Patent ID: 7615525

Claim:
A compound of the formula I in which the moieties R 1 -R 13 are independently selected from the following moieties: R 1 , R 5 , R 6 , R 8 , R 11 —H, methyl, ethyl, propyl, isopropyl; R 3 —H, methyl, ethyl, propyl, isopropyl, vinyl; R 4 —H, methyl, ethyl; R 2 , R 7 , R 9 —H, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl; R 10 —H, methyl, ethyl, propyl, isopropyl, t-butyl; R 12 , R 13 —H, C 1-6 linear or branched alkyl; or R 4 and R 11 together with the carbon atoms to which they are attached form a 5- or a 6-membered cycloalkyl ring; or R 6 and R 7 together with the carbon atoms to which they are attached form a cycloalkyl ring having 3, 4, 5 or 6 members.