23 the preferred protective group r 2 for the compound of formula 5 is a benzyl group the preparation of compound 5 r 2 u2550 ch 2 ph is taught in johnson et al at page 2599 however it is not essential that r 2 be a benzyl group other protective groups and protection reactions are described in greene et al r 1 is then removed from the hydrindane diols to yield an epimeric mixture of hydrindane triols 2a and 2b in the preferred case where r 1 is 1 methyl 1 methoxy ethyl the protective group is removed by reaction with dilute aqueous acid preferably sulfuric acid preferably 2a and 2b are separated prior to removal of r 2 in this case the separation is preferably achieved by chromatography on silica gel but can also be accomplished by other known methods r 2 is removed from the hydrindane triol 2a or 2b to produce hydrindane tetrol 3a or 3b respectively alternatively r 2 is removed from the epimeric mixture of 2a and 2b to produce the hydrindane tetrol mixture of 3a and 3b this triol to tetrol conversion is effected by known methods such as those described in the above cited publication of greene et at in the preferred case where r 2 is a benzyl group the hydrindane triol to tetrol conversion can be effected by catalytic hydrogenolysis this procedure is described by greene et at at page 47 at least one diastereoisomer of formula 3 namely compound 3a has been shown to be biologically active as a potent angiostatic agent commonly assigned u s patent application ser no 07 930 635 filed aug 17 1992 the entire contents of which are.