There are described compounds of formula I, ##STR1## wherein R.sup.1 represents H or OH; R.sup.2 represents H; in addition, R.sup.1 and R.sup.2 may together represent a second carbon-carbon bond between the carbon atoms to which they are attached; R.sup.3 represents OH or OCH.sub.3 ; X represents O or (H,OH); and Y represents O or N--OR.sup.4, in which R.sup.4 represents H or alkyl C.sub.1-6 ; provided that when R.sup.1 is OH, R.sup.2 is H and X is O, then Y does not represent O.Processes for their production and compositions containing them, eg. for use as immunosuppressive agents, are also described.