Functional isomers, basic properties

It is remarkable that, for histamine, very few compounds of plant origin have been found to have JI (or H2, H3, H4) -blocking properties (Fig. 18.17). a-Mangostin [28] is an example, although remarkably this compound (a competitive H, antagonist) does not carry a basic function. A basic tertiary amino group is also absent in cicletanide, an intriguing compound that has a chiral center and in which the antihistaminic activity resides in the levo isomer (Fig. 18.17). Rocastine and temelastine are two other antihistaminic compounds with unusual structures (Fig. 18.12). 

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