especially at a temperature of 45 55 u00b0 c at normal pressure u2248 10 5 pa or where appropriate at a higher temperature under reduced pressure in the same apparatus for 3 6 days preferably for 5 days as regards the abovementioned preferential modes a mixture ia iia iiia in a weight ratio of about 10 85 5 w w is obtained after step 130 as a function of the purifications undertaken by chromatography the following is obtained after step 140 a mixture ia iia enriched in ia especially an 80 20 w w ia iia mixture or the essentially pure compound of formula ia i e in a purity of greater than or equal to 98 or the more purified compound of formula ia i e in a purity of greater than or equal to 99 5 the compounds of formula i and in particular the novel compounds of formula iv are useful in cosmetics or dermopharmaceutics as agents for improving the texture of the skin when administered topically in the form of a solution a lotion a gel or an emulsion which may be a multiple emulsion for example an o l o or l o l emulsion the compounds of formula i or iv.