Abstract
The molecular recognition features of tolbutamide with four synthetic hosts have been studied by means of NMR titrations, NOESY experiments and Monte Carlo (MC) conformational search. The interaction strength and the most probable structure reveal new insights on the recognition phenomena of this urea derivative in comparison with close related compounds.
Highlights
In preceding papers we have carried out a systematic study of host-guest complexes using urea and biotin related compounds of biological interest as guests, with the final purpose of mimicking the function of natural receptors by means of an iterative optimisation approach [1,2,3]
For tolbutamide, during the titration, a shift in the signals was only observed for the NH proton next to the sulfonyl group while the other NH proton remained unchanged
Trying to get some information about the relative position of p-tolyl and butyl substituents we carried out NOESY experiments. In this fashion we observed weak cross peaks, indicating the closeness of the p-tolyl protons of tolbutamide (1) to the methyl group of host I and of the guest butyl protons to the host pyridine ones. Introducing this information in a new Monte Carlo (MC) search we obtained the structure shown in Figure 4c (-63.4 kJ mol-1), where the hydrogen bonds are formed between the sulfonyl group of the guest and the NH amides of the host, and between the NH bonded to the sulfonyl and the N atom in pyridine, in agreement with experimental data
Summary
In preceding papers we have carried out a systematic study of host-guest complexes using urea and biotin related compounds of biological interest as guests, with the final purpose of mimicking the function of natural receptors by means of an iterative optimisation approach [1,2,3]. Due to the interaction between host II and water, the competitive titration method was needed to determine its Kb value, measuring the NH-CIS of the urea moiety in tolbutamide and the H2O-CIS [2,4].
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