Author: Herr Dr. Amoneit
Last saved by: Saritas, Sevim

Arylmethyl Derivatives of Meldrum`s Acid – a New Class of Antioxidants
Inese Mierina,^1 Mara Jure,^1 Sindija Zeberga,^1 Anatoly Mishnev,^1,2 Daina Zicane,^1 
Zenta Tetere,^1 and Irisa Ravina^1
 ^1Riga Technical University, Riga, Latvia 
^2Latvian Institute of Organic Synthesis, Riga, Latvia
 
Malonates (e. g., di-2-ethylhexyl 4-hydroxy-3,5-dimethoxy-benzylmalonate and diethylhexyl syringylidene malonate) and lactones (e. g., benzofuranone derivatives) are used as antioxidants and powerful radical scavengers. The only derivatives of Meldrum`s acid described as potential antioxidants are 2,2-dimethyl-5-arylidene-1,3-dioxane-4,6-diones 1 [1] - these compounds act as phenolic type antioxidants. 
Herein, we present a new class of carbon centered radical scavengers – arylmethyl derivatives of Meldrum`s acid 2. We found out that the substituents in the aromatic moiety were not crucial for antiradical activity of compounds 2 – all of them demonstrated high or even very high inhibition of the free radical DPPH. It seems that the reaction of DPPH with compounds 2 proceeds as SPLET process. The role of α-CH (between both ketogroups) in the antiradical activity of compounds 2 was approved by the isolation of the reaction product and by the appraisal of the influence of the substituents at C-5 of the 2,2-dimethyl-1,3-dioxane-4,6-dione. The compounds 2 demonstrated lower inhibition of galvinoxyl (in comparison with DPPH).

Few of the compounds 2 were tested as antioxidants. It was observed that the oxidative stability of rapeseed oil methyl esters (RME) can be increased up to 5 times (the oxidation processes were characterized by peroxide values). RME samples containing compounds 2 demonstrated higher oxidative stability in Rancimat test than RME without additive.
Corresponding aromatic aldehydes and carboxylic acids have been isolated as autooxidation products of some arylmethyl derivatives of Meldrum`s acid; the plausible mechanism is provided.
1. Sandhu, H. S.; Sapra, S.; Gupta, M.; et al. Bioorg. Med. Chem. 2010, 18, 5626.