SMALL-MOLECULE IMMUNOSTIMULANTS - SYNTHESIS AND ACTIVITY OF 7,8-DISUBSTITUTED GUANOSINES AND STRUCTURALLY RELATED-COMPOUNDS

A series of 7,8-disubstituted guanosine derivatives was designed and p repared as potential B-cell-selective activators of the humoral immune response. These compounds were evaluated for their ability to ad as B -cell mitogens and to augment the antibody response of B cells to shee p red blood cell (SRBC) challenge (adjuvanticity). In addition, they w ere tested for their ability to stimulate the natural killer (NK) cell response in murine in vitro cell assays. Certain of the compounds dem onstrated in vivo activity when administered either intravenously, sub cutaneously, or orally. Analogues with a medium-length alkyl chain (2- 4 carbons, 5-7) on the 7-position of 7-alkyl-8-oxoguanosines were foun d to be particularly potent. Compounds bearing hydroxyalkyl aminoalkyl , or substituted aminoalkyl substituents on this 7-position were weakl y active. However, benzyl groups, including those substituted with het eroatoms (e.g., p-nitrobenzyl, 14), were active. Oxo, thioxo, and sele no groups on C-8 of the guanosine ring all imparted strong activity, w hereas other larger substituents did not (e.g., N=CN). Stereochemical inversion of the 2'-hydroxyl on the ribose ring in this series, giving arabinose analogue 70, lessened activity. However, removal of the 2'- hydroxyl, either with (64) or without (73) removal of the S'-hydroxyl, resulted in excellent activity and improved solubility; 64 also displ ayed good oral in vivo activity as well. A series of ketals involving the 2',3'-hydroxyls were prepared; certain of the nonpolar ketals (e.g ., 48) were remarkably active, pointing to an ancillary hydrophobic bi nding region that can augment activity. 5'-Phosphate derivative 57 was fairly active, and acyclovir analogue 90 displayed good NK-selective activity: other N-9 sugar mimetics were also active (97-104), although this activity did not carry over into the human B-cell assay. A total of 80 compounds were prepared and evaluated for their immunostimulati ng activity. Within this group, compounds could be divided into those that were active in all three assays, those that displayed some measur e of selectivity for the adjuvanticity assay, and those that preferent ially activated NK responses. Because of its overall biological profil e and ease of synthesis, 7-allyl-8-oxoguanosine (6; loxoribine, RWJ-21 757) was chosen for further development. It is among the most potent c ompounds evaluated in the three biological assays.,