Structural similarity of six pairscapsaicin and zingerone, capsaicin and vanillin, capsaicin and eugenol, zingerone and vanillin, zingerone and eugenol, and vanillin and eugenolis investigated using Tanimoto coefficient and Euclidean distance measurements. It is found that the pair vanillin and eugenol has the highest similarity and the pairs capsaicin and vanillin, and capsaicin and zingerone have the least similarity. The low values of Tanimoto coefficient of all the six pairs show that these natural products have low similarity. Similar pleasant flavor of vanillin and eugenol is addressed by their highest similarity, which shows that compounds with high similarity have similar activity. However, similar hot spicy taste of capsaicin and zingerone with lowest similarity shows that compounds having even lowest similarity may also have similar activity.

The relationship between molecular structure and molecular function or reactivity is integral to chemistry, particularly in the study of organic compounds. However, organic molecules with similar structure may have opposite function or activity (Kubinyi, 1998). Interesting examples of structure-activity relationships and irrelation can be found in two classes of compounds responsible for the sensations normally associated with pungent and pleasant flavors (Hansch et al., 1990; and Martin et al., 2000). The structures of all the four compoundscapsaicin, zingerone, vanillin and eugenol (Figure 1)are remarkably similar (Windholz and Rathway, 1983). Each contains an aromatic ring with two ortho oxygen in an ether and phenol combination. In capsaicin and zingerone, the long chain at 4^th position contains a >CO group in the same position, but in capsaicin, it is an amide group, and in zingerone, it is a ketone group. Capsaicin is the organic compound responsible for its spiciness associated with members of the genus capsicum, which includes most of the red and green peppers. Zingerone is associated with ginger, another hot spice. In vanillin and eugenol, the bond to the ring at position 4 is not a long chain like in zingerone and capsaicin. Vanillin contains aldehyde group at 4 position, and eugenol contains -CH₂-CH=CH₂. Both the compounds give a pleasant flavor in the mouth, which may be due to the activation of the cool receptors. Therefore, a slight change in the structure of organic compounds changes the behavior of the chemical compounds (Wermuth, 1996). This paper tries to investigate the structural similarity of capsaicin, zingerone, vanillin and eugenol using Tanimoto coefficient and Euclidean distance methods (Johnson and Maggiora, 1990; Flower, 1998; Leach and Gileet, 2003; Nikolova and Jaworska, 2003; and Oliver, 2008).

Chemistry Journal, Euclidean Distance Measurements, Euclidean Distance Methods, Chemical Compounds, Zingerone, Structural Fragments, Organic Compounds, Structural Fragments, Molecular Functions, Organic Molecules, Genus Capsicum.