Potassium 3-anilino-2-phenyl-3H-naphtho[1,2-d]imidazole-5-sulphonate, K[C23H16N3O3S

Abstract

M r= 453.57, monoclinic, P21/c, a= 22.991(2), b=10.128(1), c=9.283(2)A, fl= 9.6.30 (2) °, V= 2148.5 (6) ,/k 3, D x = 1.402 g cm -3, Z=4, T=298K, F(000)=936, CuK0q 2= 1.5418 A, R =0.068 for 2319 reflections. The con- stitution of the molecule is confirmed as that of a naphtho(l,2-d)imidazole, a ring whose structure had not previously been studied by X-ray diffraction analysis. The shape of the main molecular skeleton fits very well the models previously proposed for the active sites of bitter and sweet molecules. Introduction. Neri (1941, and references therein) had shown that the compounds prepared from condensation of various aldehydes with aminonaphthaleneazoben- zenesulphonates were characterized by pronounced sapidant properties. Their taste ranged from sweet to bitter to tasteless, depending on the substituents attached to the main ring system. The structure of this molecular skeleton, however, was described as that of a naphthoisotriazine, contrary to previous evidence (Fisher, 1924) that pointed to the presence of a naphthoimidazole ring in the condensation products of aldehydes with 2-aminonaphthalene-1-azobenzene. We have undertaken the crystal structure analysis of a series of these compounds with the main goal of establishing their consistency with the models of sweet and bitter receptor sites previously proposed in our laboratory (Temussi, Lelj & Tancredi, 1978; Tancredi, Lelj & Temussi, 1979). Experimental. The title compound (PANIK) was prepared through the condensation of benzaldehyde with 1-amino-2-phenylazonaphthalene-4-sulphonic acid (Neri & Grimaldi, 1937) and recrystallized from aqueous alcoholic solutions. Thin colourless needles, Ni-filtered CuK~t radiation, Enraf-Nonius CAD-4 automated single-crystal diffractometer, o>--0 mode, 20 < 120 °. 3132 independent reflections collected and corrected for polarization and Lorentz factors; 813 having I < 3 o (/) were not considered in the refinement. Structure solved by means of the direct method using the program MULTAN (Germain, Main & Woolfson, 1971) included in the Enraf-Nonius structure deter- mination package (SDP) for a PDP-11 computer. The Fourier map, calculated with the set of phases present- ing the highest combined figure of merit given by MULTAN, revealed all non-hydrogen atoms. Refine- ment was achieved by least-squares procedures for all except the H atoms; for these, positions were calculated stereochemically and isotropic thermal factors equal to those of the carrier atoms were assigned; these parameters were kept fixed in the refinement. The refinement, with weights w = 1/o(F) 2, was ended when the maximum shifts in the atomic coordinates were less than ) of the corresponding standard deviations. Atomic scattering factors were calculated according to International Tables for X-ray Crystallography (1974). The final R = 0.068, R w = 0.10.