Synthesis of the four 3-aminotricyclo [2.2.1.0(2,6)] heptane-1,3- dicarboxylic acid isomers

Article abstract of DOI:10.1081/SCC-200034793

A process to prepare the four stereoisomers of the tricyclic 3-aminotricyclo[2.2.1.0(2,6)] heptane-1,3-dicarboxylic acid, a potent selective inhibitor of the EAAT2 transporter, is described.

Full text of DOI:10.1081/SCC-200034793

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Synthesis of the Four
3‐Aminotricyclo [2.2.1.0(2,6)]
Heptane‐1,3‐Dicarboxylic Acid
Isomers
Reinhardt B. Baudy a , Jean Y. Sze a & John A.
Butera a
a Chemical and Screening Sciences , Wyeth
Research Inc. , Princeton, New Jersey,
08543‐8000, USA
Published online: 10 Jan 2011.
To cite this article: Reinhardt B. Baudy , Jean Y. Sze & John A. Butera (2004)
Synthesis of the Four 3‐Aminotricyclo [2.2.1.0(2,6)] Heptane‐1,3‐Dicarboxylic
Acid Isomers, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 34:21, 3949-3954, DOI: 10.1081/
SCC-200034793
To link to this article: http://dx.doi.org/10.1081/SCC-200034793
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 21, pp. 3949–3954, 2004
Synthesis of the Four 3-Aminotricyclo
[2.2.1.0(2,6)] Heptane-1,3-Dicarboxylic
Acid Isomers
*
Reinhardt B. Baudy, Jean Y. Sze, and John A. Butera
Chemical and Screening Sciences, Wyeth Research Inc.,
Princeton, New Jersey, USA
ABSTRACT
A process to prepare the four stereoisomers of the tricyclic 3-amino-
tricyclo[2.2.1.0(2,6)] heptane-1,3-dicarboxylic acid, a potent selective
inhibitor of the EAAT2 transporter, is described.
Key Words: EAAT2 transporter inhibitor; Excitatory amino acid trans-
porter; Glutamate.
Glutamate receptors and transporters are important central nervous
system drug targets[1,2] since (S)-glutamic acid is the major excitatory
*
Correspondence: Reinhardt B. Baudy, Chemical and Screening Sciences, Wyeth
Research Inc., Princeton, NJ 08543-8000, USA; E-mail: baudyr@wyeth.com.
3949
DOI: 10.1081/SCC-200034793
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3950
Baudy, Sze, and Butera
amino acid in the CNS participating in a vast number of physiological
and pathophysiological processes.[3] Once released into the synaptic cleft,
(S)-glutamic acid triggers a host of pre- and postsynaptic receptors. Those
receptors belong to either the G-protein coupled receptor class (metabotropic
glutamate receptors) or to the ligand-gated ion channels (ionotropic glutamate
receptors). Termination of synaptic transmission occurs when (S)-glutamic
acid is transported into neuronal or glial cells by excitatory amino acid trans-
porters (EAATs). Among the five different human EAAT subtypes cloned, the
EAAT1-3 subtypes are thought to be primarily responsible for the (S)-glutamic
acid uptake process.[2] Since many pathological conditions are believed to be
caused by either too low or too high levels of (S)-glutamic acid in the synaptic
cleft, the EAATs have been suggested as appropriate drug targets.[1] Only a
few compounds have been shown to interact with the EAATs and just a
small number of agents inhibit the EAATs in a subtype selective manner,[1]
as, for example, kainic acid and (2S, 4R)-2,4-PDC that have been shown[4,5]
to inhibit the EAAT2 subtype (Fig. 1).
We would like to report a series of novel bridged tricyclic 3-amino-tricyclo
[2.2.1.0(2,6)]heptane-1,3-dicarboxylic acids described by the formula I first
disclosed by Stack et al.[6] The four stereoisomers represented by compound
I are illustrated in Fig. 2.
The compounds described in this paper are selective inhibitors of human
type 2 excitatory amino acid transporter (EAAT2) that are located, for the
most part, on glial cells. Their mode of action causes an increase in synaptic
glutamate levels by inhibiting glutamate re-uptake and thus may show utility
for the treatment of diseases characterized by glutamate hypofunction, such as
schizophrenia, schizoaffective disorder, and schizophreniform disorders, with
particular effectiveness against the negative symptoms of schizophrenia.
Alternatively, agents of this type may be useful in the treatment of conditions
responsive to increased glutamate, such as the cognitive deficits due to aging,
stroke, Alzheimer’s disease, or other neurodegenerative diseases. The com-
pounds described are also useful as selective tools for the investigation of
excitatory amino acid transport, especially for the identification of agents,
Figure 1. Natural agonist ligand and known inhibitors of EAAT2.

Synthesis of Four Acid Isomers
3951
Figure 2. Racemic compound I and the four stereoisomers.
which selectively stimulate glutamate re-uptake. Throughout this paper the
designations Rꢀ and Sꢀ are used to indicate relative stereochemistry, employ-
ing the Chemical Abstracts convention, which automatically assigns Rꢀ to the
lowest numbered asymmetric center.
The stereoisomers of compound I can be prepared as illustrated in Sch. 1.
The starting keto-acid (Ka) is prepared according to literature procedure[6] and
then derivatized to a chiral amide using (R)-2-amino-3-phenyl-1-propanol via
a coupling reaction in the presence of 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetra-
methyl uronium tetrafluoroborate (TBTU). The resulting mixture of diastereo-
mers is separated using reversed-phase chromatography (A and B). The sep-
arated diastereomers are individually converted to spiro-fused hydantoins
by treatment with ammonium carbonate and potassium cyanide, in metha-
nol/water. The resulting mixtures of diastereomers (C, D and E, F) are
again separated using reversed-phase chromatography. The resulting four
diastereomers (C, D, E, and F) are individually hydrolyzed using sodium
hydroxide followed by elution through an ion exchange column to yield all
four aminodicarboxylic acid stereoisomers (I-C, I-D, I-E, and I-F).
EXPERIMENTAL
(1Sꢀ,2Rꢀ,4Sꢀ,6Sꢀ)-N-[(1R)-1-benzyl-2-hydroxyethyl]-3-oxotricyclo[2.2.1.0
(2,6)]heptane-1-carboxamide (A); and (1Rꢀ,2Sꢀ,4Rꢀ,6Rꢀ)-N-[(1R)-1-benzyl-
2-hydroxyethyl]-3-oxotricyclo [2.2.1.0(2,6)] heptane-1-carboxamide (B): A
mixture of 3-oxotricyclo[2.2.1.0(2,6)]heptane-1-carboxylic acid (0.3 g,
1.946 mmol, prepared according to Alder Hartmann, and Roth,[7] R-(þ)2-

3952
Baudy, Sze, and Butera
Scheme 1. Reagents: (i) TBTU, (R)-2-amino-3-phenyl-1-propanol, HPLC (ii) KCN,
ammonium carbonate, methanol, water, HPLC (iii) 2N NaOH (iv) Ion exchange.
amino-3-phenyl-1-propanol (0.324 g, 2.141 mmole), and 4-methylmorpholine
(0.86 mL, 7.784 mmol) in dimethylformamide (7 mL) was stirred at ambient
temperature. 2-(1H-Benzotriazol-1-yl)-1,1,3,3-tetra-methyluronium tetrafluo-
roborate (TBTU, 0.75 g, 2.335 mmol) was added to the reaction mixture
and stirring was continued for 18 hours. The reaction mixture was diluted
with ethyl acetate (35 mL), the organic layer separated, washed with 5%
aqueous citric acid (2 ꢁ 30 mL), followed by saturated NaHCO3 solution
(2 ꢁ 30 mL), and finally washed with brine (50 mL). The organic layer was
dried over magnesium sulfate, filtered, and evaporated to dryness. Using a
reversed-phase HPLC (C-18, 8 mM particle size, 41.4 mm and 4.6 mm ID,
25 cm L) column, 10–70% CH3CN/Water, both diastereomers were
isolated as light yellow oils. The retention times for the diastereomers A
(Yield: 544 mg, 29.4%) and B (Yield: 491 mg, 26.5%) were 15.3 min. and
15.8 min., respectively. A: MS (EI, Mþ @ m/z) 285 B: MS (APCI,
[M þ H]þ @ m/z) 286.

Synthesis of Four Acid Isomers
3953
Spiro-hydantoin diastereomers of (1Sꢀ,2Rꢀ,4Sꢀ,6Sꢀ)-N-[(1R)-1-benzyl-
2-hydroxyethyl]-3-oxo tricyclo[2.2.1.0(2,6)]heptane-1-carboxamide (A): A
mixture of (1Sꢀ,2Rꢀ,4Sꢀ,6Sꢀ)-N-[(1R)-1-benzyl-2-hydroxyethyl]-3-oxotri-
cyclo[2.2.1.0(2,6)]heptane-1-carboxamide(A,0.63 g,2.207 mmol),ammonium
carbonate (1.048 g, 10.091 mmol), and potassium cyanide (0.173 g,
2.648 mmol) was stirred in methanol/water (2 : 1, 15 mL) at 508C for 72
hours. After evaporation of the solvent in vacuo the products were isolated
using reversed-phase HPLC (C-18, 8 mm particle size, 41.4 mm and 4.6 mm
ID, 25 cm L) column, 10–70% CH3CN/water. Both diastereomers were iso-
lated in 31% (122 mg) yield (C) and 53% (206 mg) yield (D) as white
solids; mp’s A, .2608C (Decomposition) and B, 167–98C. The retention
times for the pure diastereomers C and D were 12.6 min. and 13.7 min.,
respectively. C: MS (þAPCI, [M þ H]þ @ m/z) 356, D: MS (þAPCI,
[M þ H]þ @ m/z) 356.
Spiro-hydantoin diastereomers of (1Rꢀ,2Sꢀ,4Rꢀ,6Rꢀ)-N-[(1R)-1-benzyl-2-
hydroxyethyl]-3-oxotricyclo [2.2.1.0(2,6)]heptane-1-carboxamide (B): A
mixture of (1Rꢀ,2Sꢀ,4Rꢀ,6Rꢀ)-N-[(1R)-1-benzyl-2-hydroxyethyl]-3-oxotricy-
clo[2.2.1.0(2,6)] heptane-1-carboxamide (B, 0.52 g, 1.822 mmol), ammonium
carbonate (0.9 g, 9.366 mmol), and potassium cyanide (0.142 g, 2.186 mmol)
was stirred in methanol/water (2 : 1, 15 mL) at 508C for 72 hours. After evap-
oration of the solvent in vacuo the products were isolated using reversed-phase
HPLC (C-18, 8 mm particle size, 41.4 mm and 4.6 mm ID, 25 cm L) column,
10–70% CH3CN/water. Both pure diastereomers were isolated in 34%
(109 mg) yield (E) and 76% (246 mg) yield (F) as white solids; mp’s E,
270–28C (Decomposition) and F, 80–28C. The retention times for the
diastereomers E and F were 14.7 min. and 15.3 min., respectively. E: MS
(þAPCI, [M þ H]þ @ m/z) 356, F: MS (þAPCI, [M þ H]þ @ m/z) 356.
General procedure for the preparation of all four stereoisomers of 3-amino-
tricyclo[2.2.1.0(2,6)]heptane-1,3-dicarboxylic acid: A mixture of the starting
spiro-hydantoin-N-[(1R)-1-benzyl-2-hydroxyethyl]-3-oxotricyclo
[2.2.1.0
(2,6)]heptane-1-carboxamide (0.5 mmol) and 2N NaOH (3 mL) was refluxed
for 20 hours. The reaction mixture was cooled to ambient temperature
and washed with dichloromethane (2 ꢁ 20 mL). The aqueous layer was sepa-
rated and the pH adjusted to 11 using 10% aqueous acetic acid and eluted
through an ion-exchange column (Bio-Rad AG1-X8 resin, acetate form,
100–200 mesh). The products were eluted with 1 M acetic acid and the com-
bined fractions were collected and concentrated on a lyophilizer to give the
desired pure stereoisomers as white solids.
(2)-(1Rꢀ,2Rꢀ,3Rꢀ,4Sꢀ,6Sꢀ)-3-Aminotricyclo[2.2.1.0(2,6)]heptane-1,
3-dicarboxylic acid (I-D): Yield: 98%; MS (APCI, [M þ H]þ @ m/z)
198; mp . 2608C (Decomposition); Optical Rotation (water & NaOH)
[a-D]25 ¼ 2 32.18.

3954
Baudy, Sze, and Butera
(þ)-(1Rꢀ,2Rꢀ,3Rꢀ,4Sꢀ,6Sꢀ)-3-Aminotricyclo[2.2.1.0(2,6)]heptane-1,
3-dicarboxylic acid (I-F): Yield: 45%; MS (APCI, [M 2 H]þ @ m/z)
196; mp . 2608C (Decomposition); Optical Rotation (water & NaOH)
[a-D]25 ¼ þ 31.018.
(þ)-(1Rꢀ,2Sꢀ,3Rꢀ,4Rꢀ,6Sꢀ)-3-Aminotricyclo[2.2.1.0(2,6)]heptane-1,
3-dicarboxylic acid (I-E): Yield: 51%; MS (APCI, [M 2 H]þ @ m/z)
196; mp . 2808C (Decomposition); Optical Rotation (water & NaOH)
[a-D]25 ¼ þ 21.018.
(2)-(1Rꢀ,2Sꢀ,3Sꢀ,4Rꢀ,6Rꢀ)-3-Aminotricyclo[2.2.1.0(2,6)]heptane-1,
3-dicarboxylic acid (I-C): Yield: 50%; MS (APCI, [M 2 H]þ @ m/z)
196; mp . 2608C (Decomposition); Optical Rotation (water & NaOH)
[a-D]25 ¼ 2 18.028.
The configuration of all four stereoisomers is relative rather than absolute.
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Received in the USA July 2, 2004