Sweet general structure

The sweet-tasting property of aspartyl dipeptide esters has been successfully explained on the basis of the general structures shown in Figure 1 (4). A peptide will taste sweet when it takes... 

Figure 1. General structure for sweet peptides R, = small hydrophobic side chain (1 4 atoms) R2 = larger hydro-phobic side chain (3 6 atoms) (4)...

Figure 2. General structure for sweet amino acids R, is not restricted R2 = H, CH3, or C2Hs (12)...

Continuing their studies on acetal glycosides Tietze and coworkers have made various compounds with general structure (9) (R, alkyl or chloromethyl) by treatment of trimethylsilyl tetra-Q-acetyl-/3-D-glucopyranoside with different ketones and (trimethylsilyl)methyl ether. Related aldehyde methyl acetals (10) have been tested as substrates for -D-glucosidase from sweet almond emulsin. Some of the amino-compounds were particularly... 

The detailed mechanism of its taste-inducing behavior is still unknown. It has been suggested that the miraculin molecule can change the structure of taste cells on the tongue. As a result, the sweet receptors are activated by acids, which are sour in general. This effect remains until the taste buds return to normal. 

An interesting structure-taste study of sweet Ao-vanillyl derivatives has been published <1998JFA4002, 2001QSA3>. It was found that only one enantiomer of each pair proved to be sweet, the other being tasteless. The R-(+)-enantiomer of compound 129 was the sweetest molecule among the variety tested with a relative sweetness, RS, of 20000 (RS = [sucrose]/[compound]). (The 6 -(—(-enantiomer was also tasteless.) As in these Ao-vanillyl derivatives, the difference in the taste of two enantiomers seems to be general and helps in defining receptor-active sites. 

The sweet taste and olfactory responses to a variety of stimuli are examples of chemical senses that utilize protein receptors for initial detection of the stimulus. Most bitter compounds have a hydrophobic component which enables their direct interaction with the cell membrane however, some evidence suggests a protein receptor mechanism. The cooling sensation is treated as a chemesthetic sense, where stimulation takes place at the basal membrane. However, compounds that evoke this response have very specific structural limitations, and most are related to menthol. For purposes of discussion, bitter and cooling sensations will be discussed under generalized receptor mechanisms. 

A first requirement for a substance to produce a taste is that it be water soluble. The relationship between the chemical structure of a compound and its taste is more easily established than that between structure and smell. In general, all acid substances are sour. Sodium chloride and other salts are salty, but as constituent atoms get bigger, a bitter taste develops. Potassium bromide is both salty and bitter, and potassium iodide is predominantly bitter. Sweetness is a property of sugars and related compounds but also of lead acetate, beryllium salts, and many other substances such as the artificial sweeteners saccharin and cyclamate. Bitterness is exhibited by alkaloids such as quinine, picric acid, and heavy metal salts. 

Chloral.—Chloral, or tri-chlor acet-aldehyde, was first prepared by Liebig in 1832 by the chlorination of alcohol as above. It may also be obtained by the direct action of chlorine upon acet-aldehyde. It is an oily liquid with a sweet suffocating odor. It boils at 97.7°. It does not mix with water but on boiling with water it forms a hydrated compound which crystallizes in large clear crystals, readily soluble in water. This is known as chloral hydrate. The structure of chloral hydrate is probably that of an addition product, viz., a, chlorinated di-hydroxy alcohol. In this compound we have an exception to the general rule that two hydroxyl groups can not be linked to the same carbon atom. 

As a general rule, sweeteners are rather hydrophilic and bitter molecules have a predominantly hydrophobic character. Because of the close relationships of sweet and bitter tastes (Shallenberger and Acree, 1971) and the already demonstrated (Mathlouthi et al., 1973) role of water in sweet taste chemo-reception, it was decided to record the FT-IR spectra of caffeine, sucrose, and their mixtures in water and to analyze these spectra with the aim of interpreting the taste modalities of these molecules and the inhibition of caffeine bitterness by sucrose on a structural basis. 

Pyrimidine derivatives do not generally have positive flavor notes and are considered neutral to poor. Some pyrimidine-derived flavors (although not found in tobacco or tobacco smoke) have meaty notes. There are also some pyrimidine flavorants that do possess good flavor potential for tobacco products, for example, 2-methyl-5,7-dihydrothieno[3,4- (]pyrimidine. This compound contains a bicyclic ring structure and has been identified in tobacco. 2-Methyl-5,7-dihydrothieno[3,4- (]pyrimidine is said to have a fresh roasted, sweet nut flavor with a popcorn character (17B22). It is a compound listed by Doull et al. as an ingredient in flavor formulations used by one or more members of the U.S. tobacco industry (1053). 

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