Vitamin D analogues

A compound of the formula I ##STR8## and derivatives of the compounds of formula I in which one or more hydroxy groups have been transformed into --O-acyl or --O-glycosyl or phosphate ester groups, such masked groups being hydrolyzable in vivo, R being a group of formula II ##STR9## where n is an integer from 1 to 7;

• R.sup.1 and R.sup.2, which may be the same or different, stand for hydrogen, C.sub.1 -C.sub.5 -alkyl, C.sub.3 -C.sub.7 -cycloalkyl, or taken together with the carbon atom (starred in formula II) bearing the group X, R.sup.1 and R.sup.2 can form a C.sub.3 -C.sub.8 carbocyclic ring;
• and X stands for hydrogen or hydroxy.