Compounds of formula I,

wherein R¹ represents H, OH, protected OH or alkoxy; R² represents H; R³ represents O or (H,OH); R⁴ represents methyl, ethyl, propyl or allyl; R⁵ represents OH, protected OH or alkoxy; R⁶ represents OH; R⁷ represents OH, alkoxy or NR⁸R⁹ where R⁸ and R⁹ independently represent H, alkyl or aryl; in addition, R¹ and R² may together represent a second bond between the carbon atoms to which they are attached; and R⁶ and R⁷ may together represent O; and pharmaceutically acceptable salts thereof; are useful inter alia as immunosuppressive agents. The invention also provides the novel compounds of formula I.