The invention provides pyrimidine compounds represented by the formula (1) and their pharmaceutically acceptable salts:wherein X, R1, R2, R3, R4, R5, R6, Y1, Y2, L and m are as defined herein, useful as a vaccine adjuvant.本發明提供一種作為疫苗佐劑有用之式(1):(式中,X、R1、R2、R3、R4、R5、R6、Y1、Y2、L及m如說明書中所定義)所表示之化合物及其製藥上所容許之鹽。