An efficient synthesis for the preparation of ((1R,3S)-3-isopropyl-3-{[3-(trifluoromethyl)-7,8-dihydro-1,6-naphthyridin- -6(5H)-yl]carbonyl} cyclopentyl)[(3S,4S)-3-methoxytetrahydro-2H-pyran-4-yl]amine and its succinate salt are provided. The succinate salt is crystalline and has superior properties.