Study on umami taste: the MSG taste‐enhancing activity of N2‐alkyl and N2‐alkanoyl‐5′‐guanylic acids having a sulfoxide group inside the N2‐substituent

N2‐alkyl and N2‐alkanoyl derivatives of guanosine 5′‐phosphate bearing a sulfoxide group into the side chain (3b,e; 4b)were synthesized and tested for their synergistic effect with monosodium‐L‐glutamate (MSG), which is the prototypical substance imparting umami taste to savoury‐based foods. Capacities to enhance the taste intensity of MSG were estimated (as γ values) through subjective comparisons of MSG/5′‐nucleotide mixtures in water with appropriate solutions of MSG alone, followed by statistical treatment (Probitmethod) of the resulting responses. The synergistic activity of each sulfoxide toward MSG resulted to be lower than that of the corresponding sulfide.