FORM 2
THE PATENTS ACT 1970
(39 OF 1970)
COMPLETE SPECIFICATION
(SECTION 10)
AN IMPROVED PROCESS FOR PREPARATION OF
TETRAHYDRO-N-[3-(METHYLAMINO)PROPYL]-2-
FURAN CARBOXAMIDE
UNICHEM LABORATORIES LIMITED, A COMPANY
REGISTERED UNDER THE INDIAN COMPANY ACT, 1956,
HAVING ITS REGISTERED OFFICE LOCATED AT
MAHALAXMI CHAMBERS, 2nd FLOOR,
22, BHULABHAI DESAI ROAD, MUMBAI-400 026.
MAHARASTRA, INDIA
The following specification particularly describes the invention and the manner in which it is to be performed.


AN IMPROVED PROCESS FOR PREPARATION OF TETRAHYDRO-N-[3-(METHYLAMINO)PROPYL]-2-
FURAN CARBOXAMIDE
TECHNICAL FIELD
The present invention relates to an improved process for the preparation of tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide as an one of the intermediate involved in the synthesis of an antihypertensive drug Alfuzosin.
BACKGROUND OF THE INVENTION
(±)-N-[3-[(4-amino-6,7-dimethoxy-2-quinazolinyl)methylamino]propyl]tetrahydro-2-furancarboxamide having formula (I),


m
MeO

NH2
(I)
is called Alfuzosin, which is useful as antihypertensive as well as a-antagonist agent.
In prior art Alfuzosin is prepared by a reaction of 4-amino-2-chloro-6,7-dimethoxy
quinazoline compound having formula (II)
NH,
N^^jT^r- 0Me
cr N
(III)
(II) with a tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide compound represented by the following formula (III),



in the refluxing isoamyl alcohol (J. Med. Chem., 1986, 29, 19), US 4,315007 (Philippe,
et al 1982).
However there are very few methods reported for the synthesis of tetrahydro-N-[3-
(methylamino)propyl]-2-furancarboxamide.
In the publication J. Med. Chem., 1986, 29, 19 and the US patent 4,315007 the following
route for the synthesis of tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide is
described:

rr°
O COOH O
I I CI-^^O CH,

TEA

0 O
-o. AX

H3C ""-''^CN
O' "CH, 84.12

c

N
I CH,

-CN

H,, Rh, NH,

r

N l CH,

NH,

c

NH
I CH,

The same paper states that hydrogenation of 2-Cyano-N-methyl-N-tetrahydrofuroylethylamine in methanol saturated with ammonia gas, effected in the presence of Raney Ni, afforded a 60/40 mixture of primary and secondary amines. But the same reaction when carried out in the presence of Rhodium on carbon (pressure 840 psi and temp 80°C) provided only the secondary amines. But Rh/C is a costly catalyst and the reaction conditions required are harsh. As shown in the scheme below:


O
NC

CH3
0

HO
0

Rhodium catalyst

secondary amine

Raney Ni
& methanol saturated w with ammonia gas



+

c

NH
I CH,

60% primary amine

40% secondary amine

The drawback of the above mentioned method is that the process consists of reduction of
nitrile compound in presence of Raney nickel catalyst forms unwanted isomer while the
usage of expensive catalysts like rhodium on alumina which is generally commercially
not recommendable.
Recently two publications viz. US20070066824 (Raghupathi R. et al, 2007) and
WO2007063556 (Reddy S. et al, 2007) discloses the process for the preparation of
alfuzosin hydrochloride which comprises reaction of tetrahydrofuroic acid methyl ester
and N-methyl-l,3-propanediamine gives tetrahydro-N-[3-(methylamino)propyl]-2-furan
carboxamide.
The Chinese publication CN1935806 (Hu, Gaoyun et al, 2007) on the basis of abstract
discloses a two step process for the preparation of tetrahydro-N-[3-

(methylamino)propyl]-2-furan carboxamide: (1) carrying out condensation of 3-halopropylamine and 2-tetrahydrofurancarboxylic acid or 2-tetrahydrofurancarbonyl chloride to obtain N-3-chloropropyl-2-tetrahydrofurancarboxamide; (2) carrying out condensation reaction of N-3-chloropropyl-2-tetrahydrofurancarboxamide and methylamine to obtain tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide.
The present invention provide an improved process for the preparation of tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide which eliminates the disadvantages of the prior art reported process
OBJECT OF THE INVENTION
The objective of the present invention is to provide a simple and effective process for the preparation of tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide.
Another object of the present invention is to provide a tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide with a good yield and purity.
SUMMARY OF THE INVENTION
Accordingly the present invention provides an improved and scalable process for the preparation of tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide, of formula (III), an important intermediate needed for the synthesis of an antihypertensive drug alfuzosin:

S >^ "N' "^ "NH
H I
(III)
O

which comprises a hydrogenation of formula (IV)




(IV)
in presence of Raney nickel as a catalyst, alcoholic solvent and aqueous ammonia
solution.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide of formula (III) an important intermediate needed for the synthesis of an antihypertensive drug alfuzosin is prepared by hydrigenetion of compound of formula (IV)

(IV)
using Raney nickel as a catalyst, alcoholic solvents comprises straight-chain or branched-chain C1-C4 alcohols, preferably methanol, and aqueous ammonia solution. The reduction is carried out at temperature 0 to 60°C, preferably the temperature at 30 to 35°C, and at pressure 2 to 15 Kg/sq. cm2, preferably at pressure 4 to 5 Kg/sq. cm2. The reduction is almost complete in 5 to 15 hours, preferably the time required for the reduction is about 6 to 8 hours.


The reduction is carried out using varied quantity of Raney Ni (source: Vineeth Chemicals, India) from 50% (w/w) to 200% (w/w) with respect to compound of formula (IV), preferably 100% (w/w) with respect to compound of formula (IV). The required Compound of formula (IV) is prepared by reacting 3-methylamino propionitrile with 2-tetrahydrofuroic acid by any general method of amidation, preferably by reacting 3-methylamino propionitrile with 2-tetrahydrofuroic acid using CDI (carbonyl diimidazole) as a coupling agent.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined
EXAMPLES
The following examples are presented for illustration only, and are not intended to limit the scope of the invention or appended claims.
Example 1
Tetrahydro-N-(3-cyanopropyl)-N-methylfurancarboxamide (IV):
Tetrahydrofuroic acid (379.2g, 3.27mole) was added to tetrahydrofuran (1.5L) at 25-30°C and stirred. Then N,N-carbonyl diimidazole (553.6g, 3.417mole) was added in about 30 minutes and stirred for 1 hour. A solution of 3-methylaminopropionitrile (250g 2.975mole) in tetrahydrofuran (500ml) is slowly added in 60 minutes. The reaction mixture was further stirred for 3 hours at 25-30°C and the progress of the reaction was monitored by thin layer chromatography (TLC). After the completion of the reaction, reaction mixture was distilled under reduced pressure to obtain a oily residue (1172g) which was then diluted with water (2L) to obtain a clear solution. The solution was then cooled to about 10°C and the pH was adjusted to 4-4.3 using concentrated hydrochloric


acid solution. This mixture was then extracted with methylene dichloride (1200ml x 2). The combined organic layer was dried over anhydrous sodium sulphate. The organic solvent was distilled under reduced pressure at 40-42°C to obtain the oily residue, Tetrahydro-N-(3-cyanopropyl)-N-methylfurancarboxamide (IV), (41 lg) in 76% yield. GC purity>98%; [M+l]+ is 183.6
Example 2
Tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide (III) : In an autoclave was charged methanol (2L) followed by Tetrahydro-N-(3-cyanopropyl)-N-methylfurancarboxamide, (300g, 1.648mole) and Raney nickel (300g) under nitrogen atmosphere. Then (24%) aqueous ammonia solution was charged. Nitrogen was then replaced carefully with hydrogen gas and about 5 Kg/square cm pressure was maintained for 8 hours at 30-35°C. The progress of the reaction was monitored by TLC. After completion of the reaction, the hydrogen was released and the catalyst was filtered over a hyflow bed under nitrogen atmosphere. The filtrate was distilled 40-45°C to obtain an oily residue (523g). The residue was diluted with methylene dichloride (500ml). The aqueous layer was separated and discarded. The methylene dichloride layer was dried over anhydrous sodium sulphate and was distilled under reduced pressure to get Tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide as an oily (245g) in 80% yield. GC purity>97%; [M+l]+ is 187.4;
PMR (CDC13) 5 1.39-2.48 (8H, m), 2.24 (3H, s), 3.11 (2H, m), 3.55-3.75 (2H, m), 4.0 (1H, s) 4.05-4.11 (1H) and 7.18 (1H)


We claim:
1. A process for the preparation of tetrahydro-N-[3-(methylamino)propyl]-2-furan
carboxamide compound represented by the following formula (III),
o

(no
which comprises a hydrogenation of formula (IV)


c

O

N
I CH,

,CN

(IV)
in presence of Raney nickel as a catalyst, alcoholic solvent and aqueous ammonia solution.
2. The process of claim 1, wherein Raney nickel used is in the range of 50% (w/w) to 200% , preferably 100% (w/w) with respect to compound of formula (IV).
3. The process of claim 1, wherein alcoholic solvent comprises C1-C4 alcohols, preferably methanol.
4. The process of claim 1, wherein the hydrogenation is carried out at pressure 2 to 15 Kg/sq. cm2, preferably 4 to 5 Kg/sq. cm2.
5. The process of claim 1, wherein the hydrogenation is carried out for 5 to 15 hrs preferably for 6 to 8hrs at a temperature range between 20 to 40°C preferably at 30-35°C.
6. The process of claim 1, compound of formula (IV) is prepared reacting 3-methylamino propionitrile with 2-tetrahydrofuroic acid using CDI (carbonyl diimidazole) as a coupling agent.


7. A process for the preparation of compounds of formula (III) substantially as herein described and illustrated with reference to the accompanying examples


ABSTRACT:
The present invention describes an improved and scalable process for the preparation of tetrahydro-N-[3-(methylamino)propyl]-2-furan carboxamide an important intermediate needed for the synthesis of an antihypertensive drug alfuzosin.