Patent ID: 7531507

Claim:
A compound of the formula in which R 1 is hydrogen, and R 2 is 2-ethyl-2-methylbut-1-yl, 2,2-diethylbut-1-yl, 2,2-dimethylpent- l-yl or trimethylsilylmethyl, or R 1 is trifluoromethyl, and R 2 is 2,2-dimethyiprop- l-yl, 2,2-dimethylbut- l-yl, 2-ethyl-2-methylbut- l-yl, 2,2-diethylbut- l-yl, 2,2-dimethylpent- l-yl or trimethylsilylmethyl, or one of its salts.