Synthesis, structure and sulfonamide-sulfonimide tautomerism of sulfonamide-1,2,4-triazine derivatives.

Two new 1,2,4-triazine-containing sulfonamide derivatives, namely, 4-bromo-N-(5,6-diphenyl-2H-1,2,4-triazin-3-ylidene)benzenesulfonamide, C21H15BrN4O4S, 3a, and methyl 2-{[(5,6-diphenyl-1,2,4-triazin-3-yl)sulfamoyl]methyl}benzoate, C24H20N4O4S, 3b, which crystallize in the different sulfonimide and sulfonamide tautomeric forms, respectively, were synthesized and characterized by spectroscopic, X-ray diffraction and theoretical calculation methods. Both molecules adopt a very similar conformation of the common part of the structure and the differences occur within the substituents on the sulfonamide group. The amino groups characteristic for the existing tautomeric forms are involved in strong intermolecular N-H...N and N-H...O hydrogen bonds in 3a and 3b, respectively. The Hirshfeld surface analysis showed that H...H contacts constitute a high percentage of the intermolecular interactions. Theoretical calculations at the ab initio DFT/B3LYP/6-311++G(d,p) level showed that the two tautomeric forms observed for 3a and 3b can co-exist in chloroform, ethanol and water solutions, with a distinct predominance of the sulfonamide form; the participation of the sulfonimide form increases with increasing solvent polarity.

The umami taste: from discovery to clinical use.

In the diversity of the flavor world only five basic tastes have been described. The newest one, umami, has been identified about one hundred years ago by Kikunae Ikeda but widely accepted just in the second half of the twentieth century by international scientific world. There are three umami substances: monosodium glutamate (MSG), inosine-5'-monophosphate (IMP), guanylo-5'-monophosphate (GMP). A real breakthrough in umami history concerned the finding about independent receptors for umami: T1R1 and T1R3 (taste receptors type 1 member 1 and member 3). The palatable, delicious taste of umami and its mechanism determined a lot of research studies on this highlight. Umami substances elicit salivary secretion, enhance appetite and increase food palatability. They are desirable to improve the quality of diet. Moreover, the association between umami substances and the suppression of obesity has been found. Studies suggest that umami is engaged in metabolism but also increases satiety and reduces the post-ingestive recovery of hunger.