(2R)-4-Oxo-4-(3-(trifluoromethyl)-5,6-dihydro(1,2,4)triazolo(4,3-a)pyrazin-7(8H)-yl)-1-(2,4,5-trifluorophenyl)butan-2-amine phosphate salt 790712-60-6 MK 0431 MK-0431 Sitagliptin