Esters antioxidant activity

Long-chain esters of pentaerythritol have been prepared by a variety of methods. The tetranonanoate is made by treatment of methyl nonanoate [7289-51-2] and pentaerythritol at elevated temperatures using sodium phenoxide alone, or titanium tetrapropoxide in xylene (12). PhenoHc esters having good antioxidant activity have been synthesized by reaction of phenols or long-chain aUphatic acids and pentaerythritol or trimethyl olpropane (13). 

Divalent Sulfur Derivatives. A diaLkyl ester of thiodipropionic acid (16) is capable of decomposing at least 20 moles of hydroperoxide (17). Some of the reactions contributing to the antioxidant activity of these compounds are shown in Figure 3. 

There is the often-overlooked group of polyphenols containing the derivatives of hydro-xycinnamic and hydroxybenzoic acids such as caffeic, chlorogenic, and gallic acids (Figure 29.8), which occur in food and exhibit certain antioxidant activity. For example, some caffeic acid esters isolated from propolis from honeybee hives showed antiinflammatory... 

A fully aromatic pyrazole derivative, FPL 62064 (107), also inhibited 5-LO in the usual cellular and enzymatic systems, but was not seleetive with respect to CO [276]. This compound inhibited AAE (ED50 values against PGE2, LTC4, and oedema were 3.7,28.3, and 40.8 //g/ear, respeetively), guinea-pig UV-induced erythema and phorbol ester ear oedema. The aetivi-ty for FPL 62064 was also attributed to its antioxidant activity presumably in this case the 4-methoxyaniline group is the redox-active moiety. 

Matsufuji H, Nakamura H, Chino M, Takeda M (1998) Antioxidant activity of capsanthin and the fatty acid esters in paprika (Capsicum annuum). J Agric Food Chem 46 3468-3472 WaU MM, WaddeU CA, Bosland PW (2001) Variation in P-carotene and total carotenoid content in fruits of Capsicum. HortScience 36 746-749... 

Terminalia catappa, Combretaceae, commonly used in the folk medicine in Taiwan, contains several C-glycosylflavones, two of them galloyl esters of vitexin and isovitexin. The isolated compounds were tested for antioxidative activity on Cu " /02-induced low-density lipoprotein peroxidation. IC50 values were 2.1 pM for vitexin derivatives and 4.5 pM for isovitexin derivatives compared to 4.0 pM for probucol chosen as positive control. 

In addition to their direct antioxidant activity, ferulic acid and its ester derivatives have also been shown to act as indirect antioxidants, that is, to induce cytoprotective (phase 2) enzymes [Dinkova-Kostova et al., 1998 Dinkova-Kostova, 2002], Similarly to curumin, ferulic acid derivatives also... 

Sultana R, Ravagna A, Mohmmad-Abdul H, Calabrese V, Butterfield DA. 2005. Ferulic acid ethyl ester protects neurons against amyloid beta-peptide(l-42)-induced oxidative stress and neurotoxicity Relationship to antioxidant activity. J Neurochem 92 749-758. 

Much less is known on the antioxidant activity of tocotrienols than tocopherols. Tocotrienols were shown to have similar reactivities to peroxyl radicals and antioxidant activities than tocopherols in solution and membranes (Yoshida et ah, 2003) also, in general, y-tocotrienol was a better antioxidant than a-tocotrienol, and tocotrienols were better than tocopherols in oil systems (Seppanen et ah, 2010). Recently, Muller et ah (2010) conducted a comparative study to investigate the four tocopherols, four tocotrienols, and a-tocopheryl acetate on their antioxidant activities in five different popular in vitro assays (FRAP, a-TEAC, DPPH, ORAC, and CL), which were adapted to nonpolar antioxidants. Most notably, they found that a-tocopheryl acetate, a popular ingredient in supplements, had no significant antioxidant activity in vitro. However, once ingested, tocol esters are hydrolyzed and antioxidant activities are retained. Overall, the eight tocols performed similarly in the five assays. The authors concluded that in vitro antioxidant assays performed in polar solvents are not a good way to predict in vivo antioxidant activity. 

The antioxidant activity of phenolic acids and their esters depends on the number of hydroxyl groups in the molecule, and this would be strengthened by steric... 

Because they lack the phenolic hydrogen, esters are more stable than free vitamers, but they are not antioxidants in vitro. Tocopheryl esters hydrolyze slowly under, eg., acidic aqueous systems, thus providing antioxidant activity for emulsions, soft drinks and some dairy products (Schuler, 1990). 

S. Miyamoto, T. Koga, and J. Terao Synthesis of a novel phosphate ester of a vitamin E derivative and its antioxidant activity. Bioscience, Biotechnology, and Biochemistry 62 (1998) 2463-2466. 

Caffeic, p-coumaric, ferulic, and sinapic acids (Fig. 4) and their esters and glycosides have all shown interesting antioxidant activity [122 123]. 3,5-Dicaffeoyl-4-succinylquinic acid and 3,5-dicaffeoylquinic acid (isochlorogenic acid) showed antioxidant activity in a P-carotene-linoleate method [123]. 

---