主权项 |
1. A compound of formula (I): wherein: X is selected from the group consisting of alkyl, alkoxyl, O−, and S−; R is selected from the group consisting of substituted or unsubstituted alkyl, heteroalkyl, cycloalkyl, cycloalkylalkyl, cycloheteroalkyl, aryl, heteroaryl, arylalkyl, heteroarylalkyl, multicyclic aliphatic ring systems, multicylic aromatic ring systems, fused aliphatic ring systems, fused aromatic ring systems, and combinations thereof; R1 and R2 are each independently selected from the group consisting of hydrogen and —(═O)-alkyl; and pharmaceutically acceptable salts thereof. |