L-erythrosyl nucleosides

A compound of the formula:

• ##STR5## or a pharmaceutically acceptable salt thereof, wherein:
• R.sub.1 and R.sub.2 are independently H, mono- or di-halogen, or OR.sub.5 wherein R.sub.5 is H, COR.sub.6, P(O).sub.n R.sub.7 R.sub.8 wherein R.sub.6 is substituted or unsubstituted alkyl of 1-5 carbon atoms or a substituted or unsubstituted aromatic ring structure, R.sub.7 and R.sub.8 are each H or alkyl of 1-5 carbon atoms and n is 2 or 3;
• R.sub.3 and R.sub.4 are independently B, H or OR.sub.9 where R.sub.9 is H, COR.sub.10, P(O).sub.m R.sub.11 R.sub.12 wherein R.sub.10 is substituted or unsubstituted alkyl of 1-5 carbon atoms or a substituted or unsubstituted aromatic ring structure and R.sub.11 and R.sub.12 are each H or alkyl of 1-5 carbon atoms and m is 2 or 3;
• and
• B is selected from a naturally-occurring nucleobase or a substituted nucleobase wherein said substitutions are selected from the group consisting of H, halogen, C1-C6 alkyl, C2-C6 alkenyl, C1-C6 alkoxy, C3-C6 cycloalkyl-C1-C6 alkoxy, C3-C8 cycloalkyloxy, C3-C8 cycloalkylthio, C1-C6 alkylthio, a substituted amino group, an aryl, aralkyl, aryloxy, aralkoxy, arylthio, aralkylthio, a heterocyclic ring and an amino group, provided that when the base is a pyrimidine, the atom at position 4 of the base can be sulfur and further provided that when the base is a purine, the atom at position 6 of the base may be sulfur;
• provided that:
• only one of R.sub.3 or R.sub.4 can be B;
• when R.sub.4 is B and B is 5-fluorouracil, then R.sub.1 and R.sub.2 cannot both be H;
• when R.sub.1 and R.sub.2 are each OH, R.sub.3 is H and R.sub.4 is B, then B cannot be A;
• and when R.sub.1 and R.sub.2 are each OH, R.sub.4 is H and R.sub.3 is B, then B cannot be A.