Compounds of the formula ##STR1## in which R.sup.1 represents an optionally substituted, straight-chain or branched, saturated, monounsaturated or polyunsaturated alkyl radical, an optionally substituted, saturated or one- or polyunsaturated cycloalkyl radical or an optionally substituted aryl radical or aralkyl radical,X represents CH.sub.2, O, S, NH or N-alkyl with up to 20 C atoms,R.sup.2 has the meaning of R.sup.1, and can represent hydrogen if X denotes CH.sub.2, the radicals R.sup.3 independently of one another represent hydrogen, an acyl radical or alkyl radical with in each case up to 20 C atoms, a silyl radical and/or a phosphoric acid or phosphoric acid ester radical andR.sup.4 denotes hydrogen, methyl or --CH.sub.2 --OR.sup.3, with the proviso that one of the radicals R.sup.3 always represents a phosphoric acid or phosphoric acid ester radical, which stimulate a patient's immune system and are thereby effective in combating viral disease and bacterial infection.