Field of the Invention
The present invention provides an improved process for the preparation of compound of formula (I),

Background of the Invention
Sumatriptan is chemically designated as 3-[2-(Dimethylamino)ethyl]-N-methyl-lH-indole-5-methanesulfonamide and is being administered as succinate. Sumatriptan succinate tablets are indicated for the acute treatment of migraine attacks with or without aura in adults.
US 4,816,470 & US 5,037,845 claims Sumatriptan succinate and other pharmaceutically acceptable acid addition salt. In view of medicinal importance of Sumatriptan various processes have been reported in literature such as Drugs of the Future 1989, 14(1): 35-39, Joumal of Heterocyclic Chemistry (2000), 53 (3) 665-673, US 4,816,470 & US 5,037,845. Among various processes reported the following general process is most widely used:


wherein Y is a N(Me)2 or a group which can be converted to N(Me)2.
One of the major problems associated in the synthesis of Sumatriptan is the cyclization of compound of formula (IV) to compound of formula (I or la), though this Fischer indole cyclization reaction goes smoothly with polyphosphate ester (PPE) the risk involved is in the preparation of polyphosphate ester which is prepared by utilizing the process given 'Reagents for Organic Synthesis', (Fieser and Fieser, John Wiley and Sons 1967) by reacting phosphorus pentoxide (P2O5), diethylether and chloroform. The large-scale manufacture of PPE is difficult as it involve the usage of diethyl ether, which is extremely flammable and may explode when involved in a fire. This cyclization reaction involves the use of excessive PPE, hence there is need to find out altemative phosphoric acid derivative.
With our research and intense investigation, we have surprisingly found that when the cyclization reaction was carried out in the presence of poly phosphoric acid isopropyl ester prepared according to the present invention the reaction yield better result when compared to prior art.
Objectives of the Invention
The main objective of the present invention is to provide a simple and commercially viable process for the preparation of compound of formula (I).
Another objective of the present invention is to provide a process for preparation of compound of formula (I), to avoid use of highly flammable solvent like diethyl ether, which is difficult to handle in manufacturing plants.
Summary of tlie Invention
Accordingly, the present invention provides a process for the preparation of compound of formula (I),


the said process comprising the steps of
(i) cyclizing the compound of formula (IV) using poly phosphoric acid isopropyl ester in the presence of an halogenated hydrocarbon to produce the compound of formula (la ), wherein the improvements consists of usage of poly phosphoric acid isopropyl ester (which is prepared by reacting P2O5 with IP A) and
(ii) optionally converting the compound of formula (la) into Sumatriptan succinate of formula (I) by conventional methods

wherein Y is a N(Me)2 or a group which can be converted to N(Me)2
Description of the Invention
In an embodiment of the present invention the halogenated hydrocarbon used in step (i) is selected from chloroform, MDC, EDC and the like or mixtures there of.
In yet another embodiment of the present invention the group Y represents N(Me)2 or a groups like NO25 which can be converted into N(Me)2 by conventional process as described in Drugs of the Future 1989, 14(1) :35-39.

In another embodiment of the present invention the starting material of compound of formula (IV) is prepared by utilizing the process given in literature or Drugs of the Future 1989, 14(1): 35-39.
In another embodiment of the present invention the cyclization reagent poly phosphoric acid isopropyl ester is prepared by reacting P2O5 with IPA at high temperature as given in Bull. Chem. Soc. JPN 1961, (34), 99-101.
In another embodiment of the present invention the Sumatriptan obtained can be converted in Sumatriptan succinate by conventional method.
The foregoing technique has been found to be attractive from commercial, technological and ecological perspective, and affords compounds of formula (I) with good quality.
Since the quantity of PFE or poly phosphoric acid isopropyl ester required for cyclization reaction is more, the preparation of Sumatriptan using PFE is difficult as it involves cumbersome quantity of di ethyl ether, where as the preparation poly phosphoric acid isopropyl ester needs only isopropyl alcohol, which makes this invention more commercial potential & utility.
Many other beneficial results can be obtained by applying disclosed invention in a different manner or by modifying the invention within the scope of disclosure.
The present invention is illustrated with the following examples, which should not be construed for limiting the scope of the invention.

Example 1 ; Preparation of Sumatriptan
Preparation of 4-[2-[4-(Dimethylamino)butylidene]hydrazine]-N-methyl benzene methane sulphonamide (IV wherein Y = NMe2);
To a stirred suspension of 4- hydrazino-N-methyl benzene methane sulphonamide (100 gms)in aqueous hydrochloric acid solution(200 ml), 4,4-Diethoxy-N,N-dimethyl butanamine(100 gms) was added slowly. The resultant reaction mixture was stirred at 25*^0 and a pH range in the of 0.9 - 1.5 till completion of reaction. After completion of reaction, pH was adjusted using sodium Carbonate to 8.3the product (IV) obtained was extracted using Chloroform. The Chloroform layer distilled till moisture content become 0.1%
To the Chloroform layer(150 ml) contains compound of formula (IV) poly phosphoric acid isopropyl ester(65 gms) was added slowly at 0-5°C. The reaction mixture was warmed to 35-40°C and stirred till completion of reaction. After completion of reaction the product was extracted with water. The aqueous layer pH was adjusted 10.5 using potassium carbonate(65-70 gms); again the product was extracted using ethyl acetate(2x750 ml). The Ethyl acetate was distilled out to leave foam, to this acetonitrile(80 ml) was added to yield crude Sumatriptan (I), which was again purified using acetone(400 ml) ml to yield pure Sumatriptan base(16 gms).
Preparation of Sumatriptan Succinate:
To the clear solution of Sumatriptan(16 gms) in Methanol (240 ml), Succinic acid(2.5 gms) was added and the resultant mixture was heated to reflux. The methanol was distilled out partially and the remaining reaction mixture was cooled to get Sumatriptan Succinate in pure form (18 gms), which is filtered and dried.

wherein the improvements consists of usage of poly phosphoric acid isopropyl ester and
(ii) optionally converting the compound of formula (la) into Sumatriptan succinate of formula (I) by conventional methods
2. A process as claimed in claim 1, wherein the halogenated hydrocarbon used in step (i) is selected from chloroform, MDC, EDC, preferably chloroform.

3. A process as claimed in claim 1, wherein the poly phosphoric acid isopropyl ester is prepared by reacting P2O5 with IPA.
3. An improved process for the preparation of Sumatriptan of formula (I) which comprises cyclizing the compound of formula (IV)

using poly phosphoric acid isopropyl ester in the presence of a halogenated hydrocarbon to produce Sumatriptan of formula (I),

(I) wherein the improvements consists of usage of poly phosphoric acid isopropyl ester.