Abstract: The present invention provides crystalline Form S of regadenoson which is substantially free of residual organic solvent and having an X-ray powder diffraction pattern comprising characteristic peak at 10.3, 10.8, 19.0, 21.6 and 25.5±0.2 degrees 2?.

Abstract: A process for the enantioselective synthesis of a sulphoxide of a compound of Formula I or a pharmaceutically acceptable salt thereof in the form of a single enantiomer or in an enantiomerically enriched form wherein R1 to R4 are same or different and selected from the group consisting of hydrogen, C1 to C4 linear or branched alkyl, C1 to C4 linear or branched alkoxy, aryl, aryloxy alkoxy substituted by halogen or alkoxyalkoxy; X is either CH or N, said process comprising oxidizing the prochiral sulphide, compound of Formula II in an organic solvent with an oxidizing agent in presence of titanium (IV)alkoxide, (?)-Diethyl-D-tartrate, C1-C4 alcohol, and water; and optionally converting the compound of formula I into a pharmaceutically acceptable salt.