5-(Sulfonyl)oxy-tryptamines and ethylamino side chain restricted derivatives. Structure–affinity relationships for h5-HT1B and h5-HT1D receptors Original Research Article

A number of sulfonic acid ester derivatives of serotonin (5-hydroxytryptamine; 5-HT; 1) were prepared and their affinities are compared to that of the reference compound 5-[[(trifluoromethyl)sulfonyl]oxy]-tryptamine (8b). The structure–affinity relationship (SAFIR) is discussed in terms of in vitro binding for cloned human h5-HT1A, h5-HT1B and h5-HT1D receptors. All tryptamine derivatives exhibited the best affinities for h5-HT1D receptors but still, these were comparatively lower than that of compound 8b. 5-Tosylated tryptamine 11b (Ki=6 nM) and the sulfamate derivatives 13b and 14b (Ki=7 and 11 nM, respectively) were found to have the highest affinities for the h5-HT1D receptor. Other tryptamine derivatives displayed moderate binding for h5-HT1A and h5-HT1B receptors, along with Ki values ranging from 14–20 nM for the h5-HT1D sites. In addition, the syntheses of two alkylamino side chain restricted derivatives are described. 3-Amino-6-[[(trifluoromethyl)sulfonyl]oxy]-1,2,3,4-tetrahydrocarbazole 21, as well as 4-[5-[[(trifluoromethyl)sulfonyl]oxy]-1H-indol-3-yl]piperidines 24 and 25, induced a shift in selectivity in favor of the h5-HT1B receptor. The relatively longer distance between the basic amine and a hydrogen-bond accepting oxygen in 21, 24 and 25 as compared to the non-restricted tryptamines, is likely responsible for this observation.