Process for the crystallization of a reverse transcriptase inhibitor using an anti-solvent

摘要

A method for crystallising (-)-6-chloro-4-cyclopropyl ethynyl 4-trifluoromethyl- 1,4-dihydro-2H- 3,1-benzoxazin-2-one of formula (I) comprises dissolving (I) in a solvent, then adding an antisolvent to initiate crystallisation. Also claimed are Forms I, II and III of (I).