Structure capsaicinoids

These compounds are responsible for the hotness in chillis (hot peppers), the degree of pungency being related to the length of the acid side chain. Total capsaicinoid content is around 1 % of the dried fruit, the majority of which is usually capsaicin. Structurally, capsaicinoids are vanillyl-acyl amide analogues (Tucker and Debaggio 2000). 

Capsaicin, also known as N-Vanillyl-8-methyl-6-(E)-noneamide, is the most pungent of the group of compounds called capsaicinoids It is a common ingredient in varieties of pepper such as habanero, Thai, tabasco, cayenne etc. One target with which capsaicin interacts is the capsaicin receptor, an ion channel belonging to the superfamily of TRP channels. Because of the structural relation to other TRP channels and because the vanilloid moiety is an essential component of capsaicin, the capsaicin receptor is also called TRPVI or vanilloid receptor (VR1). It is involved in heat and pain perception. 

The primary chemicals of interest in chilies are capsaicinoids, namely capsaicin (0.02%) and dihydrocapsaicin (figure 8.11). Also found are flavonoids, carotenoids (capsanthin), steroid saponins (capsicidin), and ascorbic acid or vitamin C (0.2%). Capsaicin has a vanilloid chemical structure. Mechanisms of Action... 

Stored under continuous light, and placental extracts from non-pungent fruit could synthesize capsaicinoids if vanillylamine and isocapric acid are provided. Together, these results raise the possibility that the gene product at Pml is a regulatory gene or a structural gene upstream in either the phenylpropanoid pathway or the branched chain fatty acid pathway and not capsaicinoid synthase. 

Suzuki T, Fujiwake H, Iwai K (1980) Intracellular localization of capsaicin and its analogues, capsaicinoid, in Capsicum fruit. 1. Microscopic investigation of the structure of the placenta of Capsicum annuum var. annuum cv. Karayatsubusa. Plant Cell Physiol 21 839-853 Ohta Y (1963) Physiological and genetical studies on the pungency of Capsicum IV. Secretory organ, receptacles and distribution of capsaicin in the Capsicum fruits. Jap J Breed 12 179-183... 

In all these protocols, chemoselective amidation of vanillamine with NMA was achieved in satisfactory yield (about 80 %) by activation of the add to its corresponding chloride, followed by condensation with free vanillamine. Free vanillamine is much less stable than its corresponding chloride, and, owing to its polarity, it is difficult to extrad quantitatively from water solution, with loss of about 20 % of the product routinely observed in the desalification step [59]. Furthermore, the preparation of chlorides from polyunsaturated fatty acids is not trivial, and therefore alternative coupling protocols were investigated in a series of systematic studies dedicated to the structure-adivity relationships of capsaicinoids. 

Various studies have evidenced strict structure-activity relationships within capsaicinoids, and the existence of these relationships provided a hint for the existence of a specific receptor [72]. On the other hand, different end-points have been used in the literature, and it is difficult to draw a consistent picture. In vivo assays such as pungency and ocular irritancy, functional assays such as the measurement of calcium currents in dorsal root ganglion neurons, and receptor assays such as the displacement of labeled RTX have been used. The relationship between the results of these assays is, at best, approximate [75]. 

Reilly CA and Yost GS (2005). Structural and enzymatic parameters that determine alkyl dehy-drogenation/hydroxylation of capsaicinoids by cytochrome p450 enzymes. Drug Metab Dispos, 33, 530-536. 

Chilli peppers contain capsaicin and a few other molecules with similar structures, known as capsaicinoids. Capsaicin and the very similar dihydrocapsaicin together make up some 90% of the capsaicinoid content of a chilli, with capsaicin accounting for some 70% it makes up around 0.14% of the mass of a chilli. 

Capsaicin is the hottest other capsaicinoids have similar structures but are not quite as hot . The hotness scale is measured in Scoville units (named after the inventor, Wilbur Scoville). Pure capsaicin... 

FIGURE 11.10 Chemical structures of the most common capsaicinoids found in OC. 

FIGURE 13 Structural similarities between capsaicinoids and vanillin. 

Examination of the capsaicinoid stmctures reveals a common feature, namely an aromatic ring possessing a methoxy and hydroxyl substituents. Because of the similarity of these structures to the natural substance vanilhn (Fig. 13), these pungent substances are collectively known as vanilloids [74]. 

An exhaustive analysis of the structural implications of capsaicinoids on their metabolism by P450 enzymes and how they contribute to both detoxification and bioactivation processes in humans has been proposed. CycUzation, dehydrogenation to afford the terminal diene and imides, oxidatiOTi at the end of the carbon chain to render primary and tertiary alcohols, and demethylation and aromatic hydroxylation, are typical reactions in these processes, yielding metabolites with limited pharmacological and toxicological effects via reduction in their affinity for TRPVl [148]. 

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