The invention provides novel compounds or the formula II: wherein R1, R2, R3 and R4 are independently
hydrogen of a group that liberates the free amine
in vivo, for example —CO-
alkyl, preferably —CO—C1-C3
alkyl or pivalate; or —COhaloalkyl, preferably —CO—C1-C3 haloalkyl, most preferably —CO—C1-C3 chloroalkyl; wherein W is: and @ denotes the points of attachment and wherein the ester can be located in either direction; wherein n and m are independently 0-5; wherein one but not both or X and Y can be
nitrogen, or X is C-A and / or Y is C—B; wherein A and B are independently selected from
hydrogen,
alkyl optionally substituted with a
halogen, an
electron donor group such as amino, alkylamino, dialkylamino or hydroxy, or an
electron acceptor group such as nitro, cyano. trihaloalkyl or amido, alkoxy or
halogen; and pharmacologically acceptable salts thereof. Provided that when R1 to R4 are
hydrogen, both X and Y are C—H, n is 1 and —(CH2)n— is attached to the
bridging oxygen of the ester group W, then m cannot be 0 or 1.