–82%).
OMe
O
OH
N
c
a, b
d
CH3
CH3
CH2
O
Cbz
O
Cbz
O
Cbz
O
H2N
N
N
N
H
H
H
17
15
16
14
Scheme 2. Synthesis of vinyl ketone intermediate. aReagents and conditions: (a) benzyl chloroformate, TEA, DCM (92%); (b) LiOH, 1:1:1 THF, water, MeOH, 60 °C 5 h (78%);
(c) N,O-dimethyl-hydroxylamine hydrochloride, EDC, HOAt, DMF (69%); (d) 2 equiv vinylmagnesium bromide, THF (À78 °C to 0 °C, 72%).
OTBS
5.
Cl
NHCbz
3.
NHCbz
1.
Boc
N
TBSO
TBSO
H
N
CH2
O
TBSO
a
b
10-13
c
+
22-25
NH2
26-29
NH2
Cl
2.
CH2
18-21
NHCbz
4.
Cbz
O
N
O
O
H
17
S
Cl
N
d
CF3
S
30
HO
Ph
HO
Ph
HO
Ph
HO
Ph
H
N
H
N
H
H
N
N
R
31
R
N
R
R
33
32
34
N
N
N
H
H
H
H
R = SO2Ar
Scheme 3. Synthesis of the pyrrolidine core and sulfonamides 31–34. aReagents and conditions: (a) Zhan I catalyst, DCM, 40 °C 5 h (75%); (b) 10% palladium on carbon, H2,
ethanol (92% total yield); (c) tert-butyl di-carbonate, TEA, THF, overnight (83%); (d) 4-{2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-4- yl}benzenesulfonyl chloride, DIEA, DMF,
2 h, rt (62–84%) followed by 4 N HCl in dioxane (10% water v/v), 1 h, rt (88–96%).
mixture of cis/trans pyrrolidine isomers, separation of the two
diastereomers was important to determine the most desired
pyrrolidine stereoisomer.
Separation of the cis and trans pyrrolidine isomers of compound
31 was accomplished by use of preparative SFC using a ChiralCEL
OD chiral column eluting with 20% methanol in carbon dioxane
as the elutant.22 Characterization of the major isomer (compound
35) was done with NOESY 1H NMR which supports an assignment
of the relative stereochemistry as a cis pyrrolidine.23
The cis pyrrolidine diastereoisomer 35 is 20-fold more potent
than the trans isomer 36 (Table 2). Additionally, the cis diastereomer
is more selective over both b1 and b2 ARs than the trans diastereo-
mer. Further profiling of this compound was halted, however, due
to the poor bioavailability observed in rats with compound 35. After
IV dosing, the compound exhibited a clearance of 13.2 mL/min/kg
and a half-life of 11.4 h. After oral dosing, however, poor exposures
and bioavailability was observed (dose normalized PO AUC =
0.07
l
MÁh/mpk and oral bioavailability of 3.8%).

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G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1865–1870
Table 1
Sulfonamide analogs
OH
H
N
2
5
H
S
H
NH
S
O
O
N
F3C
Compound
Chirality
Pyrrolidine
hb3
Off-target IC50’s (nM)
OH
EC50 (nM)
Act (%)
hb1
hb2
3
R
R
S
R
S
Acyclic
11
15
2030
81
95
101
89
104
104
1040
2930
1780
2150
1520
780
2180
3530
3530
2790
31
32
33
34
2(R), 5(R,S)
2(S) 5(R,S)
2(S), 5(R,S)
2(R) 5(R,S)
1307
Table 2
Separated diastereomers of compound 31
OH
OH
H
H
N
N
NH
NH
S
O
O
S
O
O
N
N
F3C
F3C
S
S
35
"cis"
36
"trans"
Compound
EC50 (nM)
Act (%)
hb1
hb2
CYP3A4
CYP2D6
35
36
4.1
83
95
76
2189
242
2509
297
>50,000
>50,000
>50,000
>50,000
Table 3
Aminothiazole amiole analog (39)
OH
NH2
H
N
O
N
S
N
H
Compound 39
EC50: 0.98 nM (99% Act)
hβ1/hβ2 IC50: >20 μM
Pharmacokinetics
Rat
Dog
Rhesus
Clp (ml/min/kg)
t1/2 (h)
Vd (L/kg)
11
23
8.3
14
0.32
18
43.4
9.9
26.4
0.14
14
7.7
5.8
0.44
12
PO AUCn (
F (%)
lMÁh/mpk)
Ancillary activity: CYP
inhibition (nM)
Solubility
(mg/ml)
Microsomal
stability: %
remaining (45 min)
2D6 2200
@pH <5.2:>1.8
@pH 7.4:1.3
hNav1.5 26%I @ 30 lM
Dog 23
Human 40
Rat 13
3A4 >100,000
2C9 >100,000
2C8 >100,000
Figure 5. Crystal structure of cis pyrrolidine enantiomer (37).
hERG IC50 11.2
lM
Rhesus 77
Boc
RO
N
HO
H
HO
N
Boc
NH
N
+
b, c
NH2
O
O
N
S
NH2
26a R =OTBS
37 R = OH
N
H
S
38
39
a
Scheme 4. Synthesis of the pyrrolidine aminothiazole amide. aReagents and conditions: (a) 1.0 M TBAF in THF, rt 4 h (78%, intermediate synthesized for crystallization
purposes only); (b) EDC, HOAt, DMF, rt 16 h (83%); (c) 4 N HCl in dioxane with 10% (v/v) water added, rt, 2 h (94%).

G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1865–1870
1869
OH
NH2
S
H
N
O
N
N
H
Compound 39
Exact Mass = 422.2
Major metabolites:
Also observed:
+30 Da
+16 Da
OH
OH
NH2
S
H
NH2
S
H
N
N
O
N
O
N
N
N
41
+14 Da
H
40
H
OH
H
+16 Da
OH
NH2
S
NH2
S
H
N
H
N
N
O
N
O
N
N
H
N
42
NH2
H
44
43
Figure 6. Proposed metabolites observed in human and rat liver microsomes.
After discovering that the cis pyrrolidine was the more potent
diastereomer, the synthetic route was modified to further improve
selectivity for formation of the cis diastereomer. Changes in the
hydrogenation step in which catalyst loading was decreased to
15% (by weight of catalyst to compound) and dilution increased to
a 0.1 M solution, afforded exclusively the cis pyrrolidine 26a with
P98% de.24 The cis pyrrolidine stereochemistry was confirmed by
X-ray crystallographic analysis of intermediate 37 (Fig. 5) obtained
from removal of the tert-butyl di-methylsilyl protecting group from
intermediate 26a. Crystallization of intermediate 26a was
attempted but did not yield X-ray quality crystals.
To assess the risk of mutagenicity for pyrrolidine aniline core
44, a full AMES mutagenicity study29 was performed. Compound
44 was dosed over a concentration range of 30
lg/plate to a
maximum concentration of 6000 g/plate to ensure a robust re-
l
sult. The compound did not produce a 2-fold or greater increase
in revertants relative to the control in any of the bacterial
strains tested, with or without the S-9 fraction, constituting a
negative result in this Microbial Mutagenesis Assay. The nega-
tive result supports further research into new b3-AR agonists
by de-risking the core and the possible aniline metabolite for
mutagenicity.
Amide 39 was synthesized using standard EDC coupling
procedures followed by acid mediated deprotection (Scheme 4).
Compound 39 demonstrated potent in vitro functional human b3-
AR agonist activity with an EC50 = 0.98 nM and excellent selectivity
over hb1/hb2 (>20,000 nM binding affinity).25 Additionally, prom-
ising pharmacokinetic parameters were observed across species
with moderate bioavailability (>10%) and half-lives P7.7 h in rats,
dogs, and rhesus monkeys. The ancillary activities were acceptable
In conclusion, we have discovered a novel pyrrolidine core
which can be utilized in the exploration of potent and selective
human b3-AR agonists. Sulfonamide 35 and amide 39 derived from
the R,R,S pyrrolidine core possessed potent human b3-AR agonist
activity with similar or improved selectivity when compared to
the clinical candidate L-796,568. Metabolite identification after
incubation of compound 39 with rat liver microsomes confirmed
that formation of metabolites similar to those observed with
L-796,568 was unlikely. Further characterization of compound 39
revealed a risk for genotoxicity due to the aminothiazole function-
ality that triggered a structure alert in DEREK and an equivocal
result from a 5-FU mutagenicity assay. On the other hand, the pyr-
rolidine aniline core 44 afforded a negative result in AMES assays.
Early de-risking of the aniline core has led to further exploration of
human b3-AR agonists that incorporate the pyrrolidine 44 and this
research will be reported in the future.
with IC50’s >70
the least selectivity seen for CYP2D6 with an IC50 observed of
2.2 M, respectively. Additionally, only moderate inhibition (28%
@ 10 M) of hNav1.5 and hERG (IC50 = 11 M) was observed (Table
lM observed against CYPs 2C9, 2C8 and 3A4; with
l
l
l
3).26 Metabolite identification was done with compound 39 after
incubation with rat and human liver microsomes over a 45 min
period (Fig. 6). The major metabolites observed were oxidation
on the aniline core with metabolites identified as having +16 and
+30 Daltons (compounds 40 and 41, respectively) compared to
the parent. Additionally, metabolites that correspond to hydrolysis
of the aniline amide (44) were observed. Metabolites resulting in
release of the left hand side or right hand side of 39 were not iden-
tified, however, suggesting that the compound indeed would not
form similar metabolites to those observed with the previous
clinical candidate L-796,568.15
Acknowledgements
The authors would like to thank Karen Dingley and Randy
Miller for their support in supplying the metabolite ID data for
compound 37 and assistance with the DMPK interpretation. We’d
like to acknowledge John DeLuca, Jennifer Smeed, and Gwendolyn
Ward for their assistance in the Genotox studies on compounds 39
and 44 which de-risked the pyrrolidine aniline core for our future
endeavors in the discovery of potent b3-AR agonists. One final
thanks goes out to Terry Butler for her guidance and helpful con-
versations which encourage the completion of this manuscript.
In order to assess the risk for mutagenicity, aminothiazole 39
and the aniline metabolite 44 were screened in silico using
DEREK.27 Aniline 44 did not trigger a structure alert by DEREK as
a possible genotoxic moiety. On the other hand, aminothiazole
39 was alerted by DEREK as a potential risk for genotoxicity. To
support the computational analyses, compounds 39 and 44 were
each examined further in mutagenicity assays.
Supplementary data
In a 5-fluorouracil forward mutation assay,28 aminothiazole 39
produced a single positive response in the presence of S-9 meta-
bolic activation, with an increase in adjusted mutants/well that
was slightly above the standard deviation recorded for the mean
historical control level. This was not considered a strong positive
result and was concluded to be equivocal.
Supplementary data (structures, experimental, and character-
ization data for all compounds including X-ray crystal structure
of compound 37 (CCDC 787767), NOE and spectral data for com-
pound 35 and HPLC trace of the separation of compounds 35 and
36 is available free of charge via the Internet at http://pubs.acs.org)

1870
G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1865–1870
14. Stearns, R. A.; Miller, R. R.; Tang, W.; Kwei, G. Y.; Tang, F. S.; Mathvink, R. J.;
Naylor, E. M.; Chitty, D.; Colandrea, V. J.; Weber, A. E.; Colletti, A. E.; Struss, J. R.;
Keohane, C. A.; Feeney, W. P.; Iliff, S. A.; Chiu, S.-H. L. Drug Metab. Dispos. 2002,
30, 771.
15. Tang, W.; Stearns, R. A.; Miller, R. R.; Ngui, J. S.; Mathvink, R. J.; Weber, A. E.;
Kwei, G. Y.; Strauss, J. R.; Keohane, C. A.; Doss, G. A.; Chiu, S.-H. L.; Baillie, T.
Drug Metab. Depos. 2002, 30, 778.
16. For the purpose of easier synthetic manipulation, the phenyl analog of
L-796,568 was chosen for comparison since it has similar in vitro potency
and metabolic properties as L-796,568.
17. (a) Liu, G.; Cogan, D. A.; Ellman, J. A. J. Am. Chem. Soc. 1997, 119, 9913;
(b) Brinner, K. M.; Ellman, J. A. Org. Biomol. Chem. 2005, 3, 2109.
18. Nahm, S.; Weinreb, S. M. Tetrahedron Lett. 1981, 22, 3815.
19. Astruc, D. New J. Chem. 2005, 29, 42.
associated with this article can be found, in the online version, at
doi:10.1016/j.bmcl.2010.12.087.
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21. This material was obtained from prior batches synthesized for the scale-up of
L-796,568. The chemistry to prepare this intermediate has been document
previously.10
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isomer eluted at 4.56 min.
23. The stereochemistry of the two pyrrolidine chiral centers was determined to be
cis based on 2D NOE NMR data (see Supplementary data).
24. Selectivity was assessed by SFC analytical analysis and the effort to improve
selectivity was studied via trial and error of changes in the reaction conditions.
Original less selective conditions: Dilution 0.02 M and stoichiometric amount
(by weight) of the catalyst (resulted in 3:1 mixture of cis/trans).
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