Computational approach to the basicity of a series of alpha1-adrenoceptor ligands in aqueous solution

Substituent effects on the basicity (pKa) of aryl guanidines and 2-(arylimino)imidazolidines: correlations of pH-metric and UV-metric values with predictions from gas-phase ab initio bond lengths

The AIBLHiCoS method accurately predicts the pK_a values of 2-(arylimino)imidazolidines using only a single ab initio bond length.

Aminoalkyl derivatives of guanidine diaromatic minor groove binders with antiprotozoal activity

Considering the strong DNA minor groove binding observed for our previous series of diaromatic symmetric and asymmetric guanidinium and 2-aminoimidazolinium derivatives, we report now the synthesis of new aminoalkyl derivatives of diaromatic guanidines with potential as DNA minor groove binders and antiprotozoal activity. The preparation of these aminoalkyl derivatives (12a-e, 13a-e, 14a-c,e, 15a-e, 16a-e) is presented as well as their affinity for DNA which was evaluated by means of DNA thermal denaturation experiments. Finally, the antiprotozoal activity of most of these aminoalkyl minor groove binders was evaluated in vitro against Trypanosoma brucei rhodesiense (8 compounds) and Plasmodium falciparum (18 compounds). The O-linked derivatives 13c and 14c showed 100 nM activities against P. falciparum, whereas for T. b. rhodesiense all compounds tested showed micromolar activity. Some of the derivatives prepared seem to exert the antimalarial activity by binding to the DNA minor groove whereas other sets of compounds could exert this antimalarial activity by inhibiting the parasite dihydrofolate reductase, for example.

Rapid Determination of Ionization Constants (pK a) by UV Spectroscopy Using 96-Well Microtiter Plates

We have developed a methodology that enables for the rapid measurement of ionization constants (pK a) of series of compounds by UV spectrophotometry. This protocol, which is straightforward to set up, takes advantage of the sensitivity of UV spectroscopy and the throughput enabled by the 96-well microplate (as opposed to the use of 1 cm quartz cuvette). The compounds, in stock solutions in DMSO, are dissolved in several aqueous buffer solutions directly in the microtiter plate, allowing the simultaneous determination of the UV spectra as a function of pH. Further treatment of the data provides the pK a values in a medium-throughput manner. The pK a values of 11 new antitrypanosomal dibasic compounds were determined using this methodology.

Synthesis and antiprotozoal activity of N-alkoxy analogues of the trypanocidal lead compound 4,4'-bis(imidazolinylamino)diphenylamine with improved human blood-brain barrier permeability

To improve the blood-brain barrier permeability of the trypanocidal lead compound 4,4'-bis(imidazolinylamino)diphenylamine (1), five N-alkoxy analogues were synthesized from bis(4-isothiocyanatophenyl)amine and N-alkoxy-N-(2-aminoethyl)-2-nitrobenzenesulfonamides following successive chemical reactions in just one reactor ("one-pot procedure"). This involved: (a) formation of a thiourea intermediate, (b) removal of the amine protecting groups, and (c) intramolecular cyclization. The blood-brain barrier permeability of the compounds determined in vitro by transport assays through the hCMEC/D3 human cell line, a well-known and characterized human cellular blood-brain barrier model, showed that the N-hydroxy analogue 16 had enhanced blood-brain barrier permeability compared with the unsubstituted lead compound. Moreover, this compound displayed low micromolar IC(50) against Trypanosoma brucei rhodesiense and Plasmodium falciparum and moderate activity by intraperitoneal administration in the STIB900 murine model of acute sleeping sickness.