1,4-Dihydropyrido(2,3-b)pyrazine-2,3-dione 2067-84-7 EINECS 218-186-9 NSC 91561 Pyrido(2,3-b)pyrazine-2,3-diol Pyrido(2,3-b)pyrazine-2,3-dione, 1,4-dihydro- (8CI)(9CI)