Disclosed are compounds having the formula ##STR00001## wherein R.sub.2 is hydrogen, a monomeric glycoside or an oligomeric glycoside, R.sub.3 is hydrogen, a monomeric glycoside, an oligomeric glycoside, or a group having the formula ##STR00002## R is a lower alkylene, R' is selected from the group consisting of moieties having the formula ##STR00003## where X=0 or 1, Y=0 or 1, R.sub.1 is hydrogen or a pharmacologically active drug residue, R.sub.8 a pharmacologically active drug residue, R.sub.4, R.sub.5, and R.sub.6 are independently hydrogen, alkyl, aryl, aralkyl, and cycloalkyl or together form a nitrogen-containing ring, and R.sub.7 is hydroxyl or hydroxyalkyl.