Guanosine Derivatives as Immunostimulants. Discovery of Loxoribine.

Abstract 7-Allyl-8-oxoguanosine (loxoribine, 5) was selected from a series of guanosine derivatives for further evaluation as an immunostimulant. Numerous related analogs were also synthesized and evaluated: 2′,3′-ketals of 5 are particularly interesting because they are active, apparently without being cleaved to the free nucleoside.