We Claim:
1. A process for the preparation of 4-[N-(5,6-diphenylpyrazin-2-yl)-N-isopropylamino]-l-butanol of formula I:
which comprises:
reacting 2-chloro-5,6-diphenylpyrazine of formula III:
with 4-(isopropylamino)-l-butanol of formula II:
in the presence of an alkali metal bromide, or in the presence of potassium iodide, to produce the compound of formula I or a salt thereof, and optionally purifying and/or recrystallizing the resulting compound of formula I or a salt thereof with a suitable solvent or a mixture of suitable solvents to produce highly pure compound of formula I.
The process as claimed in claim 1, wherein the alkali metal bromide used in the reaction is selected from the group consisting of lithium bromide, sodium bromide and potassium bromide.

3. The process as claimed in claim 2, wherein the alkali metal bromide used in the reaction is potassium bromide.
4. The process as claimed in claim 1, wherein the compound, 4-(isopropylamino)-1-butanol, of formula II is used in the reaction in a ratio of less than about 4 molar equivalents with respect to the quantity 2-chloro-5,6-diphenylpyrazine of formula III in order to ensure a proper course of the reaction; wherein the potassium bromide is used in the reaction in a ratio of less than about 1 molar equivalents with respect to the quantity 2-chloro-5,6-diphenylpyrazine of formula III in order to ensure a proper course of the reaction; and/or wherein the potassium iodide is used in the reaction in a ratio of less than about 0.1 molar equivalents with respect to the quantity 2-chloro-5,6-diphenylpyrazine of formula III in order to ensure a proper course of the reaction.
5. The process as claimed in claim 4, wherein the compound, 4-(isopropylamino)-1-butanol, of formula II is used in the reaction in a ratio of 3.3 molar equivalents with respect to the quantity 2-chloro-5,6-diphenylpyrazine of formula III; wherein the potassium bromide is used in the reaction in a ratio of less than about 0.5 molar equivalents with respect to the quantity 2-chloro-5,6-diphenylpyrazine of formula III; and/or wherein the potassium iodide is used in the reaction in a ratio of less than about 0.05 molar equivalents with respect to the quantity 2-chloro-5,6-diphenylpyrazine of formula III.
6. The process as claimed in claim 1, wherein the reaction is carried out at a temperature of about 20°C to about 200°C; wherein the compound of formula I or a salt thereof is isolated and/or re-crystallized from a suitable solvent by conventional methods such as cooling, seeding, partial removal of the solvent from the solution, by adding an anti-solvent to the solution, evaporation, vacuum distillation, or a combination thereof; and wherein the solvent used for isolating, purifying and/or recrystallizing the compound of formula I is selected from the group consisting of water, an alcohol, a ketone, an ether, an ester, a hydrocarbon, a halogenated hydrocarbon, and mixtures thereof.

7. The process as claimed in claim 6, wherein the reaction is carried out at a temperature of about 100°C to about 180°C; and wherein the solvent used for isolating, purifying and/or recrystallizing the compound of formula I is selected from the group consisting of water, methanol, ethanol, 1-propanol, isopropyl alcohol, acetone, diisopropyl ether, methyl tert-butyl ether, n-hexane, ethyl acetate, butyl acetate, cyclohexane, toluene, xylene, dichloromethane, dichloroethane, chloroform, and mixtures thereof.
8. The process as claimed in claim 1, wherein the compound 4-[N-(5,6-diphenylpyrazin-2-yl)-N-isopropy!amino]-l-butanol of formula I or a salt thereof obtained has a purity of greater than about 90% as measured by HPLC,
9. The process as claimed in claim 8, wherein the compound 4-[N-(5,6-diphenylpyrazin-2-yl)-N-isopropylamino]-l-butanol of formula I or a salt thereof obtained has a purity of greater than about 95% as measured by HPLC.
10. The process as claimed in claim 8, wherein the compound 4-[N-(5,6-diphenylpyrazin-2-yl)-N-isopropylamino]-l-butanol of formula I or a salt thereof obtained has a purity of greater than about 98% as measured by HPLC.