Bitter sweeteners: tetrazole derivatives of arylsulfonylalcanoids--synthesis, structure and comparative study

Within a research project aimed at the design of new sweeteners, the tetrazole moiety was introduced to arylsulfonylalkanoic acids (ASA) as a bioisostere of the carboxyl group. The crystal structures of four newly synthesized tetrazole derivatives and one intermediate product of the reaction were determined in order to explain the bitter taste of these compounds. Three chiral compounds crystallize as racemic mixtures in centrosymmetric space groups of the monoclinic system, whereas the non-chiral compound, with a higher dipole moment, crystallizes in the polar space group Cc. Intermolecular N-H...N hydrogen bonds between tetrazole moieties were observed in all four structures and are compared with the analogous interactions observed in tetrazole derivatives deposited in the Cambridge Structural Database (CSD). Specifically, the typical N1-H...N4 as well as N1-H...N3 interactions, which are less abundant in the CSD, are described. The formation of the latter interaction type can be hypothetically explained by an asymmetry of pi-electron distribution in the tetrazole rings caused by the crystalline environment. Important features of the crystal architecture are the chains of molecules linked by N-H...N bonds. A possible reason for the lack of a sweet taste of the tetrazoles investigated may be the improper position of the tetrazole H atom, and the mutual orientation of the proton donor and acceptor in their molecules. This orientation does not allow the tetrazoles to interact with the sweet-taste receptor in a way similar to that of ASA. The bitter taste of the investigated compounds needs further study.