Methylation of position 8 in the pyridine moiety of the N-(benzyl)-2-hydroxy-4-oxo-4N-pyrido(1,2-a)pyrimidine-3-carboxamide molecule as an attempt to enhance their analgesic properties - I. V. Ukrainets; O. V. Gorokhova; L. V. Sydorenko; S. G. Taran (Journal of organic and pharmaceutical chemistry, 2015)