Compounds for preparing immunological adjuvant

A compound of formula (16):

• wherein:
• n is 0 or 1;
• R1a is a C1-C6 alkyl group, a C3-C6 alkenyl group, a C3-C6 alkynyl group, a phosphite oxygen protecting group, or a phosphate oxygen protecting group trimethylsilyl ether, triethylsilylether, triisopropylsilyl ether, t-butyldimethylsilyl ether, t-butyldiphenyl silyl ether, 2-trimethylsilylprop-2-enyl, 2-(trimethylsilyl)ethyl, or trimethylsilyl;
• in each occurrence of R2a and R2c, one of R2a and R2c is H and the other is selected from the group consisting of tert-butyloxycarbonyl (Boc), fluorenylmethyloxycarbonyl(Fmoc), 2,2,2-trichloroethoxycarbonyl (TROC), trimethylsilylethyloxycarbonyl (TMS-ethyloxycarbonyl), cyanoethyloxycarbonyl, allyloxycarbonyl, tetrachlorophthalimide, —C(O)ORx and —C(O)CH2C(O)R6;
• or R2a and R2c taken together are a divalent nitrogen protecting group;
• R4 is a C5-C12 alkyl group or a C5-C12 alkenyl group;
• R5 and R6 are independently a C5-C15 alkyl group or a C5-C15 alkenyl group;
• and
• Rx is a substituted or unsubstituted lower alkyl;
• or a salt thereof.