3 ch 2 ch 3 preferably group r 2 is phenyl and preferably the silicate is silica gel preferably a solution of crude compound 3 as defined above is brought into contact with a silicate after a period of time sufficient for allowing adsorption the liquid phase is separated from the silicate appropriate periods of time are from 1 min to 24 h preferably from 5 min to 12 h removal of the liquid phase can be achieved using various techniques such as filtration centrifugation evaporation and the like suitable solvent are any solvents in which the substrate dissolves with a preference for alcohols such as for example ethanol and methanol elution from the silicate can be effected by applying solvents or solvent mixtures preferably a solvent mixture is applied comprising an alcohol an ester and water in a first embodiment the mixture of silicate and crude compound 3 obtained above is applied to a column of silicate prior to elution with solvent or solvent mixture it was found that this increases separation between the various components notably compounds 3 and 5 still more surprisingly in a second embodiment it was found that in compound 3 with r 1 and r 2 as defined above but with x is h h prepared as described for instance in j.