The invention relates to the generation of a library of compounds enriched in agonist and antagonists for members of the G-protein coupled class of receptors (GPCRs).The library contains compounds of general formula (I) wherein y is any integer from 1 to 8; z is any integer from 0 to 8 with the proviso that y and z cannot simultaneously be 1; X is —CO—(Y)k—(R1)n or SO2—(Y)k—(R1)n; k is 0 or 1 Y is a cycloalkyl or polycyloalkyl group (such as an adamantyl, adamantanemethyl, bicyclooctyl, cyclohexyl, cyclopropyl group); or Y is a cycloalkenyl or polycycloalkenyl group; each R1 is independently selected from hydrogen or an alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, alkynyl, alkylamino, alkylaminoalkyl, alkylaminodialkyl, charged alkylaminotrialkyl or charged alkylcarboxylate radical of 1 to 20 carbon atoms; or each R1 is independently selected from fluoro, chloro, bromo, iodo, hydroxy, oxyalkyl, amino, aminoalkyl, aminodialkyl, charged aminotrialkyl, or carboxylate radical; and n is any integer from 1 to m, where m is the maximum number of substitutions permissible on the cyclo-group Y; or alternatively R1 may be selected from a peptido radical, for example having from 1 to 4 peptidic moieties linked together by peptide bonds (for example a peptido radical of 1 to 4 amino acid residues).