Vildagliptin Impurity D Catalogue V67034 CAS 1789703-36-1 M.W 304.38 M.F C17H24N2O3 Specifications FAQs (3-Hydroxytricyclo[3.3.1.13,7]dec-2-yl)-1-oxo-hexahydropyrrolo[1,2-a]pyrazin-4(1H)-one