A method of N-alkoxyalkylating ureides according to the invention comprises reacting a ureide of structure I ##STR1## with an alkylating agent of structure III ##STR2## in the presence of a basic catalyst in an aprotic reaction medium. The ureide may be a 5,5-disubstituted barbituric acid, or it may be phenytoin, glutethimide, and ethosuximide. The alkylating agent is an ester of a sulfonic acid. The base may be a hydride or amine. A preferred process comprises N-alkoxyalkylating 5,5-diphenyl-barbituric acid with methoxymethyl methanesulfonate in the presence of di-isopropyl ethyl amine and isolating the resultant N,N'-bismethoxymethyl-5,5-diphenyl-barbituric acid. The invention also contemplates the novel compounds N-methoxymethyl-5,5-diphenylbarbituric acid, N-methoxymethyl ethosuximide, and N-methoxymethyl glutethimide, and a method comprising administering them to a patient.