DESC:Field of Invention
The present invention relates to novel processes for preparing (±)-2-(difluoromethyl)
ornithine (DFMO) also known as Eflornithine, an irreversible inhibitor of ornithine
decarboxylase. The present invention also relates to novel intermediates for the synthesis of
Eflornithine or salts thereof and processes for preparing the same.
Background of the Invention
The present invention is directed to novel processes for the synthesis of eflornithine
hydrochloride, an irreversible inhibitor of ornithine decarboxylase used to treat African
trypanosomiasis (sleeping sickness) and excessive facial hair growth in women.
Eflornithine is the first topical drug approved by FDA in July 2000, for the treatment
of unwanted facial hair and is marketed by Allergan, Inc. under the brand name VANIQA® in
the form of a cream. Besides being a non-mechanical and non-cosmetic treatment, eflornithine
is the only non-hormonal and non-systemic prescription option available for women who suffer
from facial hirsutism. It acts by irreversible inhibition of ornithine decarboxylase, an enzyme
which is necessary for the synthesis of polyamines, which play an important role in cell growth
and proliferation.
Eflornithine is chemically described as (±)-2-(difluoromethyl) ornithine
monohydrochloride monohydrate having an empirical formula of C6H12F2N2O2• HCl•H2O and
has a structural formula:
H2N
NH2
F F
OH
O
H2O
Hcl
U.S. Pat. No. 4,413,141 first disclosed the compound 2-difluoromethyl-2,5-
diaminopentanoic acid also chemically known as 2-difluoromethyl-2,5-diaminovaleric acid or
a-(difluoromethyl)ornithine (DFMO).
The method for the preparation of DFMO from ornithine methyl ester by
difluoromethylation of methyl 2,5-bis(benzylideneamino)pentanoate and the deprotection of
methyl 2-difluoromethyl-2,5-bis(benzylideneamino)pentanoate is described by P. Bey et al., J.
Org. Chem., 44, 2732 (1979), the disclosure of which is incorporated herein by reference.
U.S. Pat. No. 4,309,442 and U.S. Pat. No. 4,330,559 discloses preparation of DFMO
from ornithine. The relatively high cost of the starting material, ornithine, and the use of less
3
desirable reagents including flammable reagents, however makes the route less attractive for
commercial manufacture.
U.S. Pat. No. 7,012,158 discloses preparation of difluoromethyl ornithine, wherein an
alkyl glycine ester of the formula 2 serves as a convenient starting material for a short synthesis
of an alkyl 2-d?fluoromethyl-4-cyanobutanoate intermediate (compound of the formula 5)
which can then be converted by a number of processes to DFMO.
In the view of cited literature, there exists a continuous need to develop alternative
synthetic approaches for the preparation of eflornithine, to overcome the drawbacks of prior
art.
The present inventors have surprisingly found novel alternative pathways for the
synthesis of eflornithine or acid addition salts thereof and novel compounds useful as
intermediates, and use thereof for the preparation of pharmaceutical formulations.
Object of invention
An object of the present invention is to provide novel processes for preparing
eflornithine hydrochloride or an optically active isomer or racemic mixture thereof.
It is also an object of the invention to provide simpler processes for preparing
eflornithine in terms of yields and optical purity, resulting in a desired isomer.
Another object of the invention is to provide novel compounds useful as intermediates
for the preparation of eflornithine and preparation process thereof.
Another objective of the present invention is to provide commercially feasible
processes for the preparation of eflornithine which employs less expensive, easily available
and environment friendly reagents.
Summary of Invention
In one embodiment, the present invention provides a novel process for the preparation
of eflornithine represented by a compound (VI),
H2N
OH
O
F2CH
H2N
VI
comprising the following steps:
4
a. Reacting a compound (I) with an aryl aldehyde or ketone compound Ph(CO)R2 in presence
of a solvent and a dehydrating agent to give a Schiff base intermediate compound (II),
PhCOR2 base
Solvent
O
O
NH2
R1
I
O
O
R2 N R1
II
Wherein in compound (I), R1 is a C1-C4 alkyl group, or an aryl group, and in compound of
formula Ph(CO)R2, R2 is hydrogen, C1-C4 alkyl or an aryl group;
b. Treating the compound (II) with a halodifluoromethane alkylating reagent in the presence of
base and solvent to give the compound (III.1),
R2
N
O
O
R1
F
F
III.1
O
O
R2 N R1
II
Wherein R1 and R2 are defined as hereinbefore;
c. Contacting a compound (III.1) with a halonitroalkane, in the presence of a phase transfer
catalyst and a base to form a compound (IV.1);
R2
N
O
O
R1
F
F
III.1
R2
N
O
O
R1
F2CH
O2N
IV.1
d. Hydrolyzing the compound (IV.1) in the presence of an acid and a solvent to yield a
compound (V.1);
R2
N
O
O
R1
F2CH
O2N
IV.1
H2N
O
O
R1
F2CH
O2N
V.1
e. Subjecting the compound (V.1) to reduction to form a diamino compound, and followed by
hydrolysis to obtain eflornithine (VI), or
5
H2N
O
O
R1
F2CH
O2N
V.1
H2N
O
O
F2CH
H2N
H2N
OH
O
F2CH
H2N
VI
R1
Reduction Hydrolysis
f. Optionally the compound (V.1) may be subjected to reduction and hydrolysis in a single step
to yield eflornithine (VI) or an acid addition salt thereof.
Alternatively, the compound (V.1) may be reacted with a base metal catalyst to reduce
the nitro group to amino group, followed by cyclisation resulting in a compound of formula
VIa, which is further hydrolyzed under acidic or basic conditions to yield eflornithine
hydrochloride (VII).
H2N
O
O
R1
F2CH
O2N
V.1
NH
O
NH2
CHF2
H2N
OH
O
F2CH
H2N
HCl
VIa VII
Reduction
Cyclisation
Hydrolysis
In a second embodiment, the present invention provides a novel process for preparing
eflornithine or an acid addition salt thereof, wherein the process comprises following steps:
a. Reacting a compound (II) with acrylonitrile in presence of base, and phase transfer catalyst
to obtain compound (III.2),
O
O
R2 N R1
R2 N
N
O
O
R1
II III.2
Wherein R1 is a C1-C4 alkyl group, or an aryl group, most preferably an aryl group and R2 is
defined as hereinbefore;
b. Treating a compound (III.2) with halodifluoromethane alkylating reagent in the presence
of base and solvent to give the compound (IV.2),
6
R2 N
N
O
O
R1
III.2
R2 N
N
O
O
R1
F2HC
IV.2
CHF2X
c. The protecting groups of compound (IV.2) are hydrolyzed by reacting with aqueous acid in
the presence of an organic solvent, followed by neutralizing with a base to obtain a compound
(V.2),
R2 N
N
O
O
R1
F2HC
H2N
N
O
O
R1
F2HC
IV.2 V.2
1. Hydrolysis
2. Base
d. Subjecting the compound (V.2) to reduction in the presence of a metal catalyst resulting in
a diamino compound, followed by hydrolysis of the alkyl ester group to obtain eflornithine
compound of formula (VI),
Reduction
H2N
N
O
O
R1
F2HC
V.2
H2N
O
O
F2CH
H2N
H2N
OH
O
F2CH
H2N
VI
R1
Hydrolysis
e. Optionally the compound (V.2) may be subjected to reduction and hydrolysis in a single step
to yield eflornithine (VI) or an acid addition salt thereof.
Alternatively, the compound (V.2) may be reacted with a base metal catalyst to reduce
the nitrile group to amino group, followed by cyclisation resulting in a compound of formula
VIa, which is further hydrolyzed under acidic or basic conditions to yield eflornithine
hydrochloride (VII).
Reduction
H2N
N
O
O
R1
F2HC
V.2
NH
O
NH2
CHF2
H2N
OH
O
F2CH
H2N
HCl
VIa VII
Hydrolysis
7
In a third embodiment, the present invention provides a novel process for preparing
eflornithine or an acid addition salt thereof, comprising:
a. The compound alkyl-2-nitroacetate (1) reacted with compound (2) in presence of a base to
give compound (3),
O2N
O
O
R1 O2N O
O
R1
O2N X
Base
NO2
1 2 3
Wherein R1 is C1-C4 alkyl group or an aryl group;
b. Compound (3) reacted with a halodifluoromethane alkylating reagent in presence of base
to give compound (4),
Base
XCHF2
O2N O
O
R1
NO2
3
O
O
R1
F F
O2N
NO2
4
c. Subjecting the compound (4) to reduction in the presence of a base to yield a compound
(5),
O
O
R1
F F
O2N
NO2
4
H2N O
O
NH2
R1
F
F
5
Reduction
d. Compound (5) undergo hydrolysis to give compound (6) i.e., eflornithine or an acid
addition salt thereof.
H2N O
O
NH2
R1
F
F
5
H2N OH
O
NH2
F F
6
In a fourth embodiment, the novel processes of the present invention provides following
novel compounds useful as intermediates for the synthesis of eflornithine or acid addition salts
thereof,
8
R2
N
O
O
R1
F
F
III.1
R2
N
O
O
R1
F2CH
O2N
IV.1
R2 N
N
O
O
R1
III.2
H2N
O
O
R1
F2CH
O2N
V.1
R2 N
N
O
O
R1
F2HC
IV.2
H2N
N
O
O
R1
F2HC
V.2
O2N O
O
R1
NO2
3
O
O
R1
F F
O2N
NO2
4
Detailed description of the invention
The present invention relates to novel processes for the preparation of (±)-2-(difluoromethyl)
ornithine or a hydrochloride salt thereof, represented by a compound of formula VII.
H2N
OH
O
F2HC
NH2
HCl
VII
According to the present invention, the novel process of the present invention yields
novel compounds useful as intermediates for the synthesis of eflornithine or an acid addition
salt thereof.
The present invention also relates to novel processes for preparation of eflornithine
preferably a hydrochloride salt thereof, which is industrially feasible, cost-effective and yields
the desired isomer with a high chemical purity.
Unless defined otherwise, all technical and scientific terms used herein have the same
meaning as commonly understood by one of ordinary skill in the art to which this invention
belongs. Although any methods and materials similar or equivalent to those described herein
9
can be used in the practice or testing of the present invention, the preferred methods and
materials are described.
The terms “DFMO,” and “Eflornithine” are used interchangeably and refer to the
compound that is chemically designated as 2-(Difluoromethyl)-DL-ornithine, 2-
(Difluoromethyl)ornithine, DL-a-difluoromethylornithine
In an embodiment, the novel process of the present invention for preparing (±)-2-
(difluoromethyl) ornithine i.e., eflornithine (VI) may be represented as given in Scheme I.
PhCOR2, MgSO4
XCHF2, NaOMe
Scheme I
R2
N
O
O
R1
F
F
III.1
O
O
NH2
R1
I
O
O
R2 N R1
II
MeOH/ ACN
X NO2
K2CO3, PTC/NaI
MeCN
R2
N
O
O
R1
F2CH
O2N
H2N
O
O
R1
F2CH
O2N
Methyl tert. butyl ether
in 4NHCl
IV.1 V.1 X= Cl, Br
H2N
OH
O
F2CH
H2N
H2, Pd/C
MeOH,HCl
H2N
OH
O
F2CH
H2N
HCl
HCl
VI VII
According to Scheme I, a glycine ester compound (I) wherein R1 is C1-C4 alkyl or an aryl group
is reacted with an aryl aldehyde or ketone of formula PhC(O)R2 wherein R2 is hydrogen, C1-
C4 alkyl or an aryl group to yield a Schiff base intermediate compound (II). Preferably the alkyl
group is methyl, ethyl, isopropyl or t-butyl and the aryl group is phenyl or benzyl. A
dehydrating agent such as magnesium sulfate or sodium sulfate may be used to remove the
water generated during the reaction.
The reaction may be carried out in the presence of halogenated solvents such as
dichloromethane, chloroform, etc. However, when R2 is hydrogen, the reaction may be
advantageously carried out in acetonitrile as it simplifies reaction work-up procedures. When
10
R2 is C1-C4 alkyl or an aryl group, the reaction may be carried out in an aprotic solvent such as
xylene, toluene and a catalytic amount of Lewis acid. Lewis acids may be selected from boron
trifluoride etherate, triphenyl boron, zinc chloride, and aluminum chloride. The reaction may
be carried out at a temperature of about 10°C to about 35°C.
Alternatively, the reaction may be carried out in the presence of a base such as
triethylamine (TEA), tributylamine (TBA), or N,N-diisopropylethylamine when an acid
addition salt of compound (I) is used.
Compound (II) is reacted with a halodifluoromethane alkylating reagent at a
temperature from about -35 to about 25°C in the presence of a strong base and solvent to give
the compound (III.1). Examples of suitable halodifluoromethane alkylating agents include
without limitation chlorodifluoromethane, bromodifluoromethane or difluoroiodomethane.
Preferably chlorodifluromethane is used for alkylating the compound (II). Strong bases used in
this step may be selected from alkali metal alkoxides, alkali metal hydrides, or alkali metal
amides. Preferably alkali metal alkoxide is used, more preferably sodium alkoxide (sodium
methoxide, sodium ethoxide, or sodium t-butoxide). Suitable solvents for alkylation include
dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, acetonitrile, or an ether such as
tetrahydrofuran, 2-methyl tetrahydrofuran, diethyl ether, methyl t-butyl ether, dioxane or
mixtures thereof.
Compound (III.1) is treated with a halonitroalkane, in the presence of a phase transfer
catalyst (PTC) and a base to form a compound (IV.1). In preferred embodiments, the
halonitroalkane is 3-chloronitropropane. Examples of phase transfer catalyst include
triethylbenzylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium
bromide, tetraethylammonium chloride, or trimethylbenzylammonium chloride. Base is
selected from the group consisting of sodium carbonate, sodium bicarbonate, sodium
hydroxide, potassium hydroxide, potassium carbonate, more preferably potassium carbonate.
Solvents selected from acetonitrile, ethyl acetate, tetrahydrofuran (THF), methylene dichloride
(MDC), more preferably acetonitrile.
The compound (IV.1) is subjected to hydrolysis in the presence of an acid and a solvent
to yield a compound (V.1), wherein the Schiff’s base protecting group is hydrolyzed by treating
with acid, followed by neutralizing with a base. Examples of acids include mineral acids,
toluenesulfonic acid, methanesulfonic acid, trifluoroacetic acid and the like. In preferred
embodiments, hydrolysis may be carried out using hydrochloric acid and methyl t-butyl ether.
Further, the compound (V.1) is subjected to reduction with a transition metal catalyst
resulting in a diamino compound, followed by subsequent hydrolysis to yield eflornithine
11
compound (VI). Examples of transition metal catalyst include Pd/C, Pt/C, and platinum oxide.
Alternatively, the compound (V.1) is subjected to reduction and hydrolysis in a single step in
the presence of a metal catalyst and treating the reaction mixture with hydrochloric acid in
suitable solvents like acetone, acetonitrile, dimethyl formamide (DMF), preferably acetone
resulting in eflornithine hydrochloride.
Hydrogenation using transition metal catalysts may be carried out in suitable corrosion
resistant reaction vessels at a pressure from about 80 psi to about 120 psi and temperature from
about 25°C to about 40°C.
Alternatively, the compound (V.1) may be reacted with a base metal catalyst to reduce
the nitro group to amino group, followed by cyclisation resulting in a lactam compound of
formula VIa, which is further hydrolyzed under acidic or basic conditions to yield eflornithine
hydrochloride (VII).
H2N
O
O
R1
F2CH
O2N
V.1
NH
O
NH2
CHF2
H2N
OH
O
F2CH
H2N
HCl
VIa VII
Reduction
Cyclisation
Hydrolysis
Suitable base metal catalysts include nickel, cobalt, or copper-aluminum alloy catalysts. The
lactam may be hydrolyzed under acidic conditions using a strong acid such as 12N hydrochloric
acid or under basic conditions using 10N hydroxide solution. The hydrolysis of VIa may be
carried out in the presence of solvents selected from ethanol, methyl t-butyl ether, isopropanol,
tetrahydrofuran, or mixtures thereof.
In another embodiment, the process of the present invention provides novel compounds
useful as intermediates for the preparation of eflornithine represented as follows:
N
O
O
N
O
O
IIa IIc
H
N
O
O
IId
H
N
O
O
IIe
12
N
O
O
F
F
III.1a
N
O
O
F
F
III.1c
H
N
O
O
F
F
III.1b
H
N
O
O
F
F
III.1d
H
N
O
O
F
F
III.1e
N
O
O
F
F
III.1f
R2
N
O
O
R1
F2CH
O2N
H2N
O
O
R1
F2CH
O2N
IV.1 V.1
N
O
O
F
F
III.1g
In a preferred embodiment, the novel processes of the present invention may be further
illustrated by the following schemes;
H2N
O
O
N
O
O ClCHF2, NaOMe
MeOH/ ACN
Scheme Ia
Ia IIa
N
O
O
F
F
III.1a
MgSO4
O
Cl NO2
K2CO3, PTC/NaI
MeCN N
O
O
F2CH
O2N
H2N
O
O
F2CH
O2N
Methyl tert. butyl ether
in 4NHCl
IV.1a V.1a
13
H2N
OH
O
F2CH
H2N
H2, Pd/C
MeOH,HCl
H2N
OH
O
F2CH
H2N
HCl
HCl
VI VII
H2N
O
O
H
N
O
O
H
N
O
O
F2CH
ClCHF2, NaOMe
MeOH/ ACN
IIb III.1b
Scheme Ib
Ib
MgSO4
H
O
N
O
O
F2CH
O2N
Cl NO2
K2CO3, PTC/NaI
MeCN
H2N
OH
O
F2CH
H
Methyl tert.butyl ether
in 4N HCl
O2N
IV.1b V.Ib
H2N
OH
O
F2CH
H2N
H2, Pd/ C MeOH
HCl
H2N
OH
O
F2CH
H2N
HCl
VI VII
In another embodiment, the present invention provides an alternative process for the
preparation of eflornithine or an acid addition salt thereof, represented by Scheme II.
According to Scheme II, compound (II) may be prepared according to the method
described as hereinbefore in Scheme I. In preferred embodiments of the invention, in
compound (I) R1 is an aryl group such as phenyl or benzyl. Compound (II) may be treated with
acrylonitrile, in presence of a base selected from potassium carbonate, cesium carbonate,
sodium bicarbonate and phase transfer catalyst (PTC) selected from triethylbenzylammonium
chloride, tetrabutylammonium chloride, tetraethyl ammonium chloride, or
trimethylbenzylammonium chloride. Alternatively sodium iodide may be also be used. In
14
preferred embodiments, the conversion of compound (II) to compound (III.2) may be carried
out in the presence of potassium carbonate at temperatures of about 10 to 45°C, preferably
from about 20°C to 35°C.
PhCOR2
MgSO4
O
O
R2 N R1
K2CO3/PTC
acrylonitrile
CH3CN R2 N
N
O
O
R1
Base
O
O
NH2
R1
I II III.2
Scheme II
NaOCH3
CHF2Cl, THF
R2 N
N
O
O
R1
F2HC
Methyl tert.butyl
ether in 4N HCl
H2N
N
O
O
R1
F2HC
IV.2 V.2
H2, Pd/C
Ethanol
H2N
OH
O
F2HC
NH2
Acetone
H2N
OH
O
F2HC
NH2
HCl
HCl
VI VII
The compound (III.2) may be subjected to alkylation by treatment with
halodifluoromethane, preferably chlorodifluoromethane. The alkylation reaction is carried out
for example by deprotonation at a temperature of from about -35 to about 25°C. Suitable strong
bases may be used to deprotonate the compound (III.2) at the position a to the carboxylate.
Examples of strong bases include alkali metal alkoxides, alkali metal hydrides, and alkali metal
iodides. Preferably alkoxide base such as sodium methoxide, sodium ethoxide, or sodium
tertiary butoxide may be used. More preferably sodium methoxide. Once the a-anion has been
generated, the alkylating reagent is introduced to yield a compound (IV.2).
The compound (IV.2) can be hydrolyzed by treatment with an aqueous acid using
conditions to provide the compound (V.2). The Schiff’s base protecting group is hydrolyzed
by treating with acid, followed by neutralizing with a base. Suitable acids are toluene sulfonic
acid, hydrochloric acid. A mixture of methyl t-butyl ether and 4 N HCl is stirred at ambient
temperature to effect hydrolysis of the Schiff s base. After the reaction mixture is made basic
with hydroxide solution, the compound (V.2) isolated in neutral form.
15
The compound (V.2) can be converted in to the diamino compound by reduction of the
nitrile moiety followed by hydrolysis of the aryl ester group to obtain eflornithine compound
of formula (VI). Any reduction procedure effective to selectively reduce the nitrile moiety to
the amine with minimal competing ester reduction can be used. For example, heterogeneous
transition metal catalysts are effective catalysts for the hydrogenation of the nitrile moiety, an
acid such as hydrochloric acid is added to the reaction mixture. The transition metal catalysts
include, for example, palladium on carbon, platinum on carbon, and platinum oxide. Preferably
the catalyst used in the reduction is 5-10% platinum on carbon. Further the compound (VI)
may be treated with hydrochloric acid in suitable solvents like acetone, acetonitrile, dimethyl
formamide (DMF), preferably acetone to yield eflornithine hydrochloride (VII).
In some embodiments, the nitrile group may be selectively reduced using metal
hydrides such as NaBH4, LiAlH4, NaBH3O2CCF3 and the like.
In alternative embodiments of the invention, the compound (V.2) may be reacted with
a base metal catalyst such as Raney cobalt catalyst and a solvent, wherein the nitrile group is
reduced to amino group, followed by cyclisation resulting in a compound of formula VIa,
which is further hydrolyzed under acidic or basic conditions to yield eflornithine hydrochloride
(VII). Preferably the compound VIa may be hydrolyzed in the presence of a mineral acid such
as hydrochloric acid to yield eflornithine hydrochloride (VII).
Reduction
H2N
N
O
O
R1
F2HC
V.2
NH
O
NH2
CHF2
H2N
OH
O
F2CH
H2N
HCl
VIa VII
Hydrolysis
In another embodiment, the present invention provides the following novel compounds useful
as intermediates for the synthesis of eflornithine or acid addition salts thereof:
N
N
O
O
III.2a
H
N
N
O
O
N
N
O
O
III.2b III.2c
16
N
N
O
O
III.2d
H
N
N
O
O
N
N
O
O
III.2e III.2f
R2 N
N
O
O
R1
F2HC
H2N
N
O
O
R1
F2HC
IV.2 V.2
In another embodiment, the present invention provides a novel process for preparing
eflornithine or an acid addition salt thereof, depicted as in Scheme III:
O2N
O
O
O2N O
O
Base
CHClF2
Scheme III
O2N Cl
Base
NO2
1 2 3
O
F O F
Na2S2O4
H2N O
O
NH2
F
F
DMF
O2N
NO2
4 5
H2N OH
O
NH2
F F
1N HCl
6
According to scheme III, an alkyl-2-nitroacetate (1) is reacted with a halonitroalkane (2) in
presence of a base and catalyst to give compound (3). Base may be selected from sodium
carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate. In preferred
embodiments, halonitroalkane is 3-chloronitropropane and base is sodium carbonate. Suitable
solvents are acetonitrile, dichloromethane, acetone, preferably acetonitrile. The compound (3)
can be converted into compound (4) by treating with halodifluoromethane in presence of base
and solvent. Suitable bases are sodium carbonate, potassium carbonate, sodium bicarbonate,
17
sodium thiosulfate, preferably sodium thiosulfate. Suitable solvents are acetonitrile,
dichloromethane, dimethyl formamide (DMF), preferably acetonitrile, preferably DMF. The
compound (4) is reduced to yield a diamino compound (5), which is further subjected to
hydrolysis with 1N hydrochloric acid under reflux temperature to yield eflornithine.
In another embodiment, the present invention provides novel compounds useful as
intermediates for the synthesis of eflornithine or acid addition salts thereof.
O2N O
O
O
F O F
NO2
O2N
NO2
3 4
In alternative embodiment, the present invention provides a process for the resolution
of racemic mixture of eflornithine hydrochloride, represented in Scheme IV.
According to Scheme IV, the compound (3) is subjected to resolution with optically
active proline in the presence of chlorodifluoromethane and tetrahydrofuran to yield the
compounds 4a and 4b, followed by reduction and subsequent hydrolysis in the presence of
sodium dithionate to yield compounds 6a and 6b. The compounds 6a and 6b may be further
treated with 1N hydrochloric acid to yield the desired isomers of eflornithine hydrochloride.
N O
O
O N
O
O O
N O
O
N
O O
O
O
F
F
N O
O
OH N
O
F
F
H2N OH
O
NH2
F
F
.HCl
H2N OH
F O
F
.HCl
Proline
CHClF2
THF
Na2CO3
Na2CO3
1N HCl
1N HCl
R-isomer
S-isomer
NH2
O O
Scheme IV
3
4a
4b
6a
6b
18
Further the processes of the present invention are illustrated in the following examples. The
preparation of novel compounds or intermediates may be carried out as described herein after,
following examples are to be construed as merely illustrative, and do not limit the present
disclosure in any way whatsoever.
Examples:
Preparation of compound (II):
In a suitable reaction vessel, the glycine ester compound I (R1 = C1-C4 alkyl, aryl) was reacted
with an aldehyde/ketone compound of formula PhC(O)R2 (R2 = H, C1-C4 alkyl, aryl), followed
by addition of magnesium sulfate, acetonitrile. The reaction was maintained at room
temperature for 4-5 hours. The reaction mass (RM) was filtered, followed by solvent washing
to obtain the title compound. Compound II may be taken to next step as such or optionally
purified in one or more solvents.
Example 1: Preparation of benzyl-2-(diphenylmethyleneamino) acetate (IIa):
In a 2L round bottom flask equipped with mechanical stirrer, was charged benzyl-2-
aminoacetate (Ia) (100g). To the above, was added magnesium sulfate (80g), methanol (4 vol),
benzophenone (70g), triethyl amine (130g). The reaction mixture was stirred at 20-25ºC for
4hrs. The solid was filtered, washed with methanol and the filtrate was taken to next step.
Preparation of compound (III.1):
To a solution of compound II in acetonitrile, added sodium methoxide, stirred the mixture for
2 hrs at room temperature and then warmed to 40°C. Slowly chlorodifluoromethane was added
to the reaction mixture and maintained at 40-50°C. After the reaction is complete, the solvent
was distilled completely to obtain the title compound (III.1).
Example 2: Preparation of benzyl-2-(diphenylmethyleneamino)-3,3-difluoro prop anoate
(III.1a): In a 2L round bottom flask equipped with mechanical stirrer, charged reaction mixture
obtained from Example 1 and sodium methoxide (19.67g) dissolved in acetonitrile (500 ml).
Stirred for 90 min at RT (room temperature). Then heated the reaction mass to 40-50ºC. Slowly
passed 250gm of chlorodifluoromethane gas and maintained at same temperature for 1 hr. Then
the reaction mass was cooled to room temperature, followed by addition of saturated sodium
chloride (250 ml). The reaction mass was extracted with ethyl acetate (3 ×3 vol). Dried over
anhydrous sodium sulfate, combined the organic layers and evaporated under vacuum to obtain
title compound (90g).
Preparation of compound (IV.1):
In a round bottom flask equipped with a mechanical stirrer, was charged compound (III.1),
potassium carbonate, tetra butyl ammonium bromide in acetonitrile. Then cooled to 0-5º, 3-
19
chloronitropropane was added, maintained for 6 hours at room temperature. After the
completion of reaction, the RM was washed with acetonitrile and distilled the solvent
completely under vacuum to obtain the crude compound IV.1. The crude compound may be
optionally extracted with dichloromethane followed by washing with water, then dried over
anhydrous sodium sulfate, distilled the solvent completely. And further recrystallization with
acetonitrile to yield the pure title compound.
Example 3: Preparation of benzyl-2-(diphenylmethyleneamino)-2-(difluorometh yl)-5-
nitropentanoate (IV.1a): In a round bottom flask equipped with a mechanical stirrer, charged
benzyl-2-(diphenylmethyleneamino)-3,3-difluoropropanoate (III.1a) (90g), potassium
carbonate (49g), sodium iodide (1.8g) and tetra butyl ammonium bromide (1.53g) in
acetonitrile. Then cooled to 0-5ºC, 1-chloro-4-nitro-propane (29.5g) was added, maintained at
RT for 6 hrs. After completion of reaction, the reaction mixture was filtered and washed with
acetonitrile (100ml). Solvent was evaporated completely under vacuum. Then extracted with
dichloromethane (600ml), washed with water and dried over anhydrous sodium sulfate.
Distilled the solvent completely and recrystallized with acetonitrile to yield the title compound
(100g).
Preparation of compound (V.1):
In an RBF, was charged compound (IV.1) followed by addition of methyl tertiary butyl ether
and hydrochloric acid at 0-5ºC. Stirred the reaction mass to 1-2 hours at 20-25ºC. Then the
organic and aqueous layers were separated. Aqueous layer was extracted with methyl tertiary
butyl ether and the pH was adjusted to 9-10 with sodium hydroxide at 5°C. The combined
organic layers were concentrated under vacuum to obtain the crude compound (V.1).
Example 4: Preparation of benzyl-2-amino-2-(difluoromethyl)-5-nitropentanoate (V.1a):
In a 2L round bottom flask equipped with mechanical stirrer, was charged benzyl-2-
(diphenylmethyleneamino)-2-(difluoromethyl)-5-nitropentanoate (IV.1a) (100g), methyl
tertiary butyl ether and hydrochloric acid (5 vol) at 0-5ºC. Stirred the reaction mass to 1-2 hours
at 20-25ºC. Then the organic and aqueous layers were separated. Aqueous layer was extracted
with methyl tertiary butyl ether (2 × 2 vol) and the pH adjusted to 9-10 with sodium hydroxide.
The basic aqueous layer was again extracted with methyl tertiary butyl ether (1vol). The total
organic layers were combined and concentrated under vacuum to obtain the title compound
(60g).
Preparation of compound (III.2):
Compound (II) (R1 = aryl, R2 = H, C1-C4 alkyl, aryl) reacted with potassium carbonate in the
presence of sodium iodide, stirred for 1 hour at 20-25°C. To the RM, was added acrylonitrile
20
and stirred for 2 hours at the same temperature. After the reaction is complete, the solid may
be filtered off followed by washing with acetonitrile. The solvent may be distilled off under
reduced pressure to yield the title compound. The crude compound may be taken as such or
further purified using one or more organic solvents.
Example 5: Preparation of benzyl 4-cyano-2-(diphenylmethyleneamino)butanoa te
(III.2f) (where R1= benzyl; R2 = phenyl): To the reaction mixture obtained from Example 1,
was added potassium carbonate (270g), trimethylbenzyl ammonium chloride (14g), stirred at
20-25°C for 1 hr. To the above mixture was slowly added acrylonitrile (30g) and stirred for 2h
at same temperature. After completion of reaction, solid was filtered and washed with
acetonitrile. The solvent was removed under reduced pressure to yield a crude title compound.
Preparation of compound (IV.2):
To a solution of compound (III.2) in tetrahydrofuran, was added sodium methoxide at 5°C.
Stirred the mixture for 2 hours at room temperature and then warmed to 40°C. Slowly add
chlorodifluoromethane to the reaction mixture and maintain at 40-50°C for 1-2 hours. After the
reaction is complete, distilled the solvent completely to obtain the title compound (IV.2).
Example 6: Preparation of benzyl 4-cyano-2-(diphenylmethyleneamino)-2-(difluo
romethyl)butanoate (IV.2 where R1 = benzyl, R2 = phenyl): To a solution of crude
compound obtained from Example 5, was added tetrahydrofuran (300 ml) and sodium
methoxide (25g) at 0-5°C, stirred for 30 minutes. The temperature was raised to 20-25°C for
2h and warmed to 40°C. Slowly chlorodifluoromethane (30g) was passed into the reaction
mixture and maintained at 40-50°C. The reaction mixture was stirred for 1-2 hrs. After
completion of reaction, the solvent was distilled completely under vacuum to yield the title
compound.
Preparation of compound (V.2):
Compound V.2 may be prepared according to the same process and reaction conditions as
described for compound V.1.
Preparation of compound (VIa):
To compound V.1 and V.2, was added Raney-cobalt and ethanol, heated to 45°C, pressurized
to 125 psi and stirred for 2-3 hours. The reaction mixture was filtered and washed with ethanol.
The combined filtrates were concentrated, after multiple washings with an organic solvent,
followed by drying to yield compound VIa.
Preparation of compound (4):
In a suitable reaction vessel fitted with a stirrer, was charged a solution of methyl-2-nitroacetate
(1) in dichloromethane, followed by addition of sodium carbonate and 1-chloro-3-nitropropane
21
(2), stirred for 2-3 hours. Filtered the reaction mass, followed by solvent washing and distilling
the solvent completely under vacuum to yield a residue of methyl 2, 5-dinitropentanoate (3).
The compound (3) may be further reacted with chlorodifluoromethane in the presence of
sodium bicarbonate to yield a compound (4). The compound (4) may be further purified by
recrystallization in one or more organic solvents or taken as such in crude form to the next
reaction step.
Example 7: Preparation of Methyl-2,5-dinitro pentanoate (3): In a round bottom flask
equipped with a mechanical stirrer, charged methyl-2-nitroacetate (50g) in dichloromethane,
sodium carbonate (27g). Then cooled to 0-5ºC, 1-chloro-3-nitro-propane (16g) was added and
maintained for 2-3 hrs at RT. After completion of reaction, the undissolved salts were filtered
and washed with acetonitrile (55ml). Evaporated completely under vacuum. Then extracted
with acetonitrile (333ml), washed with water, then dried over sodium carbonate. Distilled the
solvent completely and recrystallization with acetonitrile to yield the title compound (79g).
Example 8: Preparation of methyl-2-(difluoromethyl)-2, 5-dinitropentanoate (4): In a
round bottom flask equipped with mechanical stirrer, was charged compound 3 obtained from
example 7 (79g) and sodium carbonate (15.5g), dissolved in acetonitrile (395ml). Stirred for
90 min at RT. Then heated the reaction mass to 40-50ºC. Slowly chlorodifluoro methane gas
(197.5g) was passed into the above reaction mixture, maintained at same temperature for 1 hr.
Then the RM was cooled to RT, washed with saturated sodium chloride (197 ml). Extracted
the mass with acetonitrile (3 × 3 vol). Dried over anhydrous sodium sulfate, combined the
organic layers and evaporated under vacuum to obtain title compound (117g).
Preparation of compound (VI) (Eflornithine):
From V.1: In a reaction vessel equipped with a stirrer, was charged compound (V.1), then
Pd/C and methanol were added to reduce the nitro compound to amine, followed by addition
of 1N hydrochloric acid. Purged the reaction vessel with hydrogen, pressurized to 120psi and
stirred overnight for 12-16 hours. After completion of reaction, de-pressurize the vessel and
contents were filtered. The filtrate was then washed with methanol, followed by concentrating
under vacuum to obtain the crude eflornithine hydrochloride. The crude compound may be
purified by crystallizing from suitable solvents such as ethanol/water.
From V.2: In a reaction vessel equipped with a stirrer, charged compound (V.2), then Pd/C
and ethanol were added, stirred the contents and pressurize the reaction mixture to 95 psi under
hydrogen for 1 hour. Concentrated hydrochloric acid was added and stirred for 8-9 hours. After
the reaction is complete, pressure was released and washed the RM with ethanol. Filtered the
contents and the filtrate was concentrated under vacuum to obtain a crude residue (VI). The
22
residue may be purified by crystallizing in one or more solvents such as ethanol, MTBE or
isopropanol to obtain pure eflornithine.
From 4:
A solution of compound (4) in dimethylformamide is treated with sodium dithionate to yield a
diamino compound (5). Compound 5 may be treated with 12 N hydrochloric acid and stirred
at 100-110°C for 12-18 hours. After the reaction is complete, the RM may be concentrated. To
the concentrate, add ethanol followed by reflux for 30 minutes. Adjust the pH to 3.8-4.4 using
triethylamine to form a crystal slurry. Upon cooling to 0°C, a crude compound (6) is isolated.
The crude compound may be further purified by crystallization in solvents such as isopropanol,
ethanol or mixtures thereof.
Example 9: Preparation of 2,5-diamino-2-(difluoromethyl) pentanoic acid (6): In a round
bottom flask equipped with mechanical stirrer, was charged methyl-2,5-diamino-2-
(difluoromethyl) pentanoate (5) (86g), 12 N hydrochloric acid and stirred for 12-18 hrs at 100-
110ºC. Then the reaction mass was concentrated, followed by addition of ethanol. After
refluxing for 30min, the RM was cooled to RT. The pH was adjusted to 3.8-4.4 using
triethylamine to form a slurry. The slurry was cooled to 0°C to obtain a crude compound. The
crude was purified by crystallization in ethanol, followed by evaporation of solvent, drying to
obtain the pure compound (79g).
Although the present invention has been described in terms of certain preferred embodiments
thereof, other embodiments and modifications to preferred embodiments may be possible that
are within the principles and spirit of the invention.
Without being limited by theory, the present invention may be advantageously used to
make medicaments which can be used for administration. The processes described in the
present disclosure prevents the disadvantages of the prior art. It is envisaged that by providing
the present invention, the desired product in higher yields might be achieved, thereby
contributing to a user friendly handling of the process according to art.
The systems and methods of the present invention may be embodied in other specific
forms without departing from the teachings or essential characteristics of the invention. ,CLAIMS:We Claim,
1. A process for preparing 2-(difluoromethyl)-DL-ornithine (DFMO), represented by a
compound of formula VI or a salt thereof, comprising:
H2N
OH
O
F2CH
H2N
VI
a. Reacting compound (I) with an aryl aldehyde or ketone compound of formula Ph(CO)R2
to form compound (II),
PhCOR2
O
O
NH2
R1
I
O
O
R2 N R1
II
b. Reacting compound (II) with a halodifluoromethane alkylating reagent to form compound
(III.1),
R2
N
O
O
R1
F
F
III.1
O
O
R2 N R1
II
c. Contacting compound (III.1) with a halonitroalkane to form compound (IV.1),
R2
N
O
O
R1
F
F
III.1
R2
N
O
O
R1
F2CH
O2N
IV.1
d. Hydrolyzing the compound (IV.1) to yield compound (V.1),
24
R2
N
O
O
R1
F2CH
O2N
IV.1
H2N
O
O
R1
F2CH
O2N
V.1
e. Subjecting the compound (V.1) to reduction to form a diamino compound, followed by
hydrolysis to obtain eflornithine (VI),
H2N
O
O
R1
F2CH
O2N
V.1
H2N
O
O
F2CH
H2N
H2N
OH
O
F2CH
H2N
VI
R1
Reduction Hydrolysis
(or)
f. Subjecting compound (V.1) to reduction and hydrolysis in a single step to yield eflornithine
(VI) or an acid addition salt thereof; wherein R1 is C1-C4 alkyl (methyl, ethyl, isopropyl or
t-butyl) or an aryl group (phenyl or benzyl), and R2 is hydrogen, C1-C4 alkyl or an aryl
(phenyl or benzyl) group.
2. A process for preparing 2-(difluoromethyl)-DL-ornithine (DFMO) or a salt thereof, said
process comprising:
a. Reacting a compound (II) with acrylonitrile to obtain compound (III.2),
O
O
R2 N R1
R2 N
N
O
O
R1
II III.2
b. Treating compound (III.2) with halodifluoromethane alkylating to form compound (IV.2),
R2 N
N
O
O
R1
III.2
R2 N
N
O
O
R1
F2HC
IV.2
c. Hydrolyzing compound (IV.2) to obtain a compound (V.2),
25
R2 N
N
O
O
R1
F2HC
H2N
N
O
O
R1
F2HC
IV.2 V.2
Hydrolysis
d. Subjecting compound (V.2) to reduction resulting in a diamino compound, followed by
hydrolysis of the alkyl ester group to obtain eflornithine (VI),
Reduction
H2N
N
O
O
R1
F2HC
V.2
H2N
O
O
F2CH
H2N
H2N
OH
O
F2CH
H2N
VI
R1
Hydrolysis
(or)
e. Subjecting compound (V.2) to reduction and hydrolysis in a single step to yield eflornithine
(VI) or an acid addition salt thereof; wherein R1 is C1-C4 alkyl (methyl, ethyl, isopropyl or
t-butyl) or an aryl group (phenyl or benzyl), and R2 is hydrogen, C1-C4 alkyl or an aryl
(phenyl or benzyl) group.
3. A process for preparing 2-(difluoromethyl)-DL-ornithine (DFMO) or a salt thereof, said
process comprising:
a. Subjecting compound V.1 to reduction followed by cyclisation to form compound VIa,
wherein R1 is C1-C4 alkyl (methyl, ethyl, isopropyl or t-butyl) or an aryl group (phenyl or
benzyl),
H2N
O
O
R1
F2CH
O2N
V.1
NH
O
NH2
CHF2
VIa
Reduction
Cyclisation
(or)
b. Subjecting compound V.2 to reduction followed by cyclisation to form compound VIa,
26
Reduction
H2N
N
O
O
R1
F2HC
V.2
NH
O
NH2
CHF2
VIa
c. Hydrolyzing compound VIa obtained from step a or step b under acidic or basic conditions
to yield eflornithine hydrochloride (VII).
NH
O
NH2
CHF2
H2N
OH
O
F2CH
H2N
HCl
VIa VII
Hydrolysis
4. A process for preparing 2-(difluoromethyl)-DL-ornithine (DFMO) or a salt thereof, said
process comprising:
a. Reacting compound (1) with compound (2) to form compound (3),
O2N
O
O
R1
O2N O
O
R1
O2N X NO2
1 2 3
b. Treating compound (3) with a halodifluoromethane alkylating reagent to form compound
(4),
XCHF2
O2N O
O
R1
NO2
3
O
O
R1
F
F
O2N
NO2
4
c. Subjecting the compound (4) to reduction to yield compound (5),
O
O
R1
F
F
O2N
NO2
4
H2N O
O
NH2
R1
F
F
5
Reduction
27
d. Hydrolyzing compound (5) to give compound (6) i.e., eflornithine or an acid addition salt
thereof;
H2N O
O
NH2
R1
F
F
5
H2N OH
O
NH2
F F
6
Wherein R1 is C1-C4 alkyl (methyl, ethyl, isopropyl or t-butyl) or an aryl group (phenyl or
benzyl) and X is halogen.
5. A process according to preceding claims, wherein the reactions are carried out in the
presence of acids selected from mineral acids, toluenesulfonic acid, methanesulfonic acid,
trifluoroacetic acid and the like; bases selected from alkali metal alkoxides, alkali metal
hydrides, alkali metal amides, alkali metal carbonates, triethylamine, tributylamine, or
N,N-diisopropylethylamine; halodifluoromethane alkylating reagents selected from
chlorodifluoromethane, bromodifluoromethane or difluoroiodomethane; phase transfer
catalysts including without limitation, triethylbenzylammonium chloride,
tetrabutylammonium chloride, tetrabutylammonium bromide, tetraethylammonium
chloride, or trimethylbenzyl ammonium chloride; reducing agents such as transition metal
catalyst include Pd/C, Pt/C, and platinum oxide, or metal hydrides selected from NaBH4,
LiAlH4, NaBH3O2CCF3 and the like.
6. Compounds:
R2
N
O
O
R1
F
F
III.1
R2
N
O
O
R1
F2CH
O2N
IV.1
H2N
O
O
R1
F2CH
O2N
V.1
R2 N
N
O
O
R1
III.2
R2 N
N
O
O
R1
F2HC
IV.2
H2N
N
O
O
R1
F2HC
V.2
28
O2N O
O
R1
NO2
3
O
O
R1
F F
O2N
NO2
4
wherein R1 is C1-C4 alkyl (methyl, ethyl, isopropyl or t-butyl) or an aryl group (phenyl or
benzyl), and R2 is hydrogen, C1-C4 alkyl or an aryl (phenyl or benzyl) group.