Patent ID: 8129531

Claim:
A compound of formula (I) or (II) wherein R 1 , R 2 and G independently from each other are R 1 is H, C 1 -C 20 -alkyl, C 1 -C 20 -cycloalkyl, C 1 -C 20 -aryl, or C 1 -C 20 -aralkyl, R 2 is C 1 -C 20 -alkyl, C 1 -C 20 -cycloalkyl, C 1 -C 20 -aryl, or C 1 -C 20 -aralkyl, and G is —O—, —CH 2 O—, —CH 2 —, —(CH 2 ) 2 —, —(CH 2 ) 3 —, —(CH 2 ) 4 —, —(CH 2 ) 5 —, —(CH 2 ) 6 —, —(CH 2 ) 7 —, or —(CH 2 ) 8 —.