| abstract |
The invention concerns a compound having structural formula (I), wherein R<1> represents H, substituted or unsubstituted alkyl or acyl groups, especially methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert. Butyl; X = halogen or OH; R<2> represents H, substituted or unsubstituted alkyl or acyl groups, especially methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert. butyl, halogen or OH; R<3> represents H, substituted or unsubstituted alkyl or acyl groups, especially methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert. butyl, halogen or OH; R<4> represents H, substituted or unsubstituted alkyl or acyl groups, especially methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert. butyl or is a metal radical, especially an alkali cation. |