Chemical synthesis of 1,2,4-triazolinone derivative

Details Chemical synthesis of 1,2,4-triazolinone derivative Chemical synthesis of 1,2,4-triazolinone derivative

2001-09-10

2002-06-18

Ramsuer, Robert W. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

Reexamination Certificate

active

06407255

ABSTRACT:

The present invention relates to a process for the preparation of morpholine derivatives, and in particular, the compound 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)-4-(3-(5-oxo-1H,4H-1,2,4-triazolo)methyl)morpholine, which are useful as therapeutic agents.
Compounds of formula (I), below, which are described in International patent specification No. WO 95/16679 (published Jun. 22, 1995), are potent and selective substance P (or neurokinin-1) receptor antagonists.
wherein
R
2
and R
3
are independently selected from the group consisting of:
(1) hydrogen,
(2) C
1-6
alkyl,
(3) C
2-6
alkenyl, and
(4) phenyl;
R
6
, R
7
and R
8
are independently selected from the group consisting of:
(1) hydrogen,
(2) C
1-6
alkyl,
(3) fluoro,
(4) chloro,
(5) bromo,
(6) iodo, and
(7) —CF
3
;
R
11
, R
12
and R
13
are independently selected from the group consisting of:
(1) hydrogen,
(2) C
1-6
alkyl,
(3) fluoro,
(4) chloro,
(5) bromo,
(6) iodo, and
(7) —CF
3
; and
Z is C
1-4
alkyl.
In particular, the compound 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)-4-(3-(5-oxo-1H,4H-1,2,4-triazolo)methyl)morpholine has shown potential in the treatment of emesis, depression and anxiety. Substance P antagonists are also being investigated for other neuropsychiatric diseases, including bipolar disorder and schizophrenia, as well as postherpetic neuralgia and pain.
International patent specification No. WO 95/16679 describes the preparation of 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)-4-(3-(5-oxo-1H,4H-1,2,4-triazolo)methyl)morpholine (hereinafter referred to as Compound A), which has the structure:
by a two-step process starting from 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)-phenyl)ethoxy)-3-(S)-(4-fluorophenyl)morpholine. With reference to Examples 70 and 75 in WO 95/16679, Compound A is prepared as follows:
This prior art process and in particular its requirement for a high temperature cyclisation step presents a number of practical difficulties which render it inconvenient when attempted on anything other than a relatively small scale. Therefore, there is a need for the development of a process which is readily amenable to scale-up and hence capable of practical application to the manufacturing plant.
The present invention accordingly provides a convenient, efficient process which utilizes a one-step alkylation with 3-chloromethyl-1,2,4-triazolin-5-one at ambient temperature that produces compounds of formula (I), and in particular Compound A, in a higher yield than the prior art two-step synthesis and which avoids a high temperature cyclisation. The novel process of the present invention is not only more energy efficient (since it requires no heating), but it is also more productive allowing for a shorter time-cycle on large scale and a higher operating concentration. The ability to effect the process of the present invention in one reaction vessel, in which the desired product crystallises from the reaction mixture at ambient temperature is a clear advantage over the prior art synthesis.
Thus, in a first aspect of the present invention, there is provided a process for the preparation of a compound of formula (I)
wherein
R
2
and R
3
are independently selected from the group consisting of:
(1) hydrogen,
(2) C
1-6
alkyl,
(3) C
2-6
alkenyl, and
(4) phenyl;
R
6
, R
7
and R
8
are independently selected from the group consisting of:
(1) hydrogen,
(2) C
1-6
alkyl,
(3) fluoro,
(4) chloro,
(5) bromo,
(6) iodo, and
(7) —CF
3
;
R
11
, R
12
and R
13
are independently selected from the group consisting of:
(1) hydrogen,
(2) C
1-6
alkyl,
(3) fluoro,
(4) chloro,
(5) bromo,
(6) iodo, and
(7) —CF
3
; and
Z is C
1-4
alkyl,
which comprises:
(i) reacting a compound of formula (II)
 or a salt thereof, wherein R
2
, R
3
, R
6
, R
7
, R
8
, R
11
, R
12
, R
13
and Z are as previously defined, with a compound of formula (III)
 wherein LG is a leaving group selected from halogen (e.g. bromo, chloro or iodo) or an alkyl- or arylsulfonate group (e.g. mesylate or tosylate), in an organic solvent and in the presence of a base; and
(ii) collecting the resultant crystalline compound of formula (I).
In a particularly preferred aspect of the present invention, there is provided a process for the preparation of the compound 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)-4-(3-(5-oxo-1H,4H-1,2,4-triazolo)methyl)morpholine which comprises:
(i) reacting 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)morpholine or a salt thereof, with a compound of formula (III)
 as previously defined, in an organic solvent and in the presence of a base; and
(ii) collecting the resultant crystalline 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl) -4-(3-(5-oxo-1H,4H-1,2,4-triazolo)methyl)morpholine.
In the compounds of formulae (I) and (II), preferably R
2
and R
3
are both independently hydrogen.
In the compounds of formulae (I) and (II), preferably R
6
and R
7
are independently selected from fluoro and —CF
3
. In particular. R
6
and R
7
are both independently —CF
3
.
In the compounds of formulae (I) and (II), preferably R
8
is hydrogen.
In the compounds of formulae (I) and (II), preferably R
11
is hydrogen or fluoro.
In the compounds of formulae (I) and (II), preferably R
12
and R
13
are both independently hydrogen.
In the compounds of formulae (I) and (II), preferably Z is —CH
3
.
In the compound of formula (III), preferably, the leaving group LG is chloro.
Suitable bases of use in the above reaction include organic bases or, more preferably, inorganic bases. Suitable organic bases include diisopropylethylamine or triethylamine. Suitable inorganic bases include sodium hydride or potassium carbonate.
Suitable organic solvents of use in the above reaction include diimethylformamide (especially where an inorganic base is used) and acetonitrile (especially where an organic base is used).
Most preferably, the above reaction is effected in, dimethylformamide in the presence of potassium carbonate.
Conveniently, the above reaction is effected at room temperature.
Conveniently, the compound of formula (II), and in particular 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)-morpholine, of use in step (i) of the above reaction is in the form of its free base. Preferably the compound of formula (II), and in particular 2-(R)-(1-(R)-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)-morpholine, of use in step (i) of the above reaction is in the form of its (R)-camphor sulfonic acid salt. More preferably, the compound of formula (II), and in particular 2-(R)-(1R)-(3,5-bis-(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)morpholine, of use in step (i) of the above reaction is in the form of its para-toluenesulfonic acid salt.
According to a further or alternative aspect of the present invention, there is provided a process for the preparation of 3-chloromethyl-1,2,4-triazolin-5-one which comprises:
(i) treatment of semicarbazide hydrochloride with benyloxyacetyl chloride under Schotten-Baumann conditions to give benzyloxyacetylsemicarbazide;
(ii) cyclisation of the product of step (i) under basic conditions to give 3-benyloxymethyl-1,2,4-triazolin-5-one;
(iii) hydrogenation of the product of step (ii) to give 3-hydroxymethyl-1,2,4-triazolin-5-one; and
(iv) treatment of the product of step (iii) with a chlorinating agent to give 3-chloromethyl-1,2,4-triazolin-5-one.
According to yet a further or alternative aspect of the present invention, there is provided a process for the preparation of 3-hydroxymethyl-1,2,4-triazol-5-one which comprises steps (i) to (iii) as described above.
In step (i) above, the Schotten-Baumann conditions preferably involve use of aqueous alkali in a suitable solvent such as an ether, for example, tetrahydrofuran, at a reduced temperature, for example, between −10° C. and +10° C., preferably 0° C. A particularly suitable aqueous alkali is aqueous sodium hydroxide.
In step (ii) above, c

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