# Patent

## Title
Cocaine receptor binding ligands

## Abstract

Tropane derivatives having a high binding affinity and selectivity for dopamine transporters bear, on the tropane backbone either a carboxylic ester or isoxazole moiety, as well as a substituted phenyl moiety. The compounds have utility both as pharmaceutical and as imaging agents, when one or more atoms are radioactive.

## Background
PARENT APPLICATIONS
This application is a Continuation of U.S. patent application Ser. No. 08/506,541, filed on Jun. 24, 1995, now abandoned, which is a Continuation-In-Part of U.S. patent application Ser. No. 08/436,970, filed May 8, 1995, now U.S. Pat. No. 5,736,123 and U.S. patent application Ser. No. 08/164,576, filed Dec. 10, 1993, now U.S. Pat. No. 5,496,953. The latter application is in turn a Continuation-In-Part of U.S. patent application Ser. No. 07/792,648, filed Nov. 15, 1991, now abandoned, which is in turn a Continuation-In-Part of U.S. patent application Ser. No. 07/564,755, filed Aug. 9, 1990, now U.S. Pat. No. 5,128,118 and U.S. patent application Ser. No. 07/972,472, filed Mar. 23, 1993, now U.S. Pat. No. 5,413,779, based on PCT Application PCT/US91/05553, filed Aug. 9, 1991, now U.S. Pat. No. 5,413,979. The entire disclosure of U.S. Pat. Nos. 5,496,953, 5,413,779, 5,380,848 and 5,128,118 are incorporated herein by reference.


THE INVENTORS' PRIOR DISCLOSURES
The parent applications referenced above are directed to cocaine receptor binding ligands, which show enhanced affinity for binding to cocaine receptors, particularly dopamine transporter sites, although binding affinity is also high at serotonin transporters. These prior patents and patent applications are directed to compounds having the general formula: 



Wherein Y=CH2R3, CO2R2, CONRR1, or 



    R1=hydrogen, C1-5 alkyl,
    R2=hydrogen, C1-6 alkyl, C3-8 cycloalkyl, C1-4 alkoxy, C1-6 alkynyl, halogen or amine,
    R3=OH, hydrogen, C1-6 alkyl, C3-8 cycloalkyl, C1-4 alkoxy, Cl, Br, I, CN, NH2, NHC1-6 alkyl, NC1-6 alkyl, OCOC1-6 alkyl OCOC1-3 alkylaryl,
    A=S, O or N
    X=H, C1-6 alkyl, C3-8 cycloalkyl, C1-4 alkoxy, C1-6 alkynyl, halogen, amino acylamido, and
    Z=H, I, Br, Cl, F, CN, CF3NO2, N3, OR1, CO2NH2, CO2R1, C1-6 alkyl, NR4R5, NHCOF5, NHCO2R6,

wherein R4–R6 are each C1-6 alkyl, R and R1 are independently H, C1-6 alkyl, C1-6 alkene, C1-6 alkyne, phenyl, phenyl substituted with 1–3 of C1-6 alkyl, alkene, alkyl or alkoxy, C1-6 alkoxy, phenoxy, amine, amine substituted with 1–2 of C1-6 alkyl, alkene, alkyne, alkoxy or phenyl or phenoxy or R and R1 may combine to form heterocyclic structure including pyrrolidinyl, piperidinyl and morpholino moieties, unsubstituted or substituted with 1–2 C1-6 alkyl, alkene, alkyne or alkoxy groups.



As is reflected in the parent applications and patents, due to the high binding affinity of these compounds, particularly as measured against the compound of the literature [3H]WIN 35,428 binding inhibition, these compounds have found particular use in both positron emission tomography (PET) as well as single photon emission computed tomography (SPECT). For PET use, one of the carbons of the molecule should be an [11C] labeled form, while SPECT imaging may employ a radioactive halogen label, such as the molecule on the phenyl ring of the general formula, either X or Z of the above-described general formula. In particular, the radioactive labels 123I, 125I and 131I may be used.
As this art has developed, it has proved difficult to determine what particular substitutions on the tropane backbone will yield high binding affinities while remaining pharmaceutically acceptable. The applicant has now discovered a new family of tropane derivatives, characterized by an aryl ring substituent, and either an isoxazole substituent or a carboxylic ester substituent. These particular compounds have been demonstrated to have a high dopamine transporter binding efficiency, and a high selectivity.


SUMMMARY OF THE INVENTION
Compounds of the general formula: 






Wherein


    R1 is hydrogen, C1-5 alkyl
    Ra is phenyl, C1-6 alkyl, C1-6 alkyl-substituted phenyl
    Rb is C1-6 alkyl, phenyl, C1-6 alkyl substituted phenyl and
    Z is phenyl or naphtyl bearing 1–3 substituents selected from the group consisting of F, Cl, I, C1-6 alkyl, each substituent may be or include a radioactive label, fall within the scope of this invention.


These compounds have been demonstrated to have particular high binding affinity and selectivity for dopamine transporter sites.
The compounds of the invention can be prepared according to the methodologies established in the parent applications, incorporated herein by reference. The method of making the compound, per se, does not constitute an aspect of the invention. Particular measures for preparation of the isoxazole derivatives are shown herein. Nonetheless, other methods of making the compounds will occur to those of ordinary skill in the art, without the exercise of inventive faculty.
3β-(4′-Chlorophenyl)-2β-(3′-phenylisoxazol-5-yl)tropane)(4,RTI-177)Hydrochloride
A soloution of n-butyl lithium in hexane (2.4M, 4.2 mL, 10.4 mmol) was added to a stirred solution of acetophenone oxime (0.703 g, 5.2 mmol) in a dry THF (10 mL) at 0° C. under nitrogen. After 1 h, a soloution of 3β-(4-chlorophenyl)tropane-2β-carboxylic acid methyl ester (1.18 g, 4 mmol) in dry THF (8 mL) was added, and the solution was allowed to warm to room temperature over 18 h. The mixture was poured into a stirred solution of concentrated sulfuric acid (2.28 g) in THF (12 mL) and water (2.8 mL) and was heated under reflux for 1 h. The cooled solution was basified using saturated aqueous potassium carbonate (10 mL) and extracted with 3×10 mL methylene chloride. The combined organic layer was dired and filtered. Removal of solvent under vacuum gave 1.46 g solid. Purification of the solid by flash column chromatography [20% (ether:triethylamine 9:1) in hexane] gave 0.75 g (50%) of pure 4 which was further purified by recrystallizing from ether:petroleum ether. 1H NMR (CDCl3) § 1.74 (m, 3), 2.22 (m, 3), 2.27 (s, 3), 3.24 (m, 2), 3.36 (m, 2), 6.80 (s, 1), 6.94 (m, 2), 7.12 (m, 2), 7.40 (m, 3), 7.76 (m, 2). IR (CHCl3) 2940, 1600, 1590, 1490, 1405, 1350 cm−1.
The hydrochloride salt had mp 287° C. (dec); [α2D3 −97.5 (c 0.28, CH3OH). 1H NMR (CH3OD) α 2.35 (m, 6), 2.84 (s, 3), 3.73 (m, 1), 4.09 (m, 1), 4.21 (s, 1), 7.14 (m, 4), 7.34 (m, 3), 7.57 (m, 2).
Anal. Calcd for C23H24Cl2N20.0.25H2O: C,H,N.
3α-(4′-Chlorophenyl)-2α-(5′-phenyl-1′,3′,4′-oxadiazol-2′-yl)tropane(5,RTI-188)Hydrochloride
To 0.59 g (2 mmol) of 8 in 2 mL of POCl3 was added 1.1 eq. of benzoic hydrazide, and the solution was reluxed under N2 for 2 h. The reaction miscture was cooled and poured into ice and basified to pH 7–8 using conc. NH4OH. To the aqueous layer was added 10 mL brince followed by extraction with 3×10 mL methylene chloride. The combined organic layer was dried (NaSO4), filtered, andthe solvent removed in vacuo to give 0.9 g residue. PUrification of this residue by flash column chromatography [50% (ether:triethylamine 9:1) in hexane gave 0.33 g (42%) of pure 5 which was recrystallized from ether:petroleum ether. 



Well-established protocols for determining binding efficiency have shown selected compounds, pictured below, to have particularly high binding affinity, and selectivity, for dopamine transporter sites. 













Comparison of Transporter Binding Potencies for


Selected 3β-(4-Substituted Phenyl)tropan-2β-carboxylic Acid Methyl Esters








 










IC50(nM)


















DA
NE
5-HT
NE/DA
5-HT/DA


RTI No.
X
Y
[3H]WIN 35,428
[3H]Nisoxetine
[3H]Paroxetine
Ratio
Ratio

















WIN 35,065-2
H
H
23
920
1962
40
85


WIN 35,428
F
H
13.9
835
692
60
50


RTI-32
CH3
H
1.71
60
240
35
140


RTI-31
Cl
H
1.12
37
44.5
33
40


RTI-55
I
H
1.26
36
4.21
29
3.3


RTI-51
Br
H
1.69
37.4
10.6
22
6


RTI-88
NH2
I
1.35
1329
120
984
89


RTI-111
Cl
Cl
0.79
17.96
3.13
67
4


RTI-112
Cl
CH3
0.81
36.2
10.5
45
13













 


RTI-318




0.51
21.1
0.80
41
1.6



















3β-(4′-Methylphenyl)-2β-(heterocyclic)tropane








 










IC50(nM)
















DA
NE
5-HT
NE/DA
5-HT/DA


RTI No.
Het
[3H]WIN 35,428
[3H]Nisoxetine
[3H]Paroxetine
Ratio
Ratio
















151




2.33
60
1074
26
461


 


171




0.93
254
3818
273
410


 


176




1.58
398
5110
252
3234


 


178




35.4
677
1699
19
48


 


194




4.45
253
4885
57
1098


 


195




47.48
1310
22,310
28
470


 


199




35.88
24,320
51,460
678
1434





















3β-(4′-Chlorophenyl)-2β-(heterocyclic)tropanes








 










IC50(nM)














RTI

DA
NE
5-HT
NE/DA
5-HT/DA


No.
Het
[3H]WIN 35,428
[3H]Nisoxetine
[3H]Paroxetine
Ratio
Ratio
















130




1.62
244.6
195
151
120


 


188




12.6
930
3304
74
262


 


200




15.3
4142
18,416
271
1203


 


165




0.59
181
572
307
970


 


177




1.28
504
2418
394
1889


 


189




19.7
496
1116
25
57


 


219




5.71
8563
10,342
1500
1811


 


202




1.37
403
1119
294
817





















 


IC50(nM)
IC50(nM)












DA
5-HT
NE
DA
5-HT
NE





14
156
85
0.51
0.80
21





















 


IC50(nM)
IC50(nM)












DA
5-HT
NE
DA
5-HT
NE





21
5062
1231
1.1
11.4
70.2









It should be noted that the compounds described and claimed herein are not useful solely as imaging compounds. The compounds are useful as surrogate agonists for treatment of cocaine abuse, as well as abuse of other psychostimulant drugs including amphetamines. The compounds of this invention exhibit a very slow onset of action, as well as a very long duration of action. Both of these attributes are desirable for appropriate substitute medication for psychostimulant abuse.
These compounds, because of their selectivity for the dopamine transporter are useful as antagonist drugs, or blockers of the actions of cocaine or other psychostimulants, blocking psychostimulant access but not inhibiting the functioning of the transporter. Further, treatment of neurodegenerative disorders may be affected through potentiation of neurotransmitter action. The compounds of the invention may be used to inhibit re-uptake in such situations. Finally, these compounds may find utility as analgesics. Accordingly, the compounds have utility in both their labeled and unlabeled forms.
This invention has been disclosed in terms of generic formula, as well as by specific example. Where examples are set forth, they are not intended, and should not be interpreted, as limiting. In particular, isomeric forms, as well as alternate substituents will occur to those of ordinary skill in the art without the exercise of inventive faculty, and remain within the scope of the invention, which is unlimited save by the recitation of the claims below.

## Claims

1. A 2,3-cis substituted binding ligand having high binding affinity and selectivity for dopamine transporters, having the formula: 



wherein
R1 is hydrogen or C1-5 alkyl;
Rb is C1-6 alkyl, phenyl, or C1-6 alkyl-substituted phenyl; and
Z is phenyl or naphthyl bearing 1–3 substituents selected from the group consisting of Cl, I, and C1-6 alkyl, and wherein each substituent may be or include a radioactive label.

2. The binding ligand of claim 1, wherein R1 is hydrogen.

3. The binding ligand of claim 1, wherein R1 is C1-5 alkyl.

4. The binding ligand of claim 1, wherein Rb is C1-6 alkyl.

5. The binding ligand of claim 1, wherein Rb is phenyl.

6. The binding ligand of claim 1, wherein Rb is C1-6 alkyl-substituted phenyl.

7. The binding ligand of claim 1, wherein Z is phenyl bearing 1–3 substituents selected from the group consisting of Cl, I, and C1-6 alkyl, and wherein each substituent may be or include a radioactive label.

8. The binding ligand of claim 7, wherein each substituent is not and does not include a radioactive label.

9. The binding ligand of claim 7, wherein each substituent is or includes a radioactive label.

10. The binding ligand of claim 1, wherein Z is napthyl bearing 1–3 substituents selected from the group consisting of Cl, I, and C1-6 alkyl, and wherein each substituent may be or include a radioactive label.

11. The binding ligand of claim 10, wherein each substituent is not and does not include a radioactive label.

12. The binding ligand of claim 10, wherein each substituent is or includes a radioactive label.

13. The binding ligand of claim 1, of the formula:

14. The binding ligand of claim 1, wherein said binding ligand bears a radioactive label selected from the group consisting of 11C, 123I, 125I, and 131I.

15. The binding ligand of claim 4, wherein Z is phenyl substituted by C1-6 alkyl.

16. The binding ligand of claim 15, wherein Z does not include a radioactive label.

17. The binding ligand of claim 6, wherein Z is Cl.

18. The binding ligand of claim 15, wherein Z is not a radioactive label.