Abstract: Compounds of the formula ##STR1## wherein R.sup.1 is a C.sub.1-8 alkyl group or a C.sub.3-7 cycloalkyl group;R.sup.2 is a C.sub.1-6 alkyl group or a C.sub.3-7 cycloalkyl group;R.sup.3 is a hydroxy group or a group of formula --OR.sup.4 or --OCOR.sup.5 whereR.sup.4 is an alkyl or alkenyl group which may contain up to 6 carbon atoms (or such a group substituted by halogen, C.sub.1-6 alkoxy, carboxyl, phenyl, phenyl substituted by nitro, halo, C.sub.1-4 alkoxy or C.sub.1-4 alkyl), a C.sub.3-7 cycloalkyl group, a phenyl group (or such a group substituted by nitro, halo, C.sub.1-4 alkoxy or C.sub.1-4 alkyl), or a carbon-attached 5-7 membered heterocyclic ring in which the hetero atom is selected from nitrogen, oxygen and sulphur, andR.sup.5 is a hydrogen atom or a group R.sup.4 as defined above;and the D-homo analogues thereof having the group --CO.sub.2 R.sup.2 (wherein R.sup.2 is as defined above) at the 17a.beta.