Abstract: The invention provides pharmaceutically active agents of the structural formula ##STR1## wherein n is 1 or 2;X is Z if n is 1 and X is CH.sub.2 Y, CH.sub.2 OH or OH if n is 2;Y is OH if n is 1 and, if n is 2, one of the radicals Y is Z and all other radicals Y are OH; ##STR2## R.sub.11 is a C.sub.3 -C.sub.10 linear or branched alkyl;a C.sub.3 -C.sub.5 linear or branched alkenyl or alkynyl;a C.sub.2 -C.sub.4 linear or branched alkyl substituted by C.sub.1 -C.sub.4 alkoxy, methoxymethoxy, methoxyethoxy, or hydroxyethoxy radicals;C.sub.3-8 cycloalkyl;C.sub.1-3 alkyl substituted with C.sub.3-8 cycloalkyl groups;benzyl;benzyl having 1 to 3 substituents selected from the group consisting of C.sub.1-4 alkyl, C.sub.1-4 alkoxy and cyclopropyl;phenethyl;tetrahydrofurfuryl, furfuryl;morpholinoethyl, morpholinopropyl;piperidinoethyl; andR.sub.12 is a C.sub.1 -C.sub.10 linear or branched alkyl;C.sub.3 -C.sub.5 linear or branched alkenyl or alkynyl;C.sub.1-6 hydroxyalkyl;C.sub.2-4 linear or branched alkyl substituted by C.