Erfolgreicher Versuch einer Hhlendetektion mit Georadar (GPR)

The present invention provides compounds of general formula (III) (III) [wherein R is an amino or protected amino group; R2a is a straight or branched chain alkyl group containing from 1 to 4 carbon atoms, an allyl, but-2-enyl or but-3-enyl group, or is a group of formula (wherein each of R3 and R4 is independently a hydrogen atom or a methyl or ethyl group, or R3 and R4 taken together with the carbon atom to which they are attached may be a cycloalkylidene group containing from 3 to 5 carbon atoms, and R5 is a hydrogen atom or a carboxyl blocking group); Y represents a 1-methyl-1-pyrrolidinium group and R7 represents the group -COO- or -COOR6, where R6 is a hydrogen atom or a carboxyl blocking group] and salts thereof.