Patent ID: 8764880

Claim:
A compound defined by formula (I): and salts thereof, wherein: R 1 and R 2 are different and each of Wand R 2 is a hydrocarbyl group containing a total of from 5 to 16 carbon atoms, wherein said hydrocarbyl group is selected from the group consisting of: (a) —CH 2 —CHR 3 R 4 where, R 3 is methyl or ethyl; and R 4 is alkyl; and (b) —CR 3 (CH 2 R 5 )R 6 where, R 3 is methyl or ethyl; and R 5 is H or alkyl, and R 6 is alkyl; or R 5 and R 6 are bonded to form a five or six-membered optionally substituted cycloalkyl ring.