abstract |
A compound of the formula: ** Formula ** wherein: R1a and R1b are independently selected from H and F, provided that at least one of R1a and R1b is F, R2 is selected from the group consisting of optionally substituted benzyl and optionally substituted C1-C6 alkyl, and Het is an optionally substituted five or six membered heterocycle comprising at least one N, O or S atom. |