Both capsicum and ginger are hot spices. Capsaicin present in the capsicum is responsible for its spiciness. The characteristic odor and flavor of ginger is due to the presence of zingerone. Vanillin is the principal compound responsible for flavor and aroma in vanilla. Eugenol has applications in perfumeries, flavorings and in medicine as a local antiseptic and anesthetic. The structures of all the four substances look remarkably similar. According to similarity property principle, structurally similar molecules tend to have similar properties. Similar molecules exert similar biological activities. However, there is no hard and fast rule that the similar chemical structure compounds will have similar functions. There are several similar chemical structure compounds which demonstrate that chemically similar compounds may have significantly different biological actions and activities. Structure similarity study of capsaicin and vanillin, capsaicin and eugenol, zingerone and vanillin, zingerone and eugenol, vanillin and eugenol, and capsaicin and zingerone investigated using Tanimoto Coefficient (TC) and Euclidean Distance (ED) measurements showed that vanillin and eugenol have highest similarity, while capsaicin and vanillin have least similarity. To investigate TC and ED measurements, first all the four molecules are decomposed into smaller fragments. A dictionary of the fragments is prepared. Using this dictionary 2D fingerprints are formed and using the fingerprints TC and ED are quantified by a program code implemented in MATLAB R2007b.

The study of relationship between molecular structure and molecular function or reactivity of the substances (particularly of the organic compounds) is integral to chemistry. According to similar property principle (Johnson and Maggiora, 1990), "the structurally similar molecules tend to have similar properties and similar molecules exert similar biological activities". Medicinal chemists have made use of this concept to modify the structures of biologically active compounds. However, similarity and diversity of chemical structures cannot be defined in an objective manner. Several structure-activity relationship studies demonstrate that chemically similar compounds may have significantly different biological actions and activities (Hansch et al., 1990; Dean, 1995; Wolff, 1995; and Wermuth, 1996). Sometimes, similar organic structured molecules may even have opposite function or activity.

Interesting example of structure-activity relationships and irrelation can be found in two classes of compounds responsible for the sensation that are normally associated with pungent and pleasant flavor. The structures of all the four substances written below look remarkably similar. Each contains an aromatic ring with two ortho oxygen in ether-phenol combination. In the compound capsaicin and zingerone long chain at fourth position contains a >CO group in the same position but capsaicin is an amide and zingerone is a ketone. In the substances vanillin and eugenol bond to the ring at position four is not a long chain like in the substances. The vanallin contains aldehyde group at four positions. Eugenol contains –CH₂–CH=CH₂. Both the compounds give pleasant flavor in the mouth which may be associated with the activation of the cool receptors. Therefore slight change in the structure of organic compounds changes the behavior of the chemical substances. Herein, is described the investigation of the chemical similarity of capsaicin, zingerone, vanillin and eugenol using Tanimoto Coefficient (TC) and Euclidean Distance (ED) methods (Flower, 1998; Willett et al., 1998; and Oliver, 2008). The TC is directly dependent upon the number of bits in common. The presence of common molecular features increases the value of TC. But ED effectively regards a common absence of feature as evidence of similarity. A consequence of this difference is that small molecules have lower similarity values when using TC. Smaller molecules can appear to be closer together when using the ED, which does take into account the absence of common features (Willett et al., 1998).

Information Technology Journal, Natural Products, Euclidean Distance Methods, Organic Compounds, Pythagorean Distance, Cchemical Structure Compounds, Biological Activities, Medicinal Chemists, Structural Fragments, Euclidean Distance Measurements.