Patent ID: 7491712

Claim:
A compound having formula I wherein R 1 is C 1-6 alkoxy; R 2 is hydrogen, OH or methyl-OH or together with R 3 form a methylene —(═CH 2 )— or an oxo (═O); R 3 is hydrogen, OH or methyl-OH or together with R 2 form a methylene —(═CH 2 )— or an oxo (═O); R 4 is hydrogen, OH, O-acyl, O—C 1-6 alkylsilyl or C 1-6 alkyloxy-C 1-6 alkyl; R 5 is C 1-6 alkyl, C 1-6 alkyloxy-C 1-6 alkyl or aryl; and R 6 is C 1-6 alkyl, C 1-6 alkyloxy-C 1-6 alkyl or aryl.