Curcuminoids structure

FIGURE 5.2.1 Chemical structures of curcuminoid pigments and some aroma compounds of turmeric. 

Antioxidant capacities of common individual curcuminoids were determined in vitro by phosphomolybdenum and linoleic acid peroxidation methods. Antioxidant capacities expressed as ascorbic acid equivalents (pmol/g) were 3099 for curcumin, 2833 for demethoxycurcumin, and 2677 for bisdemethoxycurcumin at concentrations of 50 ppm. The same order of antioxidant activity (curcumin > demethoxycurcumin > bisdemethoxycurcumin) was observed when compared with BHT (buty-lated hydroxyl toluene) in linoleic peroxidation tests. The antioxidant activity of curcumin in the presence of ethyl linoleate was demonstrated and six reaction products were identified and structurally characterized. The mechanism proposed for this activity consisted of an oxidative coupling reaction at the 3 position of the curcumin with the lipid and a subsequent intramolecular Diels-Alder reaction. ... 

Simon A, Allais DP, Duroux JL, Basly JP, Durand-Fontanier S, Delage C. 1998. Inhibitory effect of curcuminoids on MCF-7 cell proliferation and structure-activity relationships. Cancer Leu 129 111-116. 

The main coloured substances in the rhizomes are curcumin (1,7-bis (4-hydroxy-3-methoxy prenyl)-l, 6-heptadiene-3, 5-dione) and two related demethoxy compounds, demethoxy curcumin and fczs-demethoxy curcumin, which belong to the group of diarylheptanoids (see Fig. 6.1). Besides these three forms of curcuminoids, three minor constituents have also been isolated (Srinivasan, 1952) that are supposed to be geometrical isomers of curcumin. One of these is assumed to be a cis-trans geometrical isomer of curcumin based on its UV spectrum, lower m.p. and lower stability when compared with curcumin, which has a trans-trans configuration. Heller (1914) isolated an isomer of curcumin with a diketone structure. 

A new curcuminoid, cyclocurcumin, possessing nematocidal activity, was isolated from the mother liquor by repeated purification as a yellow gum (Kiuchi et al, 1993). It had the same molecular formula as curcumin, but differed in structure by an intramolecular Michael addition of the enol-oxygen to the enone group. The chemical structures of these components are given in Fig. 6.2. 

An interesting property of curcuminoids is their anti-HIV effect, which has been demonstrated during in vitro and in vivo experiments, including a limited number of human studies (Lin et al., 1994). HIV infection is characterized by a complex command system, the structural part of which is called Tong terminal repeat (LTR), which results in virus activation or inactivation. Drugs that interfere with LTR may be of potential therapeutic value in delaying active HIV infection and the progression of AIDS. Curcumin has been found to inhibit activation of the LTR and to decrease HIV replication effectively (Li et al., 1993). 

Figure 6.3 Chemical structures of curcuminoids, resveratrol, and gallates.

FIGURE 7.3. Structures of curcuminoids and coumarins purified using rapid fiash chromatography [92,94]. 

Masuda T., Jitoe A. Antioxidative and antiinflamatory compounds from tropical gingers isolation, structure determination, and activities of cassumunins A, B, and C, new complex curcuminoids from Zingiber cassumunar. Journal of Agricultural and Food Chemistry, 42 1850-1856 (1994). 

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