Natural curcuminoids

Further studies are required to unravel this mystery of how the methoxy substitutions and the a, p-unsaturated p-diketone moiety actually influence conformational changes, lipophillicity, electron density distribution, and redox properties of curcuminoids. Correlating these physicochemical properties with the unique pleiotropic effects of curcuminoids is a rewarding exercise. Such studies would definitely provide proper reasoning in understanding these markedly different antioxidant, antitumor, and anti-inflammatory activities of natural curcuminoids from turmeric. 

Ruby, A.J., Kuttan, G., Dinesh Babu, K., Rajasekharan, K.N. and Kuttan, R. (1995) Antitumor and antioxidant activity of natural curcuminoids (Curcuma longa) on iron-induced lipid peroxidation in the rat liver. Food and Chemical Toxicology 32, 279-283. 

Turmeric has been used for the treatment of inflammation for thousands of years in Asian countries. The active constituents were found to be curcuminoids, including curcumin as well as its two natural analogs, demethoxycurcumin and bisdemethoxycurcumin [7], Demethoxycurcumin showed the most potent anti-inflammatory activity among these three natural curcuminoids [8]. According to present studies, curcumin acts by diverse anti-inflammatory mechanisms and at several sites along the inflammation pathway, which are summarized in Fig. (3) [9]. 

Dibenzoylpropane (71) was inactive as an inducer probably due to its lack of an enone moiety. Dibenzoylmethane (69) was quite active with a CD value of 0.8 [iM the keto-enol tautomerization of the /3-diketone can provide the Michael reaction acceptor feature. The three natural curcuminoids showed similar CD values therefore, the methoxy group in the phenyl ring does not greatly affect the potency. However, the CD... 

Direct flourimetric assay for curcumin also poses problems due to the relative flourescence intensities of the three curcuminoids, which are in the ratio of 1 2.2 10.4 at equimolar concentrations (Tonnesen and Karlsen, 1983). Other methods, based on the molar absorptivity by developing coloured complexes with alkalis, strong acids and boric acid, are not consistent (Karasz et al., 1973 Krishnamurthy et al., 1976 Janssen and Gole, 1984) due to the unstable nature of the complex, except with boric acid (Dyrssen et al., 1972 Janssen and Gole, 1984). 

Commercial produce of curcumin contains the three curcuminoids that can be estimated using HPLC (Tonnesen and Karlsen, 1983), but separation is strongly dependent on the chromatographic conditions. Due to the labile nature of the curcuminoids, C18 columns are preferred for HPLC... 

Flynn, D.L., Rafferty, M.F., and Doctor, A.M., Inhibition of 5-hydroxyeicosatet-raenoic acid (5-HETE) formation in intact human neutrophils by naturally occurring diarylheptanoids Inhibitory activities of curcuminoids and yakuchinones, Leukot-rienes Med., 22, 357, 1986. 

Curcuminoids, a group of natural products originally isolated from the Indian spice turmeric, have been known to be potent antioxidant and antiinflammatory agents for many years. Curcuminoids reduce tissue factor (TF) gene expression through the inhibition of the AP-1 and NF-kB transcription factors and thus lead to the loss of angiogenesis initiation [61, 62]. 

Flynn, D.L., and Rafferty, M.F. (1986) Inhibition of 5-Hy-droxy-eicosatetraenoic acid (5-HETE) Formation in Intact Human Neutrophils by Naturally Occurring DiaryUiep-tanoids Inhibitory Activities of Curcuminoids and Yakuchi-nones. Prostaglandins Leukot. Med. 22,357-360. 

One recent example of the sensitisers proposed specifically for NIR luminescent lanthanide ions is azulene, which is a chromophore that has long fascinated photochemists [36]. Its use may have been inspired by scientific curiosity as azulene has only a modest absorption in the red, and more powerful sensitisers do exist. Another recent example is the curcuminoids [51], which are molecules of natural origin (constituents of curcuma or turmeric). The use of naturally occurring chromophores with the NIR luminescent ions is reminiscent of the application of naturally occurring dipicolinic acid and salicylic acid with Eu and Tb, which were among the very first chromophores to be used for the photosensitisation of lanthanide ions. 

Type III polyketide synthases are particularly relevant to this chapter because they catalyze the formation of phenolic compounds. This group of polyketide synthases consists of CHSs, stilbene synthase (STS), and curcuminoid synthase (CUS), which perform decarboxylative condensations between a starter unit, either p-coumaroyl-CoA 19 or cinnamoyl-CoA 18, and an extender unit, malonyl-CoA 10. CHS, STS, and CUS convert the substrate molecules into flavo-noids (Cg-Cs-Cg), stilbenoids 8 (Cg-C2-Cg), and curcuminoids 9 (Cg-C7-C6), respectively [59]. Stilbenoids 8 and curcuminoids 9 are out of the scope of this chapter but possess medicinal properties as well resveratrol is a well-known stilbenoid 8 associated with longevity, and curcumin is a common curcuminoid 9 that is responsible for the yellow color in turmeric and can be utilized as a natural pigment possessing antioxidant and anti-inflammatory properties [60-63]. For an in-depth treatment of plant polyketide production in microbes, the reader is directed to a recent comprehensive review by Boghigian et al. [64]. 

Polyketides with one or two phenylpropa-noid moieties and only one carbon derived from malonyl-Co A are the raspberry aroma/>-hydroxy-phenylbutan-2-one, the curcuminoids of turmeric Curcuma), and phenylphenalenones from Musa dmd Anigozanthos species (Fig. 23). Curcuminoids and phenylphenalenones contain two phenylpropanoid moieties on both sides of the acetate-derived carbon and are therefore classified as diaryIheptanoids. These two groups of natural products are pigments due to their conjugated system of 7i-electrons. Curcuminoids are widely used as spices and also have antiinflammatory, antioxidative, and anti-cancer properties (Joe et al., 2004). 

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