68.8 gm (0.122 mole, 95.2% de) R (+) Amlodipine hemi L (+) tartarate mono DMSO solvate prepared as per example 1 was suspended in aqueous isopropanol (90 ml IPA: 250 ml distilled water) and a solution of benzene sulfonic acid (19.35 gm of 90% technical grade, 0.110 mole) in 150 ml water was added. The reaction mixture was stirred for 2 hrs and the slurry was filtered, washed with distilled water, hexane, the solid was dried under vac. at 40° C. till constant weight to give R(+) amlodipine besylate (51.6 gm, 69.4% yield) 99.3 ee by chiral HPLC.
