The present invention relates to a compound according to formula (I) wherein R1 represents optionally substituted heteroaryl, and pharmaceutically acceptable salts, hydrates, solvates or pharmaceutically acceptable and physiologically cleavable esters thereof. The invention relates further to intermediates for the preparation of said compounds, to said compounds for use in therapy, to pharmaceutical compositions comprising said compounds, to methods of treating diseases, e.g. diseases associated with hyperplasia, neoplasia or dysplasia, with said compounds, to methods of treatment of cosmetic indications with said compounds, and to the use of said compounds in the manufacture of medicaments.
